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The hypothesis of strange quark matter (SQM) and the possible existence of strange stars have been extensively investigated within the thermodynamic bag model, typically employing the free Fermi gas approximation with or without perturbative QCD corrections at zero temperature, where quark confinement is modeled by the bag pressure. In this work, based on the perturbative inclusion of quark mass effects, we develop a thermodynamically consistent equation of state (EOS) for SQM at finite temperature, incorporating perturbative corrections up to $\mathcal{O}(α_s)$ in the strong coupling constant $α_s$ while ensuring full adherence to the Maxwell relations. These corrections are essential for accurately describing hot quark stars potentially formed during core-collapse events. We present results for both fixed and running couplings, using a phenomenological model to include the breakdown of the perturbative running of $α_s$ at low momenta. Our results demonstrate that incorporating finite-temperature perturbative QCD corrections leads to SQM configurations that fall within the absolute stability window, with equilibrium energies per baryon lying below that of iron, the most tightly bound nucleus. Our EOS supports compact stars with masses exceeding $1.4\,M_\odot$ (and above $2\,M_\odot$ for some values of the bag constant), in agreement with current astrophysical constraints from pulsar and gravitational-wave observations.

Gravitational-wave observations of compact-binary inspirals offer the opportunity to test deviations from general relativity in both strong and weak-field regimes. In previous work, we developed a theory-independent formalism for describing compact-binary dynamics in metric theories of gravity without preferred frames, using the parametrised post-Newtonian (PPN) couplings together with an additional set of scalar sensitivity parameters that encode violations of the strong equivalence principle. Here, we extend this framework to include preferred-frame effects, of the type that can arise in (for example) vector-tensor theories of gravity. This is achieved by introducing a time-like vector field that identifies the preferred frame, and then by allowing compact body masses to depend on the invariant formed from this field and the body's four-velocity. We calculate the modified equation of motion up to first post-Newtonian order (1PN), where the preferred-frame PPN parameters $α_1$ and $α_2$ acquire contributions from our new vector sensitivities. We further combine scalar and vector sensitivities in a unified formalism, which we validate with an example scalar-vector-tensor theory. This approach provides the orbital dynamics required to extend gravitational-wave constraints on PPN and sensitivity parameters to theories of gravity that admit preferred frames, as well as those that do not.

We investigate the gravitational wave (GW) signatures of compact binaries embedded in extended dark matter (DM) configurations in hydrostatic equilibrium. If a neutron star is surrounded by a sufficiently massive and extended envelope, an inspiraling companion experiences dynamical friction (DF) in addition to the standard GW energy loss. We show that this environmental effect can be isolated through a GW observable, the $D$-function, which directly characterizes the additional dissipative power induced by the surrounding medium. Since the density of the envelope is directly determined by the DM equation of state together with the stellar boundary conditions, the frequency dependence of the $D$-function provides direct information about the macroscopic properties of the dark sector. We develop a regression-based framework to reconstruct both the density profile and the DM equation of state over the density range probed by observations of the GW inspiral. Using representative DM models as benchmarks, we demonstrate that the method accurately recovers the input equation of state while remaining largely independent of the microscopic realization of DM. Our results show that future GW observations of compact binaries can provide a probe of the equation of state of DM.

Luminous red novae (LRNe) are astronomical transients arising from unstable mass transfer and common envelope phases in close binary systems, culminating in stellar mergers. Their cold, expanding ejecta provide the ideal conditions for molecule and dust formation. We investigate the late-time dust and molecular evolution of the LRN M101 OT2015-1, a high-mass LRN progenitor ($18\pm 1$M$_\odot$), using multi-band near-infrared (NIR) and mid-infrared (MIR) observations spanning up to ~5 years post-outburst. Archival and unpublished photometry from NEOWISE, Spitzer, Keck NIRC2 and MOSFIRE, are interpolated via 2D Gaussian process regression. Spectral energy distributions (SEDs) are modelled with 1D spherical radiative transfer models to track the evolution of dust mass, dust temperature, and central source properties. At +150d post-peak, the SED is well-fit by a pure stellar blackbody ($T_{\rm eff}=3330$K) with negligible dust (log$M_{\rm dust}/$M$_\odot<-6.36$). Rapid dust condensation begins around day +200 ($T_{\rm dust}=1591$K), with dust mass increasing to log$M_{\rm dust}/$M$_\odot =-3.65$ and optical depth reaching $τ_V =64$ by +1300d. A prominent NIR re-brightening at ~600d ($M_K=-12.04$), accompanied by a dust reheating bump ($T_{\rm dust}=1567$K), highlights a second phase of dust nucleation likely driven by shock interactions. Low-resolution NIR MOSFIRE spectra are analysed for line identification and also using an LTE isothermal slab model to characterise CO molecular features. The MOSFIRE spectra reveal an O-rich environment with photospheric expansion velocities of ~$430-530$km s$^{-1}$, as measured in the Pa$β$ emission line, and high CO column densities (log$N_{\rm CO}$/cm$^{-2}=20.9$ and $20.7$ at +142d and +197d, respectively). These results confirm that LRNe from massive progenitors are prolific producers of cosmic dust and are efficient molecular factories.

Gravitational-wave observations can reveal sources whose signals are not known in advance. Searches that do not require a predicted waveform are therefore an important complement to searches for specific source classes. For the Laser Interferometer Space Antenna (LISA), the challenge is to find such signals among overlapping astrophysical sources and disturbances in the instrument. We present \texttt{cWB-space}, which identifies candidate signals by following how their power is distributed in time and frequency, and then reconstructs parts of their waveforms without imposing a source model. Simulations of merging massive black holes, other burst signals, and instrumental disturbances test both candidate identification and the information carried by the detector's response. The response comparison estimates its background from the observed data. Tests of disturbances in several laser measurements examine where a similar response can arise from an instrumental origin. Searching the Sangria simulated LISA data, we recover all six injected massive-black-hole binaries as the six highest-ranked candidates. Their reconstructed waveforms agree well with the injected signals over the intervals studied. The results demonstrate another route to investigating transients, while leaving the rate of false detections and general discrimination of instrumental disturbances to future validation.

Understanding the relationship between photospheric magnetic flux evolution and coronal emission remains an important problem in heliophysics. We investigate the decay of NOAA Active Region 12781 from 7 to 11 November 2020 using observations from the Solar Dynamics Observatory (SDO). Coronal emission was measured from the Atmospheric Imaging Assembly (AIA) 193\~Å images, while the photospheric signed and unsigned magnetic flux was derived from Helioseismic and Magnetic Imager (HMI) observations of the FeĨ 6173\~Å line. The unsigned magnetic flux and mean 193\~Å intensity showed a strong inverse relationship, with Pearson and Spearman correlation coefficients of $r\_p=-0.771$ and $r\_s=-0.758$, respectively. During the five-day decay phase, the unsigned magnetic flux decreased by 36.54\\% from its maximum value, while the coronal emission increased by 21.96\\%. We also compared the remote-sensing observations with near-Earth solar-wind and interplanetary magnetic-field measurements from the OMNI database using an estimated propagation delay. The results show that the coronal emission did not vary directly with the photospheric magnetic flux during the decay of AR\~12781. The possible association with the solar wind is discussed cautiously because a direct source connection cannot be established from the time-delay estimate alone.

We develop the first time-domain reduced order quadrature for gravitational waves in the early inspiral period, motivated by the need for dataset compression in the presence of gaps, uneven sampling, and dense covariance matrices. A single reduced basis with 1290 elements can represent inspirals from supermassive black hole binary sources with chirp masses between $10^7-10^{10}$ $M_\odot$, but in the presence of non-stationary noise $\sim 1290^2$ reduced order quadrature weights must be stored. We are able to reduce the stored weights by a factor of two by partitioning our parameter space by GW frequency, with relative waveform/likelihood accuracies remaining below $10^{-5}$/$10^{-3}$ after partition. Finally, we point out that heterodyning can be combined with reduced order methods with no loss in accuracy. Our reduced order quadrature makes inspiral searches in the time domain feasible for both pulsar timing arrays and relative stellar astrometry.

We report new optical spectroscopic results for the gamma-ray blazar PKS~0903$-$57. The optical properties of this source have historically been complicated to establish, due to a bright foreground star separated from the blazar by only 0.67$^{\prime\prime}$. During its strong high-energy (HE) and very high-energy (VHE) gamma-ray flaring period between 2020 and 2022, the Southern African Large Telescope and Very Large Telescope (VLT) took spectra of its optical counterpart. Photometric monitoring with the Rapid Eye Mount (REM) telescope complemented the observations. The observational results were inconclusive. A major improvement was achieved with a repeat of the VLT observations in 2024 using a 0.5$^{\prime\prime}$ slit under excellent seeing conditions. This led to the detection of five narrow emission features in the spectra, yielding a robust redshift measurement of $z$ = 0.2621 $\pm$ 0.0006. We also detected a broad symmetric H$α$ emission component with a full width at half maximum of 4020 $\pm$ 30 km/s in the spectra. Non-thermal jet emission was found to dominate the continuum, supporting the classification of PKS~0903$-$57 as a flat-spectrum radio quasar. Another interesting observation was a significant velocity displacement of $\sim$1500~km/s between the broad H$α$ line and its corresponding narrow line. Such a displacement may be associated with unusual dynamics in the broad-line region or accretion flow, a system containing two supermassive black holes, or a recoiling black hole produced following a supermassive black-hole merger. Building on these results, we carried out additional VLT, REM, and \emph{Swift} observations towards the end of 2024 and during 2025. We present in this paper the preliminary results from the analysis of these new data.

Electric charges carried by compact objects can affect binary dynamics and imprint characteristic signatures on gravitational-wave signals. We derive next-to-leading-order post-Newtonian frequency-domain waveforms for charged compact binaries in both the gravitational-quadrupole and electric-dipole dominated regimes, including electromagnetic corrections beyond leading-order electric-dipole radiation that reduce the degeneracy between the component charge-to-mass ratios. Using gravitational wave events from GWTC-5.0, we place constraints on the charge-to-mass ratio and mass of each component of the binary system.

When propagating through the universe, gamma rays at very-high energy (VHE, E > 100 GeV) and ultra-high energy cosmic rays (UHECRs, E > 1 EeV) can interact with the optical, infrared and microwave photon fields that permeate the universe. These interactions result in a characteristic absorption imprint in the spectra of extragalactic gamma-ray sources at VHE, and in a change in the mass-composition of UHECRs. The study of both VHE gamma rays and UHECRs therefore requires precise knowledge of the intensity of the cosmic photon fields. In this work, we explore the impact of the current uncertainties on the optical and infrared photon fields on the propagation of astroparticles. We restrict the range of available models to those best matching the recent measurements, and compare the different reconstructions resulting from these models. We find that the knowledge on the cosmic background light is no longer the dominant source of uncertainties in understanding the phenomenology of astroparticle sources in the low redshift universe (z < 0.1), enabling robust spectral and composition inference with the next generation of both gamma-ray and UHECR measurements.

Gravitational-wave (GW) standard sirens have emerged as powerful probes of cosmic expansion. They are commonly divided into two classes: bright sirens, observed in coincidence with an electromagnetic (EM) counterpart, and dark sirens, detected without one. Bright sirens have often been considered the main avenue for precision cosmology; however, following the latest observing run of the LIGO-Virgo-KAGRA (LVK) collaboration, the estimates of merger rates of compact objects involving neutron stars (NSs) have decreased. In this Letter, we reconsider the role that bright and dark sirens will play in precision cosmology. We demonstrate that bright sirens, although detected in small numbers, will play a crucial role in achieving the precision needed to address the Hubble tension, primarily by breaking the degeneracy between the Hubble constant ($H_0$) and the matter density parameter ($Ω_m$) inherent to dark sirens. Alternatively, we show that dark sirens alone can resolve the $H_0$ tension when supplemented with an external prior on $Ω_m$. Furthermore, we present a self-consistent statistical framework for GW cosmology with bright and dark sirens, which have traditionally been treated as independent populations although they originate from the same underlying population of black holes (BHs) and NSs. Finally, we find that treating bright and dark sirens as independent populations will not significantly bias GW cosmology in the next LVK observing runs, but can lead to a biased reconstruction of the low-mass end of the mass spectrum.

We have developed techniques for a competitive sub-TeV time-integrated neutrino search and applied it to 11.1 years of IceCube-DeepCore data. The DeepCore subarray lowers the sensitivity of IceCube down to sub-TeV energies and is especially interesting for objects with soft spectra. Three studies were performed: a search for neutrino emission from AGN exhibiting high intrinsic X-ray flux, including NGC 1068, as identified by SWIFT/BAT; a search for neutrino emission from Galactic objects identified by Fermi-LAT as exhibiting a spectral shape consistent with neutral pion decay; and an all-sky search for neutrino point sources. Objects for this study were selected given their prospects for sub-TeV neutrino emission. No evidence for sub-TeV neutrino emission is found in any of the searches performed. Finally, for each catalog of objects, we use a statistical combination of the p-values via a binomial test to search for aggregated neutrino emission from a subset of the objects. Neither of the binomial tests yields significant results. For NGC 1068, assuming a power law spectrum with index 3.4, the 90% confidence level upper limit on per-flavor neutrino emission in the 30--400 GeV range is $Φ_{ν+\barν}|_{\mathrm{1 TeV}} < 9.5 \times 10^{-11}$ TeV$^{-1}$ cm$^{-2}$ s$^{-1}$, a factor of two higher than the extrapolation of IceCube's measurement at higher energies. We additionally provide neutrino flux upper limits for a variety of spectra.

We quantify how the treatment of a strongly supercooled phase transition affects the particle-physics interpretation of a nanohertz gravitational-wave signal. For the classically conformal Abelian Higgs model, we calculate the nucleation rate at NLO in the dimensionally reduced theory and test the gradient expansion against explicit fluctuation determinants. A calibrated correction reproduces the determinant exponent with a mean absolute relative difference of $0.8\%$ and allows this information to be included throughout the parameter scan. We propagate the corrected rate through percolation, reheating and gravitational-wave production, and confront the resulting spectra with the NANOGrav 15-year and IPTA DR2 data. The corrected NLO calculation shifts the preferred gauge coupling by $9\%$ and $13\%$, respectively, and the input scale by $18\%$ for NANOGrav. After the determinant calibration, the largest theoretical uncertainties arise from uncertainties in the gravitational-wave spectra and the relation between $R_\star$ and $β/H$.

We investigate superluminal Lorentz invariance violation (LIV) in the neutrino sector using cosmogenic neutrino fluxes generated with ultrahigh-energy cosmic-ray propagation models. Standard fluxes are calculated with \texttt{CRPropa 3.2} and subsequently modified using a prescription based on LIV-induced neutrino splitting. Superluminal LIV suppresses the flux at the highest energies while producing an enhancement at PeV - EeV energies. We use the KM3-230213A event as a benchmark to evaluate the sensitivity of current observations to these spectral modifications. Although the available statistics do not allow a formal constraint, the predicted fluxes are particularly sensitive to coefficients in the range $10^{-24} \mathrm{eV}^{-1} \lesssim δ_{ν,1} \lesssim 10^{-22}\,\mathrm{eV}^{-1}$, with the results strongly depending on the assumed cosmic-ray source properties. Intermediate coefficients can enhance the expected event rate within the reconstructed energy range of KM3-230213A, whereas larger coefficients may overproduce neutrinos in energy intervals constrained by IceCube and the Pierre Auger Observatory. These results identify a region of observational sensitivity to LIV and provide testable predictions for future neutrino telescopes.

Recent simulations suggest that heavy seed black holes may form in weakly metal-enriched atomic cooling halos, where the supermassive-star progenitor and small-scale stellar fragments emerge nearly coevally. In this picture, the newly born heavy seed is naturally embedded in a metal-enriched Pop~I/II nuclear star cluster rather than in an isolated pristine environment. We investigate whether disk-induced tidal disruption events (TDEs) from these Pop~I/II stars can provide an efficient and sustained growth channel for heavy seed black holes. We construct a semi-analytical model for stellar orbital damping, disk capture, migration, and tidal disruption around a heavy seed black hole, and incorporate the resulting disk-induced TDE contribution into cosmological merger trees with baryonic and metallicity evolution. Heavy seed host halos are selected from atomic cooling halos with $Z\lesssim10^{-3}Z_\odot$ that satisfy either a rapid gas-inflow criterion or a strong Lyman--Werner radiation criterion. We find that disk-induced Pop~I/II TDEs can dominate the early growth of heavy seeds: the median black hole mass grows from $\sim10^4\,M_\odot$ to $\sim10^5\,M_\odot$ within the first $\sim0.1$ Gyr after seed formation, and reaches several $10^5\,M_\odot$ by $\sim0.2$ Gyr. The cumulative mass supplied by TDEs initially exceeds that from gas accretion and remains comparable over the first $\sim200$ Myr. Including disk-induced TDEs shifts the black hole population toward higher masses, increases the abundance of massive black holes at $z\sim9$--10, and produces larger black hole-to-stellar mass ratios. This channel helps alleviate, but does not fully remove, the tension between heavy-seed models and the most extreme high-redshift black hole candidates, suggesting that additional growth mechanisms may still be required.

We perform high-resolution 2.5D single-fluid magnetohydrodynamic (MHD) simulations to explore the development of cool-dense structures within plasmoids during chromospheric magnetic reconnection. The model incorporates temperature-dependent ionization degrees of hydrogen and helium, resulting in improved diffusivities and viscosity, as well as adequate radiative cooling. The numerical results show that plasma is significantly hot with temperatures reaching several tens of thousands of Kelvin in newly developed plasmoids in the low initial plasma-$β$ cases, $β_0$ = 0.05. Later, the localized accumulation of plasma and decreasing temperature result in an explosive much stronger radiative cooling process. Radiative cooling peaks over the temperature range 8000 K$-$20,000 K. The co-spatial density enhancement, substantial radiative cooling, shorter radiative cooling timescales, and a significant temperature decrease support the existence of thermal-instability-like condensation within the plasmoids. Similar cool-dense structures are identified in all low-$β_0$ cases at different chromospheric altitudes, suggesting that this occurrence is not limited to a single chromospheric layer. In contrast, in the high initial plasma-$β$, $β_0$ = 0.5 case, the maximum temperature inside the dense plasmoids is only about 8000 K. Therefore, the radiative cooling has never entered into the explosive increasing stage and the thermal-instability-like condensation does not happen. These findings reveal that plasmoid-trapped condensation may develop in chromospheric reconnection once radiative losses become self-amplifying under low-$β_0$ conditions.

Pressure anisotropy in relativistic stars is commonly prescribed through a phenomenological closure, obscuring its microscopic origin and relation to stress-energy conservation. Here it is derived directly from the minimally coupled Einstein-complex-Proca theory. For spherical Proca stars, the principal-pressure difference admits an exact on-shell form whose sign is controlled solely by the local mass-shell threshold. The stress is radially dominated in the core, reverses on a surface of fixed gravitational redshift, and becomes tangentially dominated in the envelope. At the first mass maximum, the fractional anisotropy reaches about 21% near the density maximum, whilst the region beyond the reversal contains about 9% of the mass. Its exact atmospheric limit is approximately 24%, equal in magnitude and opposite in sign to the scalar-boson-star limit. Because the usual local fluid variables remain non-zero at the crossing, no sign-definite closure constructed from them can reproduce the profile. These results identify an intrinsically vectorial stress reversal, generated without additional interactions, and provide a first-principles benchmark for anisotropic bosonic compact objects.

Large primordial curvature perturbations not only produce primordial black holes (PBHs) but also inevitably source a scalar-induced stochastic gravitational-wave background upon horizon reentry. We analyze the combined LIGO--Virgo--KAGRA O1--O4a data to constrain two representative inflationary mechanisms for generating such perturbations: ultra-slow-roll inflation and an inflationary phase transition. Detecting no evidence for either scenario, we place 95% credible upper limits on the curvature-spectrum amplitude across the frequency range accessible to ground-based interferometers. Translated into the PBH context, these limits already exceed conventional constraints, probing abundance fractions far below unity. Our results remain robust even when the PBHs themselves are too rare to be directly detected or have evaporated. This work demonstrates that stochastic gravitational-wave observations offer a powerful and complementary probe of small-scale inflationary physics and PBH formation, with upcoming interferometers promising to extend sensitivity to a wider range of inflationary epochs and PBH masses.

We assess whether electromagnetically identified supermassive black hole (SMBH) binary candidates populate the rare, high-amplitude tail of the gravitational wave (GW) amplitude distribution. Using an SMBH binary population model fitted to the NANOGrav 15-year data, we find that 3C~66B and Mrk~501 are likely to stand out from the GW background, making them promising targets for individual-source searches. Furthermore, we show that individual detections can probe the binary hardening mechanism, as models with strong environmental hardening predict a higher abundance of individually resolvable binaries than purely GW-driven models. Applying the same population fits and accounting for the confusion noise from the unresolved population, we forecast that the Square Kilometre Array Observatory (SKAO) will resolve tens of individual binaries, with 3C~66B robustly detectable.

Many dark sector models predict the formation of dark objects, such as solitons and dark stars, which can be searched for through their gravitational lensing of gravitational waves (GWs). Although these objects vary widely in size and compactness, most GW lensing studies have focused on point-like lenses. The finite size of an extended lens is important when it exceeds its Einstein radius. We evaluate the frequency-dependent effects on GW waveforms from extended lenses and demonstrate that they can be probed with current and future GW data. While finite-size effects can weaken the bounds on the fraction of dark matter in these objects compared to the point-like limit, current GW data provides complementary constraints to other gravitational tests for lens masses between $10^2M_\odot$ and $10^5M_\odot$; future LIGO-Virgo-KAGRA data and next-generation observatories will surpass their sensitivity. As expected, we find that the finite-size effects are important when the lens radius exceeds $\sim \text{few} \times 10^{6}R_\odot (M_L/100 M_\odot)^{1/2}$. Interpreting these constraints within specific models (a simple dissipative dark sector and axion stars), we show that current and future observations probe significant portions of the microphysical parameter space.

At low redshift, scatter in the Type Ia supernova (SN Ia) Hubble diagram is increased by peculiar velocities (PVs) and correlations between SN distances and their host-galaxy environments, limiting the precision of cosmological distance measurements. We investigate these effects using 1086 spectroscopically-confirmed SNe Ia from the Type Ia Supernova Trove from ATLAS in the Nearby Universe (TITAN) sample in the redshift range $0.01<z<0.05$. We identify 314 group-associated SNe, including 80 SN "cousins" occurring in different galaxies within 32 common groups. We first examine whether using the group-averaged redshifts of SNe in galaxy groups can mitigate PV-induced scatter; however, we find that the Hubble residual scatter increases slightly from $0.184^{+0.017}_{-0.009}$ mag using individual host-galaxy redshifts to $0.200^{+0.016}_{-0.015}$ mag using group-averaged redshifts. For the sample of SN cousins, we next analyze pairwise differences in their distances and compare their scatter to the Hubble residual scatter of the full SN sample. For analysis variants that limit line-of-sight differences in distance modulus between cousins, we find $\sim$30-40% lower scatter from SN cousins at significances of 2.3-2.8$σ$. We also find tentative evidence that these differences in scatter may be driven by the youngest groups, with a 2$σ$ reduction in scatter for groups with high fractions of spiral galaxies. These results suggest that SN cousins may provide a novel route for increasing SN Ia distance precision and understanding the role of host-galaxy and group properties on SN Ia distance measurements.

In this paper, we report on the dynamics of the fine structure of a solar quiescent filament observed on September 28, 2023, with the Télescope Héliographique pour l'Etude du Magnétisme et des Instabilités Solaires (THEMIS). The main aim is to understand the relationship between the supersonic downflows measured in H$α$ at the filament end and an associated coronal bright point. We use a cloud-model method to derive the supersonic velocity of the falling, elongated cool blob. Besides, we use H$α$ Global Oscillation Network Group (GONG) data to track the plasma along the filament. Repetitive plasma motions are observed along the northern end of the filament. During one event of plasma motion, the THEMIS field of view was centred on the filament end, where supersonic downflows of 89.8 km s$^{-1}$ were measured with a standard deviation of $\pm$0.25 km s$^{-1}$. We suggest that the plasma moving along the filament could be falling towards the chromosphere. A ballistic trajectory could confirm this first scenario. However, we could not rule out the second scenario, in which coronal rain forms due to the thermal instability of coronal plasma. In the hot AIA channels, we identify a bright point at the same location, with a temperature reaching about 6 MK. In addition, we confirm a counter-streaming flow pattern along the fine filament strands, with widths of less than an arc second, as measured by the high-spatial- and spectral-resolution spectra of THEMIS.

The tip of the red giant branch (TRGB) can be used as a relative distance measure as part of the cosmic distance ladder to infer the Hubble constant. We present a Bayesian framework for TRGB inference that incorporates selection effects and propagates per-star uncertainties, modelling the observed catalogue as a realisation of an inhomogeneous Poisson point process which includes the RGB and contamination from the asymptotic giant branch (AGB). We derive expressions for the predicted TRGB uncertainty in terms of the photometric noise, stellar density fainter than the tip, and the ratio of the AGB to AGB+RGB number densities, $r$. We validate these using synthetic data from a simplified luminosity function. Applying the full model to synthetic catalogues, we find that the dependence on $r$ is the strongest of the three, and that reliable inference requires $r \lesssim 0.5$; beyond this, the posterior is multimodal, and the TRGB cannot reliably be identified. We then fit data from 11 Hubble Space Telescope fields of the calibrator galaxy NGC 4258. We find intrinsic field-to-field scatter beyond measurement noise of $τ= 0.067^{+0.023}_{-0.017}$ mag, and a galaxy-level, extinction-corrected TRGB magnitude of $25.324 \pm 0.026$. Combining this with the maser distance to NGC 4258, we determine the absolute magnitude of the TRGB to be ${M}_{\rm{F814W}}^{\rm{TRGB}} = -4.073 \pm 0.026$ (tip) $ \pm$ $0.032$ (dist), consistent with, but brighter than, other recent analyses of the same data.

The closest and brightest millisecond pulsar (MSP), PSR J0437-4715, is a high-priority pulsar for precision timing experiments, including the Parkes Pulsar Timing Array (PPTA) project, where it is used for both pulsar timing and for polarization calibration. Using approximately seven years of observations obtained with the Ultra-Wideband Low-Frequency receiver on Murriyang, CSIRO's Parkes radio telescope, we investigate the long-term spectro-polarimetric variability of PSR J0437-4715. We report the discovery of two consecutive discrete profile change events exhibiting the same phase-localised morphological variations, the first such behaviour reported in any MSP. Both events affect three phase-localised regions of the pulse profile that exhibit coupled and anti-correlated temporal evolution. We also identified, and corrected for, systematic profile variability induced by polarization calibration errors arising from long-term drift of the polarimetric properties of the receiver. The profile change exhibits frequency-dependent evolution in total intensity, together with variations in linear polarization, position angle and fractional linear polarization. These results confirm a magnetospheric origin for the events rather than propagation effects caused by the interstellar medium, and provide potential new constraints on MSP emission models.

We have developed a photometric method that produces clean hot (intrinsically blue) populations using Gaia and 2MASS photometry alone with [a] a very small (false positives < 1%) contamination from cool (intrinsically red) luminous sources, [b] independent of extinction (limited only by S/N), and [c] with only small losses (false negatives < 10%) of real OB stars. Applying the method to Gaia DR3 data we are able to recover extinguished OB stars down to E(G_BP-G_RP) = 5, producing a catalog of ~2x10^5 candidate OB stars that reaches beyond the Scutum-Centaurus arm. This method can potentially extend the sample of known OB stars by an order of magnitude, which would yield a large leap in our knowledge of the populations of compact-object progenitors, including gravitational-wave sources.

Prominences and coronal rain are two manifestations of coronal condensations whose formation mechanisms remain only partially understood. While previous studies have explored how localised steady or stochastic heating can trigger thermal instability and condensations, the role of wave driven energy transport and dissipation has not been extensively investigated. In the solar atmosphere, Alfven and kink waves are an abundant source of energy capable of contributing both to coronal heating and plasma structuring, making them compelling candidates in the formation processes of the structures we observe in the corona. We aim to explore how Alfven and kink wave energy and their dissipation influence the formation and evolution of condensations in coronal magnetic structures. In particular, we investigate each waves role independently of parameterised external heating mechanisms to isolate whether either wave can trigger condensations. We perform 2.5D simulations using the open source MPI AMRVAC code extended with the newly developed UAWSoM module. This module self consistently evolves Alfven and kink wave energy and their feedback on the plasma through wave pressure and heating terms. We examine the conditions under which condensations form, their morphology, and their dynamical evolution. Our results show that for our range of parameters, in 2.5D MHD, Alfven waves did not trigger the formation of prominences or condensations. We find that if the radius of the fine scale structures supporting the kink waves is of the order of 100 km, then kink waves can trigger coronal rain that differs considerably in its morphology from coronal rain triggered by parameterised heating functions. Through the use of UAWSoM, we have established that Alfven and kink waves leave distinct thermodynamic signatures on coronal loops, given the same wave energy injection.

We derive an extension of Chandrasekhar's pulsational stability criterion for relativistic stars with a pressure boundary condition at the surface. We then apply the new criterion to hylotropes, a model describing rapidly accreting supermassive stars with a core-envelope structure. We find that confinement typically stabilises stars, delaying the onset of the general relativistic instability when the external pressure at the surface is roughly $\sim10^{-3}$ of the stars' hydrostatic pressure scale. Beyond this value, the critical mass at marginal stability increases rapidly, exceeding the value of $\sim 10^5$ M$_{\odot}$ for helium burning, isolated $n=3$ polytropes by orders of magnitude. We discuss how the required pressure boundary conditions may be produced by the combined ram and magnetic pressure supplied by the accretion flow as it assembles the supermassive star, and provide a fitting formula for the final mass before collapse. As a rough estimate assuming equipartition between magnetic and thermal pressures in a standard $α$-disk, we find that the critical mass doubles at accretion rates of order $\dot M\sim100\,{\rm M_\odot}\,{\rm yr}^{-1}$, again increasing rapidly after this value. Our results show under what conditions, potentially realized in a subset of high redshift halos, non-rotating SMS may collapse into black holes beyond the typical scale of heavy seeds.

The interpretation of gravitational wave sources depends on the specific choice of model used to interpret signals. Previous analyses of GWTC-3 event candidates using SEOBNRv4PHM, IMRPhenomXPHM, and NRSur7dq4 have sometimes arrived at notably different conclusions about event properties. Subtle analysis settings and code differences can also produce notable differences. We revisit 60 publicly available events from the first three observing runs, released across GWTC-1, GWTC-2, GWTC-2.1, and GWTC-3, using a consistent analysis framework and three waveform models: two state-of-the-art time-domain models with higher-order modes (SEOBNRv5PHM and IMRPhenomTPHM) and one older frequency-domain model without higher-order modes (IMRPhenomPv2). The two state-of-the-art models agree well overall, although about 20\% of events have a visible difference in at least one one-dimensional marginal posterior. By contrast, the older model often arrives at qualitatively different conclusions for key events across the mass spectrum. We also identify a bug in published LVK GWTC-2.1 SEOBNRv4PHM results and in a later reprocessing of GW200105. At the adopted sampling rates, the model's Nyquist-frequency restriction excluded part of the allowed parameter space and artificially truncated the mass-ratio posterior away from equal mass for seven low-mass events. These results emphasize the need to use multiple state-of-the-art waveform models and carefully validated analysis settings to characterize uncertainty in gravitational-wave source properties.

The radio/X-ray/black-hole-mass Fundamental Plane (FP) is widely used to estimate masses of accreting intermediate-mass black hole (IMBH) candidates. Its inverse use is justified only when radio luminosity traces a compact jet core and X-rays arise from the same sub-Eddington hard-state accretion flow. We formulate an accretion-state validity criterion for inverse-FP masses using verified BH X-ray binary radio/X-ray tracks as the empirical reference. Using 424 detections from 21 BHXBs and candidates, we find that both standard and curved tracks are present and the luminosity at which radio/X-ray behavior changes is source dependent. A low X-ray Eddington ratio is therefore not, by itself, sufficient to establish inverse-FP validity. Within a scale-invariant jet/hot-flow framework, track steepening reduces the effective mass leverage of the inversion, while at much lower accretion rates uncertainties in the dominant emission mechanism and compact-core production can invalidate the underlying FP assumptions altogether. We apply the criterion to representative IMBH-relevant systems without fitting a new plane. NGC 4395 is low-Eddington but compact-radio deficient: its VLA-scale and VLBI jet-base luminosities imply formal inverse-FP mass underestimates of about 1.0 and more than 2.8 dex if the deficit is misread as a mass signal. Globular-cluster X-ray populations in NGC 1399 and NGC 4472 are source-identity limited: 71% and 67% lie below $L_{\rm Edd}(10\,M_\odot)$, and the high-luminosity tail alone does not identify an IMBH accretor. The radio non-detection of the $ω$ Centauri IMBH candidate constrains gas supply, accretion efficiency, and compact-core production rather than excluding the black hole. The resulting test defines which SKA/ngVLA-era radio cores can be converted into FP masses, and which instead constrain gas supply, source identity, or compact-core production.

Equations of state (EoS) for dense matter are commonly provided in tabulated pressure-energy density relations, complicating numerical implementation and potentially compromising thermodynamic consistency. In this work, we propose a universal, piecewise-continuous functional form with a common parametrization capable of representing a broad class of dense matter EoSs. We validate this parametrization against tabulated EoSs from the CompOSE and LALSimulation repositories. Following the initial deterministic fitting, we employed two distinct Bayesian approaches: one based on synthetic EoSs generated by adding noise to the fitted EoS and another based on multimessenger measurements of neutron-star masses and tidal deformabilities. In both approaches, the initial best-fit parameters are used as reference values. For the considered EoSs, spanning from very soft to very stiff, the resulting fits reproduce the defined tabulated EoSs and the associated macroscopic neutron-star observables in the repositories with sufficient degree of accuracy. The inferred parameters exhibit strong correlations arising from the continuity conditions imposed at the segment boundaries. These correlations persist in the low- and intermediate-density segments under multimessenger inference but become weak in the core, reflecting the limited constraining power of current observations at high densities. The ability of a single functional form to describe EoSs derived from different microscopic frameworks, together with the recurrence of similar parameter correlations, suggests that diverse dense matter EoSs may share a common underlying structure.

The cosmological constant $Λ$, and its generalization as Dark Energy, makes up roughly 70% of the present-epoch universe and has been part of the dominant $Λ$CDM cosmological paradigm for more than a quarter of a century. It has been put on trial by recent measurements of galaxy clustering, Type Ia supernovae, and the cosmic microwave background. In this Perspective we evaluate the strength of the evidence for a constant $Λ$, versus Dynamical Dark Energy (DDE) in the light of recent developments. We also assess what the future holds both for our Universe and our understanding of its most mysterious component.

The origin of the stellar-mass binary black holes (BBHs) observed in gravitational wave (GW) events by the LIGO-Virgo-KAGRA (LVK) detectors remains uncertain. One promising formation pathway is the active galactic nucleus (AGN) channel, in which BBHs embedded in AGN accretion discs experience enhanced merger rates and may produce rapidly spinning black holes in the upper mass gap. Previous constraints on the AGN contribution to the LVK merger population have relied either on spatial correlations between GW localisations and AGN catalogues or on modelling the intrinsic properties of GW sources. We develop a hierarchical Bayesian framework that unifies these approaches within a single likelihood for the fraction of AGN-hosted GW events, $f_{\rm agn}$. This framework, combined with the latest gravitational wave transient catalogue GWTC-5.0 and the electromagnetic Quaia AGN catalogue, cannot exclude an AGN contribution to the observed merger rate. For unobscured AGN in the optical and infrared bands with bolometric luminosities $L_{\rm bol}\geq\{10^{44.5},10^{45.5},10^{46.5}\}\,\mathrm{erg\,s^{-1}}$, we exclude $f_{\rm agn} \geq \{0.52,0.41, 0.61\}$ at the 95 percent credible level under our fiducial model. The methodology and results presented in this work lay down the pathway for combining the full GW posterior with electromagnetic observations to infer the properties of GW populations and AGN discs.

Active Galactic Nuclei (AGN) feedback plays a key role in galaxy evolution. Highly ionized outflows, detected in X-ray absorption, are a promising candidate for quasar-mode feedback. We present a new Bayesian analysis of 0.65 Ms of \emph{Chandra} High Energy Transmission Gratings (HETG) observations of MCG-6-30-15 from 2000 and 2004. Our approach detects new wind components, improving estimates of outflow demographics and impact. These include a hot ultra-fast outflow (UFO; 0.08c), recently confirmed by XRISM but seen in HETG for the first time, which has the power to potentially influence its host galaxy. We also detect the first potentially collisionally ionized absorbers in this source, a physical process typically not considered in previous analyses, but potentially important for wind impact and demographics. The warm absorber complex is resolved in unprecedented detail, uncovering evidence of a correlation between outflow velocity and ionization, constraining its geometry. We also confirm the presence of dust in the wind, clearly distinguishing it from the cold ISM components, which may impact wind acceleration. Our work highlights the power of applying new methods to deep, legacy HETG datasets, and the limitations of current atomic databases when considering OIV, V, and VI K-shell transitions. Furthermore, our work establishes a baseline for decade-scale outflow variability for new observations with XRISM and NewAthena in the future.

We perform 3D radiation magneto-hydrodynamic (RMHD) shearing-box simulations of local patches of optically thick accretion disks, applicable to sub-Eddington active galactic nuclei (AGN) at $\sim 1000$ gravitational radii around a supermassive black hole (SMBH) of $10^7-10^8M_\odot$. In particular, we set up zero-net-vertical-flux (ZNVF) simulations with strong net azimuthal fields ($B_y$) characterized by initial gas-to-magnetic pressure ratio $β_0$. We find that $β_0 \sim 1$ simulations relax to the classical MRI state with steady-state $β\sim 10-20$ and slow periodic reversals of the mean azimuthal field (dynamo cycles), losing memory of their initial $B_y$ configuration. The outcome of simulations starting from $β_0=0.1$ (superthermal magnetic pressures) depends upon the numerical resolution as quantified by the number of grid cells per thermal scale height $H_\mathrm{th}$. Resolved simulations ($Δz\le H_\mathrm{th}/5$) settle into final states similar to the larger-$β_0$ runs, exhibiting thermally dominated midplanes heated by MRI turbulence and undergoing dynamo cycles. In contrast, lower resolution $β_0 = 0.1$ runs evolve towards states dominated by a coherent mean field, similar to what is observed in recent isothermal MHD simulations. However, those disks fail to sustain sufficient turbulent heating near the midplane and undergo runaway cooling and contraction. While such states might be sustained in global models with even lower initial $β_0$ and/or continuous $B_y$ injection, our results indicate that they could arise purely from under-resolving the midplane MRI dynamo that would otherwise be able to generate and emanate randomized fields. We highlight the need to resolve a fraction of the thermal scale height (the classical MRI wavelengths) for strongly magnetized initial conditions to obtain converged outcomes in RMHD simulations.

Understanding how instrumental and mission parameters affect the ability to measure faint astrophysical signals is a key challenge in the design of future experiments. This is particularly relevant for CMB spectral distortions, whose weak signals are affected by both instrumental effects and astrophysical foregrounds. We develop a method to explore and optimise the multidimensional parameter space of an astronomical instrument, and apply it to CMB spectral distortion measurements using the FOSSIL mission concept. We combine a dedicated sky model with a realistic instrument model and use Fisher forecasts to assess measurement capabilities of the simulated instrument. Decision-tree-based regression models are then used to learn the non-linear mapping between instrumental parameters and the predicted signal-to-noise ratios of the sky observables. Random Forest and gradient boosting models accurately reproduce the forecasted measurement performance. SHAP values are used to interpret the impact of instrumental parameters on the measurement. The temperature of the warmest instrumental component is found to be the dominant parameter for all three observables, highlighting the importance of limiting internal emission and operating the instrument at cryogenic temperatures. Frequency coverage is also highly influential, revealing a trade-off between spectral coverage and instrumental sensitivity. The proposed optimisation method provides a fast and interpretable approach to explore high-dimensional instrumental parameter spaces and identify parameters that most strongly influence the scientific performance of an experiment. To the best of our knowledge, this work represents the first application of machine-learning methods to the global optimisation of an astronomical instrument and can readily be extended to other astronomical instruments and mission concepts.

Strong chromospheric absorption lines such as H$α$ 6562.8 A and Ca II 8542.1 A provide vital diagnostics of plasma dynamics and thermal structure in the solar chromosphere. Multilayer spectral inversion (MLSI) offers a physically interpretable framework for modeling these lines using a finite number of radiative-transfer layers, but conventional MLSI relies on pixel-by-pixel nonlinear least-squares fitting, making it computationally expensive for large imaging spectroscopic data sets. Here, we introduce a physics-informed neural-network (PINN) framework to accelerate MLSI while preserving its analytic radiative-transfer formulation. The network predicts MLSI parameters directly from observed line profiles and passes them through a differentiable MLSI forward model to synthesize spectra. Training follows a two-stage approach: an initial stage optimized solely via spectral reconstruction loss, followed by fine-tuning that combines spectral consistency with parameter-space supervision from conventional MLSI results on a single reference image. This strategy eliminates the need for large precomputed training sets while maintaining physical interpretability. Applied to Fast Imaging Solar Spectrograph (FISS) observations from the Goode Solar Telescope (GST) targeting both quiet-Sun and active-region regions, MLSI-PINN parameter maps reproduce the primary spatial structures of direct inversions, achieving an arithmetic mean pixel-wise Pearson correlation coefficient of 0.933 across all evaluated parameters. The reconstructed spectra closely match both observed profiles and conventional MLSI fits. Post-training, MLSI-PINN processes a raster in approximately 5-15 seconds compared to 3-5 minutes for conventional MLSI, delivering an inference speedup of about 12-60 times without substantial loss in reconstruction quality, enabling efficient MLSI analysis on large chromospheric data sets.

Although a large number of cosmological simulations are now publicly available, their spatial and mass resolutions remain insufficient to accurately follow the dynamics of compact stellar systems and black holes. A complementary approach is therefore required to exploit the cosmological assembly histories encoded in these simulations without rerunning them. We present CosmoDyn, an open-source Python framework that reconstructs time-dependent galactic environments from any cosmological simulations and explicitly follows unresolved compact objects within them. A distinctive feature of CosmoDyn is that it models not only the main host galaxy but also its accreted satellites via moving gravitational potentials. The framework can therefore account simultaneously for the delivery of ex-situ populations and for the dynamical influence of satellites on in-situ population already present in the host. The modular pipeline comprises four main stages: reconstructing the evolving host and satellite potentials; generating in-situ and ex-situ populations of compact objects; integrating their orbits with configurable prescriptions for dynamical friction, and mass loss; and modeling tidal streams. Once reconstructed, the same cosmological environment can be reused to explore different objects, initial conditions, and physical prescriptions at low computational cost. CosmoDyn thus enables rapid parameter exploration and applications to statistically significant galaxy samples, while its modular architecture is designed to incorporate progressively more realistic potentials, and formation models.

The Type I superluminous supernova (SLSN-I) SN 2025wny, multiply imaged by two foreground galaxies at $z_l = 0.375$, is the first confirmed strongly lensed SLSN and the highest-redshift ($z_s = 2.015$) multiply imaged supernova in a galaxy-scale configuration. We ask whether one discovery in seven years of Zwicky Transient Facility (ZTF) operations is consistent with expectations, and whether SN 2025wny is typical of the detectable population. We develop a forward simulation of strongly lensed SLSNe-I in ZTF, combining an empirically calibrated volumetric rate and luminosity function with a galaxy-scale deflector population, unresolved lensed light curves, and the actual ZTF observing history. We predict $0.037^{+0.022}_{-0.020}\,{\rm yr}^{-1}$, consistent with the rate of $0.14^{+0.31}_{-0.11}\,{\rm yr}^{-1}$ inferred from a single discovery in seven years of ZTF operations. Conditioning the simulation on discovery by ZTF corrects the magnifications and intrinsic luminosity of SN 2025wny for Malmquist- and magnification biases: the debiased peak bolometric luminosity, $\log_{10}(L_{\rm bol,int}/{\rm erg\,s^{-1}}) = 44.60^{+0.05}_{-0.10}$, places it at the $\sim$97th percentile of the assumed SLSNe-I luminosity function. SN 2025wny is typical of the detectable population in redshift, luminosity, and magnification, but its $4.9''$ image separation exceeds single-galaxy deflector expectations, implying our rates are conservative for wide-separation systems.

Next-generation galaxy surveys, like the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), will deliver unprecedented depth and sky coverage, enabling precise measurements of cosmic probes such as weak lensing and galaxy clustering. However, increased imaging depth leads to significant blending of galaxy images, particularly in dense fields like galaxy clusters. This blending, exacerbated by atmospheric blurring in ground-based observations, contaminates galaxy property measurements and causes source confusion. To simultaneously capture these effects, we develop a probabilistic framework introducing the blending entropy, a metric quantifying the ambiguity in matching detected objects to true galaxies or external reference sources. Using simulated data from the DESC Data Challenge 2 (DC2), we characterize blending in LSST data and quantify its impact on cluster lensing cosmology around cosmoDC2 halos. We demonstrate that imposing a blending entropy threshold of $S_b<0.2$ effectively filters out highly blended objects (around 25%), which are especially prevalent near the survey's magnitude limit and are associated with higher errors in shape measurements and photometric redshifts. Applying this cut substantially reduces blending-induced biases in cluster lensing profiles and mass estimates, thereby mitigating systematic errors in cosmological parameters---most notably reducing tension in $σ_8$ estimates. Our method is readily generalizable to other static probes and offers a practical path forward for real data analyses, particularly when leveraging overlapping high-resolution datasets from spaced-based missions such as Euclid or the Roman Space Telescope, where these external datasets can act as reference catalogs to improve the identification of blended sources in LSST data.

We investigate the latitude-time relationship between the solar green-line corona and sunspot activity during Solar Cycles 18-24 using homogeneous coronal observations and a Gaussian representation of sunspot activity fields. The activity-field model is constructed from individual sunspot areas and latitudes in order to describe the large-scale spatial organization of solar magnetic activity more realistically than traditional sunspot number or sunspot area indices. The analysis reveals a stable double-peaked latitude-dependent correlation structure centered on the active-region belts, where the strongest corona-sunspot correlations are observed. The latitude profiles remain remarkably similar from cycle to cycle, indicating that the large-scale relationship between coronal emission and photospheric activity is largely independent of cycle amplitude and parity. The lag-correlation profiles exhibit broad positive lag plateaus in most cycles. Although formal lag-correlation maxima occur at positive lags, surrogate-data tests indicate that these maxima are generally not statistically distinguishable from neighboring lag values. The results therefore suggest temporal persistence and memory of large-scale coronal magnetic structures rather than a precisely defined physical delay. The Gaussian activity-field representation produces substantially stronger and more coherent correlations with the green-line corona than conventional sunspot measures, supporting the interpretation that the large-scale distribution of magnetic activity, rather than individual sunspots alone, governs the evolution of the large-scale corona.

We study the thermodynamics of asymptotically flat five dimensional Einstein Gauss Bonnet black holes within the framework of the extended generalized uncertainty principle (EGUP). The geometry dependent localization scale is fixed by requiring the undeformed relation to reproduce the surface gravity temperature. The resulting expression consistently recovers the GUP, EUP, and semiclassical limits, while imposing a joint constraint on the minimum length and minimum momentum parameters. Due to the nonmonotonic behavior of the effective localization scale, the reality condition does not generically yield a unique minimum horizon radius. Depending on the parameter values, the admissible domain may remain connected, develop a degenerate critical radius, or split into two disconnected branches. We derive the entropy, heat capacity, and Helmholtz free energy, and analyze their behavior numerically. The Gauss Bonnet coupling shifts and suppresses the near horizon temperature maximum, whereas the EUP sector induces a temperature minimum followed by linear growth at large radius. In the two branch regime, the outer endpoint exhibits finite temperature and vanishing heat capacity but is approached from the locally unstable side, and should therefore be interpreted as a limiting thermodynamic configuration rather than a dynamically established remnant. Finally, we show that the perturbative entropy deviates from the exact result at large radius, and that the leading GUP entropy correction persists in the Einstein gravity limit.

The ultraviolet continuum from a high-redshift accreting black hole is routinely used to infer its mass. GN-z11 offers a sharp test of whether that inference is secure. A thin-disk fit to its continuum gives an Eddington mass of $M_{\rm E}=1.12\times10^{7}\,\Msun$, an order of magnitude above the $\log(\Mbh/\Msun)=6.2\pm0.3$ inferred from broad N~\textsc{iv}. We show that this apparent tension is not imposed by the ultraviolet slope alone. We derive a closed-form criterion comparing the radius where observed photons are produced with the radius where a supercritical flow departs from efficient solution. For GN-z11, the criterion places the supercritical transition inside the ultraviolet-emitting region. Composite disks retaining the outer solution confirm this numerically, requiring $\Mdot_{\rm out}=3.1$--$4.4\,\Msun\,\mathrm{yr^{-1}}$ and placing $\Rsph=(1.2$--$1.8)\times10^{3}\,\rg$ inside $\Ruv=(2.6$--$2.9)\times10^{3}\,\rg$. Replacing the inner $\sim10^{3}\rg$ by a supercritical flow shifts the fitted slope by only $Δ\betaUV=+0.08$ to $+0.11$, comparable to uncertainties from standard spectral modelling. Reversing the radial ordering requires the effective transition to move outward by a factor $1.7$--$2.1$. Within our composite models, the measured slope constrains black-hole mass only to around $10^{6}\,\Msun$, an order of magnitude below the continuum Eddington mass. Continuum Eddington masses should therefore be treated as model-dependent bounds that assume global thin-disk efficiency. The same hierarchy appears in three additional JWST sources under the disk-dominated interpretation, where separation masses are only $4$--$6$\% of continuum Eddington masses. This distinction can substantially weaken the seed-mass and early-growth demands inferred from ultraviolet continua at cosmic dawn for the first massive black holes.

This paper investigates Yamabe-type soliton structures on the Sultana-Dyer (SD) black-hole spacetime. By employing the explicit metric and curvature quantities associated with the SD spacetime, we demonstrate that the non-Killing vector field $\partial_t$ induces an $h$-almost Yamabe soliton for explicitly determined functions $h$ and $λ$. We also establish the condition under which this structure reduces to an almost Yamabe soliton and examine why the coordinate vector fields $\partial_r$ and $\partial_θ$ do not satisfy the corresponding Yamabe flow conditions. Furthermore, we show that the energy-momentum tensor, consisting of a timelike dust component and a null radiation fluid, is compatible with the Riemann, conformal (Weyl), concircular, conharmonic, and projective curvature structures. This compatibility reveals a strong geometric correspondence between the matter distribution and the causal structure of the spacetime. However, when the time-dependent scalar-curvature profile is subject to the constraints associated with late-stage cosmic expansion, the null, weak, and dominant energy conditions are violated. These findings provide a geometric characterization of the time-dependent Sultana-Dyer spacetime within the framework of generalized Yamabe solitons.

Gaia DR3 2981818948336660224 is a nearby low-mass star with a substantial warm mid-infrared excess. Identified in a Gaia-2MASS-WISE search, it lies at approximately 127 pc and has an AllWISE W3 signal-to-noise ratio of 33.1. We recover the emission in all 16 available cryogenic exposures over 1.26 d; removing any one exposure leaves the signal intact. The W3 emission is centred close to the propagated stellar position, and the known neighbour 6.1 arcsec away fails to reproduce its morphology. Nominal scene fits place 97-98 per cent of the W3 flux at the target position. This provides strong spatial support for association, although template uncertainty and a nearly coincident hidden source prevent a definitive decomposition. The excess can be described by a roughly 300-350 K component with L_IR/L_star ~ 0.022, assuming stellar association and retaining the weaker W4 detection. If produced by circumstellar dust, it falls in the extreme warm-debris regime around a dwarf with no established evidence of youth. Its origin remains unresolved. The repeatable excess and close spatial association make this a useful target for subarcsecond MIR imaging and spectroscopy to test the warm-dust interpretation.

How supermassive black holes (BHs) assemble their mass and power the luminous quasars we observe across cosmic time remain central open questions in galaxy evolution. We present BAQARO, a semi-empirical framework for BH growth. Built on subhalo merger trees extracted from the FLAMINGO-10k simulation, the model links BH growth histories to those of their host subhalos through prescriptions that capture both average trends and stochastic variability. BAQARO is constrained by the bolometric quasar luminosity function, the clustering of UV-luminous quasars, and the conditional Eddington ratio distribution function. With six free parameters controlling BH seeding, the coupling between gas accretion and halo growth, and the stochasticity and temporal coherence of accretion, the model reproduces the available observational constraints over $0 \lesssim z \lesssim 7$. Using emulators, we perform Bayesian inference and quantify the constraining power of each observable. Our main findings are: (i) BH accretion is well described by the assembly of cold gas reservoirs in halos, without requiring an explicit dependence on cosmic time. (ii) BHs rapidly assemble their mass at high redshift through stochastic episodes of super-Eddington accretion. (iii) These episodes are radiatively inefficient and persist for timescales of $\sim1\,\mathrm{Myr}$, imprinting observable signatures on quasar lightcurves, proximity zones, and clustering measurements. (iv) The merger growth channel is always subdominant, but becomes increasingly important at $z \lesssim 1$, particularly for massive BHs. BAQARO growth histories and quasar lightcurves provide a flexible framework for interpreting the rapidly expanding landscape of quasar observations, from high-$z$ accretion probed by JWST to low-$z$ mergers constrained by pulsar timing arrays.

We perform joint Baryon Acoustic Oscillation (BAO) + Big Bang Nucleosynthesis (BBN) and BAO+BBN+Cosmic Microwave Background (CMB) analyses with Planck CMB and DESI DR2 BAO data, explicitly marginalizing over BBN nuisance parameters for the first time with these data combinations and paying particular attention to the impact of BBN on these results. We find in our fiducial analyses $h=0.6833^{+0.0048}_{-0.0053}$ ($Λ$CDM, BAO+BBN), $h=0.6823^{+0.0027}_{-0.0026}$ ($Λ$CDM, BAO+BBN+CMB), as well as $h=0.6791^{+0.0069}_{-0.0075},N_{\rm{eff}}=2.974^{+0.098}_{-0.099}$ ($Λ$CDM+$N_{\rm{eff}}$, BAO+BBN), and $h=0.6838^{+0.0052}_{-0.0054},N_{\rm{eff}}=3.065^{+0.078}_{-0.076}$ ($Λ$CDM+$N_{\rm{eff}}$, BAO+BBN+CMB). We demonstrate how investigator choices can impact results of joint analyses involving BBN. We provide recommendations for the treatment of BBN in light of recent work, and demonstrate a pipeline that accurately accounts for prediction uncertainties in BBN.

Type Ia supernovae (SNe Ia) observables, such as the light-curve shape and the colour, are expected to contain information about the progenitor star. In this work, we explore this information, with a particular focus on the age of the SN Ia progenitor star. For this, we construct the SN Ia progenitor age distribution (SPAD) and compare it to the observed distributions of light-curve shape (x1) and the colour (c) parameters in a volume-limited SN Ia sample. We find that SPAD and the x1 distribution share a common shape: a young/high-x1 peak and an old/low-x1 bump in the tail, and this shape varies systematically with redshift. In contrast, this behaviour is not evident in the c distribution. We then examine the correlation of the local age at the SN Ia explosion site, used as a proxy for the progenitor age, with x1 and c. The local age and x1 are well correlated (the linear correlation coefficient ~ -0.71), whereas the local age and c show no significant correlation (the coefficient ~ 0.08). Furthermore, we find that the x1 distribution systematically evolves with the local age. Lastly, we demonstrate that an empirical mapping approach based on SPAD successfully reproduces the observed x1 distribution across different redshift bins. Taken together, our results suggest that the light-curve shape distribution indicates progenitor age at the population level more robustly than the colour does. In particular, younger progenitors are more likely to have higher-x1 SNe Ia. We discuss an application for creating a more homogeneous sample of SNe Ia in terms of progenitor age across a wide redshift range without the Malmquist bias, thereby improving the accuracy of cosmological constraints derived from SNe Ia.

The search for the origin of ultrahigh-energy cosmic rays (UHECRs) typically relies on identifying directional excesses in the particle flux. While this approach is well established, it cannot detect localized spectral features, which could provide constraints on the sources of UHECRs if measured. In this work, we propose a complementary metric for directional searches, based on a functional $μ_E$ of the energy spectrum in a given arrival direction. We demonstrate that $μ_E$ mathematically decouples the flux normalization of a sky region from the spectral shape, providing a distinct probe for direction-dependent spectra. To assess the statistical significance of this metric, we derive a generalization of the Li-Ma significance formula for energy-weighted metrics. Using a maximum-likelihood analysis within an exploratory Monte-Carlo model, we show that $μ_E$ can enhance discovery potential by identifying hard-spectrum regions that are not apparent in standard particle-flux maps, thereby providing a complementary probe of potential UHECR sources.

Ideal-GRMHD calculations provide the bulk accretion flows used in black-hole emission models. A localized dissipation prescription can add a resolved map of current-sheet activity while retaining that dynamical reference. We implement such a prescription in Athena++, using a smooth threshold on the dimensionless current proxy $α_J$ to select the magnetic-diffusion coefficient. The constrained-transport update is coupled to a conservative energy-flux correction. Gas heating follows from primitive recovery; $q_{Ohm}=ηJ^2$ is recorded as a diagnostic, without a second energy source. Static Fourier and traveling Alfvén tests measure the evolved thermal gain, and an open-boundary Schwarzschild test closes the Killing-energy ledger. The relative total-energy residual is below $2\times10^{-15}$ in these tests. A two-resolution Harris matrix gives localized rate exponents $0.510\pm0.027$ and $0.488\pm0.028$, consistent with $1/2$ over the specified early interval. The $η=10^{-3}$ rate exceeds the same-resolution ideal control by a factor of 5.96. In matched axisymmetric M87*-like runs, localized diffusion changes the early mean magnetic flux, accretion rate, and normalized flux by less than $0.02\%$, with a radial-density distance of $0.005\%$. During the late active phase, a common-restart on/off comparison keeps these mean shifts below $1.6\%$, within the intrinsic temporal variability, and gives a density distance of $0.29\%$. Uniform diffusion at the tested coefficient reduces the raw flux and accretion rate by $85\%$ and $99.8\%$. These comparisons establish a spatially selective diffusion prescription with explicit energy accounting and a quantified, small bulk-flow response.

Superoutbursts and superhumps are characteristic signatures of SU UMa-type cataclysmic variables, yet the full diversity of superhump evolutionary behaviour remains poorly constrained owing to the limitations of ground-based photometric monitoring. Here we report a systematic analysis of 30 SU UMa-type dwarf novae observed with the Transiting Exoplanet Survey Satellite, covering 37 superoutburst events. We detect coherent superhump signals in 29 systems-including five first-time detections-and determine or refine orbital periods for 13 objects. The high-cadence light curves clearly resolve the canonical three-stage (A-B-C) superhump period evolution. Using Stage A periods, we derive dynamical mass ratios for 18 systems, consistent with established cataclysmic variable evolutionary tracks. The measured Stage B period derivatives match the range of values from ground-based campaigns, with prominent positive drifts concentrated in short-period, low-mass-ratio systems. Repeated superoutbursts yield consistent evolutionary patterns, demonstrating that superhump morphology is an intrinsic, repeatable property. Two systems break the standard template: RZ LMi shows an inverted stage sequence inconsistent with classical precession theory, while ASASSN-14kj exhibits no stage evolution but a coherent long-period modulation. Persistent superhumps during normal outbursts in three systems provide direct evidence that eccentric disk structures can survive beyond their parent superoutbursts, revealing a decoupling between thermal accretion and tidal eccentricity cycles. These results demonstrate the power of space-borne photometry for probing accretion disk dynamics and testing precession models across the cataclysmic variable parameter space.

In this manuscript, we investigate the shadow and polarization images of a Simpson-Visser rotating black hole surrounded by a ballistic approximation accretion flow model. Solving the numerically geodesic and radiative transfer equations, we discuss the influence of the regularization parameter $g$, spin parameter $a$, and observer inclination angle $θ_o$ on the resulting images at $230\,\mathrm{GHz}$ with an infalling motion. The results interpret that, a bright circular ring corresponding to higher-order images is observed, accompanied by an inner region of decreased intensity. Both $g$ and $a$ has little influence on the size of the higher-order images, but significantly changes their shape and intensity distribution. Whereas, variation in $θ_o$ modify the image morphology, producing a crescent-shaped bright region on the left side. Finally, the polarization patterns trace the brightness distribution and vary with both $g$ and $a$, reflecting the spacetime structure. These results demonstrates that the intensity and polarization in thick disk models provide probes of Simpson-Visser rotating black holes and near-horizon accretion physics.

We present the first experimentally measured oscillator strengths for Ni II 3d$^8$4d - 3d$^8$4p transitions. High-resolution Fourier transform spectra were recorded of Ni-He hollow cathode lamps, and intensity calibrated using deuterium standard lamps to determine relative intensities of Ni II emission lines between 200 and 395 nm. Branching fractions were determined for observed lines from 35 3d$^8$4d upper levels in total, and account for at least 95% of the predicted transition probability for 31 of these levels, with sufficient completeness to give reliable branching fractions. Combining our measured branching fractions with four experimental and 27 theoretically calculated energy level lifetimes provided absolute oscillator strengths for 174 lines, for which no previous experimental values exist. We compare the results with three sets of previously published theoretical calculations, illustrating the improvement of laboratory measurements for these atomic data. Please note: The transition probability datasets are withheld from this pre-print to ensure that only the peer-reviewed, definitive versions are released. This approach prevents the propagation of duplicate or inconsistent data across widely used atomic databases and modelling frameworks.

An analysis of 36 hours of data from a DALI haloscope reveals no statistically significant excess attributable to dark-photon dark matter. We therefore set new constraints in the 6.88691--6.91792 GHz band, reaching a dark-photon-to-photon kinetic mixing strength of $χ\lesssim 6.8\times10^{-14}$ at $28.54 \, μ\mathrm{eV}$. To our knowledge, this result established the strongest laboratory-based exclusion limit in this frequency range.

DALI is an axion haloscope consisting of a magnetized phased array backed by a conducting mirror and coupled in the near field to a semi-open Fabry--Pérot resonator. The applied static magnetic field makes both the dielectric interfaces and the conducting mirror sensitive to axion-induced electromagnetic conversion. Each interface acts as a radiating surface, and the resulting fields are projected onto the mode collected by the resonator and delivered to the receiver. We derive the detected power in terms of the power available from the magnetized mirror, the coherent contribution of the dielectric interfaces, the transverse mode overlap, the loaded quality factor, and the receiver-coupling coefficient. This formulation separates two distinct enhancement mechanisms. The dielectric-interface emissions may add coherently, producing a dielectric boost, while the semi-open Fabry--Pérot resonator provides enhancement through resonant storage of the coupled electromagnetic field. These contributions depend differently on the dielectric thicknesses, spacings, and resonant mode, and should therefore be evaluated independently. The same assembly can operate between the limits of a coherently boosted dielectric haloscope and a mirror-sourced, resonantly enhanced Fabry--Pérot haloscope. This combined architecture offers a flexible approach to resonant axion searches at frequencies for which conventional closed microwave cavities become increasingly limited in conversion volume.

The study of massive stars in binary and higher-multiplicity systems that participate in particle acceleration is a key topic at the crossroads of massive star physics, shock physics, and galactic cosmic ray astrophysics. From an observational perspective, radio measurements are our pri- mary tool for identifying these systems through their synchrotron radio emission. Out of the 54 such systems known to date, all but two have been discovered via their non-thermal radio emission. However, identifying these systems is not straightforward. The main challenge lies in free-free absorption, which can obscure the synchrotron signature and hinder detection. This paper summarizes recent developments in our understanding of these systems, with a particular focus on the strong observational bias introduced by free-free absorption. This bias significantly limits our ability to determine the true fraction of particle accelerators among colliding-wind binaries.

We study the thermodynamics of Lorentzian Taub--NUT spacetimes in Einstein--Gauss--Bonnet AdS gravity in arbitrary even dimensions, constructed as $U(1)$ fibrations over Einstein--Kähler base manifolds. We compute the temperature from the surface gravity and the energy as the conserved charge associated with the stationary Killing vector using the off-shell Abbott--Deser--Tekin formalism. Within the same framework, we obtain the entropy as a horizon Noether charge. The result agrees with the Iyer--Wald formula and includes a Gauss--Bonnet correction to the Bekenstein--Hawking area law. Retaining the Misner strings whenever present, we formulate a first law of full cohomogeneity in which the NUT parameter varies independently of the horizon radius. This requires an additional thermodynamic charge and its conjugate potential, which we determine explicitly. We also briefly discuss the static limit.

Self-interactions between dark matter (DM) particles facilitate the inter-particle redistribution of energy within the central region of DM halos. Recent studies of dark matter spikes around massive black holes, and the diversity in rotation curves of dark matter rich low-mass galaxies motivate the exploration of self-interaction cross-section $\mathcal{O}(10)\,\rm cm^2/gm$. At such high scattering rates, DM can lead to the formation of supermassive black hole seeds, through the gravothermal collapse of halo cores, under certain cosmological conditions. Quasars near cosmic dawn are powerful probes for examining the formation scenario of high redshift supermassive black holes, and their connection to structure formation. In this work we point out the favorable initial cosmological conditions that are likely to provide the black hole seeds resulting in supermassive black holes, mediated by core-collapse in self-interacting dark matter halos. Employing a semi-analytic prescription of core formation, and realistic mass accretion and halo merger histories, we compare the existing observations of high-redshift supermassive black holes with those predicted for our core-collapse framework. We find the median values of velocity-dependent self-interacting dark matter parameter space $σ/m_χ\sim 56\, \rm cm^2/gm$, and $ω=101\,\rm km/s$, assuming an Eddington accretion rate of unity. Sub-leading values are also presented for sub and super-Eddington accretion rates. We also report the derived self-interacting dark matter model parameters to account for the observed binned supermassive black hole mass functions at high-redshifts.

We present an extended study of the gravitationally localized soliton-like solutions to the minimally-coupled Einstein-Dirac-Higgs equations, embedded in asymptotically Minkowski spacetimes. The equations of motion describing these Yukawa-coupled Dirac stars are generalized to any even number of constituent fermions. We first expand the discussion of two-fermion ground-state solutions initially analyzed in Leith et al. [Phys. Rev. D. 107, 106020 (2023)]. Upon extending our analysis to excited states and many-fermion states, we find that both exhibit different behaviors to their two-fermion ground-state counterparts. In these excited states and many-fermion states, the Higgs field may exhibit stepwise increases and at times decrease within the soliton, which has not been seen for the two-fermion ground states. We also propose the potential cause of a significant degree of ADM-to-fermion mass disparity, which is present in states with strong Yukawa-coupling.

We study the dynamical scalar tidal Love numbers of wormholes that provide viable mimickers for black holes, focusing on thin-shell Schwarzschild and Damour-Solodukhin geometries. Using a matched near- and far-zone expansion, we determine their tidal response in the low-frequency regime. The presence of a long throat introduces an additional characteristic scale and naturally separates the modes into two classes. Super-throat modes probe the global wormhole geometry and are sensitive to both asymptotic regions, whereas sub-throat modes probe only one side of the wormhole and effectively perceive the throat as a black-hole horizon. We derive the scalar tidal Love numbers analytically for both classes of modes and show that their dissipative parts exhibit distinct low-frequency behavior, reflecting whether one or both potential barriers participate in the scattering process. We further find that, as the wormhole approaches the black-hole limit, the super-throat contribution becomes progressively negligible, while the sub-throat response smoothly reduces to that of a Schwarzschild black hole. These results demonstrate that the tidal response of wormholes depends crucially on whether the perturbation probes the global structure of the throat.

In recent times there is considerable unease about the way Artificial Intelligence (AI) powered by large language models is used to do astrophysics, and, assuming that these AIs will get far better in future, several alarming situations are also discussed. In a ``white paper,'' Hogg argues that extreme cases like allowing AI to write all astrophysics papers or strictly controlling AI are not good choices and posits that it is difficult to adopt moderate policies. I examine the impact of AI on astrophysics by making two rather extreme assumptions: first, that the modern astrophysicist has become increasingly preoccupied with the administrative task of publication over the act of physical discovery (astrophysicists are busy writing papers and have stopped doing astrophysics); and second, that while AI possesses the capacity to synthesize literature and generate manuscripts, they lack the intrinsic ability to perform original astrophysical inquiry (AI can write papers but cannot do astrophysics). I provide some plausible reasons for adopting these assumptions, but, more importantly, extrapolate the implications of these assumptions to argue that AI can have a very positive impact on astrophysics. By situating AI as agents of publication rather than discovery, the focus of the human researcher can be directed towards fundamental astrophysics, leading to very positive growth in the field.

We present a fully nonlinear relativistic description of the observed pulsar timing modulations, defined through the ratio of the proper-time intervals between two successive emissions of radio pulses and their observations by a pulsar timing array. Working in the limit of a vanishing emission interval, we derive the observed pulsar timing modulation to second order in relativistic perturbation theory around a Minkowski background, without fixing a gauge and retaining the full scalar, vector, and tensor content of the metric perturbations. Although the derivation naturally introduces several gauge-dependent intermediate quantities, we explicitly demonstrate that they combine into a coordinate-independent expression. Moreover, we explicitly show that the second-order timing modulation from two neighboring radio pulses coincides with the observed redshift, defined as the fractional change in wavelength along a single geodesic. The agreement represents a nontrivial second-order realization of the exact nonlinear equivalence proven in Magi & Yoo 2026.

We report an independent identification of the ultra metal-poor (UMP) star ($\rm[Fe/H] =-4.06$) $Gaia$ DR3 $\texttt{source_id}$ 4795913112968206720 (GDR3_479591) in the $Gaia$ mission's Blue and Red Photometer 'XP' spectro-photometric catalog. We combine multi-band photometry, astrometry, and high-resolution spectroscopy to confirm GDR3_479591 as a red giant-branch (RGB) star located at ${\sim} 6\,{\rm kpc}$ from the Sun. Abundance analysis under local thermodynamic equilibrium reveals significant enhancements, relative to the solar level, in carbon ($\rm[C/Fe] = +1.54$, after evolutionary correction for depletion in the RGB), nitrogen ($\rm[N/Fe] = +2.64$), and oxygen ($\rm[O/Fe] = +2.62$). The CNO-enhanced GDR3_479591 is thus one of only 5 UMP stars with a detected oxygen abundance. The CNO excess is accompanied by enhancements in several other light elements, such as Na, Mg, Al, and Si. We demonstrate that the chemical pattern of GDR3_479591 can be reproduced by the yields of a single Population~III 'faint' supernova with progenitor mass of $\sim$21-to-28$\,M_\odot$ and a low explosion energy of ($0.3 \leq E_{\rm SN}/(10^{51}\,{\rm erg}) \leq 0.9$). Additionally, we use literature metal-poor stars to show that, contrary to recent propositions for high-redshift galaxies, a mild enhancement in [C/O] does not automatically translate to the high [C/Fe] typically observed in UMP stars in the Milky Way and its satellites. GDR3_479591 could not be dynamically associated with any of the most relevant accreted substructures in the Galactic halo, and we speculate that it was formed in an ultra-faint dwarf galaxy environment that later merged with the Milky Way.

In this study, we present the full (97.3\% complete) 0.8--12.5 $μ$m spectral energy distribution (SED) of an L/T transition object, CWISE J210640.16+250729.0 (CW2106), using the James Webb Space Telescope (JWST). We provide a full characterization of the host star's elemental abundances and age. We empirically derive the bolometric luminosity ($L_{\rm bol}\approx-4.825$ $\textup{L}_\odot$) of CW2106, and obtain estimates of its mass (M$\approx50-62$ M$_{\rm Jup}$), radius (R$\approx0.83-0.87$ R$_{\rm Jup}$), effective temperature ($T_{\rm eff}$$\approx1213$ K), and surface gravity ($\log~g$$\approx5.28$ dex). We find the near-infrared (near-IR) spectrum ($0.8-2.5 ~μ$m) is best reproduced with cloudy atmospheric models while the mid-infrared (mid-IR) spectrum ($5-12.5 ~μ$m) is best reproduced with cloudless models. This suggests a cloud layer restricted to only the deepest observable parts of the atmosphere and is qualified by the lack of a 9 $μ$m silicate feature. Making use of the Mg/Si ratio of the primary, alongside thermochemical models, we predict the clouds in CW2106 to be composed primarily of enstatite (MgSiO$_3$), removing $\sim23\%$ of the bulk oxygen out of the atmosphere. Future retrieval studies will be able to help investigate the existence and full impact of these cloud species.

We present the stellar parameters for 59,266 high-quality spectra of 24,130 unique stars from the MaNGA Stellar Library (MaStar) in the Sloan Digital Sky Survey (SDSS) Data Release 17 (DR17). The median signal-to noise ratio per pixel of the spectra is 96. We derive four stellar parameters, effective temperature (Teff), surface gravity (log g), metallicity ([M/H]), and {$α$}-enhancement ratio ($\rm [α/M]$), by comparing the data with BOSZ (ATLAS-9 based) and MARCS theoretical atmospheric models. We adopt a Bayesian method and use color and absolute magnitude derived from Gaia to select a subset of theoretical models for each star. We then perform full-spectrum fitting to estimate the likelihood of each model in the subset and then compute their likelihood-weighted mean parameters as the final parameters. We set stellar-parameter quality flags to facilitate the use of the derived stellar parameters. The MaStar stellar parameters derived herein span an effective temperature range of $\rm 2,600 \leq T_{eff} \leq 29,861 K$, a surface gravity range of $0 \leq \log g \leq 5.5$, a metallicity range of $-4.9 \leq \rm[M/H] \leq 1.0$, and an {$α$}-abundance range of $\rm -0.98 \leq [α/M] \leq 1.0$. We compare these parameters with those from APOGEE and Gaia for stars in common, finding general consistency within the uncertainties. However, some artifacts and systematic differences are present, and we discuss their potential causes. These new stellar parameters are available through the MaStar SDSS-IV DR17 value-added catalog (https://www.sdss4.org/dr17/mastar/mastar-stellar-parameters/).

We present theoretical estimations of the event rates for the interaction between a right-handed fermionic dark matter with an electron bound to a xenon atom. Motivated by recent astrophysical and cosmological constraints on a fermionic dark matter candidate in the sub-MeV mass range, we study such an interaction through an effective electromagnetic channel where the output consists of standard-model particles. This mechanism allows right-handed neutral dark matter fermions to couple with standard-model particles with the interchange of $W^{\pm}$ or $Z$ bosons, without the need to add extra fields. We generalize and extend previous results on this type of channels, by including for the ionization form factor arising from the interaction of the fermionic candidate with bound electrons. In addition, we compute the sensitivity curves for different direct detection experiments in such a challenging light particle mass range.

The energy spectra of Galactic cosmic rays (GCRs) serve as critical probes of their astrophysical origins and propagation mechanisms through the interstellar medium. Among the key physical processes shaping the observed spectra, solar modulation, driven by turbulent heliospheric magnetic fields and the variability of the solar wind, plays a dominant role in modifying GCR fluxes within the inner heliosphere. The recent release of time-dependent flux measurements for He, Li, Be, B, C, N, and O by AMS-02 provides unprecedented precision to investigate solar modulation phenomena. In this study, we demonstrate that Li, Be, B, C, N, and O nuclei exhibit solar modulation parameters consistent with those of protons (p) and He within a modified force-field approximation (FFA) framework incorporating rigidity-dependent modulation potentials. By positing that GCRs with the same charge-sign sharing the solar modulation parameters, we further forecast daily fluxes of Ne, Mg and Si from 2011 to 2020.

Axion-star mass-radius relations are commonly computed using different orders of relativistic approximation, making it important to determine where these descriptions remain reliable. We perform a unified numerical comparison of axion-star ground-state configurations in the Newtonian Schrödinger-Poisson description, first- and second-order relativistic effective field theories, and the full Einstein-Klein-Gordon system for a real scalar field. Using the same attractive quartic self-interaction in all four descriptions, we scan $|\widetildeλ|=(M_{\rm Pl}/f_a)^2$ and determine the maximum masses and corresponding enclosed-mass radii. All descriptions recover the common large-$|\widetildeλ|$ dilute-star scaling, while substantial differences appear at weak and moderate coupling. The relativistic EFTs interpolate systematically between the Newtonian and full-GR results. For part of the maximum-mass sequence where $\max|φ|/f_a=O(1)$, we test the temporal-harmonic and potential truncations explicitly in full GR. The higher-harmonic expansion shows rapid convergence, while restoring the complete single-cosine potential changes the maximum mass only at the percent level and $R_{95}$ at the several-percent level. Together with the systematic convergence of the relativistic EFT descriptions toward full GR, these results show that the large weak-coupling departure from the Schrödinger-Poisson prediction reflects the breakdown of the nonrelativistic structural description. Our results provide a systematic benchmark for determining when Newtonian, relativistically corrected, or fully general-relativistic descriptions are required for axion-star structure. The numerical implementation used in this work is available in the Axion Star Solvers repository at https://github.com/Parisa-Arabameri/AxionStar.

We study inverse source reconstruction in generalized Vaidya spacetimes. A prescribed density fixes the mass and tangential pressure, while a two-sector decomposition determines a dimensionless radial balance function. We distinguish this function from a time-directed conversion rate and identify the additional null-flux information required for a covariant exchange vector. Positivity restricts the allowed target pressures: a de Sitter core cannot be represented by nonnegative sectors with nonnegative tangential equations of state. An explicit finite-density profile admits a positive vacuum-like completion, finite curvature invariants, and inner and outer trapping horizons above a calculable threshold. Its total source satisfies the null, weak, and dominant energy conditions during monotonic accretion, while the timelike convergence condition fails in the core. We check polytropic, bag-model-inspired, and condensate-inspired profiles and the corresponding cosmological reconstruction. Finally, we compute the stationary endpoint's shadow and compare its exterior deformation with published Sagittarius A* measurements. The construction establishes local curvature regularity and marginal-sphere formation, without claiming a microscopic formation mechanism, perturbative stability, or geodesic completeness.

In this work, we investigate the thermodynamic consistency of the apparent horizon in effective loop quantum cosmology (LQC). By retaining the standard definitions of horizon thermodynamic quantities, we find that the modified LQC dynamics leads to a departure from the classical equilibrium thermodynamic description. This deviation can be naturally described by a nonequilibrium formulation characterized by an internal entropy production term. The resulting entropy production consistently recovers the classical and de Sitter limits. These results suggest that the apparent horizon in effective LQC admits a coherent nonequilibrium thermodynamic interpretation.

In this study, we calculate the relative frequency shift ($Δν/ ν$) caused by gravitational lensing resulting from the transverse motion of a spinning lens described by the Kerr metric \cite{Kerr:1963ud}. While the effect of transverse velocity on the frequency shift has previously been investigated using the Schwarzschild metric \cite{Rahvar_2020,10.1093/mnras/stae1938}, extending this to the Kerr metric provides a new window for measuring the transverse velocity of a lens or its spin parameter, a parameter often subject to degeneracy in gravitational microlensing observations. Recent microlensing observations have revealed black holes as viable lensing candidates \cite{2022ApJ...933...83S}. Since spinning black holes form naturally from stellar evolution, astrophysical black hole lenses are best described by the Kerr metric. Furthermore, recent observations of supermassive black holes at the centers of galaxies provide an ideal laboratory for testing the observational effects of the Kerr metric by measuring the frequency shifts of lensed sources.

We study the impact of flavour-specific neutrino self-interactions on the CMB anisotropy spectrum and consistently take into account neutrino mixing. Starting from the neutrino quantum kinetic equations, we derive the neutrino Boltzmann hierarchies for the neutrino mass states. Our work shows that most scenarios of flavour-specific neutrino self-interactions are well approximated by a combined fluid approach. In practice, this implies that existing CMB bounds on the effective neutrino coupling are weakened by a factor $\sqrt{2}$ for scenarios in which only two neutrino flavours interact (irrespective of which flavours). If only one neutrino flavour interacts the bounds are weaker by a factor $\sqrt{6}$, with the only caveat that the combined fluid approach is less reliable for only $ν_e$ interacting.

The origin of the heaviest elements remains a fundamental mystery, with the "actinide-boost" (Thorium overabundance) serving as a critical diagnostic of r-process nucleosynthesis conditions. While this diversity is well documented in extremely metal-poor (EMP) stars, its frequency in the mildly metal-poor (MMP) regime ($-2.0 < $ [Fe/H] $< -0.5$) is poorly constrained due to blending issues in the commonly used 4019 angstrom line. We present a systematic abundance analysis of mildly metal-poor stars, exploiting the relatively unblended Th II 5989 angstrom line. High-dispersion spectra were obtained using the 1.5 m telescope at Gunma Astronomical Observatory with GAOES, complemented by archival data from the Subaru Telescope/HDS retrieved via SMOKA. We successfully detected Th in 32 out of 42 sample stars. Our analysis demonstrates that the 5989 angstrom line is a useful diagnostic for Th abundance measurements in cool red giants. The mean [Th/Eu] ratio remains nearly constant over the MMP metallicity range, suggesting that progressive homogenization of the interstellar medium during Galactic chemical evolution would reduce abundance variations inherited from individual r-process events, or the dominant r-process events may share similar initial Th/Eu production ratios. While the [Th/Eu] ratio is nearly constant overall in the MMP regime, its dispersion appears to increase toward the metal-rich end of this regime and reaches approximately 1 dex near solar metallicity. This behavior may reflect the combined effects of variations in the initial Th/Eu production ratios of the progenitor objects, the mixing of r-process products in the interstellar medium, and the radioactive decay of Th over stellar lifetimes.

In this paper, we introduce a method to constrain the variation of fundamental physical constants predicted by grand unified theories. This approach utilizes OH sum rules, which exhibit different forms depending on the physical conditions of the OH gas. Employing a least-squares technique, we can directly derive the relative velocity offsets among four OH lines in each ground state. This circumvents the need for spectral profile fitting, which is often unfeasible for spectra with complex profiles. Moreover, this method remains robust even when portions of the spectra are contaminated by radio frequency interference (RFI). Applying this method to a Galactic source G035.1+0.5, we obtained a stringent constraint of $ΔX/X=(-1.8\pm5.1)\times10^{-6} $, where $X=μ^{-1}α^{2}g_{p}^{0.54}$. This method is expected to play a crucial role in extracting fundamental physics from large datasets of upcoming Square Kilometre Array (SKA) telescope.

We report the full sub-Kelvin characterization of the BAUSCIA high-frequency gravitational-wave antenna, based on cryogenic Bulk Acoustic Wave resonators coupled to SQUID amplifiers for signal readout. The end-to-end performance analysis of the experimental chain, from the sensor to the DAQ, demonstrates that resonator thermal noise dominates the noise budget at temperatures well below 100 mK for all investigated modes. The measurements also verify proper thermalization of the resonator modes and rule out significant SQUID backaction on the strain sensor, confirming that the system operates close to its fundamental limits with comparable resonator thermal noise and additive readout noise. From this characterization, we derive projected strain sensitivities in the range $1$--$10 \times 10^{-21}\,\mathrm{Hz}^{-1/2}$ for several resonant frequencies between 5 and 20~MHz, with corresponding fundamental thermal limits in the range $0.7$--$1.4 \times 10^{-21}\,\mathrm{Hz}^{-1/2}$. Equipped with three resonators and synchronized to an absolute global time reference for multi-site coincidences, the antenna is ready to enter a pilot science run.

This paper focuses on the quasinormal modes of a charged loop quantum black hole that preserves diffeomorphism covariance. We have examined the influence of the black hole charge Q and the quantum parameter ζ on the quasinormal modes of neutral massless scalar field, neutral massive scalar field and massless charged scalar field. For the neutral massless scalar field, our work shows that as in the case of the corresponding uncharged black hole that has been examined by other authors, the turn-on of ζ renders the real parts of the overtones a tendency to approach zero. Increasing Q can inhibit this tendency. For the neutral massive scalar field, when Q and ζ are turned on, arbitrarily long-lived modes still exist. We also observe a non-monotonic behavior in the fundamental mode as the field mass varies for the first time. For the massless charged scalar field, our study shows that the asymptotic behaviors of the quasinormal modes of charged field and uncharged field are different as the extremal charge Qis approached. We also find that the real part of the fundamental mode tends to zero at some critical value eQfor a charged scalar field with field charge e.

We investigate exact spherically symmetric and static black hole solutions in a non-minimally coupled Einstein--Maxwell theory of the $Y(R)F^2$ type, extended by a minimally coupled real scalar field and an anisotropic matter distribution. The Maxwell field is coupled to the spacetime curvature through an arbitrary function of the Ricci scalar, while the scalar field is described by a kinetic term and a scalar potential. We obtain exact solutions for power-law and logarithmic forms of the non-minimal coupling function and analyze the corresponding spacetime geometries. In particular, we identify a special $β=-1/3$ case for which the general power-law solution becomes singular and derive a new logarithmic metric by solving the field equations independently. The resulting configurations are asymptotically flat and exhibit modified gravitational properties associated with the interplay between the scalar field, anisotropic matter, and non-minimal electromagnetic coupling. We further show that the magnetic solutions admit electrically charged counterparts through an electromagnetic duality transformation, under which the metric and scalar sector remain invariant while the non-minimal coupling function is inverted. The obtained solutions provide a useful framework for investigating black hole horizons, thermodynamic properties, geodesic motion, and astrophysical phenomena such as galactic rotation curves in curvature-dependent electromagnetic theories.

The population of extragalactic black holes has been significantly expanded and better understood since the first detection of gravitational waves. Over the past decade, approximately 290 events have been confirmed to involve at least one black hole. In contrast, the galactic black hole population has grown at a much slower pace, with only 42 systems possessing mass estimates, while the vast majority remain as candidates. In this work, we present the first update of a Bayesian analysis of the mass distribution of galactic black holes since 2011, previously based on a sample of 15 low-mass X-ray binaries and 5 high-mass X-ray binaries. Our update includes 28 low-mass X-ray binaries, 6 high-mass X-ray binaries, 7 detached binaries and 1 isolated black hole, also present in the living catalog \textit{CatNoir} which we introduce. We apply a Bayesian framework using five parametric models -- Gaussian, two-Gaussian, log-normal, power-law, and decaying exponential -- and compare their performance in fitting the observed data. Furthermore, we inspect the effect of removing model-dependent systems from the sample. Our results suggest that the power law better describes the Combined sample, while the Gaussian is preferred for the LMXB-only sample, closely followed by the two-Gaussian and log-normal. We derive the $1\%$-quantile of the preferred model's posterior predictive distribution to access information about the lower mass gap. For the Combined and LMXB Samples, we find $M_{1\%} > 4.06\,M_\odot$ and $M_{1\%} > 2.56\,M_\odot$ (at $90\%$ C.I.), respectively. The LMXB result allows for the existence of a sparsely populated Gap, instead of a completely empty one.

The ringdown of a black hole following a merger is a potential candidate for revealing the signatures of quantum gravity in the emerging gravitational waves. In quantum theory, black holes are expected to have a discrete area and energy spectrum, which conflicts with the classical notion of an horizon that absorbs all infalling perturbations. We propose that the quantum black hole dissipates the energy it cannot absorb by emitting ``soft'' gravitons that carry away the energy difference between the energy of the infalling perturbation and the quantum transition energy. We find that the ringdown spectrum is consequently enriched with low-frequency components, and that there exists a weak low-frequency flux that persists for a timescale much longer than the ringdown itself.

We investigate primordial black hole (PBH) formation during an early matter-dominated era using fully nonlinear numerical relativity. The initial condition is set by a functional form of the curvature perturbation including ellipticity, which makes the configuration triaxial. Two kinds of matter descriptions are considered: dust fluid and collisionless particles. In the dust fluid description, numerical computation crashes associated with the appearance of a singularity at which the fluid density diverges, unless the singularity is hidden well inside the apparent horizon. We found that, for the dust fluid description, to observe the horizon formation before calculations crash, the initial amplitude must be larger than the previous analytic estimation by a factor of 2. On the other hand, with the particle system description, calculations do not crash, and we may observe black hole formation after subsequent evolution of the system. Then the threshold of black hole formation is significantly smaller than the previous analytic estimation by an order of magnitude.

The intracluster medium (ICM) in merging galaxy clusters exhibits turbulence and bulk flows. Unraveling these components is crucial not only for elucidating the geometry of the cluster mergers, but also for understanding the physics of magnetic field amplification and relativistic particle acceleration. XRISM/Resolve data for two $3'\times3'$ fields in the core of the Coma cluster reveales that the ICM in the central field moves with $Δcz = -430$~km~s$^{-1}$ relative to the cluster galaxy average, while that in the southern field moves with $Δcz = -730$~km~s$^{-1}$ (see \cite{2025ApJ...985L..20X}, hereinafter ``Paper I''). In this paper, we perform a more detailed analysis of these data sets to search for non-Gaussian features in the Fe-K line complex profiles. In the spectra from the northwest (NW) quadrant of the central field, in addition to the main and redshifted ICM components ($Δcz = -40$ km s$^{-1}$) reported in Paper I, we find evidence of another, blueshifted component, moving with $Δcz = -1250$ km s$^{-1}$. For a systematic search for other significant velocity components, we perform a bias-free 3 eV step multi-component fit to the Resolve full-array spectra from the central and southern fields. This search uncovers another redshifted component in the southern field, moving with $Δcz \sim +1230$ km s$^{-1}$. We estimate the energy densities of the ICM turbulence and bulk motion to be similar to each other and several times greater than the energy density of the cluster's $B\sim 5~μ$G magnetic field.

Ringdown gravitational waves from binary black hole mergers can be modeled as superpositions of quasinormal modes (QNMs), whose frequencies and excitation factors encode properties of the remnant Kerr black hole. Reliable extraction of multiple QNM components is challenging because of mode overlap and noise. We develop an autoencoder-based framework for multi-component QNM analysis, in which the latent space is trained to represent the physical parameters of individual modes, enabling waveform denoising and parameter estimation within a common framework. Using controlled model waveforms constructed as finite sums of Kerr QNMs with recently established high-precision frequencies and excitation factors, including their nontrivial spin dependence near resonant excitation, we assess the method across partitioned spin intervals. The model achieves good in-domain waveform reconstruction and parameter recovery for the two longest-lived components of eight-component input waveforms, while its performance degrades when the validation spins lie far outside the training range. In a selected spin interval, the framework also recovers the 32 parameters of an eight-component waveform with good overall agreement. These results demonstrate the feasibility of physics-informed autoencoder-based inference for a prescribed multi-component ringdown waveform family and motivate further tests with progressively more realistic signals.

We investigate the quasinormal spectra and time-domain evolution of scalar, electromagnetic, and gravitational perturbations of the Einstein-Bronnikov black hole in Einstein gravity coupled to nonlinear electrodynamics. The effective potentials associated with all perturbation sectors are shown to form positive potential barriers that vanish at the event horizon and spatial infinity. Their height increases with the magnetic charge, while the scalar perturbation possesses the largest potential barrier. Unlike the Reissner-Nordström black hole, axial and polar electromagnetic perturbations are characterized by distinct effective potentials, demonstrating the breaking of isospectrality due to nonlinear electrodynamics. Quasinormal frequencies are computed using the sixth-order WKB approximation and the asymptotic iteration method, yielding excellent agreement for both fundamental and higher overtone modes. The oscillation frequencies increase monotonically with the magnetic charge, whereas the damping rates exhibit only moderate variations, confirming the linear stability of the Einstein-Bronnikov black hole under all perturbations considered. Time-domain profiles display exponentially damped ringdown signals consistent with the frequency-domain analysis. These results demonstrate that nonlinear electrodynamics leaves measurable imprints on black hole perturbations and may provide observational signatures for testing regular black hole geometries through future gravitational wave observations.

We apply the quadratic balance relation for linear nonadiabatic pulsations to radial modes of a sequence of post-AGB envelope models covering $3.52\leq\log(T_{\rm eff})\leq4.6$. The relation separates the thermodynamic exchange power $\mathcal{P}_{\rm ex}$, response power $\mathcal{P}_{\rm rsp}$, and surface contribution $ΔB$, and introduces an effective norm through $\mathcal{P}_{\rm ex}+ΔB=2γχ_{\rm eff}\mathcal{E}_{\rm kin}$, where $γ$ is the mode growth rate. For nearly adiabatic modes $χ_{\rm eff}$ is close to unity, whereas in strongly nonadiabatic pulsations the compression and horizontal area deformation contributions can make it change magnitude or even reverse its sign. In the cooler models, a broad family of overtone modes has $χ_{\rm eff}<0$ and is damped despite positive thermodynamic exchange power. For these modes the response power supplies the opposing damping. Conversely, two low frequency modes in the hotter models are excited over a range of effective temperatures, even though their thermodynamic exchange power is negative. Their instability is produced by the positive response power. Strange modes generally have $χ_{\rm eff}>0$, apart from a narrow boundary-sensitive transition during which a cold strange mode transforms into an ordinary p-mode. The excited low frequency solution with $χ_{\rm eff}<0$ persists with a finer numerical mesh and such modes are found under the alternative outer boundary formulations examined, although their frequencies are boundary condition dependent. Thus, for strongly nonadiabatic pulsations, the sign of the thermodynamic exchange power alone does not determine mode stability.

By analyzing slit scanning spectral data obtained during 2024 total solar eclipse, presence of neutral atom corona is revealed along with a hidden inner F-corona detected within heights below half a solar radius. The inner F-corona is found to be essentially different from the Fraunhofer corona formed by dust scattering beyond about 2.3 solar radius heights. The two new kinds of the solar corona are deduced from the intensity difference between the spectral line intensity distribution and their adjacent continuum one acquired during the totality. Through analysis of the recorded spectra ranging from 516.0nm to 540.7nm, the relative depths of strong Fraunhofer lines are found to be changed among the neighboring lines from one place to another and from the photospheric lines acquired before the eclipse. Thus the resonant scattering is regarded to be responsible for the changes. Furthermore, shown in the reconstructed maps at selected spectral lines, the detected inner F-corona is found spreading globally and the neutral atom scattering acts as its dominant source. Both of their distribution patterns generally depend on specific lines and show considerably asymmetrical diffusions. The outward neutral fluxes are observed to be mainly hindered in regions of coronal magnetic loops with roughly estimated concentration above $10^{-5}$. Thus it can play a key role in global coronal heating via Cowling dissipation in these widely spread coronal loops, like heating in Tokamak by neutral beam injection(NBI). The Cowling dissipation can give a consistent interpretation of heating from the chromosphere to the corona. Thus the neutral atom corona is not only a new gradient of the solar corona but also the missed factor critical for concatenating together these coronal heating mechanisms.

We investigate solar-neutrino spin--flavor precession (SFP) induced by magnetic moments in the three-active-flavor framework. For Majorana neutrinos, SFP can convert solar neutrinos into antineutrinos of different active flavors. In the Dirac case, SFP instead produces sterile right-handed states and can lead to the disappearance of active neutrinos. Using the full $6\times6$ Hamiltonians and GS98 and AGSS09 solar profiles, we examine propagation-eigenvalue crossings at $B_\perp=0$ and the projected magnetic couplings between the corresponding states. For normal mass ordering and $1\leq E_ν/\mathrm{MeV}\leq20$, we confirm the absence of finite-density Majorana crossings. A magnetically coupled Dirac crossing emerges above approximately $12~\mathrm{MeV}$ but involves only a subdominant electron-flavor component, limiting resonant disappearance. Nonresonant Majorana conversion nevertheless offers a distinctive lepton-number-violating solar $\barν_e$ signal, motivating our sensitivity study for the Jinping Neutrino Experiment. For a proposed $3~\mathrm{kt}$ detector operating for five to ten years, we project a 90\% C.L. sensitivity of $P(ν_e\to\barν_e)\simeq(0.85-1.3)\times10^{-5}$. In the $μ_{12}$-only benchmark, optimistic solar-core transverse magnetic fields of $B_\perp=7-10~\mathrm{MG}$ imply a reach of $|μ_{12}|\simeq(2.3-4.1)\times10^{-13}\,μ_B$, numerically below existing direct-scattering limits and commonly quoted stellar-cooling bounds. This could enable Jinping to provide one of the most stringent projected terrestrial sensitivities to Majorana transition magnetic moments.

[Abridged] In this work, we compare neutron stars where dark energy or dark matter are present in the core, contrasting them against purely baryonic stars with the same central energy density. From this comparison, we find that the dark energy models are more constrained by neutron star observations than the dark matter models, suggesting that neutron stars can place strong constraints on dark energy parameters. We consider four configurations: purely baryonic neutron stars described by a piecewise polytropic (PP) equation of state (EoS), baryonic stars admixed with bosonic or fermionic asymmetric dark matter (ADM) cores, and stars with a dark energy core and baryonic shell, where the dark energy is described by the modified Chaplygin dark fluid (MCDF). Using the masses and radii of PSR J0740$+$6620, PSR J0437$-$4715, and PSR J0030$+$0451, we employ Bayesian inference to investigate how accounting for bosonic/fermionic ADM and MCDF cores affects the inferred neutron star properties. We find that MCDF cores, more than PP and ADM admixed models, substantially broaden neutron star mass-radius and pressure-energy density posterior distributions. Moreover, the MCDF EoS parameters can be tightly constrained. While bosonic and fermionic ADM cores decrease the inferred maximum mass, their posteriors strongly coincide with those of the PP model for ADM mass-fractions $F_χ\leq 5\%$. These results demonstrate that current mass-radius observations cannot rule out MCDF cores, but they can constrain the MCDF parameter space to narrow regions. ADM admixed neutron stars, however, remain observationally identical to purely baryonic stars for all explored mass-fractions, even with improved mass-radius uncertainties. This suggests that mass-radius measurements alone are insufficient to detect ADM core inside neutron stars and that independent astrophysical or particle physics probes will be required.

The model of Galactic population of stripped helium stars, the remnants of $5 \lesssim M/M_\odot \lesssim 24$ primary components of close binaries after RLOF is presented. These stars emit in the UV range of the spectrum and may be observed by detectors aboard planned "Spektr-UV" (WSO-UV) space telescope. For the current star formation rate in the Galaxy 2$\mathrm {M_\odot yr^{-1}}$, the estimate of the number of 1 to 7 $M_\odot$ objects with $T_{\rm eff} \gtrsim$25,000\,K ranges from 14700 to 28500. The number of 2 to 7 $M_\odot$ objects is 3200 to 5500. The main evolutionary factor influencing the estimate is possible formation of common envelopes and merger of components in them. Detection of candidate stripped helium stars by UV-excess is hampered by the dominance of main-sequence companions to stripped helium stars in the combined spectra of binaries. This effect of observational selection may reduce the number of candidate stripped helium stars potentially detectable by photometry to $\lesssim 1000$.

Please check the paper for full abstract. The Galactic Center Excess (GCE) is an unexplained excess of gamma-ray emission from the Galactic Center. The GRAINE experiment aims to reveal the origin of the GCE using an emulsion gamma-ray telescope with high angular resolutions of 1 deg at 100 MeV and 0.1 deg at 1 GeV. In this study, we search for the GCE in a small region near the Galactic Center using the GRAINE 2023 flight data. In particular, rather than focusing on the spectral peak of the GCE at 2 GeV, we focused on the energy range below 300 MeV, where the spectral differences between the dark matter annihilation and millisecond pulsar scenarios are more pronounced. We searched for the GCE within 1 deg of the Galactic Center in the 75--300 MeV energy range. Although no significant excess was observed, we obtained an upper limit on the GCE flux of 1.70*10^-7 GeV cm^-2 s^-1 at the 2 sigma confidence level for the 1deg-radius ROI centered on the Galactic Center, based on a direct observation of the narrow region around the Galactic Center. This observation requires high angular resolution and represents a unique result from GRAINE. The obtained upper limit is consistent with the GCE flux near the Galactic Center, which was estimated from existing Fermi-LAT observations using a wide ROI and assuming an NFW profile. Although the current upper limit constrains some models, the available statistics are still insufficient to distinguish between the dark matter annihilation and millisecond pulsar scenarios, and both remain consistent with the current results. We also estimated the projected sensitivity of future GRAINE experiments based on the present observation and demonstrated their potential to probe the origin of the GCE by comparing the projected sensitivity with the predicted GCE spectra.

We consider collisions between particles moving freely in the Schwarzschild background. We suggest classification of scenarios that lead to unbounded energy output in the center of mass frame. Although this is forbidden in the exterior of a black hole, the phenomenon becomes possible with account of white hole region and mirror universe in the complete space-time diagram. Also, we scrutinize collisions in the vicinity of the bifurcation point and reveal the role of resting observers in the inner region beyond the horizon. In some scenarios $E_{c.m.}$ not only diverges but becomes seemingly infinite that is, as a matter of fact, impossible according to the principle of so-called kinematic censorship. We resolve a corresponding paradox and argue, why this principle remains valid.

In this work, we derive phenomenological constraints on a symmetric black-bounce geometry supported by an anisotropic fluid. We investigate the effects of the bounce parameter and the matter parameter on classical and strong-field observables, considering the perihelion advance, light deflection, Shapiro time delay, and black-hole shadow. In the weak-field regime, we obtain analytical corrections to the corresponding general-relativistic predictions and use Solar-System measurements to constrain the parameter space. We find that the matter parameter is generally constrained more strongly than the minimum-radius scale, reflecting the suppressed dependence of weak-field observables on the bounce parameter. In the strong-field regime, we show that the asymptotic shadow radius depends directly on the matter parameter, whereas the bounce parameter enters through the existence condition of the outer unstable photon orbit rather than through an independent correction to the shadow size. These results highlight the distinct roles played by the matter and bounce parameters in weak- and strong-field observables and provide complementary constraints on the parameter space of the symmetric black-bounce geometry.

Context. Globular clusters (GCs) are fragments of the chemical history and evolution of the Milky Way. Their notable intra-cluster abundance variations have been used to characterise chemical trends and stellar populations. However, the origins of these populations and GCs in general are still largely unknown. Aims. Our aim is to explore the origin of the stellar populations belonging to 14 GCs making use of their abundances derived from the Gaia-ESO Survey (GES) spectra. In particular, we use the Mg-Al anti-correlation to separate the populations. Methods. The GES spectra were revisited to derive additional homogenous chemical abundances for Mg and Al. A Gaussian Mixture Model (GMM) was applied to the [Mg/Al] distribution for each cluster to define a threshold between the two main populations. Results. Eight clusters imply the presence of Mg-Al anti-correlations and dual populations. We find there is a regime transition near [Fe/H] approximately -1.4, where, the Mg-Al anti-correlation disappears at higher metallicity. Several clusters, regardless of their Mg-Al anti- correlation behaviour, exhibit metallicity spreads (e.g., NGC 2808, NGC 6752) and s-process variations (e.g., NGC 7078, NGC 1851), suggesting complex enrichment histories. Conclusions. The presence and spread of the Mg-Al anti-correlation depend on cluster mass and metallicity, with metal poor and/or massive clusters exhibiting the clearest anti-correlation. This work demonstrates additional abundances that can be retrieved from Gaia-ESO Survey spectra and provides further insight into the chemistry of multiple stellar populations within GCs. These findings highlight the chemical complexity of GCs and the need for large, homogeneous datasets to trace their formation histories.

Using nearly 17 years of Fermi-LAT data, we analyzed the diffuse gamma-ray emission associated with different spiral arms of the Milky Way in the ranges $l = 105^\circ$ to $145^\circ$ and $b = -5^\circ$ to $5^\circ$. The gamma-ray emissions from these spiral arms all exhibited clear pion-bump features, which can be well explained by a power-law spectrum of cosmic-ray protons. The spectral indices corresponding to the three distinct spiral arms -- the Local Arm, the Perseus Arm, and the Outer Arm -- are found to be approximately $-2.75$, $-2.55$, and $-2.80$, respectively. The energy densities of the cosmic rays above 10 GeV are estimated to be all around 0.2$\rm~eV~cm^{-3}$. We further compared our results with previous studies, which have established various propagation models predicting that cosmic ray density decreases and spectra soften with increasing Galactocentric radius. We found higher densities and harder spectral indices than predicted in the outer Galaxy, suggesting possible contributions from a larger halo, slower magnetic field decay, or a combination of these and other effects. In particular, the spectral hardening observed in the Perseus Arm may be attributed to locally enhanced cosmic-ray acceleration.

We forecast constraints on the parameters of the coupled dark energy model using DESI and Euclid data with the one-loop galaxy power spectrum. We investigate the distinguishability of our model from the zero-coupling scenario at the $1σ$ level and explore how the parameter constraints depend on the fiducial coupling $β_{\rm fid}$, the fixed potential slope parameter $ν$, the maximum wavenumber $k_{\max}$, and different prior choices. We find that the inclusion of mildly non-linear scales improves the constraints on the coupling by roughly a factor of five. Then, we address the question of which is the minimum value of $β$ that can be distinguished from zero at $1σ$. We find that for our reference case $k_{\rm max}=0.2 h/$Mpc, $β=0.15$ lies roughly $1σ$ above zero. In the most optimistic case with $k_{\rm max}=0.3 h/$Mpc and including a Planck prior on $Ω_{m0}$, this value can be reduced to $0.05$. These values are substantially larger than the current constraints on $β$, but the latter have been obtained assuming $β$ to be constant from at least the decoupling epoch to today, while we only employ late-time data. We conclude therefore that only models that allow for time-varying couplings can be detected with late-time datasets.

We apply a newly proposed bound state method to revisit the computation of gravitational and electromagnetic quasinormal modes (QNMs) for Reissner-Nordström black holes (RNBHs). It is found that the method yields QNM frequencies of high accuracy for low-lying modes with overtones $n\leq3$. The accuracy degrades for higher overtones, however, a homotopy deformation to the potential enables us to compute more high overtone modes reliably. It is known that the continued fraction method for computing QNMs of extremal RNBHs differs significantly from that used for nonextremal ones. In contrast, the bound state method demonstrates advantage of simplicity: one only need to account for the definition of tortoise coordinate in the extremal case, and the rest of the computational procedure remains exactly the same as that for the nonextremal case.

For the $k$-self-similar naked singularity solutions of Einstein--scalar field equations constructed by Christodoulou, we construct a family of interior gravitational perturbations leading to trapped surface formation that remain large but finite at the threshold Hölder regularity, while converging to zero in all regularities below the threshold. This extends the interior spherically symmetric result below the threshold in \cite{Li25} to non-spherically symmetric setting. We further construct a genuinely localized family of perturbations whose angular support shrinks to a single point, with smooth convergence to zero away from that point. This exploits the additional angular freedom available beyond spherical symmetry. Moreover, when measured instead in Sobolev regularity, such genuinely localized family of perturbations still converges to zero in all regularities below the same threshold.

We investigate whether the recently reported high-energy nuclear recoil event by the LUX-ZEPLIN (LZ) collaboration can be interpreted as a signal of freeze-in dark matter (DM) in a non-standard cosmological history. We consider DM production from the Standard Model thermal bath during an era of modified expansion preceding Big Bang nucleosynthesis. Requiring consistency with the observed DM abundance, cosmological and collider constraints, we identify viable parameter regions that can accommodate the LZ event. Our results demonstrate the potential of direct detection experiments to probe non-standard cosmological histories and, more broadly, alternative theories of gravity.

In this manuscript, we develop topologically charged static and spherically symmetric wormhole (WH) configurations in Einstein gravity by employing the Einasto dark matter profile to construct an analytic shape function. The resulting spacetime satisfies the fundamental traversability conditions, while the matter sector exhibits localized violations of energy conditions near the throat, indicating confined exotic matter content. We analyze equilibrium through the TOV framework, revealing a non-equilibrium force competition in which hydrostatic and anisotropic contributions self-organize to sustain static configurations within specific parameter domains. Stability is examined via the anisotropy parameter and further extended to linearized radial perturbations of the surrounding shell, uncovering parameter-dependent stability windows that characterize the system's nonlinear response. A detailed dynamical analysis shows that the monopole charge parameter significantly restructures the effective potential landscape, modifying curvature and inducing qualitative transitions in particle motion. The coupled interplay between monopole charge, angular momentum, and particle energy governs a nonlinear transition from tightly wound quasi-bound states to unbounded scattering trajectories. This transition reflects an emergent dynamical phase structure in the WH spacetime. Furthermore, the complexity factor exhibits strong localization near the throat and vanishes asymptotically, indicating that structural complexity is confined to the inner nonlinear regime, whereas a volume integral quantifier is employed to estimate the total exotic matter content required to sustain the configuration.

FOSSIL (FTS fOr CMB Spectral diStortIon expLoration) is a proposed ESA M8 mission tailored to measure the spectral distortions of the Cosmic Microwave Background (CMB) with a sensitivity three orders of magnitude beyond the COBE/FIRAS legacy measurement. Achieving this sensitivity demands an extraordinarily challenging cryogenic architecture: the scientific instrument must be maintained at the lowest achievable temperature (4.5 K), while the detector focal plane assembly operates at 50 mK. This paper presents the thermal architecture of the FOSSIL payload and instrument, from the spacecraft service module at 293 K down to the sub-kelvin detector stage. The thermal design draws on heritage from the Planck and ARIEL missions and relies on a staged passive cooling chain comprising a multi-layer insulation blanket, three V-groove radiators (operating at approximately 130 K, 90 K, and 50 K), and a 25 K actively cooled shield fed by an ESA-provided 4 K cryocooler chain. Sub-kelvin temperatures are achieved via a multi-stage adiabatic demagnetisation refrigerator (ADR) system developed for NewAthena/X-IFU, providing continuous cooling at 1.8 K and 350 mK, and 50 mK with an 80% duty cycle. The Focal Plane Assembly (FPA), which houses four Kinetic Inductance Detector (KID) arrays at 50 mK, is thermally isolated from the 4.5~K bench via a carbon-fibre reinforced polymer (CFRP) hexapod structure with staged heat interception. We present the steady-state thermal budget across all stages, demonstrating comfortable margins at every temperature level, and discuss key thermal design drivers on the Blackbody Internal Reference (BBIR).

In this paper, we derive a new class of analytic black hole solutions within the framework of Hoyle--Narlikar gravity, where the black hole is surrounded by an electric charge acting as the source. After obtaining the corresponding metric, we investigate the thermodynamic properties of the resulting black hole solutions, including the Hawking temperature and entropy. Subsequently, we compute the specific heat and Gibbs free energy in order to analyse the thermodynamic stability of the black hole in Hoyle--Narlikar gravity. An interesting result of our analysis is that the black hole becomes thermodynamically stable for large values of the horizon radius within this framework.

Identifying a shock from a moving solar brightness front requires relating the observed emission to changes in the plasma state. The Riemann framework describes shocks, rarefactions and other waves as parts of a pattern connecting different states. We present the Riemann Map Operator (RMO), an inverse diagnostic framework implemented as a web application to help observers identify magnetohydrodynamic (MHD) shock families from incomplete measurements. RMO tests candidate local connections against conservation laws, entropy requirements and characteristic conditions, while retaining observational uncertainties and model assumptions. We demonstrate the approach with five solar examples and a complementary in-situ comparison. An event combining extreme-ultraviolet (EUV) imaging and spectroscopy admits both fast and slow shock connections within the tested conditions. For an EUV-radio event, we derive an upstream-flow constraint that would exclude ordinary slow shocks within the adopted model, provided both diagnostics sample the same front. A flare-loop benchmark reproduces the published spectral profiles and recovers slow-shock ordering in the isothermal limit. The Solar Orbiter comparison recovers an Alfvenic relation between measured velocity and magnetic-field changes. Together, the examples show how RMO connects observations to admissible MHD interpretations and identifies the additional measurements needed to distinguish them.

We present the first results of two Spanish TAC programs using the WEAVE LIFU that have been obtaining data since October 2023. The first one is obtaining high-resolution multi-epoch spectroscopy of the nine stellar clusters that contain a minimum number of 3 O-type stars (and many more B stars) within the field of view of the WEAVE LIFU and that are accessible from La Palma with the purpose of studying the spectroscopic multiplicity of the OB stars. The second program is obtaining single-shot low-resolution spectroscopy of as many stellar clusters with OB stars as possible with the purpose of characterizing the OB-star population in those regions that are too crowded to be properly studied with the guaranteed time SCIP program. That program has already observed 54 clusters in a wide range of environments, from H II regions to gas-free clusters, and distances, from clusters in the solar neighbourhood to (nearby) extragalactic systems. We also present the tools developed for this program, which include a data cube processing and visualisation utility and UNWIND, a code that fits and subtracts the ISM signature in the observed spectra.

We uncover the quantum geometric structure of graviton Wigner functions and stress-energy tensors via quantum field theory in curved spacetime, revealing the phase-space geometry of spacetime and relativistic quantum-state manifolds. We show that the polarization mode expansion of the underlying graviton field operator is fully captured by quantum geometry, as encoded in the spinor-helicity formalism, thereby establishing the geometric framework from the outset. Applying this to a weak gravitational background, we demonstrate the roles of the quantum metric and connection in describing graviton transport beyond the chiral vortical effect. We also clarify the role of the quantum metric in normalizing the perfect-fluid graviton stress tensor within this approach. This work paves the path for explorations of multistate Hilbert-space geometry in high-energy and gravitational physics. In addition, this framework naturally encompasses lower-spin excitations, allowing for a unified quantum geometric treatment of bosonic and fermionic many-body systems in condensed matter and particle physics.

Black holes in asymptotically anti-de Sitter (AdS) spacetime whose extended-phase-space thermodynamics reproduces that of a van der Waals fluid exactly form a distinctive class, the van der Waals black holes (VBHs). The timelike geodesics of VBHs are solved, their periodic orbits are catalogued, and the gravitational waves emitted along them are computed, so as to trace how the thermodynamic pressure P and the molecular-volume parameter b shape the orbital dynamics. Integrating the geodesic equations numerically yields the energy, angular momentum and radius of the innermost stable circular orbit (ISCO) and maps out the family of bound orbits. To delimit the parameter window in which the effective potential stays well behaved, we introduce a critical angular momentum Ls. Within the orbit-classification scheme, we compute the energies corresponding to rational q for several parameter sets and display the resulting orbits. The waveforms produced along these orbits are generated within the "Kludge" formalism, which makes it possible to quantify the imprint of b on the wave amplitude and on the period. Both the orbital architecture and the gravitational-wave signature turn out to be strongly sensitive to b. The dynamical behavior of VBHs and Schwarzschild-AdS (SAdS) black holes differs markedly, providing a new perspective for probing black hole thermodynamics via gravitational wave observations.

Lunar laser ranging (LLR) provides a sensitive test of the equivalence principle (EP) through a possible synodic perturbation in the Earth--Moon distance. In this work, we develop an independent LLR data-reduction framework and investigate this signature in the post-fit O--C residuals obtained with the EPM21, INPOP21, and DE430 planetary and lunar ephemerides. The same observation model and parameter-adjustment procedure are applied to the three ephemerides, allowing their residual-based results to be compared within a consistent framework. To account for the nonuniform distribution of LLR observations over the synodic angle $D$, the residuals are fitted with cosine and sine harmonics up to the third order. Signal-injection tests are also performed to quantify the attenuation of a possible $\cos D$ signal during the parameter adjustment. After correcting for signal attenuation, solar radiation pressure, and the thermal response of the lunar retroreflectors, the preferred EPM21, INPOP21, and DE430 solutions yield $Δ(m_g/m_i)_{\rm EM}=(0.900\pm3.183)\times10^{-14}$, $(0.496\pm3.624)\times10^{-14}$, and $(2.669\pm7.048)\times10^{-14}$, respectively. The EPM21 and INPOP21 results are based on observations from 1970 to 2024, whereas the DE430 solution was obtained using observations up to 2016. All three estimates are consistent with zero within their uncertainties. This work demonstrates that residual-based analysis can provide an independent and transparent EP test, while also offering guidance for assessing sampling and ephemeris-dependent effects in future high-precision LLR studies.

We present a deterministic machine-learning method for denoising candidate signals from all-sky searches for continuous gravitational waves from rotating neutron stars. Using the time-domain $F$-statistic search pipeline, we post-process the resulting $F(f,\dot{f})$ candidate patterns with iterative $α$-(de)blending, a deterministic diffusion-type generative model implemented as a U-Net, well suited to the non-Gaussian, correlated noise of the $F$-statistic output. Two models, trained on data based on simulated 6- and 12-day time-domain segments with software-injected signals similar to the LVK hardware injections, are tested by comparing deblended images to the library of expected signal patterns via the Structural Similarity Index Measure. In general the method recovers the correct sky-position-dependent pattern for signal-to-noise ratios $ρ\gtrsim 4$, moderately below typical all-sky detection thresholds, with recovery depending strongly on pattern morphology, demonstrating that deterministic diffusion-based denoising may serve as a consistency/veto tool ahead of the semi-coherent coincidence stage. We also discuss limitations and possible improvements of the method.

We explore the cosmological dynamics and formation of structures within the Tsallis-Cirto modified gravity framework with a model parameter $β$ that is inspired by nonextensive statistics. By applying the gravity-thermodynamics conjecture, we modify the Friedmann equations and the evolution of the Hubble parameter. The impact of the Tsallis-Cirto entropy on different cosmographic parameters and the development of the linear matter overdensities have been analyzed by formulating perturbed field equations using the spherical collapse approach in a flat Friedmann-Lemaître-Robertson-Walker background. We present a novel and established diagnostic approach to distinguish among distinct cosmological models compared to flat and non-flat $Λ$CDM scenarios, discovering that the Tsallis-Cirto entropy-inspired modified cosmology ($β\ne 1$) successfully withstands all tests, contradicting both the flat and non-flat $Λ$CDM models. This model also meets the conditions for the Universe to reach thermodynamic equilibrium in the far future. Additionally, we investigate the halo mass function and cluster number counts within this modified gravity framework. All findings are compared to the fiducial $Λ$CDM profile, indicating that the added entropic correction affects the history of expansion, the growth rate of structures, and the dark matter halo abundance. We find that the more massive structures are less abundant and develop at later times, which aligns with the hierarchical model of formation of large-scale structures.

Image reconstruction in optical interferometry remains a challenging inverse problem due to sparse Fourier sampling and the strong dependence of the reconstructed images on user-defined parameters. We present PYRA (Python for MiRA) and MYTHRA (Mean Astrophysical Images with PYRA), two tools designed to improve the robustness and reproducibility of interferometric imaging. PYRA automatically generates large ensembles of MiRA reconstructions by exploring a wide range of reconstruction parameters, while MYTHRA statistically analyzes the resulting images to identify the most consistent solutions and derive a final averaged image with associated uncertainty estimates. The methodology is validated using the blind datasets of the 2024 Interferometric Imaging Contest, where our reconstruction strategy achieved the best overall score. We further apply the method to VLTI/MATISSE observations of the triple AGB system π1 Gru and the A[e] supergiant 3 Pup. These results demonstrate that statistical analysis of large reconstruction ensembles provides a powerful framework for assessing image reliability and reducing reconstruction artifacts in optical interferometry.

Halo assembly bias describes the dependence of halo clustering on properties beyond halo mass and provides a means of connecting halo assembly history to the large-scale matter distribution. We develop and test a relative clustering methodology for measuring differences in the large-scale bias of two halo populations using the ratio of their cluster--galaxy pair counts. In the linear regime, this ratio can be related to the difference in cluster bias, while the galaxy autocorrelation independently constrains the galaxy bias. We apply the method to a volume-limited X-ray selected galaxy clusters from the eROSITA eRASS1 catalogue, dividing them into high- and low-temperature subsamples with matched distributions in X-ray luminosity, redshift, and exposure. We first verify the validity of the linear approximation, finding $ξ(r)\ll1.0$ over $4$--$10\,h^{-1}\mathrm{Mpc}$. The joint clustering analysis yields $b_{\rm g}=1.610^{+0.018}_{-0.019}$ and a bias difference $Δb=0.8\pm1.1$. DES Y3 weak gravitational lensing measurements provide an independent test of the halo masses, yielding $\log(M_{200\mathrm{m}}/h^{-1}M_\odot)=14.33^{+0.07}_{-0.07}$ and $14.33^{+0.10}_{-0.09}$ for the high- and low-temperature samples, respectively, with a mass difference of $Δ\log M_{200\mathrm{m}}=-0.01\pm0.12$. We therefore find no statistically significant evidence for assembly bias at the $1σ$ level, but our measurement is consistent with the bias difference measured for analogous halo populations in the FLAMINGO simulation. The result therefore does not rule out assembly bias at the level expected from the simulation, while demonstrating that the relative clustering methodology provides a framework for future assembly-bias measurements with larger X-ray cluster and galaxy surveys.

Observations of the Large Scale Structure sit on the light cone. Cosmological statistics must then be projected from 3D to angular space. For the bispectrum and higher orders, the polyspectra crucially depend on the angles between Fourier modes in addition to their moduli. This leads to delicate cancellations in the squeezed limit and make Limber's approximation fail. This is problematic for predicting the Super-Sample Covariance (SSC), with no known full-sky computation of the angle-dependent terms. Here we develop a new analytical approach to the angular bispectrum, writing Fourier vectors as derivatives that we project on the sphere and tackle with spin-weighted spherical harmonics. We find bispectrum equations free of cancellations and amenable to beyond-Limber numerical methods. Limber's approximation becomes well-behaved and works in the squeezed limit and any other configuration. We then derive the consequence for the covariance between 1-point (e.g. cluster or peak counts) and 2-point statistics (e.g. galaxy clustering, weak lensing or 21cm), which relates to the squeezed bispectrum. The results split into intra-survey covariance and SSC, where we find significant differences with past literature. Our results are in line with the 2+1 geometry of the light cone, having e.g. temporal derivatives in addition to spatial ones. We also find that the tidal term is degenerate with the simpler growth-only term. The total SSC contains a wealth of new terms including wide-angle effects and responses to the background velocity. However we show numerically that it is well approximated by a single term with a density-only response. This ultimately makes our results simpler than past literature. This full-sky result should be more representative than the past flat-sky limit for large survey areas, thus being the one relevant for coming observations with e.g. Euclid, LSST and Roman.

Dark-matter self-interactions can drive subhalos through gravothermal core collapse, but conventional lensing observables vary continuously with uncertain inner profiles. We show that gravitational-wave image multiplicity provides a discrete alternative. Near a macro-critical minimum, increasing subhalo central convergence opens two caustics in sequence, converting one detectable waveform into three and then five stationary images. Using weighted SASHIMI subhalos and an ET+CE selection model, we forecast almost 2 systems with at least three copies detectable in five years if dense remnants survive, compared with the prediction of 0.36 in 5yrs for standard CDM. The much more diagnostic second case is rare: the corresponding 5yrs yield with at least four detectable copies is 0.149, versus $1.55\times10^{-6}$ for CDM. According to the Poisson statistics, this gives only a 13.8\% probability of at least one event detected in 5 years. Thus this is a rare-event, exposure-limited test rather than a guaranteed detection: a resolved second pair would be difficult to reconcile with the fiducial single-halo CDM population, whereas a five-year null result would not by itself constrain remnant survival strongly.

We study slowly rotating, nonlinearly charged black holes in arbitrary spacetime dimension $d \geq 4$, using a generalized Lense--Thirring ansatz. Working to linear order in the rotation parameters, we solve the Einstein--nonlinear electrodynamics (NLE) field equations for restricted theories ${\cal L}({\cal S})$ depending on single invariant. We provide an extension of the four-dimensional "No Go theorem" proven in ArXiv:2203.01919 and demonstrate the uniqueness of Maxwell theory in $d \geq 4$. Similar to four dimensions, it is proven that the standard rotation generating trick fails to produce full rotating solutions for any nontrivial NLE in higher dimensions. We identify a family of NLE theories admitting slowly rotating solutions with vector potentials encoding rotation effect in Maxwell-like manner; in four dimensions this reproduces the previously found RegMax theory, while in $d\geq4$ we obtain the corresponding electric potential in closed form and the associated Lagrangian implicitly as a function of the radial coordinate.

We present a new approach to constraining the delay time distribution (DTD) governing r- and s-process element production. Rather than using metallicity as a proxy for time, we work directly with stellar ages at solar metallicity, where chemical equilibrium models are most applicable. We analyze two complementary samples: more than $10,000$ red clump (RC) thin disk stars at solar metallicity from LAMOST, and solar twins with high-precision abundances; both have well-determined stellar ages $τ$. We fit chemical-equilibrium models with power-law DTDs to the evolution of [Eu/Mg]$(τ)$ and [Ba/Mg]$(τ)$ in each sample, taking europium as a canonical r-process element and barium as an s-process element, each referenced to magnesium as a near-instantaneous, CCSNe-dominated element. To validate the method, we first apply it to [Fe/Mg]$(τ)$ and recover that $\approx\!70\%$ of Fe comes from a delayed channel with a declining DTD $\propto t^{-1.2}$, in agreement with well-established results for iron production in thermonuclear supernovae. It also shows that about $60\%$ of Eu and Ba forming today originate from strongly-delayed processes, and the inferred delayed-production rates of both Eu and Ba rise with delay time, opposite to that of thermonuclear supernovae. These results provide direct temporal constraints on r- and s-process enrichment, complementary to metallicity-based chemical-evolution studies. Because we model abundance referenced to Mg, and the same trend is recovered across stars of different guiding-center radii, this appears unaffected by radial migration and chemical evolution varying with Galactocentric radius. If confirmed, it points to delayed neutron-capture production beyond NS--NS mergers.

Binary stars are the progenitors of exotic objects, such as supernovae and gravitational wave sources. However, some systems merge earlier when the primary expands into a giant star at the end of its lifetime on the main sequence and causes its companion to spiral in. TYC 4144-329-2 is a candidate post-merger first ascent giant star with a circumstellar disk seen in the infrared (IR). We detect weak X-ray and far ultraviolet (FUV) emission from TYC 4144-329-2, which we interpret as a signature of weak coronal activity. We also find variability in Ha line profiles and in the optical light curves and we suggest an intermediate geometry where the line-of-sight passes through the upper layers of a flared disk with a time variable column density. While the X-rays must be coronal, the Ha line profiles point to ongoing and variable accretion. We suggest that TYC 4144-329-2's merger was more recent than other stars in this class and that it did not yet have time to develop a deep convection zone. If this scenario holds, TYC 4144-329-2 would be a unique probe of the earliest stages in the evolution of post-merger systems.

The paper discusses the fraction of extragalactic cosmic iron nuclei with energies of 10^19 eV that reached Earth from distant sources without fragmentation in intergalactic space. It is shown that the fraction of particles with energies E = 10^19 eV is significant (about 10%), even if the redshifts of the sources reach 0.2, and not only for nearby sources.

The kinetic Sunyaev-Zeldovich (kSZ) effect is a sensitive probe of the free-electron momentum field, tapping into spatial correlations relevant for both large-scale cosmology and smaller-scale astrophysics. Precision kSZ measurements will provide a robust channel for constraining inflationary physics and equivalence principle violation, while simultaneously characterizing the small-scale gas distribution and associated baryonic feedback. However, robust kSZ measurement for cosmological applications is challenging, as the primary source of large-scale information is convolved with unknown small-scale dynamics in a degenerate combination. In this paper we address this challenge using the Effective Field Theory (EFT) framework that provides a principled way of treating the effects of small-scale dynamics on large scale-structure. Extracting the kSZ signal can be reformulated as a measurement of the one-loop galaxy-galaxy-electron momentum bispectrum. We compute here a pure dark matter version of this bispectrum in EFT and compare it to simulations. We derive the EFT counterterms that capture small-scale backreaction and find that two of them acquire a transverse direction. One transverse counterterm gets generated entirely by the vorticity of the velocity field. Our computation of the bispectrum dipole agrees with simulation data to $5\%$ up to $k_{\rm max}=0.23~iM$, which is significantly larger than the reach of tree level theory, which breaks down beyond k_max = 0.23 h/Mpc and k_max=0.07 h/Mpc (at redshift $z=0.5$). For the bispectrum computed with the projected momentum field, relevant to measuring the kSZ field, we find a similar $k_{\rm max}$, and make the first detection of the transverse counterterms from simulations. Our results suggest that one-loop bispectrum computations can play an important role in advancing kSZ cosmology.

We study a curvature-coupled dark energy model that can modify cosmological evolution both before recombination and during the late-time accelerated era. The model belongs to the class of scalar-tensor theories, in which a quintessence field is non-minimally coupled to the Ricci scalar. We specify the model through a shifted quartic coupling, $f(\varphi)=α(\varphi^2-\varphi_{\rm today}^2)^2$, and an inverse power-law potential, $V(\varphi)=Λ\varphi^{-σ}$, where $\varphi_{\rm today}$ is a constant fixed by requiring the effective Planck mass to recover its present-day normalization. We implement the model in a modified version of $\mathtt{hi\_class}$ and compute its background and linear cosmological predictions. This specific form of non-minimal coupling allows an effective crossing of the phantom divide at late times while naturally suppressing deviations from standard gravity today and satisfying local gravity constraints. At the same time, the scalar field can modify the expansion history before recombination, shifting the acoustic scale in the direction required to alleviate the $H_0$ tension, while remaining dynamically relevant as dark energy at low redshift. For the parameter choices studied here, we find tens-of-percent deviations from $Λ$CDM in the expansion history, matter clustering, and metric-potential spectra. The modified evolution of the gravitational potentials leaves characteristic signatures in relativistic observables, with weak-lensing power suppressed by $\mathcal{O}(20$-$40\%)$ at low multipoles and order-unity changes in the late Integrated Sachs-Wolfe signal. Together, these results reveal a broad, scale-dependent phenomenology that motivates both a full parameter-space analysis and an extension of the present linear treatment to a dedicated non-linear $N$-body implementation.

The neutron skin, defined by the difference between neutron and proton root-mean-square radii, is a characteristic manifestation of isospin asymmetry and an important probe of the isovector nuclear interaction. This focused review examines how neutron skins influence particle emission and collective dynamics in heavy-ion collisions, from the Fermi-energy regime to ultra-relativistic energies. By modifying the initial neutron and proton density profiles, the neutron skin affects the isospin composition and geometry of the participant region, pre-equilibrium emission, particle production, fragment formation, and collective flow. We review neutron-to-proton and $\rm{t}/^3\rm{He}$ yield ratios, light clusters, pion ratios, bremsstrahlung photons, isoscaling and fragment momentum distributions, and neutron-proton differential flow and momentum observables, emphasizing their interplay with the symmetry energy and transport dynamics. At high energies, neutron skins also modify the initial geometry, eccentricities, multiplicities, and anisotropic flows in isobar and heavy-nucleus collisions. We discuss the challenge of disentangling these effects from deformation, surface diffuseness, shell structure, clustering, and model dependence. Broader connections to parity-violating electron scattering, dipole responses, coherent elastic neutrino-nucleus scattering, SRC-induced proton skins in momentum space, and neutron-star observables are also explored. Finally, we highlight opportunities from radioactive beams, improved collision experiments, microscopic many-body and transport calculations, and Bayesian inference. Combining multiple reaction systems and observables with complementary nuclear-structure and astrophysical information will be essential for quantitatively constraining neutron skins and the density dependence of the symmetry energy.

We report the first detection of the neutral methyl radical CH$_3$ in a highly evolved C-rich object, SMP LMC 011, using JWST MIRI/MRS. CH$_3$ is well fitted by an excitation temperature of $T_{\rm ex} \simeq$~190\,K and a column density of $N_{\rm tot}(\mathrm{CH_3}) \simeq 5.6\times10^{17}$ cm$^{-2}$. We also report the non-detection of ethane (C$_2$H$_6$), consistent with CH$_3$ reacting preferentially with unsaturated radicals rather than self-recombination, which may be inefficient in SMP LMC 011. Combined with the exceptionally large benzene column density of SMP LMC 011, this supports a methyl-addition route from benzene towards alkyl-substituted aromatics. We propose that the high CH$_3$ abundance is driven by the erosion of hydrogenated amorphous carbon (HAC) dust grains in the dense warm torus by UV photons from the central star and/or by shocks, which release CH$_3$ directly into the gas phase. These results establish CH$_3$ as a key reactive intermediate in the formation of complex hydrocarbons in C-rich circumstellar environments. Chemical models that incorporate methyl-addition reactions are needed for a better understanding of PAH formation pathways in evolved stars. The potential detection of alkyl-substituted aromatics such as toluene (C$_7$H$_8$) and ethylbenzene (C$_8$H$_{10}$) in C-rich evolved stars would provide direct confirmation of CH$_3$-driven aromatic growth in circumstellar environments.

Next-generation gravitational-wave observatories like Cosmic Explorer will provide an unprecedented opportunity to probe the cosmological stochastic gravitational-wave background, providing insight into the early Universe that is inaccessible with other means. We investigate the prospects for measuring a Gaussian cosmological gravitational-wave background in Cosmic Explorer in the presence of a distinguishable, non-Gaussian foreground of binary black hole mergers, using a Bayesian search that simultaneously fits binary black hole and background parameters. We successfully recover a Gaussian cosmological background with a signal-to-noise ratio of 5 in one day of simulated data in Cosmic Explorer without contamination from unresolved signals or data exclusion. However, when introducing waveform systematic errors to our analysis, our inference on the stochastic background parameters becomes biased and can falsely infer the presence of a background when there is none. The bias is driven by signal mismatches at low frequencies (<20 Hz), especially when the recovery waveform is missing physical effects included in the injected signals. While we propose a metric for diagnosing if measurements will be strongly biased by waveform systematics, our results suggest improvements in waveform modeling or other mitigation techniques will be required to accurately recover a primordial stochastic gravitational-wave background in next-generation detectors.

We present the first application of neural-network-based baryon acoustic oscillation (BAO) reconstruction to real galaxy survey data, restoring the acoustic signature damped by nonlinear structure growth. {\texttt{NERV}} ({\bf N}eural-network {\bf E}nhanced {\bf R}econstruction of the Uni{\bf V}erse) augments standard reconstruction with a convolutional neural network trained on cubic $N$-body simulations, and explicitly accounts for realistic observational effects including the curved-sky geometry, the redshift-dependent selection function, and finite survey boundaries, by tessellating the survey volume into local patches. We validate the method on the \textsc{MultiDark-Patchy} mock catalogs, recovering unbiased BAO dilation parameters. Applied to the BOSS DR12 galaxy sample, NERV improves the precision of the BAO distance measurements significantly. These results establish neural reconstruction as a practical component of BAO analyses for ongoing surveys such as DESI, with the potential to substantially tighten constraints on the cosmic expansion history and the nature of dark energy.

We confront a class of dark-energy equations of state emerging from group field theory (GFT) quantum gravity with DESI Data Release 2 baryon acoustic oscillations and Pantheon+ type-Ia supernovae. We introduce sampling parametrisations that replace microscopic initial-condition parameters by combinations more directly measured by background probes. The GFT solutions separate into logarithmic, power-law and oscillatory branches, determined by the microscopic interaction parameter $m$. The logarithmic branch is constrained to lie extremely close to a cosmological constant, while the power-law branch permits a small phantom deviation. Without perturbative-theory priors, oscillatory solutions can reproduce the mild preference of the distance data for a dip in $w(z)$ near $z\simeq0.5$--$1$. Profile-likelihood constraints favour $m\sim-2$ and $m\sim-5$ from BAO and supernovae, shifting towards $m\sim-3.5$ when CMB information is included. Conservative perturbative priors strongly suppress these deviations from $Λ$CDM. The quantum-gravity scale $z_q$, related to the average number of quantum gravity atoms, remains unconstrained, although its role in the time evolution makes higher-redshift observations a promising route to probing it. We further find that strong projection effects highlight the importance of performing likelihood profiling alongside our marginal posterior constraints. Our results provide a first direct test of GFT-motivated dynamical dark energy and demonstrate the potential for cosmological observations to inform quantum-gravity model building.

We find the necessary and sufficient conditions for the gravitational path integral (GPI) to admit an interpretation in terms of (i) an inner product in the Hilbert space of open/closed universes or (ii) a statistical average of boundary observables. The conditions needed for (i) are necessary but not sufficient for (ii). Requiring the stronger condition (ii) places additional constraints on all wormhole amplitudes, giving a concrete diagnostic of whether the GPI computes an average or merely a pseudo-average. To exemplify the difference between the two constraints, we present a class of gravitational toy models that satisfy (i) but fail the stronger condition (ii); to emphasize the power of the stronger condition, we initiate a bootstrap study of statistical ensembles based on condition (ii), finding that the resulting constraints substantially sharpen the bounds on the moments of the ensemble obtained by imposing (i). More broadly, both of these positivity conditions impose nontrivial constraints on wormhole amplitudes and thereby restrict which gravitational effective field theories can be embedded in consistent theories of quantum gravity.

We introduce a model of dark matter charged under a new confining gauge group akin to the Standard Model's quantum chromodynamics (QCD). The fermionic sector contains both heavy and light quark-like fermions charged under the dark QCD. As the Universe cools, the gauge force confines and dark radiation transitions from free particles to low-mass dark pions. This form of dark radiation behaves as an imperfect fluid with nonzero viscosity. If the confinement occurs at the MeV scale, the model can alleviate the tension between early- and late-time measurements of the Hubble parameter, with a Bayesian posterior of $H_0 = 71.60\pm 0.63$ km/s/Mpc and a $3σ$ residual tension across Planck, ACT, BBN, Pantheon+, DESI DR2, and SH0ES. In the late Universe, the heavy dark matter can evade existing constraints on dark matter self-interactions while containing a rich phenomenology that may be accessible in future observations.

The "Little red dots" (LRDs) are a population of accreting supermassive black holes (SMBHs) in the early Universe which often exhibit undermassive or even undetectable stellar hosts. Their early emergence, high space density, and extremely large black-hole-to-stellar mass ratios pose a serious challenge to conventional seeding scenarios that rely on baryon for both the formation and growth of black holes. Here we demonstrate that the above anomalies can be naturally resolved if dark matter is self-interacting. We apply a fully relativistic, non-equilibrium halo-evolution model, first developed in our earlier work, to trace the complete gravothermal evolution of self-interacting dark matter (SIDM) halos, from the initial collapse into BH seeds to the subsequent accretion of dark matter. We find that in highly concentrated halos assembled before reionization, gravothermal collapse efficiently produces stellar-mass black-hole seeds within a few hundred million years. Remarkably, and contrary to standard expectations for dark-matter accretion, heat conduction in SIDM then sustains a prolonged super-Bondi inflow that drives these seeds to supermassive scale by the LRD epoch, without baryonic assistance. The halo conditions required for completing these processes, together with the probability of avoiding major mergers that disrupt gravothermal evolution, result in an SMBH population consistent with the observed abundance and redshift distribution of LRDs. Our findings establish a pathway in which SMBHs are seeded and assembled primarily from dark matter, well before substantial galaxies form around them, thereby offering both a compelling physical explanation for LRDs and a new observational probe of dark-matter microphysics.

Kehle and Unger have recently shown that, under suitable conditions, a massless charged classical scalar field can produce an extremal black hole in finite time. This result appears to violate the third law of thermodynamics (TLT), since extremal black holes have zero temperature. However, because the TLT is intrinsically a quantum principle, a self-consistent analysis of this problem must account for quantum effects. In particular, we point out that the electric field of the system may spontaneously polarize the vacuum, thereby creating massless charged pairs that will discharge the black hole. This mechanism guarantees the {\it quantum} validity of the TLT in the regime $|eQ|\geq\hbar/2$ (here ${Q,e}$ denote, respectively, the electric charges of the black hole and the scalar field). This leaves open the question of what happens for lower values of $|eQ|/\hbar$. Recently, Schneider derived a classical bound showing that extremal black holes cannot be formed à la Kehle-Unger in the small-charge regime $|eQ|\leq\hbar/3$. His analysis leaves open the possibility that a stronger bound may exist. We conjecture here that this bound can indeed be strengthened such that classical considerations would prevent extremal (zero-temperature) charged Reissner-Nordström black holes from forming dynamically in the regime $|eQ|<\hbar/2$, where quantum polarization effects are too weak to preserve the validity of the TLT.

We present simulations of the microwave sky at 2.5 arcsecond resolution over 100 square degrees, generated from existing full-sky, lower-resolution simulations, and use them to demonstrate extragalactic foreground removal for a CMB-HD survey. Our cleaning method detects and removes the cosmic infrared background and radio galaxies, yielding source catalogs that are 95% complete down to flux limits of 0.008 and 0.04 mJy at 90 and 148 GHz, respectively. It also identifies and removes galaxy clusters via the thermal Sunyaev-Zel'dovich effect, producing a cluster sample that is nearly complete above $M_{500c} = 5 \times 10^{13} M_\odot$. After cleaning, the residual foreground-plus-noise power spectrum of the coadded 90 and 148 GHz temperature map is 50% higher than previous idealized estimates, increasing cosmological parameter uncertainties for an 11-parameter $Λ$CDM + $N_\mathrm{eff}$ + $\sum m_ν$ + $T_\mathrm{AGN}$ + $A_\mathrm{kSZ}$ + $n_\mathrm{kSZ}$ model by less than 7%. The small impact on cosmological parameters reflects the strong constraining power of CMB polarization, the temperature-polarization cross spectra, and CMB lensing spectra reconstructed from polarization-only estimators, all of which are minimally affected by extragalactic foregrounds. In particular, the survey remains a sensitive probe of light thermal relic particles, achieving $σ(N_\mathrm{eff}) = 0.0154$, which can exclude any new species ($ΔN_\mathrm{eff} \ge 0.027$) with at least 90% confidence. Our simulation and foreground-removal codes are publicly available and should aid the development of analysis pipelines for ultradeep, ultrahigh-resolution microwave surveys.

Semiclassical analyses of regular black holes suggest that inner-horizon instabilities can drive the trapped region to evaporate faster than the Hawking time and seed a transient anti-trapped region. Whether this repeats into a cascade terminating in a horizon-free configuration requires a self-consistent solution of the semiclassical Einstein equations, which we do not attempt. Instead, within the static Bardeen family, we show that the renormalized-stress-tensor (RSET) result of Arrechea, Liberati and Spadafora (arXiv:2608.03538) does not by itself force any damping of a hypothetical cascade near extremality, since its near-extremal limit at fixed cycle duration is finite and nonzero. We then prove, under explicit nondegeneracy hypotheses on any static metric family whose horizons merge at a fold point, that the inner-horizon surface gravity scales as |kappa_-| ~ (M-M_crit)^{1/2}, and verify this in two regular black hole families, Bardeen and Hayward, with a quantified systematic uncertainty. A phenomenological closure built on this scaling gives a mass gap decaying as x_n ~ n^{-2}, generalizing to x_n ~ n^{-1/(pq)} for a fold exponent p and an uncalibrated closure exponent q; the required cycle count is a property of the closure, not a physical prediction. As a separate exercise, we build an effective adiabatic model for the outer-horizon mass from the exact Einstein tensor of a generalized Vaidya-Bardeen ansatz matched to the cited RSET flux; the resulting law includes an O(1) correction absent from the naive Schwarzschild-Vaidya relation, relaxes to M_crit only asymptotically, and gives a timescale shorter than the inner-horizon amplification timescale by up to four orders of magnitude away from extremality but longer very close to extremality. We distinguish what is derived under stated assumptions from what the closure simply postulates.

We construct the first-law-consistent entropy of a geometrically minimal-length-deformed Schwarzschild spacetime, obtained via the areal-radius substitution $R(r)=\sqrt{r^{2}+\ell^{2}}$ on $r\in[0,+\infty)$ with $f(R)=1-2M/R$, whose nonvanishing Einstein tensor sources an effective geometric fluid with no classical matter counterpart. Integrating the first law gives $S=π[r_{h}R_{h}+\ell^{2}\ln((r_{h}+R_{h})/\ell)]$. This coincides in functional form with the semiclassical term found independently by Joshi and Joshi, but we fix its boundary condition $S(r_h=0)=0$ on independent physical grounds and adopt it, rather than the Bekenstein--Hawking area law, as the complete entropy of the model, building the free energy, geometrothermodynamics, and mode-stability analysis on it. Evaporation, governed by the Helmholtz free energy $F(M)$, terminates at $M_{\min}=\ell/2$ in a previously unrecognised endpoint: a degenerate extremal regular black hole, where the regular centre coincides with a degenerate Killing horizon of quadratic order, $f\approx r^{2}/(2\ell^{2})$, at areal radius $\ell$, with $T_{H}\to 0$, $S\to 0$, $C\to 0^{+}$, and finite curvature everywhere; we display its Penrose--Carter structure for the first time. The same entropy, with $\ell$, defines the equilibrium state space of a Legendre-invariant geometrothermodynamic (GTD) description whose curvature scalar diverges independently at the Davies-type transition $M^{*}=\ell/\sqrt{2}$ and at $M_{\min}$, a divergence with no counterpart in the minimal-length black hole literature, specific to a genuine horizon at $S=0$. We embed this remnant within the observational discriminant noted qualitatively by Tsukamoto: exact shadow degeneracy combined with a measurable photon-ring flux enhancement $r_{n}=e^{-2π/a}>e^{-2π}$, accessible to next-generation very-long-baseline interferometry.

Fermionic dark matter particles remain one of the most compelling candidates for the dark matter content of the Universe, yet no positive results have been obtained from direct detection experiments. In this work, we investigate the possibility that such particles form compact gravitationally bound objects supported by degeneracy pressure. Through an extensive review of microlensing surveys, we derive constraints on the masses of these compact objects. We further analyze the accretion of baryonic matter onto these objects and evaluate their thermal and radiative properties. The estimated burst emission is found to be well below the energies associated with the Galactic Center GeV excess, suggesting that these compact objects are unlikely to be the source of the observed signal. Our analysis suggests that admixed dark matter and baryonic matter objects could potentially account for a fraction of the presently unobserved baryonic matter, thereby providing a possible explanation for a fraction of the missing baryons in the Universe.

Nonextensive Bose and Fermi state is well studied with counting near black-hole horizons in a one-function, nonextremal, static, spherically symmetric class. The calculation is organized around a $q$-deformed grand ensemble whose total partition function is a $q$-product of single-level partitions. This identifies the bosonic occupation-number sum as the primary level partition and allows us to separate two operations that are often conflated: replacing that sum by a geometric-series form and applying the ordinary reciprocal-log identity to a $q$-logarithm. A finite-energy tunneling prescription yields a leading near-horizon state-counting term controlled by the surface gravity and a horizon-response factor. Entropy matching then gives an energy scale proportional to the Hawking temperature; the geometry factor cancels from normalized nonextensive corrections and from the Bose--Fermi ratio. We derive the first-order coefficients analytically and evaluate the unexpanded $q$-integrals numerically. The linear approximation is accurate to better than one percent when $q$ lies within roughly two percent of unity. All prescriptions recover the extensive limit, but the exact bosonic level sum and the geometric approximations give opposite signs for the leading deformation of the conventional $7/8$ Bose--Fermi relation. The result isolates a robust geometry-factorized structure and quantifies a distinct $q$-algebra systematic uncertainty.

Late-time cosmic acceleration is conventionally ascribed to a cosmological constant, though $Λ$CDM continues to face several theoretical difficulties that keep alternative gravity models under active consideration. This work examines the Hu-Sawicki $f(R)$ model in a spatially non-flat background, with the modified-gravity parameter $b$ and the curvature density $Ω_k$ both treated as free parameters, constrained using DESI-DR2 BAO, BBN, and four Type Ia supernova compilations -- PantheonPlus, PantheonPlus+SH0ES, Union3, and DESY5yr. Across all four combinations, $H_0$ and $Ω_m$ stay close to their $Λ$CDM values, with a noticeable shift in $H_0$ appearing only for the SH0ES-calibrated dataset. The parameter $b$ departs from zero at better than $2σ$ in three of the four fits, most prominently for DESY5yr, whereas the SH0ES-calibrated combination alone prefers $b<0$. A strong positive correlation among $b$, $H_0$, and $Ω_k$ underlies this shift, suggesting that curvature signatures obtained under $Λ$CDM can be reabsorbed into the modified-gravity sector once this additional freedom is allowed. Statistical model comparison via AIC and BIC gives a mixed picture: AIC leans toward the Hu-Sawicki model in three of the four combinations, while BIC's heavier penalty on the extra parameter favors $Λ$CDM in most cases, and only DESY5yr is preferred under both criteria. These findings show that the Hu-Sawicki $f(R)$ scenario with unconstrained curvature is nonetheless a statistically feasible, if not obviously preferred, alternative to $Λ$CDM, and that curvature restrictions generated inside $Λ$CDM cannot be viewed as independent of the underlying gravity model.

Noether charges in gravity are always defined with respect to a reference metric, but the near-horizon extremal Kerr (NHEK) solution does not come with an obvious choice of reference metric (it is not asymptotically flat, for example). We discuss a one parameter generalization of the NHEK solution due to Kinnersley and Kelley which interpolates between NHEK and an analytically continued version of Minkowski spacetime. We use this interpolating family of solutions to compute the conformal energy of NHEK above the Minkowski reference metric. We find an interesting order of limits issue when computing the conformal energy of the Minkowski vacuum and we discuss a few natural prescriptions for fixing it, including one motivated by the Kerr/CFT correspondence.

Pulsar timing arrays are a powerful tool for probing low-frequency gravitational phenomena and physics beyond the Standard Model. We establish a general, gauge-invariant framework for the timing residual by identifying the measurable quantity as the proper time interval between consecutive pulse arrivals at Earth. In linearized general relativity, we derive a general expression for this proper time shift and show that it decomposes into Doppler, Shapiro, and Einstein delay contributions whose sum is gauge invariant, similar to frameworks that have been developed for other gravitational-wave detectors such as laser and atom interferometers. We also provide a recipe for computing the resulting timing residual for any specified perturbation, and we illustrate the method with several physically well-motivated sources, recovering known results where they exist in the literature. This recipe can be directly applied to search for new physics from real pulsar timing data using existing numerical software.

Transdimensional Bayesian inference is becoming a key ingredient in gravitational-wave astronomy. In many relevant applications, the number of components needed to describe the data is not known a priori and must be inferred jointly with their parameters. We present a transdimensional Sequential Monte Carlo (SMC) framework designed to exploit massive parallelism. The method evolves a population of particles through a sequence of tempered distributions and uses the No-U-Turn Sampler for the exploration of fixed-dimensional parameter space while reversible-jump birth and death moves allow the number of components to vary. The same SMC construction also enables posterior samples obtained from a shorter data segment to be updated as additional data become available, enhancing the overall efficiency of the analysis. We validate the approach on two proof-of-concept problems: the recovery of a sequence of Gaussian pulses and a simplified LISA Galactic-binary inference problem. In both cases, the method recovers the injected number of components and produces consistent posterior estimates. These results indicate that the proposed method is a promising avenue toward scalable and parallel Bayesian transdimensional inference for current and future gravitational-wave astronomy.

We construct exact hairy black holes in Lovelock--Horndeski gravity and establish a relation between horizon topology, scalar hair and covariant charges. Rooted in the dimensional reduction of higher-curvature gravity, this framework connects scalar--tensor dynamics to the low-energy description of heterotic strings. In five dimensions, a single fixed theory admits a continuous planar family and two isolated hyperbolic black holes. The hyperbolic solutions share a locally AdS metric with distinct scalar dressings, while the planar family is Weyl curved and has a freely varying horizon scale. Both branches carry scalar hair regular on the future horizon. The hyperbolic construction extends above four dimensions; compatibility of the displayed planar profile selects five and seven dimensions. Time translations of the scalar act through a global shift, which enters the complete covariant charge balance. Along the planar family, a changing bulk shift-charge density supplies this balance despite zero radial flux and vanishing horizon charge variation. The hyperbolic roots admit no horizon-scale variation at fixed couplings.

The young solar analog DS Tuc A (~45 million years old, spectral type G6V) serves as an excellent proxy to the Sun during early stages of the Earth's evolution. The young Sun's enhanced magnetic activity in the form of X-ray and extreme UV emission, stellar wind, and flares likely affected the magnetospheric and atmospheric environments of early Venus, Earth and Mars. Studies of DS Tuc A help constrain evolution of magnetospheric and atmospheric environments of early Venus, Earth, and Mars and create opportunities to study the impact of flares on the transiting exoplanet, DS Tuc Ab. We analyze ~11 hours of Far-ultraviolet (FUV; 1130 - 1450 $\mathring{A}$) observations taken by the Hubble Space Telescope Cosmic Origins Spectrograph during late 2023 and early 2024. We find DS Tuc A exhibited 26 flares over ~11.1 hours of observations in the transition region lines Si IV (1394 $\mathring{A}$ + 1402 $\mathring{A}$), with durations ranging 90 - 960 seconds and FUV absolute energies ranging ~ 10$^{29}$ - 10$^{31}$ erg over the observed bandpass. Si IV flares are accompanied by increases of other chromospheric and transition region lines, however the strongest Si IV flares show no enhanced coronal emission traced by Fe XXI 1354 $\mathring{A}$. We present an analysis of each detected flare, including X-ray and bolometric luminosities scaled from FUV flare energies, electron density measurements for the strongest flares, and the Far-UV continuum response to flaring. These results provide constraints on the frequency and energetics of flares comparable to X100-class solar flares and FUV-emitting regions in young solar analogs.

The Hubble tension motivates careful scrutiny of the redshift-independent distances underpinning the local distance ladder. Water megamasers afford a purely geometric distance from orbital dynamics in an accretion disc. For five of the six Megamaser Cosmology Project (MCP) galaxies, we present a Bayesian forward model that infers the angular-diameter distance and warped Keplerian disc parameters jointly from the very long baseline interferometry quasi-observables: maser spot positions, velocities, and accelerations. We then constrain $H_0$ from these distances and the host redshifts, including a physical distance prior, modelling the galaxy sample selection and testing a linear and a non-linear peculiar-velocity reconstruction. Accounting for peculiar velocities with the non-linear Manticore reconstruction, we infer $H_0 = 71.6 \pm 3.7$ km/s/Mpc, where the uncertainty is statistical. Relative to ignoring peculiar velocities, the linear and non-linear reconstructions lower $H_0$ by $0.8$--$1.4$ and $1.6$--$2.1$ km/s/Mpc, respectively, whereas changing the selection variable alters it by less than $1$ km/s/Mpc. We analyse the sixth galaxy, NGC 4258, separately. Modelling its disc as eccentric and quadratically warped, we infer an angular-diameter distance of $7.558 \pm 0.073$ (stat.) Mpc, within $0.13σ$ of the published maser distance.

We present the RMSTAR (RECONS M STAR) catalog, a 25 pc volume-limited and effectively volume-complete sample of the nearest 3352 M dwarf systems and their 305 wide stellar and 9 brown dwarf companions. RMSTAR has been created using only results from \textit{Gaia} Data Releases 3 (GDR3) and 2 (GDR2), \textit{Hipparcos}, and ground-based discoveries of M dwarf systems that are not available in the space-based results. The wide companions are identified using only results from GDR3 and GDR2, and have separations $ρ\ge0.''46$. There are 291 primaries with stellar companions, yielding a multiplicity rate of 8.68$\pm$0.49\% for these widely separated systems, with a rate of 6.86$\pm$0.44\% for projected separations $s\geq30$ au, where the sample of stellar companions is complete except perhaps for a few fringe cases. It is shown that the rate of stellar companions increases from the search limit of 30,000 au down to separations of 30 au, with a large set of companions to be characterized at closer separations in future work. We determine luminosity and mass functions for all stellar red dwarfs and their wide secondaries, finding that the luminosity function displays a classic turnover at $M_G\sim11$, whereas the mass function is described by an exponential function that rises from 0.60 M$_{\odot}$ to the end of the stellar main sequence at 0.075 M$_{\odot}$. We assess the large population of close, unresolved companions to M dwarfs by analyzing several \textit{Gaia} parameters, identifying 1089 (30\%) individual sources as having at least one of these elevated unresolved companion indication parameters.

This study investigates the impact of fermionic dark matter (DM) on the structural and tidal properties of white dwarfs (WDs). Using a two-fluid general relativistic framework, we model stars with fixed DM mass fractions (${\rm MF}=M_{\rm DM}/M_{\rm NM} $), ranging from 0\% to 8\%, with zero representing the no DM scenario. Our results indicate that DM accumulation leads to a significant compactification of the star, reflected in increased surface gravity and compactness. Furthermore, we calculate the second-order tidal Love number $k_2$ and the dimensionless tidal deformability $Λ$. For some total mass range, we find that the presence of DM significantly reduces $Λ$, suggesting that DM-admixed WDs (DMWDs) are less susceptible to tidal deformations. These structural shifts alter the gravitational wave signatures in binary systems, potentially providing a new window for DM detection with future instruments like LISA.

Brown dwarfs are common as free-floating objects but rare as close companions to Sun-like stars, a disparity known as the "brown-dwarf desert". Host-star metallicity can constrain whether these companions form mainly through metal-sensitive core accretion or through less metal-dependent disc or cloud fragmentation. We extend our homogeneous spectroscopic analysis of directly imaged planet hosts into the brown-dwarf regime and compare their metallicities with those of planet hosts and close-in brown-dwarf hosts. We compiled 54 unique directly imaged brown-dwarf systems selected over an inclusive 13-80 M_Jup interval and projected separations from about 5 au to several thousand au. Objects near the model-dependent 70-75 M_Jup hydrogen-burning boundary may instead be very-low-mass stars. For 31 hosts with archival high-resolution spectra, we derived atmospheric parameters and metallicities using Bayesian spectral synthesis. Literature companion masses and projected separations are heterogeneous and are used only for demographic context. Galactic velocities were calculated for 46 hosts solely to characterise the youth-biased imaging sample. The host stars have a broadly solar metallicity distribution, with a median [Fe/H] of +0.06 dex and a median absolute deviation of 0.11 dex, and show no strong metal-rich bias. No statistically significant metallicity difference is detected between the lower- and higher-mass directly imaged subsamples. The hosts are kinematically cold, as expected from the youth-biased selection of direct-imaging surveys. The absence of a strong metal-rich bias suggests that classical core accretion does not dominate the wide-orbit brown-dwarf population. Disc instability and cloud fragmentation remain plausible, but the current sample and heterogeneous companion properties do not permit object-by-object discrimination between these channels.

We develop an effective stochastic and semiclassical framework for dynamical thin-shell wormholes connecting two asymptotic spacetime regions. The Israel junction geometry is separated from the phenomenological open-system description: stochastic dynamics is formulated in the radial phase space $(a,\dot a)$, whereas $σ$, $P$, and the effective temperature scales are induced observables. A one-dimensional Langevin--Fokker--Planck model is obtained only after an explicit overdamped/adiabatic approximation. Local acceleration scales are interpreted as reservoir temperatures only under additional KMS and detailed-balance assumptions. For a symmetric Schwarzschild--Schwarzschild wormhole, the transparent conservative shell defines the reference potential and restoring frequency, while dissipation and noise are introduced as open-system corrections. The stable linear response is closed by the constitutive slope $β_0^2=(dP/dσ)_0$. For $2M<a_0<3M$, stability requires a lower bound on $β_0^2$ that diverges as $a_0\to2M^+$. Moreover, the derivative along the family of static configurations equals the marginal-stability slope and must not be identified with the constitutive derivative of a stable stochastic shell. The reduced model determines stationary distributions, fluctuations, correlations, Markovian and non-Markovian spectra, and entropy production. Near the horizon, the junction conditions yield $T_{\rm stress}=T_{\rm acc}+O(\hbarγ/a)$, with equality at leading order under a specified dominance condition. A peeling temperature participates only if the ray-tracing map satisfies generalized Unruh/peeling and adiabaticity conditions. Thus, the three-temperature correspondence is conditional, while the stochastic coefficients remain phenomenological pending a microscopic shell--reservoir model.

Primordial black hole dark matter is formed from the collapse of enhanced primordial density fluctuations. The formation of primordial black holes is accompanied by scalar induced gravitational waves whose infrared scaling only depends on the equation of state, $w$, of the background at leading order. Establishing whether this characteristic scaling remains robust under corrections of arbitrary perturbative order, including in the presence of non-Gaussianities, requires a physical understanding of the infrared scaling. In this work, we provide such a physical interpretation. We find that the stress of sound waves with nearly equal frequencies produces a slow beat. Although the incoming waves oscillate rapidly, this slow beat continues to source the long wavelength tensor perturbation before its horizon entry, thus generating an infrared scaling that only depends on the expanding background. We show that higher order interactions generate freely propagating waves that finally lead to the same slow beat deep inside the horizon. Since non-Gaussianities would not change the speed of the freely propagating waves, they do not modify the infrared scaling. As the source with a slow beat has enough time to accumulate before the horizon entry of the infrared tensor mode, it records the background expansion and thus the infrared scaling could provide a robust probe of the cosmological equation of state.

Massive galaxies are expected to host extended halos of hot gas that contain a substantial fraction of their baryons and feedback energy. X-ray observations probe the dense, X-ray-bright component of this circumgalactic medium (CGM), while the thermal Sunyaev-Zel'dovich (SZ) effect is also sensitive to lower-density gas through its integrated thermal pressure. We present the first spatially resolved joint X-ray and SZ analysis of a massive isolated disk galaxy, using deep XMM-Newton observations of NGC 4594 from the X-raying the Accretion Reservoir Transferred to the ATmosphere Orbiting a Massive Spiral (XART-ATOMS) program, together with multiple independent Planck-based SZ reconstructions. The measured SZ signal in the inner halo appears to exceed the value predicted from the X-ray-derived gas properties, even after accounting for major systematic uncertainties. Our preferred interpretation is that an additional lower-density CGM component contributes little to the observed soft X-ray emission but carries substantial thermal pressure. Under a simple two-phase model in approximate pressure equilibrium, the most probable X-ray-to-SZ ratio implies that the detected X-ray-emitting gas occupies only a small fraction of the halo volume, with a characteristic filling factor of f_X ~ (4-6)x10^-3 near r~50 kpc. Such a small filling factor implies that single-phase X-ray analyses can underestimate the baryon mass contained in the hot CGM by a factor of ~2.5, while the thermal energy content of the CGM is underestimated by about one order of magnitude. The non-detection of the additional component in the X-ray spectra requires it to be very hot and/or spatially extended, so weak in the soft X-ray emissions. These results favor the presence of a "hidden" X-ray-faint hotter halo component, while alternative interpretations, including a nonthermal contribution, are not excluded.

We establish a general relation between symmetries of gravitational theories and black hole (BH) quasinormal mode (QNM) spectra. We show that a symmetry implies isospectrality when it induces a bijection between the corresponding QNM boundary value problems. However, conformally related BHs have been reported to exhibit both conformal factor dependent and independent QNM spectra. To resolve this issue, we develop a reduction scheme for higher order perturbation equations. Applied to pure Weyl gravity, it yields the complete axial spectrum of Schwarzschild, including Regge-Wheeler and spin-1 branches. Our results show that these seemingly contradictory conclusions result from differences in the perturbation dynamics or in the boundary conditions.

In this paper, we investigate the chaos bound through the local radial instability of charged spinning test particles on unstable circular orbits in the black-bounce--Kerr--Newman spacetime. Our results show that violation of the bound is governed by the competition between the local orbital-instability scale and the surface gravity scale, with variations of the black hole background and the particle dynamics providing two complementary routes to the same threshold crossing. Background variations affect both scales and can drive the system into the bound-violating regime when the surface gravity is suppressed more strongly than the orbital instability. At fixed background, by contrast, the surface gravity remains unchanged, and the transition across the threshold is driven by changes in the unstable orbit dynamics induced by the particle parameters. The background-controlled and probe-dynamics-controlled routes therefore represent two realizations of a unified horizon--orbit scale competition rather than independent mechanisms. Among the particle parameters considered, the total angular momentum plays the leading role in controlling the local radial instability, while the spin and charge further modify the instability strength and shift the threshold for chaos bound violation.

We propose a new source of neutrino decoherence arising from stochastic gravitational lensing by unresolved mass substructure. Unlike traditional models that treat the lensing potential as smooth and deterministic, we decompose the lensing potential into a smooth component and a stochastic population of compact clumps. The substructure induced fluctuations of the lensing potential generate stochastic corrections to the neutrino time delay, thereby producing random relative phases between different neutrino mass eigenstates. Averaging over the clump ensemble converts these phase fluctuations into an effective dampening of flavour coherence. This framework connects stochastic gravitational lensing with neutrino phenomenology and offers a novel route to probe dark matter substructure through astrophysical neutrino flavour transitions.

The void probability function (VPF) is the likelihood of finding no tracers (galaxies or dark-matter haloes) within a given volume and is sensitive to the large-scale matter distribution. We investigate the VPF of dark matter haloes and galaxies using the \textsc{Quijote} N-body simulations across a range of cosmological models, including $Λ$CDM and several extensions. We examine its dependence on cosmology, redshift, halo mass, morphology, and sample dilution, and compare the results with theoretical predictions from the geometric hierarchical (GH) and negative binomial (NB) models. We find that the halo VPF is sensitive to cosmology and halo mass and follows the GH model at $z=0$, with $Λ$CDM showing the smallest deviation and the massive-neutrino cosmology the largest. At higher redshift and stronger sample dilution, the VPF departs from the GH model and approaches the NB model. The dependence on halo mass varies with cosmology, with low-mass haloes showing the largest deviations in $Λ$CDM, while intermediate- and high-mass haloes show stronger deviations in the modified-gravity scenario. In redshift space, the VPF shifts toward the NB model, with primordial non-Gaussianity producing the largest deviations. For galaxies, the VPF depends on morphology and cosmology, with ellipticals following the GH model and spirals following the NB model. We also find that cosmic variance introduces non-negligible scatter in the VPF measurements. Overall, these results suggest that the VPF could be useful as a computationally efficient probe to distinguish extensions of the standard $Λ$CDM model in upcoming large-volume galaxy surveys.

Interacting dark energy (IDE) models, featuring interactions between dark matter (DM) and dark energy (DE), have received significant renewed interest. However, little attention has been devoted to understanding their genuine cosmological signatures, with comparisons against $Λ$CDM often carried out at fixed cosmological parameters. Considering the widely studied model with energy exchange rate proportional to the DE density, we carry out a three-level sequence of comparisons, starting from the naïve fixed-parameter comparison, then compensating for shifts in $θ_s$ and $z_{\text{eq}}$, and then removing effects due to the modified background. We show that fixing $θ_s$ and $z_{\text{eq}}$ leads to pre-recombination evolutions of the Weyl potential, photon monopole, and baryon velocity which are nearly identical to their $Λ$CDM counterparts, and hence virtually indistinguishable Cosmic Microwave Background (CMB) temperature power spectra. Comparing IDE to a non-interacting $w$CDM model with the same background, we find small scale-dependent signatures in CMB lensing. We find larger differences in the matter power spectrum, reflecting the different values of $Ω_m$ resulting from the different partition of the dark sector into DM and DE, with only percent-level differences remaining once we compare $Ω_m^2P_m(k)$, indicating the importance of high-fidelity determinations of $Ω_m$. Our controlled comparison strategy can be a powerful tool for a wide range of models beyond $Λ$CDM.

Blue large-amplitude pulsators (BLAPs) are rare, hot, short-period pulsating stars whose rapid oscillations provide a unique probe of stellar interiors and atmospheres. In this paper, we study two short-period BLAPs in the Galactic bulge, OGLE-BLAP-142 ($P \approx 6.6$ min) and OGLE-BLAP-148 ($P \approx 7.5$ min), by combining light curves from the OGLE, KMTNet, and DREAMS surveys, spanning 17 years with cadences ranging from minutes to hours to days. We perform Generalized Lomb-Scargle periodogram analyses of their light curves and identify, for each BLAP, three closely spaced pulsation modes separated by $\sim 1\%$. The dominant mode can switch within timescales of order a year, accompanied by a likely blueward color shift ($\sim 0.1$--$0.2$ mag). The yearly period excursions of the resolved mode families imply apparent $|\dot{P}/P|$ values of order $10^{-6}$--$10^{-4}\,\mathrm{yr^{-1}}$, large enough to mimic or exceed smooth evolutionary period changes. One mode family in OGLE-BLAP-148 shows a coherent decade-long drift at the $\sim10^{-5}\,\mathrm{yr^{-1}}$ level, but its failure to extrapolate to the earliest and latest epochs suggests a transient mode-family drift rather than secular evolution. Such close-spaced multiple pulsations and mode switching may be common among BLAPs with periods shorter than 10 min, and their physical origin remains unclear.

Current methods for the gravitational-wave (GW) echo searches generally require substantial computational time and resources. Recent advances in group equivariant neural posterior estimation (GNPE) have demonstrated the potential to substantially accelerate posterior inference. In this work, we adopt this framework and train a GNPE model to perform echo searches, significantly improving computational efficiency while maintaining comparable inference accuracy. We apply it to the O4a events and find no significant evidence for the GW echo.

We investigate a stationary and axisymmetric power law Kalb-Ramond geometry, obtained as a rotating extension of the asymptotically flat static solution. We reconstruct the exact inverse Einstein source supporting the geometry and determine its energy conditions and curvature properties. We characterize the horizon and stationary limit configurations and quantify the outer ergoregion through its angular dependent radial thickness plus its coordinate and proper spatial volumes. We derive the unstable spherical photon region and show that the Kalb-Ramond deformation shifts the prograde photon orbit into the ergoregion at lower spin, while the retrograde region remains outside throughout the entire domain. From the unstable photon region, we construct the exact vacuum critical curve and analyze its area equivalent diameter and displacement, including comparisons with M87$^\ast$ and Sgr~A$^\ast$ within the asymptotically admissible domain. We further examine the fixed-$J$ geometric behavior and rotational energy extraction, with emphasis to rotating weak deflection and two dimensional weak lensing, commenting the physical consequences of our solution in terms of observable outcomes.

We study the near-horizon charged-scalar instability associated with Schwinger pair production in the charged regular black hole geometry of the zero-point-length T-duality prescription. Using the same effective geometry and regularized gauge potential, we construct the extremal branch, its ${\rm AdS}_2 \times S^2$ near-horizon throat, and the charged-scalar instability threshold for a general form factor. For the explicit T-duality form factor the extremal branch terminates at $r_\mathrm{ext} = \sqrt2 \, l_0$, where the extremal charge and the near-horizon electric field vanish while the ${\rm AdS}_2$ radius remains finite at $\sqrt3 \, l_0$. At this endpoint the exact near-horizon instability parameter is negative. In the semiclassical regime the corresponding charge-to-mass threshold diverges as the endpoint is approached. Thus, for each fixed massive species with finite $q/m$, a sufficiently near-endpoint portion of the extremal branch is free of the local charged-scalar instability. For comparison, the Ayón-Beato-García (ABG) Einstein-nonlinear-electrodynamics solution has a nonvanishing extremal near-horizon electric field. For an additional minimally coupled charged-scalar probe, the corresponding local Schwinger threshold remains finite. Thus the divergent near-endpoint Schwinger barrier found in the T-duality branch is not a generic consequence of regularity.

[Abridged] The advent of large-scale spectroscopic surveys will deliver tens of thousands of spectra of blue massive stars. This data volume renders traditional spectral classification techniques increasingly impractical. We aim to develop a robust ML framework for the automated spectral classification of massive OB stars by assessing several tree-based ensemble algorithms. Using a large catalog of high-quality optical spectra of OB stars, we design 3 hierarchical experiments of increasing complexity: classification into broad SpT; fine-grained classification within the O and B domains; and joint classification of SpT and LC. We evaluate 6 algorithms, ranging from single Decision Trees to ensemble methods and gradient boosting techniques. We further analyze model consensus and probabilistic outputs, and employ SHAP value analysis to provide an interpretation of the model decisions by identifying the features that drive each classification. Models achieve excellent performance for broad SpT classification, with LGBM reaching an accuracy of 98%. For fine-grained SpT, RF provides the most robust results (89\%). For the most challenging task combining SpT subtype and LC the XGB reaches a 77% accuracy. Decrease in performance is primarily driven by intrinsic degeneracies in the classical spectral classification scheme. SHAP analysis confirms that the models rely on meaningful spectral features. We also find a high level of agreement among different algorithms, indicating that current performance limits are largely set by the intrinsic complexity of the classification problem rather than by model choice. Tree-based ensemble methods provide a reliable and interpretable framework for the automated spectral classification of OB stars. The combination of full-spectrum modeling, algorithm comparison, and model interpretability offers a robust approach for future large-scale spectroscopic surveys.

Magnetic monopoles are a generic prediction of Grand Unified Theories (GUTs) that are in tension with modern cosmological and observational bounds. In this paper, we calculate the present-day abundance of GUT monopoles produced thermally in the early Universe. We improve on previous calculations by accounting for full relativistic corrections to the thermal abundance and enhanced monopole annihilation due to the emission of radiation and scattering off massive gauge bosons, the Standard Model fermions and their superpartners. To obtain a present-day energy density less than that of dark matter, we show that the reheating temperature of the Universe, $T_{\rm RH}$, must be less than $0.55$ times the GUT symmetry breaking scale $T_{\rm GUT}$ for the canonical 't Hooft-Polyakov monopole mass. Accounting for Parker bounds on the present-day magnetic monopole abundance, the bound is tightened to $T_{\text{RH}}/T_{\text{GUT}} \lesssim 0.45$. Furthermore, experimental bounds from Super-Kamiokande require $T_{\text{RH}}/T_{\text{GUT}} \lesssim 0.35$ in our scenario.

Recent EHT polarimetric observations provide a powerful probe of near-horizon physics and modified gravity. We investigate the shadow and polarization images of a static Schwarzschild-MOG black hole illuminated by geometrically thick, optically thin accretion flows. Adopting a phenomenological model and the Hou disk model, and solving null geodesics and relativistic radiative transfer, we study how the MOG parameter, inclination angle, anisotropic synchrotron emission, and flow geometry affect the total intensity and linear polarization. It is found that the MOG parameter mainly enlarges and brightens higher-order photon rings and broadens the shadow, while the inclination angle breaks axial symmetry and enhances polarized emission inside the shadow. The Hou disk model suppresses off-equatorial radiative interference and localizes polarization signals within higher-order rings. Electric vector position angle (EVPA) patterns are mostly azimuthal but vary rapidly near lensed images. These results provide theoretical diagnostics for constraining MOG with EHT/ngEHT polarimetric observations.

YZ Cancri is an SU UMa-type dwarf nova with sparse and heterogeneous optical spectroscopy. We present a homogeneous analysis of archival outburst-related spectra and seven new low-resolution quiescent spectra. We consistently characterize the Balmer, He I, Fe II, O I, and occasional He II and Bowen features, and assess which state-dependent differences are robustly supported. We applied a common continuum-normalization and line-measurement procedure, measuring equivalent widths, integrated line intensities, and selected profile parameters, and comparing line morphologies and intensity ratios between quiescent and outburst-related states. Because the spectra have modest and nonuniform resolving power and are not orbital-phase resolved, profile widths and centroid shifts are used only as relative diagnostics. Outburst-related spectra are dominated by broad Balmer absorption or composite profiles, whereas quiescent spectra show strong single-peaked Balmer and He I emission, recurrent Fe II λ5169, and weak O I λ7772 emission. He II λ4686 is detected in only two quiescent exposures, and the Bowen blend in one. The quiescent Balmer decrement is relatively flat, while the He I ratios show substantial exposure-to-exposure scatter. The measured Fe II ratios show no clear systematic departure from optically thin reference values, although blending limits their interpretation. These spectra establish an empirical state-dependent description of YZ Cnc and provide a reference dataset for future phase-resolved, higher-resolution spectroscopy.

We introduce a codimension one construction of coarse Ricci curvature in Lorentzian geometry. Using the $1$-Lorentz-Wasserstein distance $\ell_1$, we compare probability measures supported on small spacelike hypersurfaces through nearby events and recover, in a precise asymptotic regime, the ambient Ricci curvature in future-directed unit timelike directions, with a universal dimensional prefactor reflecting this codimension one construction. The construction echoes the Raychaudhuri equation, which relates the evolution of spatial volume expansion along timelike geodesics to Ricci curvature. Our quantitative estimates rely on transport maps with controlled displacement, constructed through a Moser-type flow. At leading order, the slice construction is insensitive to smooth weights. By smearing the spacelike slices into thin timelike tubes and calibrating the temporal and spatial scales, we recover the timelike Bakry-Émery tensor $\mathrm{Ric}+\mathrm{Hess}\,V$ associated with the weighted reference measure $\smash{\mathfrak{m}=\mathrm{e}^{-V}\,\mathrm{vol}_g}$.

Based on synthetic polarization observations, we qualitatively investigate the intermittency of the magnetized interstellar medium (ISM) through synchrotron polarization intensity (SPI) and synchrotron polarization gradient (SPG). Three principal findings emerge from our analysis: (1) The intermittency of the magnetized ISM is strongly modulated by magnetization and compressibility, with pronounced modulation effects predominantly observed in regimes characterized by strong magnetization and high compressibility. (2) The characterized intermittency of the magnetized ISM demonstrates a dependence on the electron spectral index under conditions where the random magnetic field dominates. (3) SPG enables the identification of finer three-dimensional fractal structures in the case of strong Faraday depolarization. The synergistic application of SPI and SPG substantially enhances the reliability of probing magnetized ISM intermittency from real observations.

For sixty years, the Sun served neutrino physics more than the reverse: its neutrinos established oscillations rather than probing the star itself. That is now changing. Reactor antineutrinos have pinned down the oscillation parameters governing solar-neutrino flavour conversion so precisely that the propagation-related uncertainty is becoming negligible -- closing the first of two abysses. Solar neutrinos can, at last, be turned on the Sun. Yet a second abyss remains: today's solar-neutrino detection falls an order of magnitude short of the precision the Standard Solar Model already predicts for the dominant pp flux ($>\,$90$\%$) -- a gap no reactor experiment can close. The intrinsic $^{14}\mathrm{C}$ background walls off the pp region; only new detection techniques can breach it. Bridging this second abyss demands a revolution, not an increment. Combined with helioseismology's complementary reading of the Sun's mechanical structure, precision neutrino measurements of the nuclear source terms would enable a multi-messenger heliotomography of the solar interior -- reading our star from both sides at once. A new age of solar discoveries may follow, on one condition: that the field builds the instruments equal to the task.

Accurate and unbiased determination of stellar parameters is of importance in many astrophysical domains. We therefore present an improved method to estimate stellar parameters, based on interferometric observations and stellar atmosphere models, as well as spectroscopic and photometric data. The fundamental stellar parameters were estimated by fitting a model of intensity profiles to interferometric data over a large spectral window and combining them with spectroscopic and photometric observations as an additional constraint on the fitting. Based on stellar atmosphere models, we have developed an algorithm that trains artificial neural networks (ANNs) to estimate the spectrum and intensity profile of a star over three bands: R, H, and K. The ANNs cover effective temperatures (Teff) ranging from 4500-7000 K for dwarf stars and 2500-8000 K for giant stars, with surface gravities (log g) ranging from 3.0-5.0 dex and -0.5-3.5 dex, respectively, and 12 viewing angles. As a result, consistent and precise stellar parameters, such as Teff, log g, and angular diameter ($θ$), can be estimated. We fitted $ι$ Psc (F7V) and $δ$ Ari (G9.5IIIb) observed with SPICA, MIRC-X, and MYSTIC at the CHARA Array, and archival data of $α$ Cen A and B (G2V and K1V) from VLTI/PIONIER with PIMS. For angular diameter estimations, when fitting with a one-dimensional stellar atmosphere model, we reached a precision of 0.5%. For Teff and radius, we obtained a precision of approximately 1%, while we obtained a precision of 5% for log g. Through evolutionary models, we further show how these constraints can improve the mass and age determination, as they attain a precision of approximately 2% for mass and 5-10% for age.

We report the detection of a remarkable shell around the red hypergiant VY CMa using data from the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx). The shell, which in projection on the plane of the sky appears as a ring, is almost circular in appearance. It has an external diameter of $\sim14'$ to $15'$, and is seen most clearly in the SPHEREx 7827A spectro-photometric image. Filaments, radially aligned with VY CMa, are seen to cut across the shell in several places. We discuss the possibility that the shell is matter swept out from the neighboring star forming region Sh 2-310, by the wind from VY CMa. Resonant atomic scattering, a light echo, or Extended Red Emission are explored as the source of the observed SPHEREx emission. However, no interpretation is without difficulty and further observations are most desirable.

The traditional $α$ effect is extended by the first temporal derivative, so that in turbulent flows the magnetic field entering the induction process is effectively sampled in the past. As a consequence, dynamo excitation becomes easier and cycle times are prolonged relative to solutions obtained from the local standard formulation. The temporal shape of the magnetic cycles is also modified, with rise times becoming shorter than decline times, so that the profiles acquire a characteristic ``sawtooth'' appearance. In the nonlocal formulation, the induced magnetic-field amplitudes acquire an additional dependence on the correlation time. For fixed dynamo number, the field amplitude reaches a maximum at a certain correlation time. For correlation times larger than this peak value, the model can reproduce Waldmeier-type trends known from solar sunspot observations. If the actual correlation time fluctuates around this value, the long-term magnetic cycle can occasionally enter weak-cycle episodes reminiscent of grand minima such as the Maunder minimum. For smaller dynamo numbers close to the critical one, however, rather long correlation times are required for this behaviour to occur.

We report the direct imaging detection of a stellar companion to HD 101452 (HIP 56925; Gaia DR3 5384905720847544192), an A star historically used as an infrared flux calibrator. The companion was identified from an asymmetry in the stellar PSF using short-integration (<1 min), noncoronagraphic JWST MIRI imaging from 15 - 25.5$μ$m that was obtained as part of the absolute flux calibration program CAL 4496. We detect the stellar companion in four MIRI imaging filters at a projected separation of 1.3 arcsec with a mid-infrared flux ratio of approximately $27\times$ warranting its removal from the ensemble of JWST flux calibrator systems. This detection also demonstrates that noncoronagraphic MIRI imaging can recover companions at separations below $3λ/D$ when a reference star with a closely matched flux level to the science target is available. Using the measured contrast curves from the calibration data, we evaluate the predicted sensitivity achievable with similar short MIRI observations for nearby stars (<30 pc) that are of interest to the direct-imaging community with comparable brightness to HD 101452 (W4 ~ 6.8 mag). We find that integrations of only 17-42 s are be capable of detecting sub-Jupiter-mass planets at solar system-like separations around a subset of neighboring systems if the PSF subtraction is conducted with closely flux-matched references. These results demonstrate that minutes-length, noncoronagraphic MIRI observations can provide a powerful and efficient new avenue for exploring the cold giant planet population around nearby stars.

The longitudinal evolution of second-harmonic anisotropy inherited from the first interaction in extensive air showers is investigated with CORSIKA simulations. Events with large initial anisotropy are selected. Second-harmonic observables are evaluated separately using the coordinate and momentum azimuths at several atmospheric depths and compared with their corresponding initial harmonic orientations. More than 84% of the initial second-harmonic signal is attenuated within the first 20 g cm$^{-2}$ of shower development. In coordinate space, the second-harmonic correlation with the initial orientation persists to ground level at approximately 0.09% of its initial magnitude. This residual is evaluated against a matched source-isotropized reference, constructed for each selected event by independently randomizing the azimuths of the first-interaction final-state particles and simulating the shower under identical atmospheric conditions. The positive coordinate-space ensemble-mean difference at ground level is statistically resolved, and the two samples show little event-level separation. In momentum space, a weak ensemble-level residual remains at 200 g cm$^{-2}$, and the original and source-isotropized signals become statistically indistinguishable by 300 g cm$^{-2}$ and remain so at ground level.

We construct a classical formulation of gravity in terms of the vierbein that makes the Hilbert action polynomial in gravitational perturbations and identify some matter models that admit a polynomial coupling to such perturbations as well. We introduce the density vierbein variables that factorize the inverse metric density while retaining an explicit local Lorentz frame. With the introduction of a new auxiliary field, one can construct an action that is polynomial in such variables and their perturbations. Constructed the BRST complex for the model and derived propagators and interaction rules. In four dimensions, a scalar field with the canonical kinetic term and a potential admits a finite number of coupling terms with the density vierbein perturbations. Among all Horndeski gravity models, only a narrow subclass admits a polynomial coupling to the density vierbein perturbations. For instance, the Einstein--scalar--Gauss--Bonnet model always has an infinite tower of interactions with the density vierbein perturbation. Similarly, the standard kinetic term for the Dirac fermions and the standard kinetic term for a vector field both admit an infinite tower of interactions. Consequently, the density vierbein variables provide a great simplification for scalar-gravitational couplings, but the simplification is not strong enough to produce a realistic model with a finite number of matter-gravity terms.

We present XMST, an extended minimum spanning tree framework for identifying spatially coherent stellar structures using an objective, data-driven fracture-scale criterion. XMST combines percolation analysis with Jenks Natural Breaks optimisation, restricting the MST edge-length distribution to the subcritical regime before determining the final fracture scale. The method was validated using 1000 controlled Monte Carlo realisations containing eight empirical stellar-association templates, including a deliberately overlapping pair. The Percolation-Jenks fracture scale was highly reproducible, with a median of 17.028 pc and a between-realisation standard deviation of 0.066 pc. The injected structures were recovered with a mean completeness of 0.9996 and mean purity of 0.7413, while alternative CDF and Mean Edge criteria selected substantially larger fracture scales and produced markedly lower purities. Propagation of the published distance uncertainties through 10,000 additional XMST reconstructions produced a median absolute fracture-scale change of only 0.282 pc. Under these perturbations, mean completeness was 0.8605 and mean purity 0.7126, while 99.30 per cent of injected-template cases continued to satisfy the adopted detection criterion. Individual membership was less stable, with peripheral and locally sparse members showing lower persistence than structural cores. The deliberately overlapping pair was resolved spatially in only 15 of 1000 realisations; a reddening-based post-processing diagnostic increased this to 446, although with a corresponding completeness-purity trade-off. XMST therefore provides a robust method for identifying candidate stellar structures and their stable cores, while detailed outer membership and strongly overlapping populations require additional astrophysical information.

We study the implications of a recent measurement of the primordial helium fraction from the Large Binocular Telescope for cosmological inference from the cosmic microwave background. We show that LBT establishes the robustness of cosmological parameters to theoretical assumptions about big bang nucleosynthesis: its empirical calibration of the helium fraction enables constraints on cosmology and inflation that are agnostic to BBN but as precise as those that instead enforce standard BBN predictions. Future CMB surveys require at most a marginal improvement in precision over LBT to maximize their BBN-agnostic constraining power when the radiation density is free (and no more than a factor of two improvement across all cases we consider). We then apply the LBT measurement to a number of scenarios that feature new physics in BBN and the CMB. First, we constrain nonstandard radiation sectors (interacting and free-streaming) and search for evolution of the radiation abundance between nucleosynthesis and recombination. We then test models that alleviate the Hubble tension and the tension between CMB and baryon acoustic oscillation data, including self-interacting light relics and varying fundamental constants; LBT precludes most but not all of the models we consider via their effect on BBN. Finally, we use the LBT measurement as an indirect but independent test of the neutron lifetime anomaly, inferring values that are consistent with "bottle" experiments and $2.4 σ$ below "beam" experiments.

Einstein gravity in four asymptotically flat dimensions is governed by a tower of soft theorems obeying an $\mathcal{L}w_{1+\infty}$ commutator algebra. This algebra is deformed to $\mathcal{L}_Λw_{1+\infty}$ in the conformally related AdS$_4$ and dS$_4$ spacetimes. Here we construct the larger ``conformal $w$-algebra", denoted $\mathcal{C}w_{1+\infty}$, which acts on conformal gravity in all of these spacetimes. It includes $\mathcal{L}w_{1+\infty}$, $\mathcal{L}_Λw_{1+\infty}$ and the $\mathfrak{so}(4,2)$ 4D conformal algebra as subalgebras. We show that $\mathcal{C}w_{1+\infty}$ is the conformal completion of either $\mathcal{L}w_{1+\infty}$ or $\mathcal{L}_Λw_{1+\infty}$. A derivation of $\mathcal{C}w_{1+\infty}$ is given as the symmetry of the twistor action of self-dual conformal gravity.

We report a 216-hr upgraded Giant Metrewave Radio Telescope (GMRT) Band-4 $550-850$ MHz observation of the COSMOS field, using 7 GMRT pointings to cover an area of $2.4$ sq. deg., with on-source times of $67$ hrs in the central pointing, and $89$ hrs distributed across the other six pointings. We stacked, at a spatial resolution of 90 kpc, the HI 21 cm emission signals from 8,122 star-forming galaxies with accurate spectroscopic redshifts and lying within the FWHM of the GMRT primary beam at their redshifted HI 21 cm frequencies. We detect the stacked HI 21 cm signal from the 8,122 galaxies at $4.2σ$ significance, obtaining an average HI mass of $\langle{M_{\scriptsize{\textrm{HI}}}}\rangle=(15.5\pm3.7)\times10^9 \textrm{M}_\odot$. This is only the second galaxy population at $z\approx1$ with a measurement of the average HI content; the other being the blue star-forming galaxies in the DEEP2 fields. We also detected the median 1.4 GHz radio continuum emission signal from the 8,122 galaxies by stacking the GMRT 680 MHz continuum images, obtaining a weighted-median star-formation rate (SFR) of ${8.90\pm0.92}~M_\odot$ yr$^{-1}$. We measure a characteristic HI-to-stellar mass ratio of $\langle{M_{\scriptsize{\textrm{HI}}}}\rangle/\langle{M_\star}\rangle=(1.15\pm0.27)$ and a characteristic HI depletion timescale of $\langle{M_{\scriptsize{\textrm{HI}}}}\rangle/\textrm{SFR}=(1.74\pm0.45)$ Gyr for star-forming galaxies at $\langle{z}\rangle=1.081$ in COSMOS, both consistent with earlier measurements for the blue, star-forming DEEP2 galaxies at $z\approx1$. Our results support the evidence from the DEEP2 survey that the observed decline in the SFR density at $z<1$ is due to insufficient accretion of atomic gas from the intergalactic medium to replenish the gas reservoir consumed in the process of star-formation.

The treatment of convection is one of the largest remaining uncertainties in models of low mass stars. The Mixing Length Theory (MLT) for super-adiabatic convection has come under particular scrutiny. Evidence is mounting that a single value of the mixing length parameter ($α_\mathrm{MLT}$) should not be applied universally across stellar model grids, although simulations and asteroseismic calibrations disagree on how it should vary with stellar parameters. A variable $α_\mathrm{MLT}$ causes critical systematic changes to the ages of low mass stars, the key age tracers for galactic and exoplanetary studies. In this work we use classical (non-seismic) geometric radii and specialized MIST isochrones with a variable $α_\mathrm{MLT}$ to measure mixing length in detached eclipsing binaries (DEBs) and interferometrically resolved stars, finding plenty of evidence for non-solar $α_\mathrm{MLT}$. In particular we find that standard evolutionary models overpredict the radii of metal-poor interferometric stars and that a sub-solar $α_\mathrm{MLT}$/$α_{\mathrm{MLT},\odot}\sim0.50-0.75$ can neatly explain this discrepancy, consistent with other empirical calibrations and in stark contrast to simulations. We infer low convective efficiency in cool, rapidly rotating lower main-sequence stars, consistent with the known phenomenon of magnetically-induced radius inflation. We also identify several slowly rotating DEBs whose measurements cannot be reproduced by standard isochrones, and we propose these systems as useful case studies of non-solar mixing length in stars outside of the Sun. However, we find no definitive population level correlations between $α_\mathrm{MLT}$ and stellar parameters among the DEBs, calling into question the existence of a ubiquitous mixing length calibration in low mass stars.

The traceless field equations of unimodular gravity determine the source of a given geometry only up to a pure-trace contribution. We study the consequences of this reconstruction freedom for a static, spherically symmetric black-hole geometry containing the leading inverse-cubic deformation of Schwarzschild not fixed by weak-field data. We show that among the standard combinations entering the energy conditions, only the two null projections are independent of the reconstruction, whereas the energy density and the strong and dominant combinations depend on the chosen split between matter and vacuum. This yields a general criterion: conclusions based on the null energy condition are reconstruction invariant, while those based only on the strong or dominant conditions are not. Applied to wormhole throats, this criterion reproduces the null-energy no-go result for every split. For the black-hole family, the inverse-cubic parameter carries the complete trace sector. Within the Rastall restriction of the reconstruction family, nonconservation is controlled by the product of this parameter with the Rastall coupling, and the traceless split is selected by the energy conditions. We also derive strong-field observables and identify a charge-independent combination of photon-sphere and innermost-stable-orbit shifts that isolates the trace-sector parameter, while current observational precision remains insufficient to measure it.

In this paper, we investigate the cosmological dynamics of a modified gravity framework based on the function $f(T)=β(-T)^{1/2}+γ(-T)$, where $T$ denotes the torsion scalar. The matter sector is modeled using the Generalized Chaplygin Gas (GCG) with the equation of state $p=-\frac{\mathcal{A}}{ρ^η}$, allowing the model to describe the evolution from an early-time matter-like phase to a late-time accelerated universe. By deriving an analytical expression for the Hubble parameter $H(z)$, we perform parameter estimation using Bayesian statistical techniques based on the $χ^{2}$-minimization method with the Cosmic Chronometer (CC) and joint (CC+Pantheon) observational datasets. The deceleration parameter exhibits a transition from deceleration to acceleration, while the present-day value indicates the current accelerated expansion. The model yields a present-day EoS parameter consistent with dark-energy-like behavior, while the energy conditions indicate that the NEC and DEC are satisfied and the SEC is violated at late times. The $ω-ω'$ plane shows a freezing quintessence behavior, approaching the $Λ$CDM-like point $(ω,ω')=(-1,0)$, while the cosmographic analysis offers additional insight into the evolution of the cosmic expansion. The estimated age of the universe is also consistent with current observational bounds. These results demonstrate that the GCG scenario within $f(T)$ teleparallel gravity provides a viable and observationally consistent framework for explaining the late-time accelerated expansion of the universe.

We present the first dark matter density profile derived directly from James Webb Space Telescope JADES Data Release~3 NIRSpec observations of $N = 587$ galaxies spanning the cosmic noon epoch $1.5 \leq z \leq 3.5$. From each NIRSpec G235M/G395M spectrum we extract the H$α$ emission-line velocity dispersion $σ_{\rm ha}$, stack galaxies in four redshift bins of $Δz = 0.5$, and reconstruct representative group rotation curves within the General Theory of Relativity. Fitting the four-parameter modified exponential model and deriving the exact GTR energy density, we reduce the profile to a compact $[2/3]$ Padé approximant with all coefficients determined in closed form from JWST observations. The profile is cusp-free, fully analytic, and redshift-dependent. Energy conditions, causality, and orbital stability are all satisfied. Most strikingly, the central density $ρ(0)$ varies by less than $15\%$ across $z = 1.5$--$3.5$ despite a $35\%$ decline in the asymptotic rotation velocity, revealing a universal dark matter core saturation density at cosmic noon decoupled from baryonic evolution.

This paper investigates the holographic Casimir effect in AdS/BCFT with a brane-localized scalar field. The scalar field takes different values at the strip's two boundaries, leading to mixed boundary conditions. The massive brane-localized scalar field typically breaks the boundary conformal symmetries, allowing us to study the holographic Casimir effect in non-CFTs. In two-dimensional spacetime, we apply the holographic g-theorem to prove the holographic bound on the Casimir effect for general brane-localized matter fields. In higher dimensions, we find that the brane-localized scalar field reduces the Casimir amplitude when the mass squared \(m^2=0\), but can increase it when \(m^2 < 0\). Additionally, there is a no-hair theorem for the cases where \(m^2>0\). These findings indicate that relevant boundary deformations can enhance the Casimir effect. As a byproduct, we obtain a gravitational dual of the repulsive Casimir force under mixed boundary conditions and argue that it aligns with the cosmic censorship conjecture.

We study a thick braneworld model in asymptotically anti-de Sitter spacetime, supported by a non-topological lump-type scalar field. Unlike in boson stars, which are also non-topological solutions, the complex scalar field in our setup must have zero oscillation frequency. Consequently, the background scalar field is static and real, which breaks the global $U(1)$ symmetry. This is similar to spontaneous symmetry breaking, but it is not the same. We then investigate the localization of vector and fermion fields within this framework. By introducing a specific non-minimal coupling, we demonstrate that the zero modes of both fields can be successfully localized. Notably, this mechanism allows for the simultaneous localization of both left- and right-handed fermion zero modes.

RR Lyrae stars are essential standard candles for distance measurements in the Milky Way and nearby galaxies. Traditional estimates rely on the Period--Absolute Magnitude--Metallicity relation but are limited by uncertainties in metallicity determinations. We present a deep learning approach that directly predicts absolute magnitudes from RRab and RRc light curves, eliminating the need for metallicity estimates. Our model achieves validation precisions of 0.053 mag and 0.036 mag (approximately 2.5% and 1.7% in distance) for individual RRab and RRc stars, respectively. Tests on globular clusters yield typical distance precisions of 1.0% for RRab and 1.7% for RRc stars. For the benchmark systems, combining the RRab- and RRc-based models yields distance moduli of 18.498 $\pm$ 0.001$_{\text{stat}}$ $\pm$ 0.018$_{\text{sys}}$ mag for the Large Magellanic Cloud and 19.564 $\pm$ 0.003$_{\text{stat}}$ $\pm$ 0.019$_{\text{sys}}$ mag for the Sculptor dwarf spheroidal galaxy. These measurements are in excellent agreement with previous results, achieve a distance precision of approximately 1%, and represent a 1.8-fold improvement over traditional RR Lyrae calibration relations. Our approach showcases the ability of AI to directly extract key physical parameters from complex, information-rich light curves, resolve degeneracies, and scale to broader applications.

We study extremal mass branches in four-dimensional Einstein gravity coupled to one dilaton and two Maxwell fields with opposite-sign dilaton couplings. For generic couplings the extremal mass is governed by a nonlinear first-order equation with no known closed-form solution. We prove that this equation has a unique positive $C^2$ solution on the full real charge-ratio line and that the solution is real analytic, so positivity on the entire positive charge cone selects a unique global mass branch. Along this branch, any two nonproportional positive charge vectors attract for $ab>-1$, have vanishing leading force at $ab=-1$, and repel for $ab<-1$. The same transition fixes the transverse convexity of the extremal mass surface and the sign of the mass difference under arbitrary finite positive-charge partitions. The sign theorem extends to higher dimensions through the known dimensional rescaling. A radial reconstruction then shows that every point of the mass branch defines an asymptotically flat exterior with a finite-area inner endpoint, while smooth or analytic horizon extension is a separate condition that restricts the couplings and scalar flow.

The LUX-ZEPLIN experiment has reported a single nuclear recoil candidate at $E_R = 248 \pm 23(\mathrm{stat}) \pm 23(\mathrm{sys})$~keV, disfavouring the background-only hypothesis at a global significance of $2.6σ$. The difficulty such an event poses is not the recoil energy itself but the absence of any accompanying excess at low energy as elastic scattering of halo dark matter yields a monotonically falling spectrum, and supplying the required momentum transfer $q \simeq 246$~MeV already demands $m_χ\gtrsim 79$~GeV. We confront the event with the two kinematically distinct mechanisms that evade this limitation, endothermic inelastic dark matter, in which a mass splitting $δ\sim \mathcal{O}(100)$~keV forbids low-energy recoils and boosted dark matter, in which a light relativistic flux supplies the momentum, treating both with the same model-independent scalar--scalar, pseudoscalar--scalar and pseudoscalar--pseudoscalar effective operators. The two scenarios prove spectrally distinguishable. The inelastic spectra sit near the observed energy for every operator, placing only $6$--$17\%$ of events below 150~keV, whereas the boosted spectra depend critically on the operator: the scalar and pseudoscalar--scalar interactions place $99\%$ and $92\%$ of their events below 150~keV, while the pseudoscalar--pseudoscalar interaction places $75\%$ above it. Momentum dependence is thus essential to the boosted interpretation, but in the inelastic case it trades against the splitting, the preferred $δ$ decreasing monotonically from $\mathcal{O}_{ss}$ to $\mathcal{O}_{ps}$ to $\mathcal{O}_{pp}$. Because the scenarios differ across the whole high-energy window, a handful of additional events would separate them, placing the question within reach of the full LZ exposure.

In this literature, we derive an approximate black hole metric within the \( f(R, G, T) \) gravity framework, where the black hole is surrounded by an anisotropic fluid as the matter source. This approach allows us to study the influence of anisotropic pressures on the black hole structure. We then investigate the thermodynamic properties of the approximate solution, considering various types of matter fields. We analyze the thermodynamic quantities such as Wald's entropy, Hawking temperature, and specific heat for each case. After examining the specific heat, we find that the black holes are thermodynamically stable, with positive specific heat values indicating stability. This result suggests that the black holes under these conditions do not undergo thermal instability, ensuring their long-term viability.

Context. Accurate stellar spectra are essential to derive stellar properties. Traditional model atmospheres often oversimplify phenomena that break spherical symmetry, such as rotational deformation or multiplicity. The Spectroscopic PAtch Model for Massive Stars (SPAMMS) accounts for these effects, but its applicability has been limited by the spectral types covered by its model atmosphere grids. Aims. We aim to extend the parameter space of the model atmosphere grids available to SPAMMS, enabling spectral synthesis across a broader range of stellar types. Methods. We computed specific intensities, $I\left(λ,μ\right)$, for $101$ emergent angles using PRISMAS (Pipeline of Radiative Intensity Synthesis for Meshed Atmospheric Surfaces), and pre-computed LTE and non-LTE atmospheres from two ATLAS9-Kurucz grids and the TLUSTY-based OSTAR2002 and BSTAR2006 models. Results. The intensity grids cover effective temperatures from $3500$ to $55000\,\mathrm{K}$ and surface gravities from $0.0$ to $5.0\,\mathrm{dex}$, spanning O- to K-type stars. They include metallicities from $0$ to $30\,\mathrm{Z_\odot}$ and microturbulent velocities of $1$, $3$, $5$, and $10\,\mathrm{km\,s^{-1}}$. The spectral range extends from $3000$ to $9000\,\mathring{\mathrm{A}}$ with $Δλ=0.01\,\mathring{\mathrm{A}}$. As a proof of concept, we modelled with SPAMMS a rapidly rotating B-type star and an eclipsing Algol-type binary. Conclusions. The new LTE-Kurucz and NLTE-TLUSTY grids substantially expand the parameter space accessible to SPAMMS. The code can now generate synthetic spectra for a broader range of stellar types and geometries, including rapidly rotating and multiple systems -- providing a more comprehensive framework for modelling non-spherical stellar surfaces.

The cosmic web governs the growth of dark matter halos through anisotropic matter flows, yet the role of local velocity-field dynamics in halo mass assembly remains poorly understood. The velocity field carries non-linear information about matter transport that is not fully captured by density alone, particularly within filaments. We investigate this connection through velocity divergence and vorticity using dark matter halos in the IllustrisTNG TNG50-1-Dark simulation at $z=0$. Cosmic filaments are extracted with the 1-DREAM framework, and we statistically study how halo mass relates to divergence, vorticity, and radial distance from filament spines across three overdensity regimes. The velocity field correlates strongly with the cosmic web, with converging flows tracing filaments and vorticity arising primarily in overdense, non-linear regions. Within filaments, both divergence and vorticity show enhanced kinematic activity at intermediate distances from the spine, with amplitudes increasing with overdensity. We confirm a clear mass segregation, with more massive halos preferentially located near filament centers. Most notably, halos with masses $M \geq 10^{12} M_\odot$ are found almost exclusively in regions of low absolute divergence and low vorticity, while highly dynamical environments are dominated by low-mass halos. We further find that halos residing in kinematically calm regions assembled later and maintain higher recent accretion rates than those in dynamically active environments, linking present-day velocity-field properties to halo growth histories. These results demonstrate that the local kinematic state of the cosmic flow encodes information about halo mass and assembly beyond that contained in density alone, providing a complementary dynamical description of halo growth within the cosmic web.

Photometric galaxy clustering is a major probe of large-scale structure whose interpretation relies on accurate characterization of the galaxy redshift distribution, $n(z)$. Standard analyses assume the $n(z)$ of a selected lens sample to be isotropic, whereas observational systematics can imprint spatial variations. We quantify how this anisotropy biases angular galaxy clustering, internal consistency, and cosmological inference. We develop an analytical formalism for clustering under spatially varying $n(z)$ and forward-model realistic observational systematics, galaxy selection, and tomographic binning. For a fiducial magnitude-limited sample, modeling $w(θ)$ with a single global $\bar n(z)$ underestimates the clustering signal by up to $\sim10\%$ at small scales in the highest-redshift bin, decreasing towards lower redshift. In a $2\times2$pt analysis, cosmological parameter shifts remain below $1σ$ for KiDS-like and DES-like setups. For an LSST-like setup retaining KiDS-like selection and observing-condition variation, $σ_8$ is biased low by $1.7σ$ and $Ω_m$ high by $1.4σ$, while the high-redshift galaxy bias shifts by up to $\sim4σ$. The anisotropy also affects whether the probes are consistent enough to combine: a calibrated posterior-predictive internal-consistency test finds the contaminated angular clustering improbable given the joint cosmic-shear and galaxy--galaxy-lensing constraints (median calibrated $\tilde p\approx8\times10^{-4}$ under LSST-like noise). Anisotropic redshift distributions are therefore a potentially significant systematic for future photometric clustering analyses. Our forward model can be used to mitigate it given a realistic selection function and galaxy population model.

The recent observation of a single event at nuclear recoil energy $248\pm23\pm23$ keV by the LZ collaboration has prompted dark matter (DM) model builders to explore new physics explanations. While most of the existing literature invokes an endothermic scattering by a TeV-scale DM to explain the event, the favored DM interaction strength is in tension with the indirect detection constraints for most of the models. To evade this, this work explores exothermic DM scattering in a hadrophilic $q_1-q_2$ gauge extension setup with a new $Z'$ boson as a mediator to the dark sector. This can naturally escape the indirect searches in the absence of tree-level coupling of the mediator to neutrinos, $W,τ$, and $b$ quark. We consider freeze-in production at a low reheating temperature to populate DM in the early universe, with a comparatively smaller coupling than the thermal freeze-out scenario. We identify the $Z'$ parameter space that can explain the observed relic density and LZ event simultaneously. We also discuss the relevant constraints coming from flavor mixing and FCNC.

In this paper, we derive the complete transformations of a generic first order perturbative metric in Schwarzschild spacetime to the Newman-Unti (NU) gauge in series expansion near null infinity. This allows us to determine the asymptotic shear, the mass aspect and the angular momentum aspect of the perturbative fields. As a direct application, we derive the corresponding asymptotic NU data for quasinormal modes (QNMs) of a Schwarzschild black hole. The total energy and angular momentum of QNMs obtained from the asymptotic NU data vanish but classical supertranslation charges are non-trivial, which can be applied to fix the BMS frame at first perturbative order.

Many well-motivated dark matter (DM) scenarios, including dark photon DM, axion-like particles, sterile neutrinos, and primordial black holes, can deposit energy into ordinary matter and significantly raise the thermal energy of astrophysical gas. We present a simple, model-independent implementation of DM-induced heating in the RAMSES hydrodynamic simulation code, parameterized by an effective local heat-transfer rate $Γ_{\rm heat}$. Using simulations of an isolated gas-rich dwarf galaxy with properties similar to WLM, we find that DM heating substantially alters the thermal structure of the circumgalactic medium (CGM) while leaving the star formation rate and the dense ISM nearly unchanged. For $Γ_{\rm heat} = 10^{-27}$ to $10^{-25}\ {\rm s}^{-1}$, the neutral hydrogen column at 10 kpc is suppressed by 0.6 to 3.9 dex relative to the control simulation. Similarly, the C II and Si II column densities decrease by 4.1 and 5.5 dex, and by 2.2 and 3.0 dex for C IV and Si IV. These signatures are accessible to quasar absorption-line spectroscopy, so CGM observations of nearby field dwarf galaxies provide a promising avenue for constraining dark matter models that inject heat into ordinary matter.

Thermal conduction can act as a heating mechanism for cool-core clusters, yet the same transport must erode any temperature discontinuity it crosses. Ophiuchus permits both effects to be tested in the same atmosphere. Its temperature rises from about $1$ keV in the innermost core to $9$ keV at $r\sim30$ kpc, making conductive heating especially favorable, while two sharply resolved cold fronts independently constrain the same transport. \textcolor{black}{We construct a steady radial energy balance from deprojected \textit{Chandra} density and temperature profiles, with XRISM-based limits on turbulent heating and a subsonic inflow contribution.} Closing the balance with conduction requires only sub-Spitzer coefficients --- \Ftwentyfive\ at 25 kpc and \Finner\ and \Fouter\ at the inner and outer cold fronts --- so conduction can energetically supply the missing heat. Yet the same coefficients, applied normal to the cold-front surfaces, would broaden the fronts to their observed width limits within \Tinner\ and \Touter\ Myr, short compared to the characteristic sloshing timescales that generate and sustain such interfaces. For a representative 200 Myr residence time, the radial conductivity demanded by the energy balance exceeds the cross-front conductivity permitted by front survival by roughly a factor of three, with the required anisotropy exceeding unity in 99.9\% and 98.8\% of accepted models. The result leaves two broad regimes. Thermal conduction is either subdominant in Ophiuchus or contributes substantially but is strongly anisotropic, with heat transport suppressed across the cold fronts relative to the radial direction. Together they disfavor locally isotropic conduction as a dominant heating mechanism in cool cores generally.

We investigate the effect of $α$-core breakup on the strong conversion of \({}^{6}_{ΛΛ}\mathrm{He}\) into a deeply bound \(H\) dibaryon. In addition to the coherent \(H+{}^{4}\mathrm{He}\) channel, we evaluate the open final states \(H+p+{}^{3}\mathrm{H}\), \(H+n+{}^{3}\mathrm{He}\), and \(H+d+d\) using a translationally invariant Gaussian cluster description, including spin-isospin recoupling and full nonrelativistic three-body phase-space integrations. The breakup widths are normalized to Gal's intact-\(α\) result. At \(B_{ΛΛ}^{H}=176~\mathrm{MeV}\), corresponding to \(m_H\simeq2055~\mathrm{MeV}\), the summed breakup width exceeds the intact-\(α\) width by a factor \(R_{\mathrm{br}}=2.49\times10^{3}\). The resulting inclusive width and lifetime are \(Γ_{\mathrm{inc}}=3.87\times10^{-4}~\mathrm{eV}\) and \(τ_{\mathrm{inc}}=1.70\times10^{-12}~\mathrm{s}\), respectively, compared with \(τ_α=4.25\times10^{-9}~\mathrm{s}\) for the intact-\(α\) channel alone. The mass-dependent calculation shows that the inclusive lifetime crosses the characteristic hypernuclear weak-decay timescale near \(m_H\simeq2020~\mathrm{MeV}\) and increases rapidly as the \(H\) mass decreases. In the representative dark-matter-motivated interval \(1865\leq m_H\leq1885~\mathrm{MeV}\), we obtain \(6.59\times10^{-4}\lesssimτ_{\mathrm{inc}}\lesssim 6.80\times10^{-3}~\mathrm{s}\), far exceeding the weak-decay timescale. Thus, although core breakup can dominate the inclusive strong width near \(m_H\simeq2055~\mathrm{MeV}\), weakly decaying double-\(Λ\) hypernuclei remain compatible, within the present framework, with a deeply bound \(uuddss\) state in the mass range relevant to sexaquark dark matter.

The high-overtone quasinormal-mode spectrum encodes the near-singularity Kasner scaling of black-hole interiors. We show that distinct structures in this spectrum independently determine the temporal and spatial Kasner grades, allowing the corresponding metric exponents to be reconstructed without imposing Kasner constraints or invoking holography. We demonstrate this independent reconstruction at the fixed Kasner point of five-dimensional asymptotically flat Schwarzschild and planar Schwarzschild--AdS$_5$, and then extend it to a continuously varying Gibbons--Maeda black-hole family. The reconstructed exponents satisfy the Kasner relation a posteriori, providing a nontrivial geometric consistency check. More generally, the high-overtone spectrum separates into global spectral data and local algebraic corrections whose fractional powers are fixed by the near-singularity Kasner geometry. These fractional corrections therefore provide a direct spectral probe of the local geometry behind the horizon.

We investigate a regularized charged black hole (BH) spacetime constructed by applying the Simpson-Visser (SV) prescription to a BH in Einstein-Euler-Heisenberg (EEH) theory. The resulting Simpson-Visser Einstein-Euler-Heisenberg (SV-EEH) geometry incorporates nonlinear electromagnetic corrections through the parameter $(a)$ and the SV regularization through the length scale $(b)$. By varying these parameters, spacetime provides a smooth interpolation between a regular BH, a one-way wormhole, and a traversable wormhole configuration. Introducing the effective areal radius $(R=\sqrt{r^{2}+b^{2}})$, we analyze the horizon structure and derive the conditions for degenerate and extremal configurations. Furthermore, we examine the null and timelike geodesic structures, computing the photon sphere radius, the BH shadow size, and the innermost stable circular orbit (ISCO). Our results demonstrate how nonlinear electrodynamics and SV regularization jointly modify the causal and geodesic structure of charged BHs while preserving the appropriate Reissner-Nordström and SV limits.

The first exact solution to the field equations of general relativity was found by the German physicist and astronomer Karl Schwarzschild in 1916. Due to its simplicity and its various astronomical applications, the Schwarzschild solution is the most important, which gives it great educational potential. However, this potential is not usually exploited, since the Schwarzschild solution is generally taught in advanced undergraduate physics courses or in specialized graduate courses. The objective of this article is to offer a friendly introduction to the Schwarzschild solution, and at the same time analyze some concepts of Riemannian geometry and general relativity, employing only simple mathematical tools that do not go beyond the rudiments of differential and integral calculus.

We present FOSSIL, a proposed space mission which is designed to deliver unprecedented absolute spectroscopic measurements of the sky intensity over a broad frequency range (50GHz to 2THz) to accurately measure chemical-potential mu-type, Compton y-type, and Compton relativistic y-type CMB spectral distortions. FOSSIL will reach monopole sensitivities representing a gain of roughly three orders of magnitude over COBE/FIRAS. These capabilities will allow us to constrain primordial density fluctuations on scales k~(10 to 10^4)Mpc^-1, test inflationary models, probe dark matter annihilation/decay/interactions, constrain primordial black hole seed scenarios, and pin down feedback models in galaxy evolution and structure formation by measuring the cosmic thermal energy content. Furthermore, its 130 spectral channels will enable legacy astrophysics, including precise characterisation of the Cosmic Infrared Background, line intensity mapping during cosmic noon, and detailed Galactic dust mapping.

We present the public release of OpenGadget3 (OG3), a substantially extended and re-organised version of the widely used Gadget-2/3 family of cosmological simulation codes. Since G2 was made publicly available, the absence of continued official development led to the creation of numerous, mutually incompatible developer versions of G3 across the community. This made it effectively impossible to track bug fixes, reproduce published results, or consistently credit the many individual contributors. OG3 addresses this by consolidating these disparate developments into a single, documented, and continuously maintained code base, released under the GNU GPLv3 through a GitLab repository (with an accompanying wiki), regularly synchronised with the active developer branch, and supported by a dedicated continuous-integration (CI) pipeline. OG3 retains the core algorithmic backbone of its predecessors, a Barnes\&Hut oct-tree combined with a Particle-Mesh method for gravity, and a choice of Smoothed Particle Hydrodynamics or Meshless-Finite-Mass solvers for gas dynamics, within a hybrid MPI/OpenMP parallelisation framework, extended with GPU offloading via OpenACC and OpenMP. The code integrates an extensive suite of sub-resolution and physical modules, including primordial chemistry, radiative cooling, star formation, stellar feedback and chemical enrichment, dust formation and evolution, black hole growth and AGN feedback, MHD, thermal conduction, physical viscosity, SIDM, and massive neutrinos. OG3 introduces new features improving robustness, reproducibility, and usability: a flexible mixed-precision framework spanning 16- to 128-bit representations; expert-level tagged parameters with restart-time change log; extensive consistency checks against invalid configurations; and FAIR-compliant reporting of all settings, parameters, and specific publications. (shortened and abridged)

Weakly interacting massive particles (WIMPs) constitute one of the best-motivated dark matter (DM) candidates. In this study, we consider a simple extension of the WIMP paradigm in which WIMPs are coupled to a heavier particle that interacts only with them and can decay into WIMPs. In the early Universe, when WIMPs are in thermal equilibrium with the Standard Model (SM) bath, they serve as a portal to populate the heavy partner through inverse decays. Depending on the lifetime of the partner particle, its eventual decay into WIMPs can significantly alter the WIMP abundance. If the partner decays into WIMPs before their freeze-out from equilibrium, the standard thermal history remains unchanged. When the decay occurs after WIMP freeze-out, however, the injected non-thermal population of WIMPs can result in an overproduction of DM, therefore requiring a larger WIMP annihilation cross section relative to the standard scenario without the partner. For a given partner lifetime and WIMP annihilation cross section, freeze-out may be delayed due to re-annihilation or followed by a freeze-in phase. By solving the Boltzmann equations both semi-analytically and numerically, we explore these thermal histories and study the required enhancement in the WIMP annihilation cross section compared to the canonical value. This enhancement, which can reach up to three orders of magnitude, leads to stronger annihilation signals in the late Universe. As a result, current and upcoming indirect detection experiments are able to probe the lifetime of the partner particle. We briefly explore possible connections between our scenario and the baryon asymmetry of the Universe. As an example, we show that the Next-to-Minimal Supersymmetric Standard Model (NMSSM) can provide a realization of our scenario, with the possibility of accommodating light higgsino DM with the correct relic abundance.

Recent modeling of the JWST spectra of the Y-dwarf CWISEPJ193518.59-154620.3 (Faherty et al. 2024; Suárez et al. 2025) and the T-dwarf SIMPJ013656.5+093347.3 (Nasedkin et al. 2025) indicates the presence of a thermal inversion in their atmospheres, implying an additional source of heating. Auroral energy deposition has been proposed as a potential mechanism. In this work, we model auroral energy deposition processes and the resulting atmospheric response to assess whether physically motivated auroral electron beam energy spectra can reproduce the inferred thermal inversions. We simulate the effects of several auroral electron beam energy spectra consistent with observations of the Jovian population of auroral electrons and scale them to the total electron flux expected for brown dwarfs. We find that auroral energy deposition alone cannot reproduce both the magnitude and pressure level of the inferred inversion in either object. While inversions are produced in our models, they occur at pressures that are too low compared to those required by the observations. These results suggest that the actual population of auroral electrons includes a stronger high-energy component than considered here, that additional heating mechanisms contribute to the observed thermal inversions, and/or that heterogeneous heating of the atmosphere is important for determining the observed emission.

We study the quasinormal-mode and quasibound-state spectra of a massless scalar field in weakly magnetized Ernst--Schwarzschild spacetime. In the separated $O(B_0^2)$ regime, the Klein--Gordon equation reduces to a radial confluent-Heun equation. We construct an endpoint-selected spectral Wronskian directly from the canonical confluent-Heun recurrence and its regular-to-irregular connection limit. Quasinormal modes and quasibound states are then obtained as zeros of the same analytic spectral function on the radiative and bound sheets, respectively, providing a unified treatment of the two spectral sectors within the separated weak-field problem. The resulting QNM and QBS frequencies agree with independent weak-field Ernst and massive-Schwarzschild benchmarks available in the literature. We further show, for representative cases, that the frequencies selected by the local Heun-series termination relation examined here do not satisfy the endpoint-selected quasibound-state condition. The construction therefore provides a direct horizon-to-infinity spectral condition for both radiative and bound states within the weak-field Ernst problem.

Proto-planetary nebulae are considered to be the evolutionary link between AGB stars and planetary nebulae. They possess many of the physical characteristics expected of such a link and provide valuable information about the evolutionary process in these objects. One important characteristic of proto-planetary nebulae is the prevalence of very strong bipolar and point-symmetric morphologies. In planetary nebulae, these shapes are widely considered to be the result of shaping by a binary companion. Indeed, a number of studies have shown links between strong axial or point-symmetry in planetary nebulae and close binary central star systems that have gone through a common envelope phase. Here, we explore whether the observed proto-planetary nebulae may be the progenitors of planetary nebulae with close binary central stars. We find that despite the strong shaping of proto-planetary nebulae this is unlikely to be the case. We also discuss options for evolution to close binaries and the alternatives.

The Bekenstein-Hawking entropy, proportional to one quarter of the horizon area, is fundamental in black hole thermodynamics and can also be understood via the AdS/CFT correspondence, such as the 3D BTZ black hole and 2D CFT. In this work, we adopt the Kerr/CFT approach to analyze the central charge and black hole entropy for regular extremal black-bounce spacetimes, including the counterparts of the Kerr, Kerr-Newman, and Reissner-Nordström black holes. These spacetimes are free of curvature singularities at $r=0$. We derive the near horizon geometries of these spacetimes and find that they exhibit enhanced symmetry, namely SL$(2,\mathbb{R})\times \mathrm{U}(1)$ or SL$(2,\mathbb{R}) \times \mathrm{SO}(3)$. By imposing appropriate boundary conditions, we analyze their asymptotic symmetry groups, which contain diffeomorphisms as well as the $\mathrm{U}(1)_{\rm gauge}$ symmetry arising from the electromagnetic field. We then extract the central charge from the charge algebra and evaluate the left-moving temperature of the Frolov-Thorne vacuum. It is worth emphasizing that in the black-bounce Kerr-Newman case, the central charge from the electromagnetic contribution vanishes. Furthermore, in the black-bounce Reissner-Nordström case, we uplift the 4D geometry to a 5D configuration by incorporating a $\mathrm{U}(1)$ gauge fiber. Our results show that the microscopic entropy calculated from the Cardy formula is consistent with the Bekenstein-Hawking entropy. This agreement suggests that the Kerr/CFT approach remains valid for certain regular spacetimes without curvature singularities, thereby providing a microscopic statistical understanding of black hole entropy.

The Higgs vacuum expectation value (VEV) alters both the electroweak and strong interaction rates. We study both effects on Big Bang Nucleosynthesis (BBN) and seek concordance between observed primordial abundances of light elements and cosmological constraints from cosmic microwave background (CMB) fluctuations and anisotropies. We find a strong negative correlation between primordial 4He abundance and the Higgs VEV. Consequently, using a 1.58% uplift of the Higgs VEV during BBN from the current value, an agreement can be achieved among the new primordial 4He abundance, observed by the EMPRESS group, Deuterium abundance determined from absorption lines in the Lyman-alpha forest along the line-of-sight of high-redshift quasars, and the lithium abundance on the Spite plateau. This agreement requires a baryon-to-photon ratio different from the CMB determination, indicating the need for non-standard cosmological evolution between BBN and recombination epochs.We also demonstrate that a 0.2% uplift in the Higgs VEV can partially alleviate the "cosmic Li problem", keeping consistency with the CMB with remaining discrepancy potentially accounted for by stellar depletion mechanisms.

We explore a class of Lorentz-violating scalar-field models where the effects of the scalar field on antimatter can be strongly enhanced compared to matter. Non-trivial differences in phenomenology arise for spectroscopy measurements depending on whether the scalar field changes slowly or rapidly on the atomic scale. We highlight opportunities for precision tests in the laboratory including dark matter searches, in particular with spectroscopy and interferometry measurements, as well as certain types of antimatter experiments.

We use controlled N-body simulations to investigate whether dark matter subhaloes leave detectable signatures in the internal kinematics of dwarf spheroidal galaxies. At each snapshot, we fit a velocity distribution function to stellar line-of-sight velocities and proper motions, construct normalised residual fields for the projected velocity components, and analyse their power-spectra. We show that subhalo encounters generate a plethora of kinematic features. Amongst the most prominent are rotation-like signals, which arise in our models even though the stellar component is initialised without intrinsic rotation. In line-of-sight velocity alone, several snapshots resemble the classical blueshift--redshift pattern associated with stationary rotation. The plane-of-sky components, however, bring complexity, with alternating regions of expansion and contraction, as well as clockwise and anticlockwise streaming. Although we observe coherent streaming globally, these structures depart from typical equilibrium configurations, while their residual power-spectra quantify the characteristic spatial scales involved. This signal strengthens in models containing more massive subhaloes and becomes difficult to recover for small stellar samples: robust power-spectrum recovery of the full velocity-space signature usually requires O(10^{4}) tracers, although a rotation signal alone can be recovered with considerably smaller samples. These results suggest that dwarf spheroidal velocity fields can retain signatures of subhalo heating. Future spectroscopy, improved Gaia astrometry, and chemo-dynamical information should turn these diagnostics into population-level probes of dark matter substructure.

We study the optical properties of electrically charged black holes sourced by generalized Heisenberg-Euler nonlinear electrodynamics (NLED) in the second-order formalism. Using the exact parametric form of the static spherically symmetric solution, we analyze the photon sphere, the black hole shadow, and the light deflection angle, and compare the results with those of the Reissner-Nordström and Schwarzschild cases. We find that the photon sphere and shadow radii decrease with increasing charge and increase with black hole mass, while NLED effects become significant mainly near extremality. By confronting the dimensionless shadow radius with the Event Horizon Telescope (EHT) bounds from Sgr A* and M87*, we derive phenomenological upper limits on the charge, with Sgr A* providing the stronger constraint. We further show that, for fixed impact parameter and charge, the deflection angle is systematically larger than in the corresponding Reissner-Nordström spacetime, and that the critical impact parameter is shifted to larger values. Our results show that NLED corrections produce observable modifications in the optical properties of charged black holes, especially close to extremality.

Sakurai's object provides a rare opportunity to observe stellar evolution on human timescales.Since its born-again event and detection in 1996, its evolution has been extensively monitored, and recent optical spectroscopy has suggested the emergence of [WR]-type emission features. In this Letter, we present a secure spectroscopic identification of its central star based on new VLT/FORS2 observations and NLTE expanding atmosphere models. Several observed emission lines arise in a [WR]-type stellar wind, establishing the central star as a [WR] object. The strongest stellar features are due to C II-III and He I. We derive the stellar and wind parameters of Sakurai's object and discuss its evolutionary status. The [WR] star is much cooler (Teff ~ 30.5 kK) than the born-again star V605 Aql (Teff} ~ 95 kK), which erupted about 80 years earlier. The inferred temperature is lower than predicted by models suppressing convective mixing efficiency during the VLTP, but is consistent with higher time-resolution calculations involving slightly lower-mass (<~ 0.6Msun) remnants. Continued spectroscopic monitoring and atmospheric modelling will be crucial for tracing its reheating curve and constraining the physics of this rapid evolutionary phase.

This study focuses on propanethiol (or propyl mercaptan, C3H7SH), a sulfur analogue of propanol and a key target for investigating interstellar sulfur chemistry. We report the laboratory rotational spectroscopic characterization of its two structural isomers, propane-1-thiol (1PT) and propane-2-thiol (2PT). For 1PT, experimental analysis led to the observation of three almost isoenergetic conformers, Aa,Ag and Gg, marking the first-time report of the latter. For 2PT, both the anti and gauche conformers were identified. We also assigned, for the first time, several monosubstituted isotopologues in natural abundance: the 34S, 13C1, and 13C2 species for the anti-2PT conformer, as well as the 34S species for the gauche-2PT conformer.Resolvable tunneling splitting, caused by the large-amplitude motion of the sulfhydryl (SH) group, was observed for both the Ag-1PT and gauche-2PT conformers. Global fittings, integrating previous measurements, allowed for the accurate determination of rotational constants, quartic centrifugal distortion constants, and vibrational coupling parameters. The newly derived spectroscopic parameters were utilized to conduct an astronomical search toward the chemically rich Galactic Center molecular cloud G+0.693-0.027. While no evidence for propanethiol was found, we established rigorous upper limits for their column densities. These results indicate that 1PT and 2PT are approximately 13 and 5 times less abundant than ethanethiol in this source, respectively. Furthermore, the derived lower limit for the O/S ratio (29) for the 1-propanol/1-propanethiol pair is consistent with the solar value (37), proviiding a valuable benchmark for understanding the depletion of sulfur in the ISM.

Our central premise is that quantum mechanics may be the statistical limit of a more fundamental discrete theory: any such theory equips a physical system with a finite information capacity, and its departure from quantum statistics is controlled by how much of that capacity the system uses. We show that commercial cloud photonic quantum processors have reached the precision required to bound this capacity from below, using the binary-sequence model of Powers et al. as the concrete test theory: outcome probabilities arise from counting discrete sequences of length $n$, quantum mechanics is recovered as $n \to \infty$, and $n$ measures the information capacity of the register behind a prepared state. Photon Fock states $|1\rangle$, $|1,1\rangle$, heralded $|2\rangle$, and cascaded beam-splitter pairs are measured on programmable interferometers with dominant systematics determined in situ. The model's composition-consistent parametrization, singled out by requiring that rotations compose, recovers quantum mechanics with deviations $1.24/n$; a random-effects likelihood analysis calibrated by parametric bootstrap excludes all $n \le 100$: the information capacity of the register carrying the two-photon state, if finite, exceeds $10^2$. Cascaded beam splitters test the composition law directly: the data are split-invariant, excluding naive count composition at $8σ$ and confirming the interference-sign rule. Model-independently, curve-averaged deviations from the quantum partition law larger than $2.3\times10^{-2}$ are excluded at 95% CL, and the originally published linear parametrization is excluded outright. Because the compilation offset is frozen per circuit it is calibratable, opening the $10^{-3}$ floor ($n \sim 10^3$) to current hardware: cloud photonic processors are quantitative instruments for quantum foundations, and information capacity an experimentally boundable quantity.

Anti-de Sitter (AdS) spacetimes are not globally hyperbolic, so boundary conditions are generally needed for well-defined dynamics. Ishibashi and Wald (IW) determined boundary conditions yielding well-posed dynamics with conserved positive energy for scalar, electromagnetic, and linearized gravitational fields, using nonlocal potentials and individual spherical harmonic modes. In this paper, we determine which IW conditions are local in the primary fields and which are AdS-invariant. In four spacetime dimensions, the standard AdS-invariant boundary conditions set the rescaled magnetic field to zero for electromagnetism and the rescaled magnetic Weyl tensor to zero for Einstein gravity on the conformal boundary. We generalize these standard boundary conditions by setting arbitrary linear combinations of the electric and magnetic fields, or the corresponding Weyl tensors, to zero, and we conjecture that these exhaust the local, AdS-invariant, conservative boundary conditions in AdS$_{1,3}$. Boundary conditions with non-AdS-invariance and in different spacetime dimensions are also studied. The AdS-invariant conditions in AdS$_{1,3}$ extend to Yang-Mills theory and nonlinear gravity in a general Fefferman-Graham setting. We construct phase spaces for these general boundary conditions. The covariant phase spaces for general conditions are naturally associated with Lagrangians containing Pontryagin terms and, in gravity, a Gauss-Bonnet term. In gravity, except for the standard boundary condition, no nontrivial asymptotic gauge symmetries exist and all conserved charges such as ADM mass vanish identically, as in a closed universe. Spacetimes with Killing fields including AdS then exhibit linearization instability in the sense of Fischer and Marsden and Moncrief. For nonstandard boundary conditions, the modified symplectic structure yields new expressions for the entropy formula of black holes.

Strong-field rays that traverse a wormhole can carry optical information about an exterior inaccessible to the observer. We investigate this mechanism in a reflection-asymmetric thin-shell wormhole formed by joining a pure-polymer exterior containing the observer and emitting disk to a polymer geometry with a Kiselev-type anisotropic environment on the opposite side. Equal masses and a common polymer scale, angular geometry, and throat position isolate the effect of one-sided quintessence. We derive the shell-frame optical matching and calculate matched critical scales, null-ray topologies, orbit numbers, transfer functions, and face-on intensity maps for three emission prescriptions. The matching projects the opposite-side photon barrier onto a distinct inner edge of the observer screen, while the outer cosmological-type horizon partitions cross-throat rays into returned and terminal families. Across the admissible parameter grid, increasing the environmental amplitude widens the returned screen interval, increasing the polymer correction contracts it, and changing the environmental exponent produces competing trends. Observer-side orbit numbers and ordinary transfer branches remain invariant under changes confined beyond the throat, providing an exact control, whereas returned branches move and broaden. Once these branches enter the emitting support, they generate additional inner annuli at source-dependent onset strengths. The combined geometric and radiative analysis identifies a controlled cross-throat optical response to one-sided quintessence and shows how environmental information beyond the throat is encoded in matched critical structure and image morphology.

This paper investigates Lagrangians with arbitrary dependence on the Riemann tensor and any number of derivatives. Noether's second theorem is applied separately to ${\cal L}_{G}$ and ${\cal L}_{M}$, where the matter Lagrangian depends on a scalar field. For ${\cal L}_{G}$ diffeomorphism invariance requires that the generalized Einstein tensor satisfy $\nabla_αE^{αβ}=0$ and that there is a current satisfying $0=\partial_α(\sqrt{g}\, J^α_{G2})$. The main result is an explicit formula for the superpotential $Φ^{[αμ]}$ that solves $\partial_μΦ^{[αμ]}=\sqrt{g}\,J^α_{G2}$. Some applications to $f(R)$ gravity and various quadratic gravity theories are discussed. There are analogous results, including superpotentials, for the matter sector whenever the couplings to the matter fields contain derivatives of the metric.

Non-Gaussian weak lensing statistics improve the constraining power of cosmic shear data by harvesting information unavailable to two-point statistics, within and beyond the GR+$Λ$CDM scenario. Dark energy, total neutrino mass and deviations from GR have all been shown to be better measured with non-Gaussian lensing probes, in simplified conditions. Previous studies typically overlook the impact of secondary lensing signals, which can be large and therefore can significantly affect the conclusions. Here we investigate the impact on measurements of cosmological and modified gravity parameters in the presence of galaxy intrinsic alignments. We focus on the power spectra, lensing PDF, peaks and minima counts, void abundance and void profiles. These non-Gaussian statistics are measured from the MGLenS mock weak lensing maps, in which three cosmological parameters and one gravitational parameter are varied, either in the $f(R)$ or nDGP scenario, assuming Stage-IV lensing survey precision. These simulations are infused with the non-linear linear alignment model, allowing us to build emulators for each statistic with or without IA, and to study biases in full MCMC analyses. We show that in the absence of IA, lensing void profiles and abundance generally yield the highest Figure of Merit in the $S_8 - f_{R0}$ and $S_8 - H_0 r_{\rm c}$ planes, at times improving by an order of magnitude over two-point functions. When IA is unaccounted for, major parameter biases are observed in the cosmology sector, while the modified gravity sector is relatively unaffected. We find that these biases can generally be flagged from poor goodness-of-fit measurements, except for a few cases where IA can fully masquerade as a lower $Ω_{\rm m}$ and lower $S_8$ cosmology.

We present a clustering-based method for inferring halo masses of high-redshift galaxies, validated using the COLIBRE simulations combined with the HOMA empirical model, which assumes star formation to be proportional to halo accretion rate and is calibrated to JWST observations. Our approach matches the two-point correlation function of galaxies in stellar mass bins to reference halo clustering, establishing the stellar-to-halo mass relation over an optimal radial range 0.5 < r_p/cMpc < 1.0. Validation against true halo masses shows minimal bias, with scatter below 0.3 dex for volumes down to (50 cMpc)^3 and redshifts to z=12, even for photometric data. Cross-validation using the native COLIBRE population shows that the method is robust to the different galaxy-halo prescriptions. Survey volume dominates the error budget: field-to-field variations in the clustering amplitude vary by factors of 3 (2) for photometric (spectroscopic) samples, translating to 0.3-0.5 dex uncertainty in halo masses. Splitting the sample by properties such as SFR, colour, and age mitigates assembly bias, offering a key advantage over abundance matching. Application to JWST (JADES) samples at z=6 and 10 yields halo masses of log M_h/M_sun = 10.52_{-0.21}^{+0.12} and 9.91_{-0.34}^{+0.19} for M_UV < -17 galaxies, with linear biases of b_h = 4.2_{-0.41}^{+0.26} and 7.7_{-1.16}^{+0.77}, respectively. Current data cannot distinguish between star formation models. Our Roman Deep Tier forecasts indicate that at z=10, the inferred halo masses for M_UV < -21 galaxies differ by 0.5 dex between bursty and non-bursty models, but the expected number of pairs limits the constraining power. Our framework provides robust, empirically-calibrated halo masses essential for interpreting JWST observations and constraining galaxy formation during reionization.

We investigate whether a Dymnikova regular black hole can be observationally distinguished from a Schwarzschild black hole through strong gravitational lensing, taking into account effective field theory (EFT) corrections to photon propagation. We derive the modified photon propagation law induced by non-minimal couplings between the electromagnetic field and spacetime curvature and analyze the resulting photon trajectories in the Dymnikova spacetime. Within the strong deflection limit, we derive the EFT corrections to the photon sphere and the strong-deflection coefficients characterizing the logarithmically divergent behavior of the deflection angle. Although the EFT corrections are parametrically small, their effects can become relevant in the strong-deflection regime, where the deflection angle is highly sensitive to photon propagation near the critical orbit. We evaluate the strong-deflection observables for representative values of the Dymnikova parameter $\ell$ and compare them with the corresponding Schwarzschild results. We find that EFT corrections to photon propagation leave characteristic imprints on the strong-lensing observables. Furthermore, the contribution of the EFT corrections becomes more pronounced as the Dymnikova parameter $\ell$ approaches its critical value, indicating that the near-critical regime provides a particularly sensitive setting in which curvature-dependent corrections to photon propagation may affect gravitational lensing. These results suggest that strong gravitational lensing, together with EFT-induced modifications of photon propagation, may provide a means of distinguishing Dymnikova regular black holes from Schwarzschild black holes.

We study the notion of temperature in uniformly accelerated frames within a relativistic thermodynamic framework. Considering a perfect fluid at rest in a non-inertial (Rindler) frame, we derive the condition for thermal equilibrium from energy--momentum conservation. This leads to a position-dependent temperature profile consistent with the Tolman--Ehrenfest relation. We emphasize that this temperature characterizes the local thermodynamic equilibrium of the fluid in the accelerated frame and does not arise from a transformation law between different observers. The physical interpretation of the result and its relation to acceleration-induced effects are briefly discussed.

Magnetic fields play a crucial role in regulating the collapse of dense molecular clouds, shaping the early stages of protostellar evolution. We present polarization observations in submillimeter wavelengths with the SCUBA-2/POL-2 instrument on James Clerk Maxwell Telescope toward the Class 0 protostellar system L1527 IRS (IRAS 04368+2557). The magnetic field morphology varies across the core of L1527 IRS. Magnetic fields in the eastern region are perpendicular to the outflow axis, while those in the western region show a pinched morphology, overall aligned with the outflow cavity. These distinct bipolar outflow regions also have a clear color difference in near infrared observed by James Webb Space Telescope. In addition, the spectral index derived from 450 μm and 850 μm observations reveals that the northwestern region of the protostellar system is colder and denser compared to the southeastern region. Furthermore, in the large-scale structures and magnetic fields revealed by Herschel and Planck, we find a ~0.1 pc scale filamentary structure parallel to the large-scale magnetic fields in the eastern region and a relatively isotropic mass distribution in the western region. Based on these results, we propose an accretion scenario of the protostellar system in which an asymmetric mass distribution causes the distinct features observed in near-infrared and submillimeter wavelengths.

From its birth, celestial mechanics has been deeply intertwined with the question of the Solar System's dynamical stability. For the inner planets, this question is now statistically settled: Mercury's orbit carries a $\sim$1% chance of destabilization before the Sun leaves the main sequence. The outer Solar System has seemed more secure, with its intrinsic dynamical lifetime estimated at $\sim10^{18}$ years. Even accounting for the Sun's mass loss and stellar flybys, the orbital architecture of the giant planets had been expected to persist for $\sim$100 Gyr. Here we show that these estimates rest on the assumption that solar mass loss is smooth. The recently measured white dwarf recoil demands asymmetric mass loss that is most readily attributed to discrete, independently directed ejections that impulsively perturb stellar motion. As the Sun sheds its envelope in such parcels, the planets' orbits random-walk with amplitude set by the mass-loss granularity. At a coarseness corresponding to observationally permitted kicks, this stochastic forcing restructures the outer Solar System concurrently with the Sun's death. In particular, our numerical experiments reveal that orbit crossings can commence on the red giant branch, with $\sim$40% of realizations undergoing disruption or violent scattering before the white dwarf forms and $\sim$90% self-destructing within 3 Gyr. The outer Solar System's dynamical lifetime thus collapses from $10^{18}$ years to approximately a gigayear after white dwarf formation.

Accelerating black holes in General Relativity are described by the C-metric. We study how this geometry is modified by higher-derivative corrections, focusing on cubic curvature terms of even and odd parity. Using a suitable metric ansatz, we obtain closed-form solutions at first order in the coupling constants. The corrected geometries contain new integration constants, which correspond to physical deformations of the C-metric, and exhibit different behavior depending on the parity of the correction. In particular, parity-violating terms generate an off-diagonal metric component and induce rotation. For AdS solutions, we analyze the thermodynamics, including the Hawking temperature, entropy, and string tensions, and discuss the subtleties in defining the mass and thermodynamic string lengths.

Born-Infeld New Massive Gravity (BINMG) is an all-order curvature extension of New Massive Gravity in three dimensions, whose linearized spectrum around its unique maximally symmetric vacuum contains the two polarizations of a massive spin-two field. Whether an additional scalar degree of freedom appears in the full nonlinear theory has remained an open question. We perform a nonlinear canonical analysis of BINMG using its auxiliary-metric formulation. On the regular branch connected to the maximally symmetric vacuum, the Dirac algorithm yields three first-class diffeomorphism constraints and a second-class pair of scalar constraints. The resulting count gives exactly two local degrees of freedom per spatial point. Thus, nonlinear BINMG propagates no additional Boulware-Deser-type scalar mode on this branch.

We present the results of a driven, ideal magnetohydrodynamics simulation of a molecular cloud to study the formation of filamentary structures in molecular clouds and their fragmentation into dense cloud cores. Shock compression results in the formation of sub-parsec long filamentary structures. Large-scale supersonic flows push these small filaments together and form massive filamentary clouds. The main filament that forms stretches across the full 4.4 pc length of the simulation and has a median FWHM of 0.075 pc, similar to that observed in many molecular clouds. Subfilaments inside the main filament have a median FWHM of 0.03-0.04 pc, similar to the ``fibers" observed in molecular lines. The collision and merger of subcritical subfilaments is an important mechanism for the formation of prestellar cores. Colliding subfilaments and the resulting core at their intersection is a hub-filament system similar to that associated with massive star formation, but on a smaller scale. Core mergers can be significant in the growth of pre-stellar cores and may play a role in the formation of binary stars.

Recent orthodoxy, which we call Curvature Fundamentalism, posits that the field strength $F$ on spacetime exhausts the physically significant content of electromagnetism, at least on prosaic (contractible) spacetimes. We argue that it is gauge invariance that constrains physical significance. As a result, there are physically significant quantities that $F$ does not capture, even on contractible spacetimes. We show that this result is robust: in the presence of charged matter fields, there are interference experiments whose outcome cannot be predicted by $F$ or any other point-local gauge invariant quantities on the basis of initial Cauchy data. We prove this using the example of relative phase of a Klein-Gordon-Maxwell field, and use it to identify a context in which the widely-claimed equivalence between the Maxwell-Faraday formulation $EM_1$ and the gauge formulation $EM_2$ of electromagnetism is untenable, and that new strategies may be needed for the reductionist project.

We propose a framework for understanding the information loss paradox in the context of canonical quantum gravity. We first revisit several approaches to black hole evaporation that do not involve an event horizon. In these models, we assume that each time slice corresponds to a coherent state in the gravitational phase space. Due to this property, the quantum state associated with a given spatial configuration will have a nonzero overlap with another spatial configuration. We show how this property can account for both semi-classical dynamics and unitary time evolution. We introduce an explicit toy model that follows semi-classical time evolution at the coarse-grained level; in addition, its time evolution is unitary at the fine-grained level. The only price that one must pay is the violation of the entropy bound; we discuss reasons why this may be justifiable.

We study the Einstein-Vlasov system near the Schwarzschild spacetime in spherical symmetry. In particular, we consider the case when the matter is supported on bounded geodesics. In this regime, the decay of the matter is driven by phase mixing rather than dispersion. For the linearized problem, we obtain quantitative phase mixing; the key new ingredient proved here is a monotonicity property of the period function. For the nonlinear coupled problem, we prove phase mixing up to the timescale expected from the nonlinear echo mechanism; this is achieved by analysis on dynamical action angle variables and the integral estimates with the vector field method. This construction is made possible by our gauge choice, an isotropic coordinate system together with a foliation of prescribed mean curvature, in which the Einstein equations gain derivatives over the matter due to its elliptic nature.

Bouncing cosmological models replace the big bang singularity with a regular bounce, but face a well-known obstacle: the anisotropic shear grows as a^(-6) during contraction, where a is the average expansion factor, threatening to dominate before a homogeneous, isotropic universe can emerge from the bounce. A standard remedy is a scalar field with an ekpyrotic-like potential that turns negative near the bounce, pushing its effective equation of state above unity so it outgrows the shear. Here we examine how this mechanism affects the subsequent inflationary phase within mLQC-II, a modified loop quantum cosmology (LQC) model in which inflation is otherwise generic. Taking a potential combining ekpyrotic and inflationary components, we numerically evolve the dynamical equations across the bounce for various parameter choices. We find that while some choices of the free parameters of the theory allow the ekpyrotic potential to dominate near the bounce and resolve the shear problem, it substantially reshapes the post-bounce evolution. In particular, parameter choices that yield sufficient inflation without the ekpyrotic mechanism now often fail to do so. Sufficiently long inflation remains possible but appears to require fine-tuning. As our results are numerical, a more systematic analysis will be needed to establish their generality.

We analyze the presence of X-ray surface brightness (SB) discontinuities, such as shocks and cold fronts, in the intracluster medium (ICM) of the 116 galaxy clusters from the CHEX-MATE sample. These features arise from accretion-related processes, including the merging of subclumps onto the main cluster halo and the sloshing of cold gas in a higher-entropy environment. We identify these structures in the XMM CHEX-MATE maps by examining both the SB residuals, obtained by subtracting a cluster model from the observations, and the gradient variations across X-ray images. We validate our method with an extensive analysis and comparison of the discontinuities described already in the literature. Our analysis reveals 66 discontinuities, 32 of which are newly detected, in 48 objects ($\sim$41%). We find that discontinuities in relaxed systems tend to be closer to the core, weaker, and less aligned with the global X-ray morphology compared to those in disturbed systems. Using wavelet-based temperature maps, we provide a preliminary classification of these discontinuities, proposing the occurrence of 8 putative shocks and 34 cold fronts. Furthermore, about 48% of the systems with extended radio emission show evidence of ICM discontinuities; conversely, $\sim$88% of the objects with detected discontinuities have an associated diffuse radio emission. This work also explores the limitations of using XMM data, characterized by relatively low spatial resolution, for detecting and analyzing such features, highlighting the challenges and potential biases introduced by instrumental constraints.

We study the local canonical thermodynamics of the quantum Oppenheimer--Snyder (qOS) black-hole exterior previously obtained from loop quantum cosmology. The spacetime is adopted from the literature; no new black-hole solution, regular extension, or singularity-resolution mechanism is claimed here. At fixed quantum parameter $α$, we rewrite the outer horizon in a dimensionless form and obtain exact expressions for the mass, Hawking temperature, entropy, and heat capacity. These expressions reproduce the logarithmic entropy term and the heat-capacity divergence reported in earlier analyses. We then place those results in an explicit, regulated canonical-ensemble framework. The off-shell canonical action has a local minimum on a near-extremal branch with positive heat capacity and a local maximum on a large-black-hole branch with negative heat capacity. The two saddles merge at $r_h/\sqrtα=\sqrt{(4+2\sqrt{7})/3}$, where the temperature is maximal and the heat capacity diverges. Because the asymptotically flat partition function is not normalizable without boundary data, this divergence is interpreted as a Davies-type local stability transition, not by itself as a global first-order phase transition. The principal contribution of this work is therefore a transparent canonical-saddle organization of known qOS thermodynamic results, together with a precise statement of its domain and limitations.

We present the mid-infrared variability study of 120 long-lived disk candidates (ages 10-100 Myr) and 13 confirmed "Peter Pan" disks using NEOWISE to constrain the longevity of dynamic disk processes beyond the standard 10 Myr dispersal threshold. We identified 32 sources exhibiting significant variability by combining stochastic flux metrics and the Stetson $J$ index. The majority of these variables belong to the 10-25 Myr age range, suggesting a sharp decline in disk brightness variability after 25 Myr. Morphologically, the variability is characterized by irregular fluctuations with mean amplitudes of $ΔW2 \approx 0.5$ mag, consistent with variable extinction or inner disk warping induced by embedded planetesimals. We also report a strong correspondence between mid-infrared and optical variability for the Peter Pan disks, with all 9 mid-IR variables confirmed as optical variables in the literature. Our findings reveal a population of 23 new long-lived disk candidates that retain active, gas-rich environments, supporting the existence of a rarefied class of systems that survive well into the debris disk era.

We fit the circular velocity data, derived from weak lensing observations of isolated galaxies selected from the KiDS survey in four baryonic mass bins, using three different dark matter profiles. These include NFW, Burkert, and pseudo-isothermal profile. We find that the NFW and Burkert profiles cannot adequately fit the circular velocity data for all the four baryonic mass bins, whereas only the pseudo-isothermal profile can fit the data for all the four bins.

A collection of evidence is presented showing that the conjectured reverse isoperimetric inequality (RII) for asymptotically anti-de Sitter (AdS) as well as de Sitter (dS) black holes, ${\cal R}_\text{RII} \ge 1$, is of fundamental importance and its violation (${\cal R}_\text{RII} < 1$) gives rise to either thermodynamic instabilities, or physically unreasonable solutions, or naked singularities. We show that AdS black holes violating reverse isoperimetric inequality, known as superentropic black holes, satisfy neither mechanical stability requirement of ${κ_T} \geqslant {κ_S} \geqslant 0$ nor thermal stability requirement of ${C_P} \geqslant {C_V} \geqslant 0$. This property makes them thermodynamically unstable for the whole range of parameter space and explains all the diverse behaviors so far reported. We conjecture this statement holds for all superentropic black holes. We confirm that there is no counterexample to the thermodynamic instability conjecture of superentropic black holes and extend this to dS space by presenting the first example of superentropicity in dS space. By bringing evidence, we then propose two other conjectures: 1) there is no asymptotically flat limit of superentropic black holes, and 2) there exist two stronger versions of Penrose isoperimetric inequality (PII) for asymptotically flat black holes; the first is the asymptotically flat limit of the RII and the second is a new inequality in terms of the ADM mass and the thermodynamics volume, that we call thermo-volumetric inequality, obtained via insights from the $Λ\to 0$ limit of extended black hole thermodynamics in AdS. We show that the Penrose isoperimetric inequality (PII) is weaker than the reverse isoperimetric inequality (RII), as demonstrated explicitly for $D=4,5$ and for all black hole families we have examined.

In the context of the AdS/CFT correspondence, the Jafferis-Lewkowycz-Maldacena-Suh (JLMS) formula relates the boundary modular Hamiltonian to the HRT area operator and the corresponding bulk modular Hamiltonian. In standard discussions of a holographic code built from perturbative excitations on a fixed classical background, the $A/4G$ term dominates over the bulk modular Hamiltonian in the limit $G \to 0$. However, this setup is insufficient to describe the action of boundary modular flows that change the classical background. In contrast, our recent discussion of `large' codes provides a useful framework to obtain a JLMS formula that relates bulk and boundary modular flows acting on appropriate states in the code. Here, one sees that the bulk modular Hamiltonian is not in fact subdominant when the modular flow defined by one state acts on another state peaked around a sufficiently different classical background. Instead, the bulk modular Hamiltonian can be of order $1/G$ and can dominate over the $A/4G$ term. Nevertheless, we show that if the two states have the same classical background except for data conjugate to the HRT area then, under mild assumptions and over a large range of flow parameters, the modular-flowed state is described by a classical background given by the HRT-area flow alone.

We develop a general framework for constructing massive black bounce geometries from massless wormhole seeds by introducing a position-dependent mass function while preserving the underlying areal-radius profile. We apply this procedure to the generalized Ellis-Bronnikov wormhole and obtain a new family of generalized Bardeen-like black bounce space-times, which continuously interpolates between traversable wormholes and regular black holes. We investigate the motion of massive particles and photons and show that, in contrast with the simpler orbital structure of the massless generalized Ellis-Bronnikov geometry, the generalized Bardeen-like space-time can exhibit multiple circular orbits and a rich light ring structure, including configurations with two unstable circular photon orbits separated by a stable one. We determine the corresponding photon sphere and shadow radii and compare our predictions with Event Horizon Telescope observations of Sgr A*, deriving observational constraints on the parameter space of the model. We further investigate the optical appearance produced by a geometrically and optically thin accretion disk through ray tracing. Multiple light rings generate characteristic nested structures in the high-resolution intensity profiles, whose relative brightness is strongly affected by the mass deformation and gravitational redshift. However, after modeling the finite angular resolution of the EHT with a Gaussian beam convolution, these fine structures are largely washed out, revealing a strong observational degeneracy between these exotic compact objects and standard black hole geometries at current EHT resolution.

We propose a hybrid inflation model based on gauged scale symmetry, in which an axion-like field drives inflation while the Standard Model Higgs serves as the waterfall field. During slow-roll inflation, the Higgs is trapped in the electroweak-symmetric vacuum. When the inflaton reaches a critical value, the Higgs acquires a nonzero vacuum expectation value and and triggers electroweak symmetry breaking (EWSB) through the waterfall dynamics. We identify viable parameter regions that simultaneously accommodate current cosmic microwave background observations and Higgs data from the Large Hadron Collider. The relaxation mechanism connects the inflationary and electroweak scales by reducing the large vacuum-energy contribution required during inflation. Our framework thus provides a dynamical connection between inflation and EWSB.

Recent observations suggest intrinsic links between the stellar components of massive halos and their assembly histories. Using massive halos with $\log[M_{\rm halo}/M_\odot] \geq 13.0$ from the IllustrisTNG-300 simulation, we explore differences in secondary halo properties between samples selected by central galaxy stellar mass and satellite richness. For group-like masses, we find that halos selected by the outskirts stellar mass of their central galaxies between 50 and 100 kpc ($M_{\star,[50,100]}$) have similar halo mass distributions to those selected by intrinsic satellite richness ($λ_{10, R_{200}}$), but differ significantly in assembly history: $M_{\star,[50,100]}$-selected halos are more concentrated and formed earlier. At higher masses ($\sim10^{14}~M_\odot$), intrinsic richness becomes the better halo-mass proxy, but only when projection effects are ignored. We find that the difference-set test selects comparable halo-mass samples most effectively when the two proxies have similar scatter. Projection effects and baryonic physics do not alter the main trends but remain important caveats for observational applications. Our findings show that the central stellar mass-richness plane is a powerful tool for selecting halos with particular accretion histories, offering new insights into the galaxy-halo connection in the era of deep imaging and precision lensing surveys such as Euclid and LSST.

In Einstein-Cartan spinor gravity under the irreversible vierbein postulate, only the spinor among the first-order variables has a kinetic term of its own at tree level. Any nonzero background vierbein breaks the local-Lorentz (LL) symmetry spontaneously. Our previous work showed that the spinor loop generates the kinetic and mass terms of the LL gauge field, manifesting LL as a hidden local symmetry. Here we show that the spinor loop also generates the vierbein two-point function, while respecting the background gauge invariance and satisfying the Ward-Takahashi identities of the true gauge invariance, for both the general-coordinate and LL symmetries. The scheme-independent logarithmic divergence assembles the familiar induced-gravity ingredients: a cosmological constant, an Einstein-Hilbert and a Weyl-squared term for the metric sector, and a mass and a higher-derivative kinetic term for the totally antisymmetric torsion. In the vierbein sector, this torsion is carried by the derivative of the antisymmetric part of the linear vierbein fluctuation. This part is the would-be Nambu-Goldstone boson of the spontaneously broken LL symmetry, and its couplings in the minimally coupled action are all fixed by general-coordinate and LL gauge invariance. The five induced terms form a single effective action, manifestly invariant under both symmetries, completing the vierbein sector of the hidden-local-Lorentz emergent-gravity scenario.

Perturbative quantum gravity is ultraviolet divergent and, as shown by 't Hooft and Veltman, non-renormalizable. A recent object-relative, Lorentz-invariant weighting of internal electromagnetic modes renders selected one-loop contributions of quantum electrodynamics finite without counterterms. Here that weighting is derived rather than postulated: causality defines a mode resonator bounded by the Hubble radius and re-defined in every inertial frame, and the self-gravitation of each mode quantum deforms its spectrum. Applied to linearized gravity, the graviton self-coupling reaches order unity at the Planck wave number, so that the mode content available to a loop is suppressed beyond it. Any suppression exceeding a threshold fixed by the diagram renders the one-loop integrals finite; no cutoff is imposed and no mode structure above the Planck scale need be derived. For pure gravity the same power counting extends to every loop order, and the leading suppression already meets the resulting condition for every topology with more than one vertex; a single class of single-vertex insertions is excluded. The Bianchi identity takes the role of the Ward identity at one loop, and the transformation between the resonators of two inertial frames is unitary. The same finite mode content yields a vacuum energy density of order H^2/G, of the observed sign and magnitude, from the Planck and causal infrared wave numbers alone. A contribution tracking the instantaneous expansion rate is an exact rescaling of the gravitational constant and is excluded by primordial nucleosynthesis, so the mode basis must be frozen in any inertial system; referring it to the stationary de Sitter horizon fixes the remaining coefficient to the geometric value 6/pi and makes a value for the energy density of gravitational vacuum fluctuations possible which can be interpreted as origin of the dark-energy effect.

We study whether orbital redistribution in a self consistent spherical Einstein--Vlasov environment can change the asymptotic normalization of a black hole horizon while the horizon mass, particle rest mass and ADM mass are all held fixed. The matter variable is the occupation of regular bound orbital actions, so the stress tensor, orbital energies and gravitational field are determined by the same distribution. Linearization of the spherical mass constraint gives a kinetic variation law in which orbital energy is conjugate to occupation and the inner lapse ratio multiplies the horizon mass variation. On a locally regular equilibrium branch, mixed variations imply an integrated reciprocity relation between the central mass derivative of orbital energy and the directional response of the horizon normalization. We construct finite mass populations and trace constant mass redistribution curves. For the reference rest mass ratio $0.30$, the calculated endpoint surface gravity shifts are approximately $+15.37$ and $-15.33$ parts per million. The constrained response cancels at simultaneous dilute and Newtonian order, is nonzero for exact Schwarzschild orbits, and is further modified by self gravity. Independent balance, integral, derivative and refinement tests resolve the response well below its reported magnitude.

Observations have established that the circumbinary discs formed around post-asymptotic giant branch (post-AGB) binaries have striking similarities to protoplanetary discs around young stars. In this study, we examine the feasibility of the different stages of growth in the core accretion framework of planet formation in post-AGB discs, in order to assess whether planet formation is possible in these systems. We find that dust coagulation up to mm sizes is possible within the lifetimes of post-AGB discs, consistent with observations. We then investigate the subsequent growth of planetesimals through pebble and planetesimal accretion. If the streaming instability operates in these discs, the resulting planetesimals formed in higher-mass post-AGB discs ($M_{\rm disc}\sim0.1M_\odot$) can enter rapid pebble accretion and reach their isolation mass within the estimated disc lifetime. By contrast, in lower-mass post-AGB discs ($M_{\rm disc}\sim0.01M_\odot$), planetesimal accretion is too inefficient to produce substantial further growth. We also show that the larger aspect ratios of post-AGB discs compared to protoplanetary discs around young stars imply high pebble isolation masses and therefore potential formation of rocky planets with masses extending up to Jupiter masses. After assessing gas accretion and concurrent migration in these discs, we conclude that second generation planet formation in post-AGB discs is theoretically possible within their estimated lifetimes ($10^4$--$10^5$yr) provided that local dust-to-gas ratio enhancements and sufficiently high disc masses are achieved.

We present the first application of neural field-level baryon-acoustic oscillation (BAO) reconstruction to real spectroscopic survey data. We develop Linear Field Transformer (LiFT), a 3D vision transformer that takes as input the observed galaxy field, its standard reconstruction, and a set of context channels encoding local line of sight, survey coverage, and redshift, and learns to correct standard reconstruction toward the linear density field. We construct a forward-modeling pipeline to produce mock lightcones similar to the DESI Data Release 1 (DR1) luminous red galaxy (LRG) sample, and train LiFT on these. We validate LiFT on held-out simulations, as well as on additional mocks which differ in gravity solver, halo finder, HOD, cosmology, and fiber-assignment history, as well as on mocks analyzed with a distorted distance-redshift relation; ultimately, we find unbiased dilation parameters with consistently tighter constraints than standard reconstruction. Applied to the DESI DR1 LRGs, LiFT improves errors on $α_{\rm iso}$ by 13%, 24%, and 30% and on $α_{\rm AP}$ by 5%, 22%, and 30% relative to the DESI DR1 standard reconstruction analysis in the LRG1, LRG2, and LRG3 bins respectively; meanwhile, our DR1 central values remain consistent with DR1 and DR2. This equates to a factor of 1.2, 1.7 and 2.0 increase in Figure of Merit (or effective survey volume) if one were to only use standard reconstruction. Ultimately, these results establish LiFT as a validated, survey-ready tool for current and upcoming galaxy surveys.

The LUX-ZEPLIN (LZ) experiment has reported a high-energy nuclear recoil candidate, LZ230616, at $E_R = 248 \pm 23_{\rm stat} \pm 23_{\rm sys}\,$keV, which is difficult to reconcile with elastic scattering of halo dark matter (DM). Endothermic inelastic scattering offers a natural explanation, but it rests on a nucleon coupling that is off-diagonal rather than diagonal. We show that this feature arises automatically within a radiative Dirac neutrino mass framework. The Standard Model is extended by three right-handed neutrinos (RHNs), a pair of vector-like neutral fermions for each generations, and a scalar sector comprising an inert doublet and a real singlet, governed by a $\mathcal{Z}_2 \times \mathcal{Z}_4$ symmetry. The $\mathcal{Z}_2$ symmetry stabilizes the DM, while the $\mathcal{Z}_4$ symmetry forbids the tree-level Dirac Yukawa coupling together with all renormalizable Majorana mass terms, thereby allowing the generation of Dirac neutrino masses at the one-loop level through a softly broken scalar trilinear coupling `$κ$'. Since the neutral dark-sector fields can be expressed in terms of real scalar mass eigenstates, the $Z$ boson couples to them purely off-diagonally and elastic $Z$-mediated scattering is absent identically rather than simply suppressed. The singlet--doublet mixing induced by `$κ$' governs both the inelastic rate and the one-loop Dirac neutrino mass, which therefore vanish as $κ\to 0$. We find that DM masses in the few hundred GeV to TeV range, with splittings of $\mathcal{O}(340-360)\,$ keV, simultaneously reproduce the observed relic abundance, account for the LZ event and yield neutrino masses of the correct order, while respecting elastic direct-detection limits and all relevant theoretical and experimental constraints. A substantial part of the surviving parameter space lies within reach of DARWIN.

We investigate the loss of coherence of a two-level Unruh--DeWitt detector coupled to massless real scalar fields in $(1+3)$-dimensional de Sitter spacetime. Treating the detector--field interaction perturbatively to second order, we derive analytic expressions for the real asymptotic coherence-decay coefficients for conformally and minimally coupled scalar fields. For the conformally coupled field, the coefficient remains finite in the small-gap limit and grows linearly with the detector energy gap in the large-gap regime. For the massless minimally coupled field, the logarithmic sector of the Wightman function produces an additional positive contribution. This provides an explicit analytic extension of the previously known infrared enhancement of detector transition responses to the asymptotic coefficient governing detector coherence. The explicitly average-time-dependent sector does not contribute to the real nonzero-frequency asymptotic coefficient under the adiabatically regulated half-line prescription adopted here, when the regulator is removed at fixed average time and fixed positive detector gap. This asymptotic result does not describe the complete finite-time dynamics, which depends on the switching function and observation interval. Within the stated prescription, the coefficients satisfy $Γ_{\rm MMC}>Γ_{\rm CC}$ for $ω>0$, with $Γ_{\rm MMC}/Γ_{\rm CC} =1+(H/ω)^2$. The distinction is most pronounced in the small-gap regime, whereas the two coefficients approach one another for large detector gaps.

We discuss the effectiveness of the recently proposed quantity $J_{s}$ in suppressing the contribution of a string's self-field to its spectrum, which is used in field theory simulations to track the emission of axions by decaying cosmic strings. We compute the contribution of the self-field to the spectrum of this quantity and to the usually computed spectrum of $φ\partial_{t}α$ for an infinitely long straight string. Although we demonstrate that the $J_s$ approach is a substantial improvement, we also point out that this highly symmetric model doesn't capture the full contribution of the self-field to the spectrum emitted by strings of a more complex shape, which are typical in network simulations. We then illustrate this point numerically using a simulation of a sinusoidally perturbed straight string. For this simple configuration, we managed to separate the contribution from the self-field and the radiation to the spectrum of $J_{s}$, using the self-field subtraction method. This allows us to show that the spectrum of $J_{s}$ is still dominated by the $n=1$ mode of the string's oscillation, which can be attributed to the self-field and is largely suppressed when the self-field is removed. We also demonstrate that this mode is predominantly sourced by variations along the direction parallel to the string, which is missing in the unconnected segment model, used by arXiv:2512.13653 to claim the effectiveness of $J_{s}$ in suppressing the self-field's contribution to the spectrum.

The project called Measuring at Intermediate metallicity Neutron-Capture Elements (MINCE) primarily focuses on the photospheric abundances of several neutron-capture (NC) elements from high-quality spectra of metal-poor stars within the metallicity range of ${\rm -2.5 \leq\![Fe/H]\!\leq -1.5}$, aiming to provide homogeneous information on their chemical compositions. Furthermore, based on the Gaia mission, chemical abundances can now be coupled with kinematic properties, enabling investigations of the constituent substructures of the Milky Way. We analyse the fourth sample of MINCE stars in terms of atmospheric parameters and chemical composition. The results are then compared with the previously analysed MINCE samples. The observations were conducted with HARPS-N (${\rm R \approx 120\,000}$) at the Telescopio Nazionale Galileo (TNG) and FIES (${\rm R \approx 67\,000}$ ) at the Nordic Optical Telescope (NOT), providing optical spectra with a high signal-to-noise ratio (S/N) and high resolution. We then used the methods developed in previous MINCE works and Gaia photometric data to obtain the stellar atmospheric parameters. The chemical abundances were analysed using 1D-LTE model atmospheres. We present the photospheric abundances in 37 stars of up to 26 elements, including $α$, iron-peak, light-odd, and 10 NC$-$elements (Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, and Eu). Kinematic properties and membership assessments are provided for all stars. The MINCE catalogue is thus expanded by 13 thin-disc stars, 9 thick-disc stars, 1 star in a transition zone between the thin and thick disc, 9 stars of the halo, and 5 Gaia-Sausage-Enceladus stars. The results agree excellently with previous MINCE works. The comparison with a Gaia Sausage Enceladus GCE model is consistent with the scenario of a major accretion event on the Milky Way from a dwarf galaxy.

In this paper we investigate accelerated gluodynamics for a broad intervals of temperature and acceleration. Our study is carried out within lattice simulation in the co-moving reference frame parameterized by the Rindler coordinates. We developed the renormalization prescription that allowed us to calculate renormalized Polyakov loop as a function of coordinate in the Rindler spacetime. Using the data for the renormalized local Polyakov loop, we calculated spatial dependence of the static quark free energy and effective mass of static quark. Besides the Rindler coordinates, it is believed that accelerated gluodynamics can be approximated utilizing non-accelerated gluodynamics with a properly adjusted temperature gradient in accordance with the Tolman-Ehrenfest law. We compared these approaches for the observables under study. It was found that they agree quite well close to the critical temperature and demonstrate disagreement at higher temperatures. We believe that this disagreement might be attributed to the Tolman-Ehrenfest law corrections which appear in the Rindler gluodynamics.

We explore the thermodynamic properties of static black holes in conformal gravities in arbitrary, even dimensions. In the spherically symmetric case, up to local Weyl rescalings, these spacetimes are static and unique, due to a Birkhoff's theorem that applies for all conformal gravities whose Lagrangians are complete contractions of $k$ Weyl tensors in dimension $D=2k$. The solutions can be chosen to be asymptotically locally (A)dS or flat, and the horizon can be extended to be a surface of arbitrary constant curvature, $γ$. We focus on the asymptotically AdS case, for which the cosmological constant at infinity is an integration constant, and compute the mass of the spacetime in terms of the diverse hair parameters which have a purely gravitational origin. We show that the first law of thermodynamics is satisfied, and study phase transitions in the canonical ensemble, showing the existence of zeroth-order black-hole/black-hole phase transitions for arbitrary dimension.

The Baade-Wesselink (BW) method compares the linear and angular variations of Cepheids to derive their distance. This method is limited, however, by the projection factor, which relates the observed radial velocity to the true pulsation velocity of the star. Using simultaneous observations from the CHARA Array interferometer in the K, H, and R bands with the MYSTIC, MIRC-X, and SPICA combiners, respectively, we aim to understand the physics of Cepheid atmospheres better. Applying a specific method to multi-chromatic simultaneous interferometric observations of Cepheids, we derived robust limb-darkened angular diameters that were then used to calibrate the SBCR and study the projection factor. We also developed a strategy to measure the limb-darkening of Cepheids in R, H, and K bands. These measurements were then used to constrain the geometrical component of the projection factor. From the limb-darkened angular diameter curves of three Cepheids, we decreased the scatter of the SBCR in $V-K$ colour to 0.0011 magnitude and to 0.0040 for the SBCR in $G_{BP}-G_{RP}$. These SBCRs are particularly robust because they are based on multi-chromatic diameters and are homogeneous, which previous calibrations for Cepheids were not. For the very first time, we derived the limb-darkening of Cepheids in R, H, and K bands. For $δ$ Cep, we derived an R-based projection factor of $1.275 \pm 0.051$, and the geometrical part obtained from the measured limb-darkening coefficient in R band was estimated to $1.420 \pm 0.016$ (on average), as expected from stellar static and hydrodynamical atmosphere models. The limb-darkening coefficients obtained in H and K band are consistent with models. These results demonstrate that multi-chromatic interferometry can improve the accuracy of the BW method. It is therefore essential to continue the CHARA survey of Cepheids in the coming years.

Whether classical spacetime remains welldefined at arbitrarily high curvature is a central question. In general relativity, singularities signal the breakdown of the classical description, motivating modifications of spacetime's short-distance structure. Pseudocomplex general relativity (pcGR) extends spacetime geometry to pseudo-complex coordinates, naturally introducing two metric sectors, the physical metric gμν and an auxiliary field fμν. The magnitude of the pseudo imaginary component defines the invariant acceleration scale a0, a direct consequence of the pseudo-complex structure. The simultaneity condition, requiring both idempotent sectors to satisfy the pseudo-complex Einstein equations independently, fixes the auxiliary field algebraically, with no new propagating degrees of freedom, and sets a lower bound on the lapse that regularizes curvature. The regularization is achieved through the combined effect of the lapse-gap condition eν(r) gt. a0, which ensures the radial metric component remains nondegenerate, together with the regularity conditions at the areal-radius origin, B(0) = 1 and B'(0) = 0, which emerge naturally from the pseudo-complex geometry. These conditions jointly eliminate the Schwarzschildtype curvature divergence, rather than the gap condition acting alone.

We identify the spatial projection of a conserved string charge density with a bit-thread flow. This correspondence gives bit threads a string worldsheet description and allows us to compute black hole entropy from the maximal entropy flux of a worldsheet-derived current. We first reproduce the BTZ entropy and then extend the construction to the ten-dimensional F1-NS5-P and D1-D5-P systems. Under Type IIB S-duality, the F1 current maps to the D1 current. Although the local currents, metrics, and flow norms change, the maximal physical flux remains unchanged and gives the same entropy. This provides a nontrivial check of the correspondence. Finally, we propose a D1-D5 boundary-matching conjecture. In the coarse-grained picture, each string-charge line defines an entropy-carrying tube. The boundary CFT entanglement entropy and the bulk black hole entropy both fix the product of the number of tubes and the maximum entropy carried by each tube. For a fixed tube discretization, they assign the same capacity to each tube. They therefore describe the same conserved maximal entropy flux, providing an information-flow interpretation of the equality between entanglement entropy and black hole entropy.

We investigate how neutrino-mass constraints from cosmology depend on the assumed thermal history of the universe. Photon injection after neutrino decoupling would decrease the neutrino abundance inferred from the temperature of the cosmic microwave background (CMB), potentially loosening the upper limit on their masses. We first evaluate how the cosmological neutrino-mass bound is altered by the decay of massive particles into photons and dark radiation after Big Bang nucleosynthesis. To test the robustness of this constraint more generally, we also assess the impact of varying the temperature of the cosmic neutrino background without assuming a specific physical mechanism. We perform MCMC analyses of both frameworks with primary CMB observations from Planck, CMB lensing measurements from Planck and ACT, and baryon acoustic oscillation data from DESI. For the degenerate mass ordering, the $95\%$ credible limit tightens from $\sum m_ν<0.0691$ eV in a standard thermal history to $\sum m_ν<0.0652$ eV if the massive particles decay only into photons, while the injection of dark radiation in addition to photons slightly relaxes this limit to $\sum m_ν<0.0710$ eV. The same pattern holds for the normal and inverted orderings, and the decay scenario shifts the bound on the sum of the neutrino masses by at most $0.004$ eV for fixed mass splittings. Allowing model-agnostic changes in the neutrino-to-photon ratio yields a $95\%$ credible limit of $\sum m_ν<0.0724$ eV for the degenerate ordering, indicating that the stringency of our neutrino-mass bounds is not driven by constraints on the decay scenario. We find that the neutrino temperature and the sum of the neutrino masses are positively correlated, which implies that reducing the pre-recombination radiation density will only worsen the emerging tension between cosmological bounds on the neutrino masses and the measured mass splittings.

Gravitational sums over spacetime topology suggest a baby-universe field theory whose quanta are entire universes. We develop such a description from group-averaged amplitudes that impose gravitational constraints and define physical inner products in the single-universe theory. To sharpen the contrast with ordinary QFT, we start with gravity on one-dimensional worldlines, which can arise from reducing higher-dimensional cylinders. For multiple noninteracting worldlines that pair boundary components, the baby-universe Hilbert space is the symmetric Fock space over the physical one-universe Hilbert space, and the universe field expands in the on-shell modes spanning the latter. Each mode multiplies the sum of creation and annihilation operators, so the mode coefficients commute. The mode expansion thus makes explicit the field's commutativity and its Wheeler-DeWitt linear field equation. Diagonalizing the coefficients recovers a statistical description by a Gaussian path integral over on-shell field configurations labelling superselection ($α$-)sectors. We take exploratory steps toward more general topologies. Disk-like topologies coherently shift the no-boundary state, turning on the Hartle-Hawking wavefunction as a one-point function. Even with nontrivial topologies represented by interacting Feynman diagrams, we argue that group averaging near each boundary still enforces the same linear field equation, while interactions instead enter through a non-Gaussian measure over $α$-sectors. In the topological Marolf-Maxfield model, we promote a disk-and-cylinder truncation to an exact Fock-space representation of the full theory incorporating all topologies. We also relate the truncated and exact inner products by an insertion of interactions, whose perturbative expansion produces a sum over time evolutions generated by pairs of pants, evoking an analogy to group averaging.

We investigate the non-equilibrium thermodynamics of a Swiss-cheese (SC) braneworld universe. By employing Hayward's unified first law and the Clausius relation at the apparent horizon, we first show that the standard equilibrium treatment of the effective SC braneworld fluid, together with the usual Hawking temperature, reproduces the Bekenstein-Hawking area law without any braneworld correction to the entropy. This demonstrates that the brane quadratic energy density corrections cannot, by themselves, generate a modified entropy area relation within the equilibrium framework. We therefore formulate a non-equilibrium thermodynamic description in which deviations from the Bekenstein-Hawking entropy are accompanied by an internal entropy production term. For a general horizon entropy functional, we derive the corresponding entropy production rate and then specialize to a logarithmic and inverse area quantum-corrected entropy. The resulting irreversible contribution is expressed in terms of the Hubble parameter and its derivative. We apply the formalism to a nonsingular matter-bounce solution in the SC braneworld. During the expanding phase, the total entropy production remains positive satisfying the GSLT. Moreover, the late-time behavior of the second derivative of the total entropy becomes negative, indicating a decelerating entropy growth and an asymptotic approach toward thermodynamic equilibrium. Far from the bounce, the equation of state parameter $w \approx -1$, indicating a dark energy-dominated regime. Significant departures from $w = -1$ are confined to the bounce vicinity, where high energy braneworld corrections drive the nonsingular transition. Thus, the model naturally transitions from a high energy bounce into an asymptotic dark energy phase during late-time expansion.

We prove the existence of solutions to the Lorentzian Monge problem on synthetic Lorentzian spacetimes that satisfy the forward timelike measure contraction property $TMCP^+(K,N)$. The cost for this problem is the time separation function $\ell(x,y)$ (the Lorentz distance), which represents the maximum amount a particle can age when traveling from $x$ to $y$. The solution is based on the needle decomposition technique, and amounts to a reduction of the full problem to its one-dimensional counterparts. As an application of needle decomposition, we show that the Lorentzian timelike measure contraction property $TMCP^+(K,N)$ is equivalent to the $TMCP^+_{rLip}(K,N)$ condition, where the curvature dimension conditions are defined on gradient flow curves of reverse 1-Lipschitz functions.

Hyperbolically symmetric wormholes provide a setting in which negative energy densities arise from the throat geometry and finite matter configurations can be matched to the hyperbolic Schwarzschild vacuum. We construct such configurations from a matter-first perspective using an effective Casimir source corrected by a gravitational-memory contribution, $ρ(r)=-α/r^4+η/r^7$. The $r^{-7}$ term is motivated by the persistent shift of the Casimir vacuum energy after a transient gravitational perturbation, while its promotion to a radial source is treated phenomenologically. The density determines the shape function, and the temporal geometry is fixed through complexity-based conditions. Full vanishing complexity, $Y_{TF}=0$, is first imposed and then relaxed through a one-parameter deformation, $Y_{TF}=(p-3)r_0/(2r^3)$. Decomposing the complexity factor into local and throat contributions shows that local vanishing complexity occurs at $p=β'(r_0)$. At this value, besides the constant-redshift solution of the finite-$r$-derivative branch, a second lapse branch is regular in radial distance. We show that pressure-free Darmois matching in the finite-$r$-derivative family requires $p<β'(r_0)$, enforcing tangential null and strong-energy-condition violations at the throat throughout the matching domain. The density remains negative in the matter-supported region, implying weak- and dominant-energy-condition violations independently of the lapse branch. The memory parameter modifies the flare-out domain, redshift profile, and matching data, while finite pressure-free junctions permit smooth matching to the hyperbolic Schwarzschild vacuum without thin shells. The construction combines a memory-corrected Casimir source with a unified complexity framework in which the temporal sectors emerge as related branches of the same radial geometry.

A cosmological source can have identically zero comoving energy density and still gravitate through its pressure. This differs from an energy density passing through zero at an isolated time. Maintaining zero density with nonzero pressure requires energy exchange in a nonstatic FLRW universe. We construct proportional-pressure and constant-pressure backgrounds, including steady-state, bouncing, recollapsing, and $Λ$CDM expansion histories, and relate them to creation pressure, bulk viscosity, and time-dependent vacuum descriptions. Scalar fields can realize zero density along a trajectory; imposing it as an identity on a timelike $P(X,φ)$ domain selects $P=A(φ)\sqrt{X}$, locally a signed potential-free cuscuton for nonzero $A$. We formulate linear perturbations without dividing by the vanishing background density. For a nondegenerate $P(X,φ)$ scalar with a timelike field gradient, zero density and negative pressure cannot coexist with positive kinetic and gradient coefficients when the interaction leaves its principal kinetic structure unchanged. Two models couple the scalar to number-conserving dust through a field-dependent mass. The proportional-pressure trajectory is a homogeneous saddle and has no growing power-law dust mode on its accelerating branch in the matter-sourced quasistatic subhorizon approximation. A distinct constant-pressure model reproduces the $Λ$CDM expansion history, but in the same approximation the dust mode that initially grows during matter domination reaches a maximum at low redshift and then decays. These restrictions apply to the stated scalar class and models. Exact Bianchi I solutions demonstrate separately conserved zero-density sources supported by anisotropic stress. An inverse-pressure construction distinguishes the density of an interacting constituent from an inferred dark-energy density that may cross zero.

We employ the statefinder hierarchy along with the fractional growth parameter to investigate the recently proposed noninteracting Viaggiu holographic dark energy (VHDE) model with the future event horizon as the infrared cut-off. By adjusting different values of the VHDE model parameter $δ$, we illustrate the evolution trajectories of several important parameters, prticularly, the statefinder hierarchy $S_3^{(1)}$, $S_3^{(2)}$, $S_4^{(1)}$, $S_4^{(2)}$ and the fractional growth parameter $ε$ against the redshift $z$ and the fractional energy density of matter, $Ω_m$. Together with the growth rate of matter perturbations, we present the statefinder hierarchy that defines a composite null diagnostic (CND), which can differentiate dynamical dark energy from $Λ$CDM. The joint use of the statefinder hierarchy and the fractional growth parameter offers a powerful diagnostic tool for probing VHDE, effectively resolving the degeneracy between different parameter choices within the model. We find that employing a CND pair, rather than a single diagnostic, significantly enhances the diagnostic power for the VHDE model. Finally, we perform an $ω_d-ω_d'$ analysis and, in addition, assess the squared sound speed $v_{s}^{2}$ to determine the model's dynamical stability under small perturbations.

The galaxy--electron cross-power spectrum $P_{ge}(k)$ measures the small-scale distribution of gas around galaxies, the quantity reshaped by feedback. We measure $P_{ge}$ from the kinetic Sunyaev--Zel'dovich (kSZ) signal of the photometric DESI Legacy Imaging Surveys luminous red galaxies, cross-correlating a velocity-weighted galaxy momentum template with the CMB temperature from ACT DR6 and, for the first time, SPT-3G. The absolute normalization of the cross-spectrum is fixed by a surrogate-field Monte Carlo that propagates the survey mask, lightcone evolution, and photometric-redshift weights, converting the measured pseudo-spectrum into $P_{ge}(k)$ in physical units. We detect $P_{ge}$ at $11.7σ$ with ACT and $8.4σ$ with SPT-3G, and at $12.3σ$ combining SPT-3G with the ACT northern cap, which it does not overlap. The two surveys have independent optics, beams, filtering and noise and share about two thirds of the SPT-3G galaxies; their amplitudes agree channel by channel, the largest difference being $0.7σ$. All $26$ null tests on the adopted night maps are consistent with zero signal, among them the six ACT frequency differences, the three SPT-3G frequency differences, and the four ACT cap differences of the main selection. Turning the amplitude into a gas fraction requires the host halo masses of the sample, which the cross-spectrum does not itself measure; taking them from its measured number density and from a published CMB-lensing calibration of the same galaxies, the gas within the virial radius is $25$--$33\%$ of the cosmic baryon budget of the halo.

We leverage the high resolution and spectral stability of the Keck Planet Finder (KPF) spectrograph to investigate macroturbulence broadening via the stellar cross-correlation function (CCF). As our calibration sample, we use main sequence benchmark slow-rotators v$\sin$i < 4 km/s where rotation rates were derived from the most robust asteroseismic mode splitting measurements, independent from spectral line broadening. We fit a linear relationship for macroturbulence as a function of derived $ν_{max}$, the frequency of maximum power due to stellar oscillations, with an RMS scatter of 90 m/s. Previous studies have calibrated macroturbulence against T$_{eff}$, but we find $ν_{max}$ to be a lower dispersion predictor by a factor of 4 indicating a deeper relationship between $ν_{max}$and convective motions.

Space-based photometry has detected solar-like oscillations in thousands of stars, whose global seismic parameters yield stellar properties via the asteroseismic scaling relations. Because these relations systematically overestimate red-giant masses and radii empirical calibration is required. Double-lined eclipsing binaries hosting oscillating red giants provide precise dynamical masses and radii without external calibration, making them ideal benchmarks. We present KIC 8129189 and KIC 10920813, two Kepler eclipsing binaries containing less-evolved oscillating red giants, as new benchmarks that extend the calibration sample toward smaller radii. We measured radial velocities from high-resolution spectra, extracted global asteroseismic parameters from Kepler light curves, and modeled the binaries with JKTEBOP and PHOEBE-2 using both full light curves and selected eclipse sets, adopting benchmark masses and radii from the envelope of tested model/data configurations. We then fit correction factors $f_{Δν}$ and $f_{ν_{max}}$ to the underlying $Δν$-density and $ν_{max}$-surface-gravity relations. We obtain $M_{RG}=1.413 \pm 0.037 M_\odot$ and $R_{RG}=4.296 \pm 0.061 R_\odot$ for KIC 8129189, and $M_{RG}=1.383 \pm 0.022 M_\odot$ and $R_{RG}=5.914 \pm 0.043 R_\odot$ for KIC 10920813. The adopted 15-star calibration gives $f_{Δν}=0.9777 \pm 0.0048$ and $f_{ν_{max}}=1.024 \pm 0.008$, corresponding to $C_M=0.850 \pm 0.020$ and $C_R=0.9333 \pm 0.0090$. Neither correction factor depends significantly on radius, nor does $f_{ν_{max}}$ depend on metallicity; model-based $f_{Δν}$ values are systematically lower than the dynamically derived ones. Both systems agree with the correction from previous benchmarks, showing that continued expansion of the eclipsing-binary sample is essential for testing the scaling relations across evolutionary stage.

We present dynamical measurements of dark matter halo masses at $z\approx7$ using galaxy pairs. Galaxy pairs in the early Universe are usually in their first infall, before substantial orbital evolution or phase mixing. Their relative velocities closely trace the halo mass, especially when the pair separation is near the halo virial radius. In the TNG100 simulation, we find that dynamical mass estimators can recover halo masses with an intrinsic scatter of $\sim$0.2 dex. We apply this method to 10 pair systems at z=6-8 with [O III] spectroscopy from the JWST Advanced Deep Extragalactic Survey (JADES). We infer the stellar-to-halo mass relation while marginalizing over projection effects, measurement uncertainties, and intrinsic scatter. We find a mean halo mass of $\log\,(M_{200}/M_\odot)=11.06\pm0.21$ at $\log\,(M_{*}/M_\odot)=9$. These galaxies do not appear to inhabit unusually massive halos. Our results instead indicate a high stellar-to-halo mass ratio, corresponding to an integrated star formation efficiency of $5^{+3}_{-2}\%$, about twice the TNG100 prediction, although the current statistical significance is limited. Future observations with larger samples will tighten these constraints and directly examine whether enhanced star formation efficiency drives the overabundance of luminous galaxies at cosmic dawn.

We investigate the extremization of Perlick's proper time in non-integrable Weyl geometry. We derive the corresponding generalized Euler--Lagrange equations and show that the resulting extremals do not, in general, coincide with the autoparallels of the Weyl connection, their difference being governed by the Weyl length curvature and vanishing in the integrable case. A distinctive feature of the extremal equation is its nonlocal character: in the Weyl proper-time parametrization, the acceleration depends explicitly on the remaining proper time to the endpoint of the variational interval. We illustrate this behavior for a weak constant Weyl field and show that a local Lorentz-force dynamics emerges in a double-scaling limit in which the Weyl field vanishes and the terminal proper time diverges while their product remains finite. These results uncover a nontrivial relation between proper-time extremization, Weyl non-integrability, and local force dynamics.

Context: Non-linear gravitational evolution affects the growth of density and velocity fluctuations and leads to previrialization effects before virialized structures are formed. Therefore, understanding and quantifying the leading nonlinear corrections to the correspond- ing variances is crucial for describing the departure from linear structure formation. Aims: We calculate the first nonlinear correction to the variance of the cosmic density and velocity fields. Methods: We analyze the 1-loop contributions associated with the second and third order perturbative kernels of both the density and velocity-divergence fields. The relevant form of the third-order kernels F3 for density, and G3 for velocity divergence, are clearly non-symmetric under exchange of k with q. However, the calculation of the variance involves a symmetric double integral of these variables, so in this particular case the kernel can be additionally symmetrized. We therefore explicitly symmetrize these kernels F3 and G3, and express them as functions of the two scalar variables: the cosine of the angle between the two wavevectors and a symmetric function of their magnitudes. This representation enables us to identify and isolate the terms which are divergent before performing the angular integration, and to show their cancellation between the second- and third-order terms. Results: The divergent contribution from Pdelta22 to the one-loop power spectrum cancels exactly that arising from Pdelta13. Angularly averaged divergence-free part of F3 turns out to be remarkably close to a constant. Conclusions: The coefficient of the nonlinear correction to the linear variance of the density field is in a narrow range, from 1.817 to 1.843, for any form of the linear power spectrum.

We present an updated strong lensing model for the galaxy cluster RXJ0437.1+0043 (z=0.285) using new JWST NIRCam imaging in four pass-bands. The cluster field notably displays at least three separate gravitationally lensed galaxies in hyperbolic-umbilic (H-U) configurations, which in the JWST imaging show exquisitely resolved stellar clumps at scales as small as 0.04''. We identify 13 new systems of multiply-imaged lensed galaxies and determine the redshifts for two sources based on archival spectroscopic observations. We also identify over 50 individually resolved substructure clumps in the multiple images of eight galaxies and add them into the lens model, for a total of 275 positional lensing constraints between all 26 lensed sources used in the model. We investigate the impact of different modeling choices on our results. In the final lens model, we reproduce the observed multiple images with a precision of 0.23'' , and achieve 0.13'' specifically for the H-U systems. We estimate a total enclosed mass in the cluster's strong lensing regime of M(<110 kpc) ~ 8.2 x 10^13 Msun, reconstruct the source images of the most highly magnified galaxies, and measure time delays in the most magnified, morphologically detailed systems. The isotropic lensing effect from the H-U configurations enables future detailed studies of the properties of their source galaxies, and the number and spatial density of additional constraints improve the model's ability to detect dark matter substructures within the cluster core.

The systematic generalisation of the well-established $S$-matrix positivity and bootstrap bounds from $2 \to 2$ scattering processes to higher-point amplitudes has, to date, remained elusive. To address this, we consider a large class of tree-level UV-completions of a single-scalar EFT. Specifically, we consider the most general renormalisable $N$-scalar theory in $D=4$. By explicitly computing tree-level amplitudes for four-, five- and six-point scattering and expanding at low energies, we can search for positivity relations among the expansion coefficients. We find that quite generally positivity bounds are unavailable due to contamination from a specific class of Feynman diagrams that are linear in sign-indefinite cubic couplings. However, by isolating a sector of the full crossing-symmetric low-energy amplitude that is unaffected by these sign-indefinite cubic couplings, we find that selected six-, five- and four-point Wilson coefficients organise into positive semi-definite matrices. While a violation of these positivity statements only implies that a given EFT is inconsistent with our class of UV completions, the result helps to guide towards what more general positivity bounds for higher-point interactions could, and could not, look like.

We present RadioAstron observations of the M87 jet obtained on 2014 February 4-5 at 4.8 GHz ($λ=6.2$ cm). The correlated signals between the 10-m space antenna and ground-based radio telescopes were detected up to projected baselines of $\thicksim3$\,Earth diameters (0.65~G$λ$). The orientation of the jet downstream of the core shifts northward, consistent with the long-term oscillating trend reported in other studies. An elliptical body mode of the Kelvin-Helmholtz instability can create the observed helical shape of the jet. The estimated wavelength of this instability mode suggests that its origin may be related to some processes in the accretion disc. We present 1.7 - 4.8 GHz and 4.8 - 15.4 GHz spectral index maps showing flattening of the spectrum along the outer streamlines and along the jet spine. Simulations and analysis show that this spectral flattening is partially artificial and is a common systematic effect of the CLEAN procedure of VLBI imaging. The spectral index of the M87 jet is consistent with the optically thin emission, while its steepening can be produced by the propagation of the instability modes causing higher pressure regions near the jet boundary and in its interior.

Can quantum entanglement continue to grow even after the entanglement entropies of subsystems have saturated? We address this question using genuine multi-entropy, which probes multi-partite entanglement structure beyond bipartite entanglement. In a two-sided BTZ black hole, this quantity grows linearly with time after every subsystem entropy of a fixed tripartition has saturated, extending the interval in which entanglement detects Einstein-Rosen bridge growth. The result refines the ER=EPR relation by identifying multi-partite structure invisible to ordinary entanglement entropies. Some spin-chain models and the spatially partitioned Sachdev-Ye-Kitaev (SYK) model exhibit distinct transients, while the late-time plateau values in holography, the SYK model, and Haar-random states share a universal behaviour.

In this paper, we investigate the localization of various $q$-form fields on a codimension-two brane. In particular, the $0$-form scalar field, the $1$-form $U(1)$ gauge vector field, and the $2$-form Kalb-Ramond field are considered with gravitational coupling, where a coupling function $F(R)$ is introduced into the six-dimensional actions of these fields. The function $F(R)$ depends on the scalar curvature of the bulk. Within this framework, we find that the massless modes of different $q$-form fields can be localized on the thick brane for positive values of the coupling parameters $t_1$ and $t_2$. For the massive modes, the different $q$-form fields exhibit similar localization properties determined by the coupling parameter $t_2$. When $0<t_2<v^2/24$, the massive modes of these fields cannot be localized on the brane, while they may exist as the resonant modes. In the case $t_2=v^2/24$, a finite number of massive modes can be localized on the thick brane, and the number of localized modes increases with the coupling parameter $t_1$. Finally, when $t_2>v^2/24$, the effective potentials associated with the Kaluza-Klein modes of these $q$-form fields form infinitely deep potential wells, so that all massive modes can be localized on the brane. Moreover, the tachyonic massive modes can always be excluded for different $q$-form fields.

We investigate slowly rotating traversable wormholes in Einstein--scalar--Gauss--Bonnet gravity beyond the linear rotation regime. The static backgrounds are obtained without expanding in the Gauss--Bonnet coupling, while rotational effects are treated perturbatively up to second order. Both monopolar and quadrupolar deformations are included, allowing us to determine the spin-induced changes in the asymptotic charges, throat geometry, energy-condition behavior, and mass quadrupole. The quadrupolar equations develop an internal regular singular point, which is handled by selecting the regular local solution through a Frobenius analysis. The rotation-induced response of the throat source is incorporated consistently through the junction conditions. Independent shooting and collocation calculations of the quadrupolar sector give mutually consistent solutions. The rotating throat remains oblate throughout the fixed-coupling family, while at $χ=0.15$ the smooth-bulk near-throat radial null-energy-condition violation persists but its radial extent becomes latitude dependent. These results provide a self-consistent second-order description of rotating Einstein--scalar--Gauss--Bonnet wormholes.

We investigate a family of $k$-essence cosmological models selected by the requirement that the field equations admit a nontrivial variational symmetry. For the $k$-essence theory with Lagrangian function $F(R,X,φ)=f_{1}R+f_{2}(φ,X)$, where $f_{2}(φ,X)=αX+β\exp\left((n-1)φ\right)X^{n}$, the existence of a scaling symmetry introduces a conservation law which we use to obtain an exact vacuum solution. We generalize our analysis and investigate the structure of the phase-space of the cosmological field equations by performing a dynamical systems analysis, both in the absence and the presence of a pressureless matter source. We employ Hubble-normalized variables and the Poincaré compactification, so as to determine the asymptotic behavior of the model and identify all admissible cosmological epochs, from early-time to late-time behavior. We discuss in detail the existence and stability conditions of each fixed point as functions of the free parameters, and characterize the full asymptotic structure of the cosmological history as provided by this symmetry-driven $k$-essence model. We explore the conditions under which the model can describe cosmic acceleration. We find that the symmetry driven $k$-essence model can describe the inflationary epoch with a natural exit to the matter dominated era, where the $k$-essence mimics the pressureless matter component.

In 1854 Riemann presented his Habilitationsvortrag {\it Über die Hypothesen welche der Geometrie zu Grunde liegen} to the Faculty of Philosophy of the University of Göttingen. The lecture does not contain analytical developments and Riemann never explained the reason for this choice. According to Dedekind this choice was done in order to make the lecture understandable to the non-mathematician professors of the Faculty. This is the suppression thesis. Nevertheless, in 1851, three years before, Riemann has presented his Inauguraldissertation {\it Grundlagen für eine allgemeine Theorie der Functionen einer veränderlichen complexen Grösse} to the same professors of the Faculty of Philosophy. The Inauguraldissertation contains many analytical developments but, on that occasion, they were not suppressed. Therefore, the presence of non-mathematician professors is unrelated with the presence or absence of analytical developments in the lectures. The ideas contained in Riemann's Habilitationsvortrag --manifold, line element, curvature-- were so new at the time that there was not even a proper language to express them. Therefore, Riemann was forced to adopt a non-technical expository style. This explanation for the absence of analytical developments in Riemann's Habilitationsvortrag is more credible than the suppression thesis.