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The discovery of the strongly-coupled quark-gluon plasma (sQGP) in high-energy heavy-ion collisions has revealed remarkable properties of matter at high temperature, with transport coefficients close to conjectured bounds from quantum field theory at strong coupling. The high sQGP collision rates imply very large energy uncertainties and the melting of quasiparticle structures. Deploying quantum many-body theory based on the self-consistent $T$-matrix approach for the sQGP at high temperature, we investigate its manifestation at high baryon density and low temperature, as present in neutron stars and their mergers. We constrain the chemical-potential dependence of the quark interaction kernel using first-principles information from Quantum Chromodynamics on baryon-number susceptibilities. Very large collisional widths persist at large density and are found to relegate superconducting phases to rather small temperatures. Instead, a strongly coupled diquark liquid prevails in the thermodynamics under the conditions relevant to neutron-star mergers. At lower densities, the diquarks take over from the single-quark contributions, suggesting a pathway toward hadronization. Our results are consistent with observational constraints on the equation of state of neutron stars, corroborating the presence of strongly coupled quark matter in the interior of these objects.

Supermassive black hole binary (SMBHB) candidates with sub-parsec (sub-pc) orbital separations are rare, high-value systems, thought to be the dominant sources of the recently detected nanoHertz (nHz) gravitational wave (GW) background. Alongside pulsar-timing-array searches for localized nHz GW sources from SMBHBs, an increasing number of candidates have been identified from synoptic surveys of large quasar optical light curves over increasingly long baselines. The optical light curve of the quasar PG~1302-102 at a redshift of $z=0.278$ exhibits a pronounced, smoothly varying periodic signal of ~5.2 years over approximately 20 years. Although the cause of this periodicity remains debated, a plausible explanation is a binary system of two SMBHs with a sub-pc separation. At this close distance, the $10^{8.3-9.4} M_{\odot}$ nuclear black holes in PG 1302-102 are expected to merge within $\sim$$10^{5}$ yr solely due to GW emission. We present a multi-frequency radio light curve analysis of PG~1302-102 spanning a $\sim$19-year baseline, with observations between 2005 and 2024 drawn from the Australian Telescope Compact Array (ATCA). The ATCA radio light curve is highly variable at 5.5~GHz but shows no significant evidence of the periodicity seen at optical wavelengths. However, we report fractionally stronger evidence of periodicity in the in-band spectral index time-series at 5.5~GHz, with a period consistent with the optical periodicity. Furthermore, the recently reported change in optical periodicity is also present in the radio in-band spectral index light curve. These two results suggest that radio and optical periodicity may be physically coupled despite very different emission mechanisms. We argue that this radio-optical coupling reinforces the SMBHB interpretation, despite the optical periodicity change, and provides an intriguing case study ahead of the LSST-SKAO era.

M-dwarfs produce frequent flares, and their associated mass ejections are expected to significantly affect the habitability of close-in exoplanets. Recent spectroscopic observations have revealed several prominence eruptions-indicative of stellar mass ejections-on M-dwarfs through Doppler shifts of the H$α$ line. However, systematic and statistical studies, particularly regarding their association with white-light flares, have been limited due to the lack of intensive and continuous simultaneous photometric and spectroscopic monitoring of the same target star. We conducted one month of continuous spectroscopic observations of the active M-dwarf YZ CMi using the 3.8-m Seimei telescope with an unprecedentedly high time cadence of $\sim$1 min, simultaneously with TESS. We detected four prominence eruptions, among which two events showed rapid, short-duration eruptions with velocities of $\sim$300-500 km s$^{-1}$ and durations of $\sim$5 min. Such short-duration events may have been missed in previous observations due to insufficient time cadence. We further performed a systematic analysis using 35 H$α$ flares on YZ CMi observed simultaneously with TESS. Notably, most prominence eruptions (6 out of 7) were not associated with detectable white-light flares. This result suggests that most observed prominence eruptions on M-dwarfs may have occurred near the stellar limb, where white-light flares are difficult to detect, which may imply a potential observational bias in their detectability due to low contrast with the background emission. These first statistical constraints, together with the discovery of rapid, short-duration prominence eruptions, indicate that previous observations may have underestimated both the frequency and velocities of mass ejections on M-dwarfs due to observational biases and highlight the necessity of reassessing their impact on close-in exoplanets.

In the era of wide-field surveys and big data in astronomy, the SNAD team is exploiting the potential of modern datasets for discovering new, unforeseen, or rare astrophysical objects and phenomena with machine learning (ML). The SNAD pipeline was built under the hypothesis that, although automatic ML algorithms have a crucial role to play in this task, the scientific discovery is only completely realized when such systems are designed to boost the impact of domain knowledge experts. Our key contributions include the development of the Coniferest Python library, which offers implementations of two active learning algorithms with an ``expert in loop'', and the creation of the SNAD Transient Miner, facilitating the search for specific types of transients. We have also developed the SNAD Viewer, a web portal that provides a centralized view of individual objects from the Zwicky Transient Facility's (ZTF) data releases, making the analysis of potential anomalies more efficient. Finally, when applied to ZTF data, our approach has resulted in more than a hundred new supernova (SN) candidates, along with a few other non-catalogued objects, such as red dwarf flares, superluminous SNe, RS CVn type variables, and young stellar objects.

We develop an entropy-stable and physical-constraint-preserving discontinuous Galerkin spectral element method for symmetry-reduced general-relativistic hydrodynamics on prescribed stationary spacetimes. Using a local orthonormal transformation, the fluid variables are expressed in a form for which the relativistic hydrodynamic algebra and the admissible set are independent of the spatial metric, while the spacetime geometry enters through stationary coefficients. This separation allows entropy-conservative special-relativistic fluxes to be combined with a compatible discretization of the geometric source terms. On affine tensor-product meshes, the resulting DGSEM is conservative and satisfies a semidiscrete entropy inequality, while the transformed variables provide a convex framework for physical-constraint preservation. For practical stabilization, we use a geometry-only causal speed that is sufficient for both classical local Lax--Friedrichs entropy dissipation and the physical-constraint-preserving Lax--Friedrichs splitting. The fully discrete method combines this stabilization with SSP Runge--Kutta time stepping, oscillation elimination, and conservative local-orthonormal-state scaling. Numerical experiments cover smooth and strongly shocked special-relativistic flows, an axisymmetric jet, stationary Michel accretion, Schwarzschild Bondi--Hoyle flow, and four Kerr accretion cases. The results demonstrate the designed high-order accuracy in smooth regimes and robust performance for demanding relativistic flows on curved stationary backgrounds.

The discovery by the James Webb Space Telescope (JWST) of an abundant population of compact little red dots (LRDs) and supermassive black holes at high redshifts poses a severe timing challenge for standard Eddington-limited growth from stellar remnants. In this work, we present a unified hybrid assembly framework in which intermediate-mass seed black holes are formed via hierarchical primordial black hole (PBH) mergers within dense clusters in Hu-Sawicki $f(R)$ gravity, followed by galactic gas accretion. We demonstrate that the screened $f(R)$ fifth force nonlinearly accelerates early seed formation through a quadratic enhancement of the gravitational-wave radiation-capture kernel, while environmental chameleon screening dynamically self-regulates the growth. Because subsequent gas accretion scales multiplicatively with seed mass, the $f(R)$ seed enhancement is preserved throughout the accretion history, drastically reducing the time-averaged Eddington ratios required to assemble $10^{6}\text{-}10^{9}\,M_{\odot}$ LRDs by cosmic dawn. Confronting our active mass functions with JWST data reveals that a small clustered PBH fraction ($f_{\rm PBH} \lesssim 10^{-3}$) under a realistic active galactic nucleus duty cycle ($δ\approx 10^{-2}$) naturally matches observed LRD space densities at $z \sim 5.5\text{-}6.5$ while remaining fully compliant with LIGO-Virgo-KAGRA limits, with modified gravity naturally driving the high-mass tail. Finally, we show that parameter degeneracies between modified gravity and cluster density can be cleanly broken by combining three multi-messenger diagnostics: remnant spin state signatures, a stochastic GW background cutoff, and a scale-dependent inversion in the PBH spatial correlation function.

Vortex pinning is central to the standard interpretation of pulsar glitches, but the mechanical load exerted by a pinned vortex array on the solid crust has received less attention than the angular-momentum reservoir itself. We calculate the axisymmetric elastic response of a continuously stratified neutron-star crust to this load using realistic SLy4 and BSk21 stellar backgrounds and composition-dependent Coulomb shear moduli. The superfluid-crust lag sets the Magnus force, while the mesoscopic pinning force of Seveso et al. (2016) provides a local upper bound. At low lag the response is linear; progressive local saturation then produces a broad transition and a finite high-lag envelope. The stress maximum is robustly located at the deep crustal boundary towards the rotation axis, although the local Magnus force vanishes on-axis, showing that the localization is produced by global elastic-gravitational redistribution. Realistic elasticity changes the stress amplitude by 10-20 per cent relative to the common mu=10^-2 P prescription and reverses the SLy4-BSk21 ordering. At a Vela-motivated lag of 10^-2 rad s^-1, the maximum strain is only 3.1 x 10^-5 (SLy4) and 4.7 x 10^-5 (BSk21), remaining below 1.4 x 10^-4 on the formal plateau. A 1.2-2.0 solar-mass scan changes the stress amplitude by only about 20 per cent and leaves the deep-polar localization unchanged. Pinning therefore supplies a structured and astrophysically relevant crustal pre-stress, but cannot by itself break an initially relaxed crust.

It has been proposed that the radio-weak Seyfert galaxy GRS 1734-292 is the counterpart of 3EG J1736-2908 and of the nearby Fermi/LAT source. I examine this identification, considering that the radio weakness could result from free-free absorption of a relativistic jet. An association with the EGRET detections is plausible, whereas the latest Fermi/LAT localization no longer favors GRS 1734-292. New observations, especially at radio frequencies of tens of GHz, would help to settle the issue.

The Advanced X-ray Imaging Satellite (AXIS) was a mission concept designed to improve upon the sensitivity and spatial resolution of the Chandra X-ray Observatory and XMM-Newton. Although AXIS was not selected for implementation, the concept study defined a mature instrument design with low-background, arcsecond imaging over the $0.3$-$10$ keV energy range, a large effective area, and a wide field of view. These capabilities provide a useful benchmark for the dark matter decay sensitivity of future X-ray observatories. We estimate the reach of a future AXIS-like instrument for narrow photon lines from decaying keV-scale dark matter, including axion-like particles and sterile neutrinos. For Galactic center observations, we find projected lifetime sensitivities of order $10^{31}$ s, improving upon existing limits by up to an order of magnitude over part of the keV mass range.

We provide a first-principles definition of Cotton tensors on conformal Carroll geometries by gauging the conformal Carroll algebra. On the mathematical side, this analysis yields a conformally covariant object designed to quantify deviations from conformal flatness in Carrollian geometries. On the physical side, it offers a powerful geometric tool to describe gravitational radiative degrees of freedom at the conformal boundary of four-dimensional asymptotically flat spacetimes. Unlike the Bondi news, whose fully-covariant definition requires amendment by supplementary data that we identify with the Geroch tensor, the Carroll-Cotton tensors offer the natural geometric objects to quantify deviations from stationarity due to the emission of gravitational waves.

The James Webb Space Telescope (JWST) has identified an abundant population of faint Active Galactic Nuclei (AGN) at $z \gtrsim 4$ which display broad emission lines, compact morphologies, and blue ultraviolet--optical continua. These ``Little Blue Dots' (LBDs) have been suggested to belong to the same family of objects as the more controversial ``Little Red Dots' (LRDs), with differences between the two largely owing to viewing angle effects. In this scenario, super-Eddington accretion resulting in high Extreme UV (EUV) and weak X-ray emission is invoked to explain the properties of both populations. We study the consequences of this super-Eddington scenario for the timing of Helium reionization. We find that observations which support an end to helium reionization no earlier than $z \approx 3$ disfavor scenarios in which the majority of observed $3 \lesssim z \lesssim 7$ LBDs are highly super-Eddington. For our fiducial super-Eddington accretion scenario, we find that the fraction of the LBD population in this state must be $\lesssim 10\%$, assuming LBDs make up $5\%$ of the $M_{ m UV} < -18$ galaxy population and have average escape fractions of $15\%$, comparable to recent observations. Our constraint assumes that LBDs dominate the Helium reionization budget, and would be tighter if bright quasars also contributed significantly. For a majority of LBDs to be super-Eddington, they would need to have small escape fractions ($\lesssim 1.5\%$) and/or be less abundant than observations suggest. Our conclusions are sensitive to the shape of the EUV spectra of super-Eddington black holes, motivating further study.

Precision tracking of Earth--Moon and Earth--satellite ranges offers a novel, low-frequency avenue for detecting gravitational waves from inspiralling massive black hole binaries, complementary to space-based interferometers. In this paper, we propose a first study of the reconstruction of the binary parameters from a synthetic set of range observations. \textit{Set-up}: Assuming an ideal unperturbed Keplerian motion for the earth-satellite binary, we develop a framework for reconstructing the chirp mass $\mathcal M_c$ and luminosity distance $D_L$ of chirping sources from the perturbations they induce on ranging observables, using both Lunar Laser Ranging (LLR) and a two-satellite ranging configuration (GUEST) as concrete case studies. \textit{Result}: We find that chirp-mass recovery tightly converges as a power law in SNR ($σ_{M_c}/M_c \propto \mathrm{SNR}^α$, $α\simeq -1$ to $-1.8$) for both LLR and GUEST. In contrast, the luminosity distance suffers from a severe, SNR-independent degeneracy with the sky-orientation angles in the LLR configuration, yielding fractional biases and uncertainties of tens to over a hundred percent regardless of signal strength. The two-satellite GUEST configuration breaks this degeneracy and restores a convergent, SNR-dependent recovery of $D_L$ comparable in scaling to that of the chirp mass. These results demonstrate that multi-baseline ranging architectures are essential for extracting luminosity-distance information from ranging-based gravitational wave searches, while chirp-mass measurements remain reliably accessible even with a single ranging baseline such as the Earth--Moon system.

We analyze 17 years of Fermi-LAT data to study the diffuse $γ$-ray emission along the Galactic plane and its connection to cosmic-ray (CR) propagation. Accounting for correlated instrumental systematics, we find decisive evidence for a spectral break at $\sim20-30$ GeV, present across the inner Galactic disk, with a preference of $Δχ^2=39.78$ ($4.44 σ$ global). The energy and amplitude of this feature are in striking agreement with the spectral feature observed in local CR nuclei, indicating that it is a global property of the Galactic disk rather than a local phenomenon. The measured slope change, $Δγ\simeq 0.20$, is consistent with local CR data and with expectations from a transition in the CR diffusion regime from Kolmogorov to Kraichnan turbulence. Our results provide strong evidence that diffuse $γ$-ray emission along the Galactic disk is dominated by $π^0-$decay emission up to a hundred GeV. These findings provide key insights into the origin of the CR spectral hardening and the propagation of CRs throughout the Galaxy, and illustrate how this multimessenger approach can be used to probe the origin of features in the CR spectra, such as the long-studied CR Knee.

[Abridged abstract] The objective of this study is to measure the magnetic field within the prominent inter-cluster filament recently detected in X-rays by the extended ROentgen Survey with an Imaging Telescope Array (eROSITA). This filament spans over 13 Mpc projected on the sky, connecting the galaxy clusters Abell 3667 and Abell 3651. We employed the Polarisation Sky Survey of the Universe's Magnetism (POSSUM) Rotation Measure (RM) grid to isolate the RM dispersion and median value of background polarised sources induced by the filament's magnetised plasma, and to infer the strength of this magnetic field. The filament region is sampled by 54 background polarised sources. After subtracting the foreground Galactic RM, we detected a marginal residual RM dispersion in the filament region of $6.9\pm3.6$ rad/m$^{2}$, together with a coherent residual RM signal with median $6.3\pm1.3$ rad/m$^{2}$. Assuming simplified single-scale magnetic-field models and adopting informed priors on the thermal electron density distribution derived from the X-ray analysis, we constrained the magnetic field strength to the range 0.1-3.5 $μ$G within 95$\%$ confidence, with preferred values around 0.2-0.3 $μ$G depending on the assumed magnetic-field coherence scale. However, we also found that the Galactic foreground RM in this region is highly structured on angular scales comparable to the extent of the filament itself, representing a major source of uncertainty for the RM analysis. Our results provide the first magnetic field constraints based on Faraday rotation measurements in an individual X-ray-detected inter-cluster filament, with field strengths consistent with theoretical expectations for gas in bridges and cluster outskirts. Our analysis also highlights the critical importance of accurately modelling Galactic RM foregrounds for future studies of extra-galactic magnetism with POSSUM and the SKA.

In Huang et al (JCAP08(2023)003), the work claimed that the Hubble constant can be constrained from lensed gravitational waves, despite the absence of information on GW source redshift or Einstein radius (angular size of the lens), as long as lens redshift is provided independently. To demonstrate, the authors set up a singular isothermal sphere lens model and applied Fisher information matrix and Bayesian parameter estimation on injected lensed GWs. However, their conclusion contradicts our previous work on degeneracies of GW lens system parameters. In this comment, we illustrate that Hubble constant cannot be measured with lens redshift alone, in the absence of source redshift or (Einstein radius).

Two track-like events with exceptionally large charge deposits, pointing back to the region of maximum overburden ($>18$ km.w.e.) of the Pico de Orizaba volcano, were reported by the HAWC Collaboration in a search for Earth-skimming neutrinos. Using exclusively published information, including the published Monte Carlo charge distributions and the scattered-muon background model, we show that these events are kinematically inconsistent with all identified backgrounds. A conservative energy-conservation bound places the in-tank energy deposit of the candidates above $\approx$190--210~GeV, with a worst-case minimum of 122--136~GeV, in either case exceeding the 100~GeV maximum of the scattered-muon background model. Calibration systematics derived from the published simulations act unidirectionally, pushing the implied deposits into the multi-TeV regime. Direct atmospheric muons require $E_μ\gtrsim 0.67$~PeV to penetrate the overburden and contribute $4.5\times10^{-5}$ expected events ($\lesssim 10^{-3}$ under the largest possible prompt-charm flux); collinear muon bundles are excluded by five independent arguments. Conversely, the neutrino hypothesis predicts identifiable events precisely in the observed charge window ($10^{3}$--$10^{4}$ photoelectrons) and in the highest-overburden analysis region, both observed. The two track-like events imply a rate that exceeds the conventional atmospheric neutrino flux expectation at the 2.1--2.5$σ$ level. The charges of the observed candidates require an emerging lepton above about 20~TeV; the published calibration does not bound the energy from above. These would constitute the first neutrino candidates detected in Mexico and the first obtained with the Earth-skimming volcano technique.

The origin of dust in the early Universe remains uncertain. We explore whether Little Red Dots (LRDs) could provide a high-redshift dust-production channel. Motivated by an analogy with Type IIn supernovae, we investigate whether LRDs may share the efficient dust-forming conditions. We consider dust formation in outer winds and later in a shielded cold dense shell after the central source fades. Such dust may avoid a global remnant-phase reverse shock, while longer LRD lifetimes may promote grain growth. We model the SEDs of two low-redshift LRD analogs as a thermal pseudo-photosphere plus optically thin dust components, obtaining dust reservoirs of order $10^{2}$-$10^{3}\,M_{\odot}$. Although photometry cannot exclude pre-existing dust, the narrow Balmer components of both analogs are close to the Case B ratio and their narrow-line environments are metal-poor, disfavoring a dominant diffuse host-ISM origin for the inferred reservoir. Formation within the LRD outflow is consistent with our optical-depth, sublimation, and energy-balance checks. In this scenario, the large dust masses do not produce a strong optical attenuation because a clumpy or asymmetric distribution can leave the dominant optical sightlines relatively unobscured. Our population calculation shows that the LRD contribution to early-Universe dust production can range from negligible to dominant. At higher efficiencies, LRDs can approach or exceed the lower CCSN contribution above $z\approx5$, whereas less favorable assumptions yield a minor contribution. We therefore propose that LRDs can act as early-Universe dust factories and, under some conditions, may dominate over CCSNe or provide seed grains for subsequent growth in the early ISM.

We report Bayesian evidence for a subpopulation of black holes, grown via accretion during the gaseous birth-stage of star clusters, in the cumulative GWTC-5.0 released by the LIGO-Virgo-KAGRA collaboration. This accretion channel predicts a saturating spin--mass relation, with low spins at low masses, rising continuously with mass through all intermediate spin values, to high spins at high masses. We test this prediction directly against the component spins of the catalogue. We single out 10 events with positive support and many others with weaker support across the whole component-mass range of the catalogue. We identify a preferred mass scale $m^t=20.7^{+11.6}_{-1.2}\,M_\odot$ (90\% credibility) separating regimes with different accretion-mixture fractions, with $\ln B=5.5$. Above this inferred scale, the evidence for an accretion-driven subpopulation is strongly concentrated, reaching a natural log Bayes factor of $16.6$ against the LVK fiducial spin population.

Stellar X-ray emission serves as a direct diagnostic of coronal activity, which is fundamentally linked to coronal heating processes. It also strongly influences the atmospheres and long-term habitability of orbiting exoplanets. Investigating how this high-energy emission evolves is therefore essential for understanding the evolution of stellar magnetic dynamos and planetary atmospheres and habitability. In this work, we investigate the evolution of X-ray activity and XUV irradiation for a sample of F-M dwarf stars based on Chandra and XMM-Newton observations. We find that F- and G-type stars broadly follow the traditional evolutionary picture of an early saturated (or weakly declining) phase followed by a modest decline, whereas K- and M-type stars exhibit a clear three-phase evolution of a saturated phase, an intermediate phase of rapid decay, and a final modest decline phase. By combining X-ray, ultraviolet, and Ca II H&K bands, we show that coronal emission becomes increasingly dominant toward lower-mass stars. Based on the cumulative XUV emission calculated from our fitted relation, planets around F- and G-type stars experience relatively moderate XUV environments, while those around K- and M-type stars may exceed the empirical cosmic shoreline shortly after reaching the main sequence, though this conclusion depends on the adopted shoreline value.

Superconducting microwave cavities loaded with radio frequency fields are a powerful tool to search for weak forces or electromagnetic perturbations due to new physics. One source of such signals can be high-frequency gravitational waves emitted from cosmological or unknown astrophysical events. However, large sensitivity improvements are still necessary to reach the parameter space motivated by theoretical models. In this work, we present a formalism to guide the design of such detectors across a broad range of frequencies and signal forms. By incorporating the interdependencies of all relevant parameters and the back-action of the electromagnetic fields on the cavity structure, we describe how figures of merit can be derived for a broad class of relevant experimental setups. Using a two-dimensional model, we demonstrate this formalism and present examples for optimized cavity geometries. We find that the choice of geometry alone can increase the signal-to-noise power ratio by an order of magnitude compared to an existing prototype of the same size. We also show that different physics goals lead to different optimal cavities, thus proving the need to consider such figures of merit at an early stage when designing a new detector.

Elastic photon--dark matter scattering attenuates gamma-ray spectra along a line of sight, probing the same operators as dark matter annihilation to photons but at a rate linear, rather than quadratic, in dark matter density. We consider Standard Model gauge-invariant effective operators of mass-dimension 5 to 7, suppressed by a cutoff scale $Λ$, coupling scalar, Majorana or Dirac dark matter to the photon. The leading operators with non-vanishing real-photon amplitudes enter at dimension-5 for Dirac dark matter and dimension-7 for Majorana dark matter. In the electroweak-doublet dipole portal, the inelastic splitting invoked to evade direct detection also closes the CMB annihilation bound, leaving attenuation the only one of the three photon-sector probes that survives. Applying this to a pixel-level reanalysis of 17 years of \textit{Fermi}--LAT Pass~8 data toward the Galactic centre, we derive the first operator-resolved sensitivity estimates for photon--dark matter scattering from the Galactic halo: $Λ\simeq 0.32~\mathrm{GeV}$ for the dimension-5 Dirac dipoles, $0.21~\mathrm{GeV}$ for the dimension-6 scalar Rayleigh operator and $0.79$--$1.06~\mathrm{GeV}$ for the dimension-7 Rayleigh family. The reach is weak: it lies below the EFT-validity threshold across the cold dark matter mass range, and is superseded on the dipole plane by CMB and direct-detection constraints. The framework is calibrated against pseudo-experiments, and recomputes the sensitivity for any instrument that provides a per-bin spectrum with uncertainties and a line-of-sight column density.

Ion-scale waves are believed to play an important role in heating of the solar corona and wind, though their generation mechanism remains unclear. Based on Parker Solar Probe observations, this Letter investigates the occurrence of ion-scale waves in the near-Sun solar wind with heliocentric distances between 0.1 and 0.2 au. Results show that the occurrence rate of left-handed polarized waves significantly depends on the plasma beta ($β$) and cross helicity ($σ_c$). The occurrence rate rapidly increases with decreasing $β$ and increasing $σ_c$. Overall, the occurrence rate exceeds 45$\%$ when $β<0.2$ and $σ_c > 0.7$ are satisfied. These observations are consistent with the direct predictions of the helicity barrier theory that suggests the generation of ion cyclotron waves via imbalanced magnetized turbulence.

Black Holes are the key to solving many unanswered questions in fundamental physics: in particular, the very extreme properties shown by supermassive black holes at the centers of galaxies make them obvious candidates for testing gravity theories in the strong-field regime. Since X-rays are generated by matter under extreme physical conditions, ultra-high resolution X-ray imaging (uXRI) will directly image the region near the event horizon of black holes in X-rays, similar to the Event Horizon Telescope in the radio band, enabling unprecedented tests of General Relativity and alternative theories of gravity near supermassive black holes. On the other hand, clusters of galaxies hold the potential of unveiling many unknowns in cosmology. uXRI will unlock this potential by probing small-scale plasma properties in the intracluster medium, providing the missing link required to establish galaxy clusters as reliable tools for high-precision cosmology. Moreover, uXRI will enable mapping of Dark Matter from galaxy cluster dynamics via proper motion measurements. Finally, uXRI will open a new field of precision X-ray astrometry, allowing for measuring pulsar parallaxes to support nanoHertz gravitational wave searches.

The coefficients of the transport equations, describing the propagation features, are particularly important in astrophysics, interplanetary physics, and experimental plasma physics. In this paper, the variable-dependent diffusion coefficients are investigated. For the momentum transport equations, we find that the coefficients are related to statistical quantities, some of which are new. In addition, these coefficients take logarithmic forms, which are different from the results derived in previous papers. For isotropic pitch-angle scattering, we also obtain a formula that takes a logarithmic form. For fractional transport equations, the coefficients expressed in terms of the moments are obtained from the governing equations.

Neutrinos produced at the highest energies can interact with cosmic neutrino and radiation backgrounds during their propagation to Earth. The many available $νν$, $ν\barν$, and $νγ$ channels can lead to their absorption or energy redistribution, whilst the leptonic and hadronic final states may feed secondary fluxes of neutrinos, protons, and electromagnetic particles through the decay or hadronisation of the heavy leptons, bosons, and quarks produced. We present a framework to characterise these propagation effects in detail, \texttt{$ν$propa}, an extension of the CRPropa Monte Carlo code that interfaces with event generators and to dedicated computations of the relevant cross sections. It also treats flavour oscillations in vacuum. Using this code, we investigate sources at high redshifts ($z = 10$), and find a strong absorption of the prompt flux beyond~$\sim 10^{21} \; \text{eV}$, although the copious secondary neutrinos partially compensate this depletion, also contributing to the spectrum at lower energies. The framework is designed to study scenarios of cosmological neutrino production beyond~EeV energies such as superheavy dark matter, cosmic strings, and primordial black holes, and to yield reliable predictions for the forthcoming neutrino observatories.

Recently, the Large High Altitude Air Shower Observatory (LHAASO) reported the first TeV gamma-ray detection from a low-luminosity active galactic nucleus (LLAGN) lacking a strong jet. This source, NGC 4278, is one of the nearest LLAGNs that can be studied in detail as a template for more distant objects. Most previous studies have focused on the month-scale-variable gamma-ray activities, seeking to explain them with weak jets. We focus instead on NGC 4278's quiet-period emission, proposing a different mechanism based on a wind launched from a radiatively inefficient accretion flow (RIAF). In particular, we model particle acceleration at a wind-driven shock and calculate the resulting multimessenger emission. To match the TeV gamma-ray fluxes reported by LHAASO in the quiet period, our model requires a wind power of $\lesssim2\times10^{43}~\mathrm{erg~s^{-1}}$ with a spectral index of injected cosmic rays of 2.0. We show that this is achievable through Bondi accretion of the ionized gas observed on the 100-pc scale, for a shallow accretion profile. We discuss the testability of our wind-driven shock scenario with multimessenger observations. As another important application, we extend our model to Sgr A*, the nearest LLAGN, and show that its TeV gamma-ray emission is reproduced with reasonable parameters. Our results suggest that RIAF-driven winds may be a generic emission mechanism in LLAGNs, making this class a potentially important population of both gamma-ray emitters and cosmic-ray accelerators.

Three-minute ($\sim$5 mHz) oscillations are a prominent signature of wave propagation in the solar chromosphere, but their measured power can vary substantially between full-disc observations and small, high-resolution fields of view. We investigate whether chromospheric magnetic canopy topology, particularly its lateral continuity and areal filling, modulates field-of-view-averaged three-minute power. We analyse H$α$ and Ca II 8542 Å spectral imaging from the Swedish 1-m Solar Telescope, comparing canopy-poor quiet-Sun scenes with canopy-dominated active-region environments, complemented by radiative-MHD Bifrost simulations of canopy-poor and canopy-rich atmospheres. We compute field-of-view-averaged power spectra from fixed-wavelength intensities and bisector-derived velocities in the observations, and from synthetic intensities, velocities, and temperature proxies in the simulations. We also quantify the relation between integrated 3-5 mHz excess power and canopy filling factor, using HMI-based magnetic-field extrapolations for the observations. In both observations and simulations, canopy-poor scenes show clear 3-5 mHz power enhancements, whereas canopy-dominated scenes show strongly reduced measured power. The trend is present in H$α$ and Ca II 8542 Å intensities and is supported by complementary velocity and temperature proxies. Integrated 3-5 mHz excess power decreases with increasing canopy filling factor. We conclude that chromospheric field-of-view-averaged three-minute power is a topology-weighted observable: dense, laterally continuous magnetic canopies can strongly reduce the measured large-scale three-minute signature without requiring the absence of local wave activity. This provides a practical criterion for interpreting chromospheric oscillation power as a proxy for atmospheric wave energy in the Sun and in magnetised cool-star atmospheres.

The design of the IceCube-Gen2 observatory, proposed as a next-generation extension of IceCube, includes a surface array consisting of scintillators and radio antennas. In addition to several such detectors already deployed at IceCube's surface array at the South Pole, a complete prototype station including three SKALA antennas has been operating at the Pierre Auger Observatory for several years. This setup has been used to successfully observe radio signals from air showers, demonstrated through coincident observations with the Auger Surface Detector. In this contribution, we present an updated analysis of these radio signals, and compare them to CoREAS simulations using the reconstruction from the Auger Surface Detector as input.

Layering is a ubiquitous feature of astrophysical objects. Motivated by the fact that physical black holes retain the layered structure of their progenitor stars when viewed in the time concepts synchronizable with the clock of an outside fixed-position probe, we investigate linear perturbations and gravitational-wave (GW) echoes from a compact object composed of two concentric thin shells. Compared with the single-shell case, the double-shell structure introduces an extra barrier in the effective potential and partitions the wave propagation space into four coupled effective cavities. As the mass ratio of the inner shell increases, new spectral peaks enter from the high-frequency side of the echo spectrum; the second and later peaks shift toward higher frequencies; and the lowest-frequency peak first shifts toward lower frequencies and then returns to its $q=0$ position. We call this variation pattern spectral-peak queueing (SQ). Its existence suggests that GW echoes can be used as probes for the internal structure of compact objects under consideration.

In this work, we investigate the resonant interaction between stochastic gravitational waves (GWs) and chiral Alfvén waves in a magnetized chiral plasma in the early Universe. Starting from covariant chiral magnetohydrodynamics coupled to linearized gravity, we derive a closed system of equations for the coupled chiral-Alfvén velocity and magnetic-field perturbations. Both analytics and numerics show a parametric resonance at the sum frequency of the two CVE-split branches, with an instability band that widens as the GW strain grows. This CVE-to-Alfvén ratio is not a free parameter. In the early Universe, it is fixed by the Standard Model's relativistic degrees of freedom. Including the plasma's backreaction on the GW makes the energy exchange nonlinear, breaking the usual single-frequency Manley-Rowe picture. For a self-consistent choice of parameters, where backreaction is only a small correction, the unsuppressed resonance still drives the system to a finite-time blow-up within a few Hubble times. We then work out the resonant frequencies and growth rates involved, mapping out what current and future gravitational-wave detectors could observe.

The Askaryan Radio Array (ARA) is an ultrahigh energy (UHE) neutrino detector at the South Pole that searches for impulsive broadband radio signals from neutrino-induced particle showers in glacial ice. ARA consists of five autonomous stations with receiving antennas deployed up to 200 m deep and has accumulated the largest livetime of any in-ice radio array. We present the first array-wide diffuse UHE neutrino search using data collected from January 2013 to December 2023, incorporating improved detector characterization and simulation, including data-driven noise and electronics models, revised antenna responses, and updated neutrino interaction and lepton propagation modeling, within a unified framework for event processing, background rejection, and cut optimization across independently operating stations. This search is expected either to identify the first UHE neutrino candidates observed by an in-ice radio detector or to set the most stringent UHE neutrino diffuse flux limits above a few EeV, while informing analysis strategies for under-construction and future radio arrays, such as RNO-G and IceCube-Gen2 Radio.

Black holes link gravity, thermodynamics and information via limits on the relaxation rate of a perturbed system. The Bekenstein-Hod bound imposes a minimum relaxation time at fixed temperature, but its observational test demands both black hole thermodynamic characterization and decay time measurement. Here we test this bound with GW250114, the loudest gravitational-wave signal yet observed from a binary black-hole merger. We infer the remnant temperature from pre-merger data truncated at least $10\,M$ before the peak and its longest-lived decay time from post-merger data, thereby avoiding direct reuse of the same strain samples. The ringdown frequencies and damping times are allowed to vary independently rather than being fixed to the Kerr spectrum. For the primary $t_{<}=-10\,M$ analysis, the bound is verified at $3.3-3.6σ$ across the focal ringdown start times, representing a substantial improvement over the $91\%$ confidence level set by GW150914. The conclusion remains robust under varied pre-merger cutoffs and explicit inclusion of the short-lived first overtone in waveform modelling. This separated-data measurement converts an information-theoretic relaxation bound into a precision test of a single astrophysical black hole.

For eccentric systems with aligned spins, we compute all spin contributions to the gauge-invariant conservative map between the constants of motion (energy and angular momentum) and the fundamental (radial and azimuthal) frequencies at the fourth post-Newtonian order. This extends the nonspinning map derived in [arXiv:2511.10735] to include terms that are linear, quadratic, cubic, and quartic in spin, as well as the associated spin-deformability parameters. We also obtain derived quantities such as the redshift and gyroscopic invariants, as well as circular links. We notice that the Blanchet-Iyer-Favata post-Newtonian stability criterion that determines the dimensionless frequency of the innermost stable circular orbit (ISCO) is in fact intricately related to the periastron advance for circular orbits. Finally, in the case of unbound orbits, we complete the 4PN scattering angle with all spin contributions.

Astrophysical observations of our universe have been key to our understanding of how the universe works. Shortly after the turn of the millennium, the National Research Council delivered \textit{Connecting Quarks with the Cosmos: Eleven Science Questions for the New Century}. In the subsequent quarter-century, we have made substantial progress in answering each question. These advancements have, in part, arisen because of the success of major US facilities across several domains of physics, guided by long-term planning documents which still largely focus on these questions. This report seeks to provide a status update on each question, and to outline what space-based facilities are crucial for future progress, intended to guide NASA's preparatory work for the Astro2030 Decadal.

Nambu-Goto cosmic string loops generically develop cusps, points where the string momentarily reaches the speed of light. These cusps produce strong gravitational wave bursts with a characteristic strain spectrum $\tilde{h}(ω)\propto (Gμ)\,ω^{-4/3}$, making them prime targets for gravitational wave searches, where $μ$ is the string mass per unit length. However, this picture is modified when one accounts for gravitational backreaction. Using a convenient gauge, we reformulate the Nambu-Goto equations of motion for a loop moving in its own dynamically sourced gravitational field, enabling the first continuous numerical evolution of loops under this backreaction. A key finding is that locally cusps survive backreaction. Nevertheless, the gravitational waveform calculated in this formalism is significantly modified, weakening the cusp burst and introducing a high-frequency cutoff at $f_c\propto(Gμ)^{-3/2}$. This suppression above $f_c$ reduces the expected signal-to-noise ratio in current and near-future detectors relative to unperturbed waveform predictions.

We investigate whether horizonless compact stars made of dark glueball matter from a broken exceptional $G(2)$ gauge sector can reproduce selected Kerr observables within a Thomas--Fermi effective-fluid description. We introduce GC9, a scale-separated $G(2)$-inspired positive nonic-density closure whose high-density stiffness, bag-free surface and Q-ball safety make it a useful compact-star benchmark. After Thomas--Fermi rescaling, reduced stellar observables are independent of the microscopic glueball mass $m_G$, while the collective stiffness $Λ_T$ fixes the dimensional mass and radius. Solving the TOV, Hinderer and Hartle--Thorne systems, we obtain a stable maximum-mass compactness $C=0.3247$, tidal deformability $Λ=4.37$, $\bar I C^{3/2}=0.947$, and slow-rotation quadrupole $\bar Q=1.522$. At $j=0.328$, the same-order ISCO shift is $1.24\%$. The stable endpoint has no light ring, but its exterior Regge--Wheeler barrier supports a genuine static axial mode, $Mω=0.463846-0.098881i$, with a damping time about ten percent shorter than Schwarzschild and a real frequency $24.1\%$ higher. A polarization-balanced vector realization has the same isotropic bulk EOS; moderate residual anisotropy changes static and first-order observables only at the few-percent level, while the full coupled vector spectrum remains open. Cowling calculations identify matter-supported quadrupolar modes. The scalar-burst, seeded-collapse and cosmological sections are phenomenological: a fixed $Λ_T$ gives a compact Kerr-comparison branch only near its own maximum mass, so the multi-sector scenario assumes distinct constant-$Λ_T$ branches from the keV supermassive sector to the PeV asteroid-mass sector. GC9 therefore defines a falsifiable restricted Kerr-mimicry framework for gravitational-wave, horizon-scale and compact-dark-matter tests.

We show that for static & spherically symmetric black hole geometries, the angular components of the Brown-York tensor on a finite radius boundary can be interpreted as the product of the Tolman-Ehrenfest temperature and a quasi-local entropy. This entropy vanishes at spatial infinity and monotonically increases as radius decreases, taking its maximum value on the horizon where it is equal to the Bekenstein-Hawking entropy. Thus, the behaviour of this entropy provides explicit verification of the covariant entropy conjecture.

We investigate the reconstruction of a stochastic gravitational-wave background generated by a first-order phase transition in flavour-deconstruction models using the Laser Interferometer Space Antenna (LISA). In these scenarios, the spontaneous breaking of an extended flavour-non-universal gauge symmetry at the TeV scale can both generate the observed hierarchies of Standard Model fermion masses and mixing angles and induce a strong first-order phase transition. We consider representative benchmark points of the model, compute the corresponding thermodynamic transition parameters, and construct the resulting gravitational-wave spectra using a state-of-the-art sound-wave template. We then inject these spectra into simulated LISA data and perform Bayesian inference with SGWBinner, jointly reconstructing the cosmological signal, instrumental noise, and astrophysical foregrounds. We find that the strongest benchmark signal can be successfully reconstructed, whereas weaker signals are substantially degenerate with the unresolved extragalactic compact-binary foreground. We further show that tighter prior information on this foreground, motivated by observations with ground-based detectors, can reduce this degeneracy and improve signal reconstruction. Our results demonstrate that flavour-deconstruction models can produce signals accessible to LISA, while highlighting the importance of astrophysical-foreground modelling for their identification and characterization.

Yellow hypergiants are rare, evolved massive stars generally interpreted as post-red-supergiant objects evolving blueward through or near the dynamically unstable Yellow Evolutionary Void. V509~Cassiopeiae is a remarkable example: its spectroscopically inferred effective temperature increased from approximately 5000~K in the mid-1980s to about 7900~K by the late 1990s and has since remained near this value during its post-heating state. We use simultaneous six-telescope CHARA observations obtained in 2023 with MIRC-X in the $H$ band and MYSTIC in the $K$ band to measure its photospheric diameter, search for a luminous companion, and constrain any spatially extended CO atmosphere. Interferometric data fitting with fixed atmosphere-model center-to-limb variation profiles yield limb-darkened angular diameters of $1.1840$--$1.1950$~mas. Although nominally about 5\% smaller than the previous Palomar Testbed Interferometer measurement, the difference is only $1.8σ$, indicating no significant secular change over 17--21~yr. The closure phases are consistent with a centrosymmetric brightness distribution, and no near-infrared-bright companion is detected over the sampled separations. The median $3σ$ limits are $ΔH=5.28$~mag and $ΔK=6.48$~mag. The B1~V companion proposed from ultraviolet spectroscopy is expected to lie below these limits and is not excluded. The CO first-overtone channels give a weighted mean CO-to-continuum diameter ratio of $1.011\pm0.004$, below the adopted $3σ$ detection criterion. We find no significant CO-band angular extension. V509~Cas is thus hot and molecularly compact despite retaining spectroscopically visible atomic circumstellar gas.

Since the first exact solutions of General Relativity (GR) were obtained, it became clear that the theory predicts a new class of compact objects: black holes. The Hawking--Penrose singularity theorems show that, under appropriate assumptions, gravitational collapse in GR leads to singular behavior. Motivated by the expectation that such regimes require physics beyond classical GR, effective approaches inspired by Loop Quantum Cosmology (LQC) and braneworld scenarios introduce high-density corrections. In this work we consider the static exterior geometry introduced by Gao, Lu, Shen, and Faraoni, associated with a comoving interior model in which the singularity is avoided through a sequence of collapse and bounce phases. Using the Newman--Janis algorithm in the Azreg-Aïnou formulation, we construct a stationary rotating exterior extension of this geometry. The resulting line element describes a stationary axisymmetric rotating spacetime whose horizon geometry, angular velocity, surface gravity, and Hawking temperature recover the Kerr and Schwarzschild limits when the quantum/braneworld correction becomes negligible ($l\to 0$). We further analyze the thermal response at fixed rotational state-space parameter, identify Davies-type singular points, and formulate an extended thermodynamic state-space relation.

The magneto-hydrodynamic (MHD) description of the solar wind has long been regarded as one of the most successful frameworks for investigating solar wind heating and acceleration. Under a set of simplifying assumptions, it provides a reduced large-scale description that is widely used to study the energetic role of electromagnetic fluctuations in the solar wind energy budget. In practice, applying simplification to MHD can result in the loss of some physics compared to an exact set of equations. However, an observational energy budget can help us to verify whether any energetic information has been lost in the process of simplification. To do so, we directly test the validity of the large-scale non-linear ideal MHD energy budget with solar wind observations from Parker Solar Probe (PSP) and Solar Orbiter (SO). After verifying the reliability of the measurements through comparison with previous studies of similar solar wind properties, we test the conservation of the total energy predicted by the MHD theory. We find that the average total energy increases with radial distance by $56\%$ ($\pm9\%$) between 14 and 203 solar radii. The increase in kinetic energy is not sufficiently compensated by the decrease of the thermal and electromagnetic contributions. We investigate the major sources of observational uncertainty and find that they cannot account for the observed energy increase. These results suggest that the large-scale theoretical description may neglect an energetically significant contribution to solar wind acceleration. Assuming that such a contribution exists, we predict that this extra energy would scale with radial distance as $r^{-0.54\pm0.38}$.

The existence of quantum gravity is the most important question in theoretical physics. Besides the theoretical development in this direction, looking for its low-energy consequences can provide clues. However, besides availability, it is crucial to ensure that what is observed uniquely comes from quantum gravity and not from other forces in the environment. What is the unique feature of gravity? The spin-$2$ nature of its propagator. In this Letter, we calculate what the unique feature of the spin-$2$ graviton is in the interaction of two spin-$\frac{1}{2}$ particles. This unique feature shows itself in intertwining the spin and momentum of two particles simultaneously as a dipole-dipole interaction. This cannot happen for any spin-$0$ or spin-$1$ propagator, at least at leading order, which scales as $\frac{1}{r^3}$ in real space. We re-calculate the results using an independent approach, i.e., the Foldy-Wouthuysen transformation, and reach the same results. Due to simultaneous coupling of both particles' spins and momenta, a four-partite entanglement framework is suggested to observe this effect.

We investigate primordial black hole formation in a Dirac-Born-Infeld inflationary framework in which the background dynamics are determined by explicit functional forms of the inflaton potential $V(φ)$ and the warp factor $f(φ)$. The background equations are solved numerically to obtain the evolution of the slow-roll parameters. We show that a localized feature in the potential, accompanied by a correlated structure in the warp factor, dynamically induces a transient suppression of the slow-roll parameter, leading to a short-lived non-attractor phase. This behavior generates an enhancement of the curvature power spectrum on small scales, while preserving consistency with CMB-scale observables. The Mukhanov-Sasaki equation is then solved numerically to compute the resulting power spectrum, which exhibits narrow and localized peaks in the PBH abundance across different mass ranges. We also evaluate the associated stochastic background of induced gravitational waves and find that the predicted signal can fall within the sensitivity bands of future pulsar timing arrays and space-based interferometers, depending on the scale of the inflationary feature. A parameter scan in the $(r,n_s)$ plane shows that the large-scale predictions remain consistent with current observational constraints.

The motion of a spinning test particle in a curved spacetime is governed by the Mathisson--Papapetrou--Dixon (MPD) equations and deviates from geodesic motion already at first order in the spin. While essentially all existing studies truncate the dynamics at linear order in the spin, we present an exact, nonperturbative treatment of planar motion in Schwarzschild spacetime under the Tulczyjew--Dixon spin supplementary condition: eliminating the four-velocity recasts the MPD system into a closed algebraic form and reduces the radial motion to an effective-potential problem, with no expansion in the spin at any stage. This exact framework uncovers qualitative features that are absent from---and in fact unattainable within---the linearized description. Most notably, for sufficiently large spin the effective potential develops a double root at a characteristic radius determined solely by the particle mass and spin, marking an impenetrable \emph{spin wall} of purely spin origin; beyond a critical spin the wall lies outside the event horizon and shields it from generic infalling particles. Moreover, the wall is a filter for particle: only orbits with a specific combinations of spin, angular momentum and energy can penetrate it, all others being reflected before reaching the horizon. In addition, the innermost stable circular orbit, which in linear treatments merely shifts continuously with spin, is obtained in closed form in the weak-field limit and is shown to cease to exist at sufficiently large spin. We further compute the spin correction to the perihelion precession in the weak-field limit and verify that all results reduce to the standard ones at vanishing spin. The spin wall and its filtering rule are genuine nonperturbative phenomena, invisible to any finite-order expansion in the spin, with potential observational signatures in accretion flows around compact objects.

More than 700 S-type planets have been identified from Gaia and TESS observations, including over 150 transiting targets, enabling the precise dynamical orbits and planetary mass characterization in binary environments. Here we present the first systematic N-body dynamical mass determination for 40 single S-type (Satellite-type orbit) planets in close binaries using an improved Markov Chain Monte Carlo (MCMC) framework with Gaussian priors to model stellar companion perturbations. {For binary systems with $a_\mathrm{B}<100$ au, companion-induced perturbations can bias the RV semi-amplitude and consequently the inferred planetary masses. The impact is strongest for short-period sub-Jovian planets, whose masses decrease by up to 20% when transitioning from Keplerian to N-body modeling, while massive Jovian planets with $M_{\mathrm{Jup}} < M_{\mathrm{p}} < 5$ $M_{\mathrm{Jup}}$ show only a 7.2% reduction.} Applying the NAFF stability criterion to TOI-4633, $i_{\mathrm{mut}} = 70^{\circ}$ is the upper limit for the fast rejection of unstable orbital solutions. Our results reveal that intermediate-mass planets exhibit both positive or negative biases in the inferred masses and influence the observed population of the sub-Jovian desert.

Inspired by holographic dark energy models, we extend the analysis performed in Ref.\cite{RGPC} taking into account Yukawa deformations on the different energy density (HDE) profiles. The profiles we have explored are: the Bekenstein-Hawking HDE, the Moradpour energy density, the Standard Renyi HDE and the Mixed Energy Density. With the help of an inhomogeneous Equation of State of the form $p_{r}(r)=ω_{r}\left( r\right) ρ(r)$, we have considered Zero Tidal Forces. Differently from the original case, only a particular case of the family of the Bekenstein-Hawking HDE profiles distorted by the Yukawa term has developed a divergent $ω_{r}\left( r\right) $ for $r\rightarrow \infty $. To cure such a divergence we have introduced a modification at large distances in order to have a finite result. This means that the Zero Tidal Forces can be imposed in a very large but limited region of the spacetime. Such modification did not change the behavior of the Equation of State close to the throat. For every proposal we have computed the components of the Stress-Energy Tensor. What we have found is that the Yukawa-Bekenstein-Hawking HDE is the only positive profile, while the Yukawa-Moradpour and the Yukawa-Renyi have a limited region where the energy density is positive. The remaining Yukawa-Mixed Energy Density is always negative. This means that the Yukawa distortion introduces a kind of negative energy density.

We investigate timelike bound motion, resonant periodic orbits, and their gravitational-wave signatures in the rotating Konoplya-Zhidenko (KZ) black hole spacetime. Using the separability of the Hamilton-Jacobi equation, we parameterize eccentric and inclined bound orbits by $(p,e,z_1)$, derive the corresponding constants of motion $(E,L_z,Q)$, and use the orbital frequencies to identify resonant configurations. We study a range of resonances, including radial-polar resonances of inclined orbits and radial-azimuthal resonances of equatorial eccentric orbits. We further construct physically scaled quadrupole-kludge waveforms for representative equatorial resonant orbits and analyze their frequency-domain characteristics. Our results show that the KZ deformation shifts the resonance locations and modifies both the orbital trajectories and the resulting gravitational-wave signals. The corresponding characteristic strain lies predominantly in the millihertz band, placing these signals in the frequency range relevant to space-based gravitational wave detectors.

We present a comprehensive photometric study of three W UMa-type contact binary systems, V1104 Her, V1284 Her, and V2822 Ori, based on a combination of ground-based observations and space-based TESS photometry. The light curves were modeled using the BSN application under a contact configuration, with parameters and their uncertainties estimated through the Markov Chain Monte Carlo (MCMC) approach. The derived solutions indicate that the target systems are in a shallow-contact configuration. The target systems are classified as W-subtype contact binaries, with the more massive component cooler than its companion. The light curve of V1284 Her shows a pronounced O'Connell effect, which is reproduced by introducing a cool starspot on the primary component. Absolute parameters were estimated using the empirical parameter relationship between orbital period and semi-major axis, yielding component masses in the range $0.48$-$0.86\,M_\odot$ and confirming the low-mass nature of the systems. Orbital period variations were investigated using eclipse timings from the literature, ground-based observations, and TESS data by examining both linear and cyclic models. Statistical model comparison indicates that the cyclic model provides a better description of the eclipse timings for V1104 Her and V1284 Her, whereas the linear model is preferred for V2822 Ori, although the difference between the two models is relatively small.

Recent results in the study of gravitational scattering amplitudes indicate that some highly-symmetric relativistic systems may exactly conserve a version of the Laplace-Runge-Lenz (LRL) vector in two-body bound states. We make a systematic study, in the context of a generic EFT of long-range interactions due to the exchange of massless mediator particles of spins 0, $\frac{1}{2}$, 1, $\frac{3}{2}$, 2, of the conditions for the conservation of a hidden LRL vector; both classically (no orbital precession) and quantum mechanically (hydrogen-like degeneracy of bound states). The calculations require several new technical developments including the extension of relativistic post-Minkowskian potential matching to quantum corrections and the incorporation of long-range forces due to the exchange of pairs of massless fermions. We find that while classically the absence of precession is a generic property of a large class of models, including Kaluza-Klein theories, with vector and scalar exchanges, maintaining the degeneracy quantum mechanically requires a surprising cancellation between gravitons and 6 Majorana gravitinos, hinting at a special role for $\mathcal{N}=6$ supergravity.

We present the second release of the MEGARA spectral library, MEGASTAR, which now includes all spectra collected during ten observing semesters at the Gran Telescopio CANARIAS. This new release supersedes our first release and incorporates a substantial number of additional observations (2000 new spectra), obtained at high spectral resolution, R(FWHM)$\sim$20000, in two wavelength ranges centred on H$α$ (6420 - 6790 A) and on the CaII triplet (8370 - 8885 A). The aim of this paper is to introduce MEGASTAR DR2 to the community as its high-resolution spectra can serve as a valuable resource for numerous types of research. In particular, we will use MEGASTAR spectra to construct SSP blocks within the HR-PyPopStar evolutionary synthesis models. The stars were observed using the integral field spectroscopy mode of the instrument. We process the data in a uniform way with the MEGARA data reduction pipeline. We estimate the stellar flux by adding the spectra from 37 spaxels, centred on the spaxel with the highest flux in the IFU reconstructed image. This approach guarantees that the effective slit width, and therefore the spectral resolution, are the same for all spectra. The second MEGASTAR release consists of 2838 spectra corresponding to 1408 stars, providing a better coverage of the stellar parameter space than the first release. The spectra were acquired with an average continuum S/N of about 215. This second release meets the standards of a modern empirical library: it offers reliable calibrations, data free from slit effects, observations of a large number of stars, and provides high spectral resolution to model both individual stellar clusters and entire galaxies observed with MEGARA.

Not much. It has been proposed that applying a rational filter to a black hole ringdown gravitational waveform reveals a direct wave component sourced near the event horizon. By solving the Teukolsky equation for a point particle plunging into a Kerr black hole, I show that the maximum amplitude of the waves sourced within the prograde light ring is $\lesssim 10\%$ that of those sourced by the full trajectory no matter if the waves are filtered or not. This agrees with the interpretation of quasinormal modes as waves orbiting the light ring and the direct wave as the power of these modes redistributed in time. Therefore, both quasinormal modes and direct waves are more a probe of the light ring than the near-horizon region. For GW250114, I estimate that the component of the waves sourced within the light ring have a signal-to-noise ratio $ρ\lesssim 1$ measured after the peak of the filtered waves.

We derive an endpoint-free optical rigidity theorem and use it to separate two rigidity regimes in Bianchi I spacetimes, without assuming that the spatial metric is diagonal in a fixed basis. For a smooth, regular, twist-free null congruence, the affine Raychaudhuri equation expresses a finite null-Ricci integral as an expansion boundary term minus a nonnegative optical bulk. If the past and future cutoffs are removed independently and their two-end liminf is nonnegative, two-sided completeness forces the optical tensor and the null Ricci contraction to vanish pointwise. In Bianchi I this freezes the spatial metric on the fixed kernel of the conserved covector. We classify the resulting saturation geometry: a non-static metric has zero, one, or two unoriented saturated lines, equivalently zero, two, or four oriented rays, and a third line forces staticity. Under the stronger pointwise null convergence condition, the existence of a single two-sided complete null geodesic already forces the spatial metric to be constant and the cosmic-time interval to be all of $\mathbb R$; on the Cartesian universal cover the spacetime is Minkowski. Periodic models attain the four-ray saturation bound in the weaker cutoff-stable regime, with $I_p^{\mathrm{ind}}=-\infty$ in every nonsaturated direction, while pointwise null convergence fails on open time intervals. Matter and achronal averaged-null-energy consequences are stated under an explicit matching assumption on field equations and cutoff prescriptions.

In this paper, we investigate the late-time accelerated expansion of the Universe in power law $f(Q)$ gravity, where a logarithmic dark energy parametrization is considered: $ω_{de}(z)=ω_0+ω_1\ln(1+z)$. This description gives a smooth deviation from a constant equation of state within the complete range of redshifts. We obtain an analytical expression for the Hubble parameter and we use a Markov Chain Monte Carlo to compare the model with the most recent observational data obtained from Pantheon$^+$ Type Ia supernovae, Baryon Acoustic Oscillation measurements from the second data release (DR2) of the Dark Energy Spectroscopic Instrument, and Cosmic Chronometers. We then perform a statistical comparison between our model and the standard $Λ$CDM model using the Akaike Information Criterion and the Bayesian Information Criterion. From our results, we conclude that the use of logarithmic parametrization in the $f(Q)$ gravity model $f(Q)=Q+6γH_0^2\left(\frac{Q}{Q_0}\right)^n$ is a valid and more flexible alternative to standard dark energy models, as it provides a richer phenomenology at low redshifts.

Inspired by interaction of gravitational waves, dark matters and dark energy, we study the Einstein scalar field equations with the nonzero cosmological constant for the Bondi-Sachs metrics. We provide the asymptotic expansions under the outgoing radiation condition. Unlike the case of the zero cosmological constant, the asymptotic expansions depend on four additional $Λ$-independent functions $B(u, θ, φ)$, $\tilde{X}(u, θ, φ)$, $\tilde{Y}(u, θ, φ)$ and $\tilde{I}(u)$. We show that, under suitable coordinate transformation, we can make $B(u, θ, φ)=0$. We prove the peeling property for the Einstein scalar field equations if $\tilde{I}=0$, and derive a loss formula of the Bondi energy-momentum for the nonzero cosmological constant. We remark that, for certain real data from gravitational waves, the loss formula is likely to indicate the loss property of the Bondi energy-momentum.

Quantum resonances and black-hole quasinormal modes (QNMs) are described by closely related mathematics: radiative boundary conditions, analytic continuation of Green functions or resolvents, poles on nonphysical sheets, and non-self-adjoint spectral representations. This article does not introduce that equivalence but reconstructs its genealogy. Nuclear resonance theory grew from radioactive decay, reaction cross sections, metastable compound states, and complex energies, whereas black-hole perturbation theory grew from spacetime stability and causal response. We place the two developments on a common chronology, from Sommerfeld's radiation condition and early nuclear-decay theory through Regge--Wheeler perturbations, Vishveshwara's 1968 dissertation and 1970 papers, Press's 1971 quasi-normal terminology, and the independent Aguilar--Balslev--Combes theory of analytic dilation, then follow their later mathematical reunification in scattering-resonance theory. Alongside the chronology, we give a working dictionary relating no-incoming and horizon-ingoing/infinity-outgoing conditions, pole energy and complex frequency, width and damping rate, residues and excitation factors, and nonresonant background with branch-cut and prompt contributions. The aim is to make the cross-disciplinary equivalence operational without flattening its history, and to distinguish mathematical equivalence from historical genealogy.

In this work we investigate how exotic spinorial topology modifies the propagation of fermionic modes in the Schwarzschild geometry. By incorporating a topological gradient, $\partial_μ\varphi$, into the Dirac operator through a tetrad deformation, we show that the exotic spinorial sector naturally induces an effective geometric deformation of the Schwarzschild background. The central consequence of this construction is the emergence of a topological impedance surface at $\rtopo=1/q$, which suppresses the radial group velocity of the exotic spinorial modes, yielding a birefringent propagation pattern. Using a spinorial perturbation we discuss the greybody factor and the quasinormal response. The quasinormal spectrum shows the stability of the background metric and the absence of isospectrality for the superpartner potentials.

We systematically investigate the zoom-whirl periodic orbits of a small compact object orbiting a magnetically charged black hole in $f(R, T)$ gravity coupled with Euler-Heisenberg nonlinear electrodynamics. We evaluate the impact of the magnetic charge $Q_m$ and the Euler-Heisenberg parameter $a$ on the characteristics of the innermost stable circular orbit (ISCO) and the marginally bound orbit (MBO). Particularly, we focus on the precession parameter q and systematically examine how the magnetic charge and other parameters affect the trajectories of periodic orbits. Using the numerical kludge method, we generate gravitational waveforms for these periodic orbits. The results presented in our work demonstrate that the magnetic charge can significantly modify not only the precession parameter but also the orbital trajectories of the periodic orbits. Moreover, changing the magnetic charge $Q_m$ could cause a significant phase shift in the gravitational waveforms, while other parameters exert a relatively weaker influence on the gravitational waves.

Runaway stars ejected from the Galactic disc span a range of velocities, with two extreme regimes of particular interest. Hyper-runaway stars reach velocities approaching the local Galactic escape speed while remaining gravitationally bound to the Galaxy, while hypervelocity stars (HVS) have speeds which exceed the escape speed, leaving them formally unbound. Studying both populations places stringent constraints on star cluster formation, supernova explosions in massive binaries, and the shape of the stellar halo. Here we present a spectroscopic search for such extreme-velocity stars using data from the first data release of the Dark Energy Spectroscopic Instrument (DESI DR1). Because these objects are typically located at distances beyond the range where \textit{gaia} parallaxes are reliable, we derive stellar parameters through a combined analysis of spectroscopy and spectral energy distributions (SEDs). These parameters are then compared with stellar evolutionary tracks to infer distances, which are subsequently used to compute the kinematics of the candidates. We identify a sub-sample of eight stars that appear unbound to the Galaxy, likely of extragalactic origin. These stars exhibit projected rotational velocities exceeding $50$ km s$^{-1}$, consistent with a main-sequence nature. An additional eleven stars are identified as potential HVS candidates under the assumption that they are main-sequence stars. This interpretation is not supported by their rotational velocities, making their unbound status less secure. Finally, $26$ stars show evidence of being main-sequence runaway stars ejected from the Galactic disc. The fastest object in the sample is a metal-poor HVS candidate with a Galactocentric velocity upper-limit of $934 \pm 110$ km s$^{-1}$. The star with the largest measured radial velocity of $513$ km s$^{-1}$ is most likely a slowly pulsating B-type runaway star.

First-order phase transitions in the early universe can generate a stochastic background of gravitational waves, offering a unique probe of high-energy physics. In this work, we investigate aspects of bubble nucleation and transition timescales, which play a central role in shaping the resulting gravitational wave spectrum. Many common approaches characterise the transition rate via a Taylor expansion of the false vacuum decay rate. We argue that a more fundamental description is instead given by the distribution of bubble lifetimes, and define a new timescale, $β_ν$, as the first moment of this distribution. We show that $β_ν$ reproduces the behaviour of previous timescale definitions in the appropriate limits, while avoiding their pathologies, and offers a more natural description of the ensemble of nucleated bubbles. We then quantify the impact of this improved timescale on the predicted gravitational wave spectrum, finding that it shifts the peak amplitude by up to an order of magnitude relative to previous definitions. As next-generation gravitational wave detectors come online, robust theoretical predictions will be essential; we hope this work represents a step in that direction.

Within the framework of quasi-topological gravity, we systematically investigate the correspondences among three classes of observables---the shadow, the quasinormal modes, and the graybody factors---of regular black holes in $D = 5$ dimensions. Using the WKB approximation and GrayHawk numerical integration, we test the applicability of the GBF--QNM correspondence and the shadow--GBF correspondence in the low-mode ($l=2$) and higher-dimensions ($D=5$): the difference between the GBF--QNM correspondence and the numerical results remains small in magnitude; we apply the known Langer correction (replacing $l$ by the effective angular momentum $κ= \sqrt{l(l+D-3)} \simeq l + (D-3)/2$), which reduces the error of the shadow--GBF correspondence at low modes to a level comparable with that of the GBF--QNM correspondence. Our work extends the shadow--GBF correspondence to higher-dimensional regular black holes, providing a viable route to predict the black hole spectrum and the Hawking radiation profile from a single observable, and thereby to realize multi-messenger tests of gravity.

A large sample of OB stars plays an important role in studying the stellar parameters of massive stars, as well as the formation and evolution of the Milky Way. With the help of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Data Release 10 (DR10), we are able to construct a large sample of OB stars with spectroscopic data. In this study, we identify 48,463 spectra of 34,550 OB stars from LAMOST DR10, based on the Hertzsprung-Russell (H-R) diagram constructed with Gaia DR3 data and spectral line indices measured from LAMOST DR10 low-resolution spectra. Among these, 6907 OB stars are newly identified. We use the MKCLASS tool to derive the spectral subtypes of the OB sample. The spatial distribution of 25,287 OB stars and the Toomre diagram of 20,397 OB stars indicate that the majority of these stars are located in the Galactic disk. Based on their peculiar velocities, we identify 1960 runaway star candidates.

The distribution of bio-essential elements is key to assessing the chemical fertility of galactic environments. We analyse phosphorus abundances for 233 nearby FGK stars from the Hypatia Catalog, separating thin- and thick-disk populations. We study [P/Fe] as a function of [Fe/H] and other elemental abundances using non-parametric tests and bootstrap resampling, and we examine residual correlations at fixed [Fe/H] together with molar ratios involving P. We find a [P/Fe]-[Fe/H] trend broadly similar to that of alpha elements, supporting a dominant origin in core-collapse supernovae, while deviations point to additional nucleosynthetic channels. Phosphorus shows strong positive correlations with several CHNOPS, alpha, and Fe-peak elements, especially in the thin disk. These co-enrichment patterns remain significant at fixed [Fe/H], indicating that they are not a trivial consequence of global metallicity. Thin-disk stars are also more enriched than thick-disk stars in many elements. The solar P/Mg and P/Si ratios are representative of the local stellar population, whereas solar P/O is relatively elevated. Overall, phosphorus emerges as a tracer of genuine multi-element co-enrichment and of the chemical fertility of the solar neighbourhood.

We perform an observational and thermodynamic analysis of four cosmological models $Λ$CDM, CPL, MPL, and the three-parameter MmAH parametrization. All dynamical models improve the fit relative to $Λ$CDM, with $Δχ^2 \sim 6$-$6.5$, with MPL providing the best fit, while MmAH remains viable. Although Bayesian evidence mildly favors $Λ$CDM due to its lower complexity, the dynamical dark energy models remain competitive alternatives given current observations. We then reconstruct thermodynamic quantities within observationally constrained cosmological models, extending previous theoretical studies. The bestfit heat capacity reconstruction indicates that the divergence associated with a second order thermodynamic phase transition coincides with the deceleration-acceleration transition only in $Λ$CDM, whereas for the dynamical dark energy models it occurs at distinct redshifts, suggesting that this coincidence is not universal. The generalized second law is satisfied for all models over $0 \le z \le 1$, while the Hessian analysis reveals a transient instability at the phase transition; however, the late time thermodynamic stability is model dependent, with CPL and MPL remaining stable and $Λ$CDM and MmAH failing to satisfy both stability conditions simultaneously. These results show that thermodynamic properties reconstructed within observationally constrained cosmological models provide a complementary probe of dark energy, with the thermodynamic phase transition emerging as an intrinsically model dependent phenomenon.

Context. The Pennsylvania-Toruń Planet Search, which operates on a sample of $\sim$1000 northern-hemisphere stars, has been underway since 2004. Stars with radial velocity (RV) amplitudes exceeding 2 km s$^{-1}$ represent a backup subprogram sample dedicated to monitoring binary stars with multiple instruments. Aims. We used almost 21 years of combined RV measurements to search for Doppler signals consistent with stellar or brown dwarf companions and to produce a catalog of both known and previously unpublished binary stars in our planet-search sample. Methods. We analyzed the combined RV measurements, searching for stellar companions and obtaining orbital solutions for both known and new binary systems. We also searched for periods in available long-term photometric monitoring data from All Sky Automated Survey (ASAS), and applied Gaia astrometric data whenever available. Results. We report the results of long-term RV monitoring of 16 systems: new detections of low-mass companions to 11 stars and updated orbital elements based on combined sets of our new and literature data for five systems. For two objects (TYC 3318-00789-1 and TYC 3318-01538-1), we find evidence of activity or the influence of another unseen companion, possibly due to line-profile variations or unresolved spectral contamination. We present true masses for three systems in our sample: TYC 1931-1040-1, TYC 3451- 1449-1, and TYC 3667-1636-1. We obtained these masses using Gaia DR3 non-single star data.

The estimation of stellar angular diameters can be performed from the surface brightness - color relation (SBCR) and photometry. The SBCR have been considered by the PLATO space mission as an independent empirical alternative for estimating stellar radii of FGK stars. In this context, we have implemented an homogeneous approach not only for calibrating the SBCR for FGK-IV/V stars but, also for determining their fundamental parameters in order to place the stars reliably on the HR diagram and to study their impact on the SBCR. We have performed interferometric observations of 18 quiescent FGK-IV/V stars in the Gaia color range of $3.088 \leq G \leq 5.498$. For the first time, we used 3 different interferometers operating in the $R$, $H$ , and $K$ bands to measure polychromatic limb-darkened angular diameters (LDAD). In parallel, by using public domain spectra we have estimated the stellar parameters ($T_{eff}$, $log g$ and Z) by using the open python tool iSpec. We achieved an average accuracy of 2.3% for the LDAD based on polychromatic observations. However, we have observed that our SBCR does not follow the calibration of the relation between surface brightness and color in Gaia found in the literature. Furthermore, we found that $log g$ and $Z$ have no impact on the SBC relation; given the characteristics of our sample of quiescent stars, it constitutes an ideal set of targets for conducting a new SBCR calibration within the framework of the PLATO space mission. In this context, we reported a SBCR calibration with $σ_{RMS} = $ 0.012, 0.009, 0.009 in the $G, G_{BP}$ and $G_{RP}$ Gaia bands, respectively. This article is part of a series of papers reporting the first results obtained using a polychromatic approach to measure LDAD, employing a fully homogeneous methodology for both determining the fundamental parameters of stars and measuring the LDAD, $θ_{LD}$.

Strong magnetic fields affect particle dynamics through two distinct channels: gravitational backreaction deforms the spacetime, while direct coupling to an intrinsic magnetic moment depends on the relative orientation of the field and the dipole. We disentangle these effects by studying equatorial orbits and near-horizon collisions of electrically neutral magnetized particles in the exact Kerr--Bertotti--Robinson spacetime. The field-induced geometric deformation shifts turning points and circular-orbit domains and can eliminate a finite effective-potential well together with its bound orbits. Even without direct dipole coupling, it can also offset the Kerr periapsis advance and produce a finite-radius zero-precession orbit. Direct dipole coupling breaks the symmetry under magnetic-field reversal and shifts the radius, energy, and angular momentum of the innermost stable circular orbit in an orientation-dependent manner. The formal ultrarelativistic endpoints of these orbit branches, however, remain fixed by the background geometry and approach circular null orbits. In the Bañados--Silk--West mechanism, both magnetic effects modify finite-radius potential barriers and hence the ability of a critical particle to reach the near-horizon collision region. In the representative nonzero-field cases examined here, an exactly critical particle released from infinity is blocked before reaching an extremal horizon, although a locally admissible collision between critical and usual particles can still produce unbounded center-of-mass energy. Finite dipole coupling shifts the barriers but does not change the leading near-horizon divergence. Near a nonextremal horizon, an exactly critical particle is excluded and the collision energy remains finite.

The Epoch of Reionisation imprints its history and morphology on the Cosmic Microwave Background temperature and polarisation anisotropies through two effects: The kinetic Sunyaev Zel'dovich (kSZ) effect and Thomson scattering. To perform joint analyses of these observables and put tight constraints on the reionisation history and morphology, a common reionisation model is necessary. We present a quick, physically-accurate analytical approach to derive consistently the angular power spectra of the three main resulting imprints that are the spatial fluctuations of the Thomson optical depth, the patchy kSZ effect, and the scattering and screening B-modes. The approach differs from existing analytical models, as it is calibrated on high-resolution hydrodynamical simulations and depends on physical parameters of reionisation. Our predicted power spectra are consistent with the ones derived from cosmological simulations, whilst including more physical information -- such as the typical size of ionised bubbles and the duration of reionisation. We provide an updated detectability assessment and show that both $C_\ell^{ττ}$ and $C_\ell^{BB}$ could be measured by experiments similar to CMB Stage 4 and CMB-HD, respectively. We show the complementarity of the three observables in constraining reionisation history and morphology, and illustrate the potential of their joint analysis to get a global picture of reionisation. This analytical model will be a powerful tool in the analysis of upcoming CMB data, either alone or in combination with independent datasets such as measurements of the high-redshift 21cm signal. The code to derive these spectra is publicly available online as the preion Python package.

We studied the evolution of a butterfly-shaped coronal hole (CH) observed from 2025 September 8 to 14 using SDO/AIA 193~Å images and SDO/HMI line-of-sight magnetograms. The CH boundary was identified using a fixed 100~DN intensity threshold, and its area, mean EUV intensity, and total unsigned magnetic flux were tracked across the solar disk. As the CH approached the central meridian, its area increased from approximately $7.70\times10^{16}$ to $1.63\times10^{17}$~m$^{2}$ and its unsigned magnetic flux from $8.68\times10^{21}$ to $1.91\times10^{22}$~Mx, while the mean 193~Å intensity decreased from about 61 to 45~DN. The area and unsigned flux showed similar temporal trends, whereas the intensity varied oppositely. Near central-meridian passage, these quantities remained relatively stable for several days. A high-speed solar-wind stream was detected at 1~AU about 2--4 days later, reaching 600--750~km~s$^{-1}$, consistent with the CH being its likely solar source. These results link the morphological, radiative, and magnetic evolution of the CH with the subsequent high-speed solar-wind stream.

We consider the difference between ensemble and volume average in cosmology. It is known that for sufficiently weak long-range correlations the root mean square of the difference, which we call ergodicity bias, decays like $R^{-3/2}$ in the limit of large volume $R^3$. We calculate the condition this imposes on the power spectrum of a Gaussian random field. We quantify the bias for finite $R$, and show that the $R\to\infty$ limit is of little relevance for cosmological observations when the measured scales and correlations extend to the size of the observable universe. We consider curvature, density, and velocity perturbations. On large scales the bias is important in all three cases. For the density perturbations, which are observationally the most relevant, the relative bias first exceeds 100% at the separation $r=177$ Mpc, and is larger than 100% for all $r>560$ Mpc. It should be taken into account when comparing ensemble and volume averages for large-scale structure. The bias is also large for the cosmic microwave background temperature perturbations on large angular scales, but this is not relevant for observations, as their analysis does not involve volume averaging.

The so-called ``cosmic dipole tension'' challenges the Cosmological Principle by positing a discrepancy between the Solar System's peculiar velocity inferred from the Cosmic Microwave Background (CMB) dipole and that derived from large-scale structure number-count dipoles. Here we provide a high-precision determination of the kinematic dipole using the redshift-dipole method applied to the first data release (DR1) of the Dark Energy Spectroscopic Instrument (DESI). By exploiting the Doppler-induced modulation of observed redshifts, this estimator is intrinsically less sensitive to imaging systematics and selection-function uncertainties that can bias traditional number-count measurements. We conduct a tomographic analysis of four tracer populations, Bright Galaxy Sample, Luminous Red Galaxies, Emission Line Galaxies, and quasars, spanning $0.1<z<2.1$. Survey geometry and statistical uncertainties are quantified using 1,000 \texttt{EZmock} realizations. We find that the high-redshift QSO sample implies a peculiar velocity of $v = 357.95_{-48.47}^{+55.05}\,\mathrm{km\,s^{-1}}$, in excellent agreement with the CMB-inferred value of $369.82 \pm 0.11\,\mathrm{km\,s^{-1}}$. By contrast, a complementary number-count analysis yields a significantly enhanced dipole amplitude, which we attribute to leakage of large-scale power and to incompleteness within the DESI DR1 footprint. These results indicate that the redshift dipole provides a cleaner and more reliable probe of the kinematic rest frame, offering strong support for the standard kinematic interpretation at high redshift and helping to resolve the apparent dipole anomaly.

We investigate the Saha ionization equilibrium in the exterior Schwarzschild spacetime. Starting from the mass-shell condition for a massive particle, we derive the conserved energy associated with the timelike Killing symmetry and obtain its nonrelativistic limit in terms of the Schwarzschild lapse function. This energy is then incorporated into the Maxwell--Boltzmann distribution to construct the ionization balance as seen by an asymptotic observer. We show that the gravitational field modifies the Saha relation through the redshift of both the particle energies and the thermodynamic variables. By imposing the Tolman--Ehrenfest and Klein equilibrium conditions, the formulation expressed entirely in terms of locally measured quantities reduces to the standard flat-spacetime Saha equation. We further analyze the gravitational redshift of the ionization energy, the relative departure from the flat-spacetime ionization ratio, and the corresponding shift of the ionization fraction as a function of the asymptotic temperature. We also present the relativistic classical counterpart based on the Maxwell--Jüttner distribution and show explicitly that its leading correction is negligible in the temperature range where neutral hydrogen is appreciably abundant. These results provide a consistent description of ionization equilibrium in a static gravitational field and clarify the distinction between gravitational redshift effects and intrinsic modifications of local atomic physics.

The Auger Radio Infill SKALA Extension (ARISE) at the Pierre Auger Observatory in Argentina was deployed in 2025 and measures cosmic-ray air showers in the energy region of the Galactic-to-extragalactic transition. ARISE is comprised of 18 SKALA-2 antennas featuring two polarization channels each, deployed within $100\,$m of a surface detector station in the enhancement area of the Pierre Auger Observatory. This area of the surface array features a denser spacing of $433\,$m between surface stations, each equipped with underground muon detectors. One of these surface detector stations provides a trigger for simultaneous readout of all ARISE antenna channels. The wide frequency range of ARISE, from $50$ to $350\,$MHz, includes the sub-band of optimum signal-to-noise ratio for air-shower radio emission against the Galactic radio background. In combination with the dense antenna spacing, this enables a relatively low detection threshold, and ARISE aims at demonstrating full detection efficiency for near-vertical air showers above $100\,$ PeV. As an advantage over the current radio detectors at Auger, which are more efficient for inclined air showers, this would enable low systematic uncertainties for physics analysis combining ARISE radio measurements with coincident measurements of the underground muon detectors in the same area. In this presentation, we will provide an overview over the ARISE instrumentation operating at the Pierre Auger Observatory and will outline the science goals.

Polluted white dwarfs provide a unique window into the composition of exoplanetary material, but interpreting their surface abundances requires a quantitative understanding of the mixing processes in their envelopes. Accretion of metal-rich debris onto hydrogen-rich white dwarfs drives thermohaline (fingering) convection in the underlying radiative zone. Previous studies have modeled this as enhanced diffusive transport, often inferring mass accretion rates, $\dot{M}_{\rm acc}$, that exceed constraints from X-ray observations. Here we develop a time-dependent model that treats thermohaline mixing as a propagating front whose evolution is coupled self-consistently to the surface abundance of heavy elements. We perform hydrodynamical simulations which demonstrate that thermohaline mixing drives the composition gradient towards marginal stability. Using this condition, we derive analytic solutions in shallow and deep stratification regimes, finding that the mixed layer depth, $h$, and surface abundance, $X_{\rm surf}$, both scale as $t^{1/2}$ at early times, transitioning to $h \propto t^{4/27}$ and $X_{\rm surf} \propto t^{10/27}$ at later times. The mixed layer reaches depths of only $\sim 100$ km over $10^5$ yr and, without gravitational settling, never reaches a steady state. Including settling leads to an equilibrium surface abundance scaling as $X_{\rm surf, eq} \propto \dot{M}_{\rm acc}^{30/43}$. Applied to G 29--38, the model matches the observed heavy-element abundance for $\dot{M}_{\rm acc} \sim 2\times 10^9$--$4\times 10^{9}~\mathrm{g~s^{-1}}$, in better agreement with X-ray constraints than prior estimates incorporating thermohaline mixing. We also present a general scaling relation for inferring accretion rates directly from observed surface abundances and stellar properties, giving a practical prescription for other polluted white dwarfs.

We present a map of the cosmic microwave background (CMB) lensing potential reconstructed from observations taken during the 2019 and 2020 seasons with the third-generation camera on the South Pole Telescope (SPT), covering the $1500\,{\rm deg}^{2}$ SPT-3G Main field, referred to as the SPT-3G D1 dataset. From the multi-frequency temperature and polarization data, we reconstruct the CMB lensing field using a quadratic estimator that jointly accounts for the $T$, $E$, and $B$ fields and their covariance. The resulting lensing map is dominated by polarization information for $L \lesssim 600$ and provides the highest signal-to-noise measurement per mode reported to date. With nuisance parameters fixed to their best-fit values, we measure a lensing amplitude consistent with unity at $2\%$ precision relative to the $Λ$CDM model that best fits the combined Planck, ACT DR6, and SPT-3G D1 $TT/TE/EE$ likelihoods (${\rm CMB}_{\rm SPA}$). We further measure the structure-growth parameter $σ_{8}Ω_{\rm m}^{0.25}$ to be $0.6046\pm0.0096$ from the SPT-3G D1 lensing spectrum alone and $0.6020\pm0.0084$ when combined with ACT DR6 and Planck PR4 CMB lensing. By further combining this with ${\rm CMB}_{\rm SPA}$ and the latest DESI DR2 BAO data, we obtain $\sum m_ν < 0.072\,\mathrm{eV}$ (95% C.L.) when allowing the neutrino mass to vary within $Λ$CDM. Compared with previous work, the better agreement of our measurement with DESI DR2 BAO yields both this relaxed upper bound and reduced ($\mathord{\sim}2σ$) preferences for nonzero spatial curvature and for deviations of $(w_0,w_a)$ from the $Λ$CDM expectation. When we combine CMB lensing with the DES Y3 3$\times$2pt analysis, we obtain $S_{8}=0.811\pm0.011$, corresponding to a $1.4\%$ constraint on the late-time clustering amplitude. This precision is competitive with that obtained from the primary CMB within $Λ$CDM.

General relativity is a century-old subject. Yet modern explorations through generalized symmetries, scattering amplitudes, and effective field theory have raised open problems, motivating a reassessment of conventional views on gravitation, spacetime, and spin. First, do generalized symmetries exist in dynamical gravity as a low-energy EFT? Second, is there a field-theoretic explanation for the tree-level double copy relationship between general relativity and Yang-Mills theory? Third, what are the exact equations of motion or Lagrangians of four-dimensional spinning black holes in external fields, in point-particle effective theory? In this dissertation, three different perspectives on gravity are developed to shed light on each of these puzzles. In Part I, we view gravity as a gauge theory of Lorentz group to establish a one-form symmetry of dynamical gravity. In Part II, we investigate how far gravity can be viewed as a gauge theory of diffeomorphisms, in connection with color-kinematics duality and double copy. In Part III, we view four-dimensional gravity as a nonlinear interaction between self-dual and anti-self-dual parts. We apply this view to the derivation of four-dimensional spinning black hole solutions as well as their dynamics in point-particle effective theory. First, we derive a new self-dual black hole metric from classical double copy and show that the Kerr metric represents a pair of self-dual and anti-self-dual Taub-NUT solutions, elevating the Newman-Janis algorithm to a rigorous derivation. Second, we propose a dynamical probe counterpart of Newman-Janis algorithm. We give a Lagrangian derivation of spinning black hole Compton amplitudes that exhibit correct factorizations and are free of spurious poles for all helicity configurations while developing a chiral formalism that manifests and maximally utilizes the simplicity of the self-dual sector.

In this paper we consider some general aspects of Euclidean conformal field theories on curved spaces of dimension $D\ge 3$. We first look at the OPE of scalar primary fields on conformally flat spaces. Extending the results of \cite{Konechny:2026bqg}, we give a general construction of the descendants' contributions to the OPE in the scalar channel. We then discuss CFTs on non-conformally flat spaces in the ambient space formalism. We investigate the short-distance behaviour of three-point functions on such spaces using the general ansatz proposed by Parisini, Skenderis, and Withers \cite{Parisini:2022wkb, Parisini:2023nbd}. We find that some additional corrections need to be added to the ansatz to ensure the existence of a local covariant OPE.

We introduce a new set of boundary conditions for three-dimensional Einstein gravity with negative cosmological constant. The canonical generators plainly realize the semidirect sum of Virasoro and $u(1)$ Kac-Moody algebras in its standard form, without the need of additional redefinitions of the global charges. We show that requiring Euclidean BTZ and thermal AdS$_3$ to be diffeomorphic precisely induces the warped modular $S$-transformation of the chemical potentials. The corresponding warped Cardy formula then exactly reproduces the Bekenstein-Hawking entropy, where the ground state is identified as Euclidean AdS$_3$. An explicit comparison with the boundary conditions of Brown-Henneaux and Compere-Song-Strominger is also addressed.

Convective turbulence in planets and stars is often driven by internal heating. This forcing mechanism has also been proposed as a means of accessing the diffusion-free scalings of the geostrophic turbulence (GT) regime at modest forcing. We test this with the asymptotically reduced quasi-geostrophic model, which is formally valid in the limit of vanishing Ekman number, $Ek \rightarrow 0$, and retains the Prandtl number as an independent parameter. We find no such shortcut: the Nusselt and Reynolds numbers are no closer to their diffusion-free predictions than in the boundary-heated case, and at $Pr = 7$ they are further from them; the predicted $Pr^{-1/2}$ collapse fails; and the prefactor depends on the form of the heating. Our no-slip/stress-free cases track the radiatively driven simulations of Hadjerci et al. (2024) case by case, yet a $25\%$ variation in $Nu$ persists between sweeps that share the same reduced Rayleigh and Prandtl numbers but differ in Ekman number. Those data span only the narrow range of forcing over which the compensated Nusselt number is stationary; across the wider range accessible to the reduced model it rises to a maximum and then falls. We argue that bulk transport scalings are incomplete diagnostics of GT, whereas the saturation of the interior mean temperature gradient and of the vertical velocity kurtosis remain reliable indicators.

We present a new family of exact solutions representing accelerating, rotating, point particle and black hole solutions in three-dimensional Einstein gravity. We investigate their geometric properties and the global embedding in three dimensional anti-de Sitter space. Our results extend the catalogue of exact solutions in three-dimensional Einstein gravity and provide a useful setting for the study of black hole thermodynamics, asymptotic symmetries, and holography.

Many modified-gravity frameworks employ non-Riemannian connection degrees of freedom, including torsion and nonmetricity. In Einstein-Cartan-type theories, torsion is associated with spin density, while more general metric-affine frameworks can be investigated through phenomenological searches for in-matter torsion and nonmetricity backgrounds. This work applies an effective field theory approach to characterize general couplings of electron and neutron operators to spacetime torsion and nonmetricity up to mass dimension six, predicting novel neutron-polarization signatures in the presence of an electron background. Neutron spin-rotation data from a polarized-electron ensemble inside a compensated ferrimagnet are used to constrain for the first time axially symmetric, direction-dependent in-matter torsion and nonmetricity combinations.

Compactified spectral discretisations may yield stable negative-imaginary-axis (NIA) eigenvalue ladders, but finite-matrix convergence does not establish quasinormal poles. For axial Schwarzschild perturbations, ingoing--outgoing factorisation leaves an unwanted horizon solution behaving as $t^{4α}$ at $Ω=-iα$, and a $C^\infty$-flat unwanted infinity solution. Thus endpoint $C^k$ regularity is nonselective for $4α>k$, so the $C^2$ continuum problem cannot have a discrete NIA spectrum over $α\simeq15$--32. Exact Chebyshev-grid formulas give roots-grid maximum radius $O(n^{2p})$ for $x\sim C(1-y)^{-p}$, explaining C1, $x=2/(1-y)$, versus C2, $x=4/(1-y)^2$. Arbitrary-precision pencils nevertheless reveal a reproducible 68-point C1 ladder, while C2 reorganises it. Both physical lateral Jost determinants remain stably nonzero at every C1 frequency. A 0.05-spaced on-cut scan finds no zero, and refined argument-principle calculations give zero winding in both continuation strips. This rejects all 68 candidates, although the mesh and strip evidence is not interval-certified. Same-damping controls recover Schwarzschild QNMs $n=60,100,130$, with $|\widehat{\mathcal D}|=10^{-48}$--$10^{-56}$. The ladder has surface-gravity quarter spacing, follows the parameter-free Casals--Ottewill branch-cut-strength phase, and pairs with damping projections of QNMs $n=62,\ldots,129$. At its first member, a finite-frequency calculation finds a branch-strength zero at $α_q=15.07832396512359$, between the asymptotic prediction and the C1 root, supporting, but not proving, sequence-wide cut-phase locking. Thus accurate finite-pencil eigenvalues can fail the invariant Jost/Evans pole criterion. Whether representation-dependent nodes with Keldysh weights converge collectively to the Schwarzschild cut response and Price tail remains open.

Star formation takes place in varied environments, from isolated clumps to massive molecular cloud complexes. However, whether the environment in which a star forms has any effect on the formation process remains a matter of debate. The molecular outflows, launched during the formation of protostars present a more easily accessible way to study star formation in different environments. The DR21 ridge, in the Cygnus-X high-mass star-forming complex, hosts a high number of massive dense cores and embedded protostars with outflows. We aim to identify molecular outflows associated with dense molecular cores along the DR21 ridge, and investigate whether the extended environment impacts the formation process of stars within it. We identified molecular outflows along the DR21 ridge using HCO+ J=1-0, H13CO+ J=1-0, and SiO J=2-1 observations obtained with the IRAM 30m telescope and NOEMA as part of the CASCADE program. We calculated outflow properties and performed statistical comparisons between the DR21 ridge sources and a literature sample of low- to high-mass outflow sources. Based on the morphology of HCO+, H13CO+ and SiO, we identify molecular outflows in 14 out of 34 dense cores (41%) along the DR21 ridge. Despite the high density of star formation in DR21, the resulting outflow properties are found to be in good agreement with the established correlations between outflow and source properties. Little variation is seen in the outflow properties of sources along the ridge, with the exception of sources located at the intersection of the DR21 ridge with large-scale (~1 pc) accretion filaments. These sources are found to drive the most powerful outflows. Overall, our results indicate that protostellar outflow properties, even when driven by sources forming in an extreme and clustered region, such as the DR21 ridge, remain largely unaffected.

Models where an axion-like inflaton is coupled to a $U(1)$ gauge field are theoretically well motivated and can display a rich phenomenology. The regime in which the quanta of the gauge field strongly backreact on the rolling inflaton has been studied for well more than a decade, and yet we cannot say that it is fully understood. In this paper we present an analytical study of the onset of the strong backreaction regime. Our formalism relies on a Laplace transform to convert a complicated integro-differential equation into the search of the poles of an analytic function. We confirm the existence, previously observed using a completely different formalism, of a stable region of strong backreaction. Our work provides, for the first time, analytical formulae that allow to study the evolution of the system as it transitions from the weak to the strong backreaction regime.

Context. Phosphorus (P) is an essential element for life on Earth and a potential tracer of planet formation history. However, there has been no detection of P-bearing molecules in protoplanetary discs so far. Herbig Ae/Be stars constantly accrete matter from their pro- toplanetary disc, which alters the composition of the stellar photosphere due to their shallow convective, or fully radiative, envelope. The altered surface composition reflects the composition of the accreting matter, and thus that of the inner protoplanetary disc. This accretion contamination of stellar photosphere can persist after accretion has ended in young A and B-type stars (age < 50 Myr). Aims. We aim to quantify the fraction of P locked in dust (the refractory fraction of P) compared to gas in the inner protoplanetary disc around Herbig Ae/Be stars. Methods. We measure the stellar parameters and abundance of 5 Herbig Ae/Be stars using optical and UV spectra, to compare their P and Fe abundances. We also used a 20 Myrs old main sequence B-type star, which has P and Fe abundance estimated from optical spectrum. Fe is assumed to be completely locked in refractory reservoirs in the inner disc. A parameterised relationship between the stellar P and Fe abundance gives the fraction of P locked in refractory reservoirs. Results. We find the refractory fraction of P in the inner protoplanetary disc to be > 96 % within 95th percentile of the posterior distribution. Conclusions. Consistent with a previous finding in the HD 100546 system, we conclude most of the P in the inner protoplanetary disc is locked in dust, likely in refractory minerals like schreibersite or apatite. Our result, combined with the low cosmic abundance of P, is also consistent with the lack of infrared and mm-wavelength observations of P-bearing molecules in protoplanetary discs to date.

This work investigates the original Penrose process (PP), as well as black hole (BH) thermodynamics, within the framework of conformal Weyl gravity. The theory is characterized by the dimensionful constants $γ$, which encodes the asymptotic rotational curvature of galactic rotation curves in an otherwise asymptotically flat spacetime, and $κ$, which is associated with the cosmological background constant $Λ$. We determine the locations of the event horizon and the extreme configurations for rotating BHs in this theory, and we provide both perturbative and exact expressions for the event horizon radius. The geodesic equations are restricted to the equatorial plane, and the corresponding dynamics, including energy extraction processes, are studied exclusively in this plane. As the principal results, we examine the feasibility and efficiency of the original PP, analyze BH deceleration mechanisms, and test the validity of the four laws of BH thermodynamics in the context of conformal Weyl gravity.

Context. Evolutionary models translate the observable luminosity, temperature, and colours of giant planets and brown dwarfs into mass and age. Generating their cooling tracks normally requires integrating the internal energy over time with an ordinary differential equation (ODE) solver coupled to pre-computed atmospheric grids, which becomes numerically stiff at sharp transitions such as cloud condensation and the onset of electron degeneracy, and is fragile inside Bayesian retrievals. Aims. We aim to generate continuous cooling tracks and photometric light curves directly from discrete atmospheric grids, without an ODE solver. Methods. We mapped the grids into a logarithmic thermodynamic space and extracted localised surrogate models with Gaussian-weighted regressions at fixed planetary parameters. We fitted the entropy and cooling rate against the internal temperature using bounded piecewise softplus functions to capture structural and cooling-rate transitions; the radius was fitted on the same temperature axis; and band photometry was represented with fixed-knot cubic B-splines. The age followed from numerical integration of these analytic functions, and uncertainties were propagated from the residual scatter of each fit. Results. The surrogate, CoolTrack, reproduces the transition into electron degeneracy and the L-to-T spectral-type transition in the colour-magnitude diagram, converges on Solar System benchmarks, and evaluates a full evolutionary track in milliseconds on a standard desktop CPU. Conclusions. By removing the forward-modelling bottleneck, CoolTrack is suitable for direct use in Bayesian retrieval pipelines, where the age, mass, and formation entropy of a planet can be inferred jointly with its atmospheric properties.

We study the holographic duality between free vector models and Higher-Spin Gravity in 4-dimensional de Sitter space. On both the bulk and boundary sides, we introduce new reality conditions, which allow us to include odd spins in the bulk, and to extend the duality from type-A to type-B (i.e. from boundary scalars to spinors). The new reality conditions are closely related to a higher-spin-symmetric Hilbert-space norm for the single-particle (super)multiplet in de Sitter space. We construct two alternative viewpoints on the type-A and type-B theories. In one view, the two co-exist in "parallel universes", specifically in even vs. odd antipodal identifications of de Sitter space. In the other view, type-A and type-B are Legendre-transformed descriptions of the same twistor-space theory in Euclidean AdS (this involves the observation that the higher-spin partition function is Legendre-dual to itself). In this way, higher-spin holography reconciles the two-boundary nature of de Sitter space with the one-boundary nature of Euclidean AdS. The supersymmetric theory that unifies type-A and type-B with bulk fermions fails to be consistent under the appropriate reality conditions.

We present a chemo-kinematical, structural, and photometric analysis of the old open cluster Berkeley 36 using Gaia DR3 astrometry and photometry together with high-resolution spectroscopy from the Gaia-ESO Survey DR5.1. Applying a Gaussian Mixture Model to Gaia astrometry, we identify 946 high-probability cluster members. We derive a core radius of 2.63 +/- 0.21 arcmin and a tidal radius of 14.84 +/- 0.47 arcmin, indicating a moderately concentrated and dynamically relaxed system. By fixing the cluster metallicity to the spectroscopic value of [Fe/H] = -0.19 +/- 0.02 dex and adopting an independently determined geometric distance of 4377 +/- 510 pc, we minimize the classical age-reddening-metallicity degeneracy and derive a robust isochrone age of 6.8 +/- 0.5 Gyr. Independent Ba-based chemical clocks yield a mean age of 7.75 +/- 1.94 Gyr, supporting the isochrone solution. The cluster exhibits a high main-sequence binary fraction of 48.0 +/- 1.7% and hosts 83 blue straggler star candidates with an extended spatial distribution, contrary to classical mass segregation. Orbit integration shows that Berkeley 36 follows a nearly circular orbit in the outer Galactic disc at R_GC = 11.42 +/- 0.44 kpc. Accounting for the Galactic warp and disc flare increases the cluster's maximum vertical excursion by 86% and the local disc scale height by 17%, respectively. Comparison with its chemically inferred birth radius at R_b = 6.71 +/- 0.66 kpc indicates an outward radial migration of approximately 5 kpc, predominantly driven by churning. These results establish Berkeley 36 as a benchmark for investigating radial migration, secular evolution, and the dynamical history of old Galactic open clusters.

We introduce \emph{latent geometry} in BFSS/BMN models. Before an emergent geometry evaporates at the geometric transition, large-$d$ Gaussianization encodes its information in the exceptional $N=2$ sector selected by the baby fuzzy sphere, a single active spin-$1/2$ Pauli block. Dimensional reduction, finite-$N$ Gaussianization and exact Molien--Weyl projection transport this encoding to mass-deformed BFSS$_2$. At $N=2$, the same stable BFSS$_2$ oscillator admits inequivalent unitary $\mathbf{H}^2_θ=\mathbf{EAdS}^2_θ$ and $\mathbf{dS}^2_θ$ decodings, realizing spacetime transmutation and the emergence of Lorentzian time.

The No-Scale gravity is a compelling framework to describe particle physics, gravity and cosmology, in which all mass scales are an illusion given by the value of a scalar field $φ$. This theory, however, falls under the umbrella of more general scalar-tensor theories, which propagate different modes depending on the scalar field, and faces the extensive debate regarding the equivalence between its Jordan and Einstein frame descriptions. In this work we advocate that by excluding the singular point in the transformation between the two frames (e.g., $φ=0$) we can have the classical equivalence between them. To show the merit of removing this singular point, we argue the Jordan frame makes the symmetries of the model manifest, which creates a suitable playground for the particle-physics model building which we illustrate by showing the emergence of discrete symmetries which leads to a high-quality axion and also naturally incorporate the seesaw mechanism.

On a compact connected section ${\cal S}$ of a supersymmetric $M$-horizon the Killing-spinor bilinears give a pointwise identity relating the warp factor $Δ$, the rotation one-form $h$ and the two spinor norms, with nothing assumed about the norm of the Killing spinor. We derive three consequences of that unreduced identity. First, a single-point rigidity theorem: if $Δ$ and $h$ vanish at one point of the section, then the flux vanishes identically, ${\cal S}$ is Ricci-flat and the horizon is $\mathbb{R}^{1,1}\times{\cal S}$. A single point replaces the usual global spinorial hypothesis. Second, the ${\rm Spin}(7)$ decomposition of the flux fixes $h$ algebraically and exhibits the invariant flux content of the scalar square $Δ=4Φ^2$ known in an adapted gauge, $Δ=\frac{1}{108}\|w_{\bf 7}\pmσ({\cal Y}_{\bf 7})\|^2$. Only the two ${\bf 7}$-summands $w_{\bf 7}$, ${\cal Y}_{\bf 7}$ reach the warp factor, and the square is degenerate rather than definite: it vanishes on the linear subspace $w_{\bf 7}=\mpσ({\cal Y}_{\bf 7})$ rather than at the origin, so positivity of $Δ$ yields no case list. Third, the two combine into a pointwise budget: the single constant of supersymmetry is shared between the deviation from staticity and the ${\rm Spin}(7)$ mismatch of the flux, each bounded by that constant. The same identities characterise the constancy hypothesis, equivalent to $V=-fh$ for the bilinear one-form $V$, which fails on the static branch of known warped $AdS_2$ solutions; they fix a weighted integral of the warp factor; and they reduce the Komar angular momentum of the horizon to a positive bilinear integral. Two no-go statements, for hidden symmetries built from the Killing spinor and for a second isometry from its bilinears, are stated with their hypotheses.

The internal structure of galaxies encodes the complex baryon cycle driven by gas accretion, star formation, and feedback, together with secular evolution and environmentally driven processes such as mergers and tidal interactions. We present a population-level census of massive nearby galaxies ($\log(M_\star/M_\odot) > 10$) by comparing Hyper Suprime-Cam Subaru Strategic Program observations with matched mock images from IllustrisTNG, EAGLE, and SIMBA. Using a consistent, like-for-like imaging pipeline, we construct structural abundance functions (SAFs) for key morphological parameters, revealing a structural abundance crisis. Across Sérsic index, concentration, size, and ellipticity, all simulations exhibit large, systematic discrepancies ($>5σ$; RMSE $\sim 0.2$--$1.8$\,dex), typically corresponding to abundance differences of factors of several. While individual simulations display diverse failures---underproducing or overproducing compact spheroids, extended or round galaxies ---all underproduce highly flattened disks. Although TNG shows the closest agreement and SIMBA the largest offsets, this shared failure indicates that current models---despite matching global demographics such as the stellar mass function---do not uniquely constrain internal galaxy structure. Our results demonstrate that agreement in integrated observables can mask fundamental shortcomings in the modelling of mass and angular momentum redistribution. We therefore establish SAFs as a stringent, multidimensional, and observationally accessible benchmark for testing and calibrating next-generation galaxy formation models in the era of upcoming deep, wide-field surveys.

The cross section for galaxy-galaxy strong lensing (GGSL) events in galaxy clusters has repeatedly been found to be higher in observations than in cosmological simulations. We revisit this discrepancy using updated simulation methodology and investigate the dependence of the GGSL probability, $P_{\rm GGSL}$, on host-cluster lensing properties, baryonic physics, and correlated and uncorrelated line-of-sight structure. We find that correlated material within $\sim 35$ cMpc of the cluster along the line of sight enhances $P_{\rm GGSL}$ by a few percent for typical systems and by up to $\sim15\%$ for the most efficient lenses. At fixed cluster mass, dark-matter-only simulations yield GGSL probabilities up to an order of magnitude lower than hydrodynamical simulations. We also find a strong dependence on the host-cluster Einstein radius, with an approximate scaling $P_{\rm GGSL} \propto θ_{\rm E}^{2}$. Matching simulated and observed clusters in both mass and Einstein radius seems to reduce the discrepancy relative to previous comparisons. However, our analysis does not clearly resolve the GGSL discrepancy, as the inferred tension depends strongly on the field-of-view definition: square fields are approximately consistent with simulations, while cluster member-bounded fields yield observed probabilities a factor of $\sim 2-3$ higher. Until observations and simulations share a matched selection function and matched measurement methodology, the residual tension cannot be cleanly attributed to either astrophysics or cosmology.

CO isotopologue emission is widely used to infer gas masses and volatile carbon abundances in protoplanetary disks, but converting line emission into a CO column depends on optical depth, temperature structure, linewidth, and isotope ratios. Inferring CO/H$_2$ additionally requires an independent constraint on the local hydrogen column. We use high-resolution $^{13}$C$^{18}$O $2$-$1$ observations of HD 163296 to derive a spatially localized empirical constraint on the CO column at the resolved CO snowline edge. We focus on the 70-75 au annulus, on the inner, high-column side of the observed profile steepening near 75 au. Using RADEX slab calculations conditioned on a two-dimensional temperature structure, we infer an effective beam-averaged CO column from the absolute integrated intensity. Across representative temperatures, isotope-ratio pairs, and effective local linewidths of 0.30 and 0.50 km s$^{-1}$, we find $N_{\rm CO}^{\rm beam}=(1.6-2.4)\times10^{20}$ cm$^{-2}$ and $^{13}$C$^{18}$O line-center optical depths $τ=0.39-0.97$. Thus, even this rare isotopologue is not safely optically thin at the snowline edge. Adopting $N_{\rm H2}=2.5\times10^{24}$ cm$^{-2}$ from a published parametric gas surface-density profile gives the conditional abundance ${\rm CO/H_2}=(6.4-9.5)\times10^{-5}$. A beam-forward radial-profile analysis gives consistent columns, and a physical disk model with a near-canonical warm-layer CO abundance supplies a comparable CO column. The measurement is consistent with the higher C$^{17}$O-based MAPS estimate. For the adopted hydrogen column, the inferred CO/H$_2$ ratio is consistent with a near-canonical abundance on the warm side of the snowline.

Helicity in gravity is a multifaceted concept, and several inequivalent definitions exist in the literature. In this work, we reduce the topological Pontryagin and Nieh-Yan terms to a constant time spacelike hypersurface. Remarkably, upon applying the SVT decomposition at the linearized level, we obtain four distinct helicity densities. The helicity density arising from the Nieh-Yan term is termed the spin-1 and spin-2 gravitomagnetic helicity density, depending on whether it originates from vector or tensor modes. Meanwhile, the helicity density arising from the Pontryagin term is termed the spin-1 and spin-2 gravito-current helicity density, according to the corresponding mode contributions. We study the mode and multipole expansions of these helicity functionals and apply them to leading order Newtonian two-body systems, weak field boosted Kerr, a locally defined slowly varying gyratonic pp-wave model, and a linearized gravitational Hopfion.

We study the algebraic and differential structure of the Riemann curvature tensor of the higher-dimensional Kerr-NUT-(A)dS spaces, motivated by the eventual goal of finding an IDEAL (Intrinsic, Deductive, Explicit and ALgorithmic) characterization of this family of metrics. The special geometry of these spaces is governed by the principal tensor $h_{ab}$, a non-degenerate closed conformal Killing-Yano $2$-form, whose existence singles out the Kerr-NUT-(A)dS family; we therefore focus on the algebraic relationship between the Riemann curvature $R_{abcd}$ and $h_{ab}$. In our investigations we encountered an obstruction, which results in a no-go theorem: no non-trivial $2$-form, including $h_{ab}$ itself, can be constructed covariantly from the undifferentiated Riemann tensor alone. Despite that, we do characterize the family of Riemann-symmetric tensors that could be the curvature of a Kerr-NUT-(A)dS metric by an algebraic and a differential condition, stemming from the integrability of the defining equation of $h_{ab}$ and the second Bianchi identity. Our calculations apply in all higher dimensions, which becomes feasible by a judicious application of representation theoretic techniques related to a semi-direct product group $U(1)^n\rtimes S_n$ that stabilizes $h_{ab}$.

We investigate the equilibrium abundance ratio of the molecular hydrogen ion \(\mathrm{H}_2^+\) and the negative hydrogen ion \(\mathrm{H}^-\) in stellar atmospheres using compact Saha-type equilibrium expressions and layer-by-layer partial pressures from MARCS model atmospheres. The analysis distinguishes the temperature-dependent coefficient ratio \(K_{\mathrm{H}_2^+}(T)/K_{\mathrm{H}^-}(T)\) from the full abundance ratio, which also depends on the local ionisation factor \(N_{\mathrm{H}^+}/N_e\). The internal partition function \(Z_{\mathrm{H}_2^+}(T)\) is included in the \(\mathrm{H}_2^+\) equilibrium coefficient. We processed \(51{,}994\) MARCS models, corresponding to \(2{,}911{,}664\) atmospheric layers, and computed \(N(\mathrm{H}_2^+)/N(\mathrm{H}^-)\) directly from the tabulated equilibrium partial pressures, constructing the first systematic map of this ratio across the MARCS grid. \(\mathrm{H}_2^+\) exceeds \(\mathrm{H}^-\) in \(827{,}350\) layers, corresponding to \(F=0.284\), or \(28.4\%\) of all analysed layers. Although \(\mathrm{H}^-\) remains dominant in the global logarithmic mean, with \(\langle \log_{10}[N(\mathrm{H}_2^+)/N(\mathrm{H}^-)] \rangle=-4.229\), \(\mathrm{H}_2^+\) becomes comparable to or more abundant than \(\mathrm{H}^-\) in a substantial subset of layers. Its relative significance increases toward higher \(T_{\mathrm{eff}}\), lower \([\mathrm{Fe}/\mathrm{H}]\), and deeper layers. The balance is therefore controlled by the combined local thermodynamic and ionisation structure, not by temperature alone. These ratios are equilibrium abundance diagnostics and do not imply opacity dominance; assessing opacity requires wavelength-dependent cross-sections and radiative-transfer calculations.

We derive a $2d$ effective action for semi-classical AdS$_3$ gravity with an EOW brane of arbitrary tension by solving the radial Hamiltonian flow in a derivative expansion. Interpreting the radial flow as an RG flow, the effective theory is identified with a $T\bar T$-like deformed CFT. This leads us to propose that the holographic dual for semi-classical AdS$_3$ gravity with Neumann or conformal boundary conditions is obtained by setting the $T\bar T$-like deformed CFT free. We verify our proposal explicitly for saddles corresponding to $(A)dS_2$ branes in empty AdS$_3$. We discuss three useful ways to decompose the effective brane theory into a matter sector ($T\bar T$-deformed, $T\bar T$-like deformed, and undeformed CFT, respectively) and a corresponding braneworld gravity sector. In particular, the split into $T\bar T$-deformed CFT coupled to $T\bar T$-like deformed Liouville gravity directly extends the Liouville description of the integrated Weyl anomaly into the bulk. The effective action is then used to perform an island-rule calculation for a non-asymptotic brane in an AdS/bCFT set-up, finding exact agreement with the Ryu-Takayanagi result. This extends previous holographic checks on the island rule to non-asymptotic regimes of application, as well as provides a Wald entropy interpretation for $T\bar T$ entanglement. Finally, we relate our effective theory and its higher derivative corrections to AdS$_3$ gravity with a fluctuating radial cutoff by explicit calculation of the on-shell action.

(Abbreviated) The interpretation of high-precision astrometry for intrinsically variable stars remains challenging, particularly for unresolved binary systems containing asymptotic giant branch (AGB) stars. In such systems, large-amplitude pulsations and evolving convective surface structures induce time-dependent photocentre displacements that perturb the observed orbital motion. At the same time, Gaia DR4 epoch astrometry offers the prospect of deriving accurate orbital solutions and parallaxes for nearby unresolved AGB binaries. Building upon the variability-induced mover (VIM) framework, we extend the astrometric model for unresolved evolved binaries by combining Keplerian photocentre motion, pulsation-induced flux-dependent photocentre shifts, and convection-induced photocentre motion. In the forward simulations, convection is represented either by stochastic photocentre displacements drawn from an exponential correlation function or by photocentre time series extracted from 3D radiation-hydrodynamic simulations. We then test a retrieval framework that fits the orbital and VIM signal while incorporating a red-noise covariance matrix to account for correlated astrometric residuals produced by convection. We show that Gaia epoch astrometry can recover reliable orbital and astrometric parameters for unresolved AGB binaries despite strong pulsation- and convection-induced photocentre variability. Pulsation-induced variability produces a coherent VIM signal that can be modeled jointly with the Keplerian photocentre orbit, while convection-induced photocentre motion behaves primarily as temporally correlated astrometric noise. Retrievals that ignore this correlated component lead to biased proper motions and parallaxes, whereas the inclusion of a physically motivated red-noise covariance model enables accurate recovery of the underlying orbital solution and astrometric parameters.

Interstellar grains play key roles in star and planet formation, including the coupling of the gas to the magnetic field during the protostellar collapse. These roles depend on the local grain size distribution, which requires a multifluid treatment of charged dust. We aim to understand the fundamental physics of the dynamics of a dust distribution in interaction with the gas and the magnetic field. In particular, the purpose is to characterize the (de)coupling conditions of these different components. We provide a multifluid model of charged dust which accounts for the inertia of the grains. A chemical network is used to simulate the charge equilibrium in collapsing protostellar cores. We compute the Alfven modes and the magnetosonic modes to understand the coupling regimes between the gas, the dust fluids, and the magnetic field. We also analyze and compare to the predictions of existing models, that are the neutral dust multifluid and the standard non-ideal magnetohydrodynamics. The charged multifluid model agrees with non-ideal magnetohydrodynamics on the larger scales of a collapsing dense core and the forming disk, while we successfully extend to new regimes where the inertia of dust grains matters. We found that high charge-to-mass dust grains carry the propagation of magnetohydrodynamical waves in protostellar envelopes. We provide analytical expressions of the speed of these waves depending on the dust distribution. The magnetocompressive perturbations lead to local dust-to-gas ratio variations at au scales. A theoretical understanding of the dynamics of a charged dust distribution is provided in the linear regime. The closed set of magnetohydrodynamics equations can be implemented in numerical codes to explore nonlinear effects during the protostellar collapse such as turbulence, angular momentum transport and magnetic dust clumping.

Our work clarifies the origin of enhanced symmetry of near horizon geometries. We relate this property to an existence of specific foliation by non-expanding horizons. The existence of this foliation can be shown in any spacetime satisfying null convergence condition. Our proof is geometric and based on analyzing null hypersurfaces in near horizon geometry spacetimes.

Large-scale, high-resolution spectroscopic surveys map detailed chemical abundance patterns for millions of stars. However, libraries of stellar evolution models and isochrones still rely on a simplified description of chemical abundances, generally assuming either solar-scaled compositions or a constant enrichment for all $α$-elements. Moreover, the definition of $α$-enrichment is survey-dependent and is not necessarily the most relevant quantity for stellar structure and evolution. In the era of precision stellar astrophysics, stellar models need to better account for the wealth of chemical information provided by spectroscopic surveys. We develop a perturbative method to compute stellar evolution tracks for stars with arbitrary patterns of $α$-elements. We quantify the response of stellar evolutionary tracks to variations of individual $α$-elements through polynomial expansions, which can be linearly combined to produce synthetic tracks for a given abundance pattern. We also introduce the evolutionary $α$-enhancement, [$α$/Fe]$_{\rm ev}$, a constant enhancement for all $α$-elements that reproduces the impact of an observed abundance pattern on stellar models. We validate both methods using stars with detailed APOGEE abundances and quantify the differences between spectroscopic [$α$/Fe] and [$α$/Fe]$_{\rm ev}$ for different surveys. We identify a minimal set of chemical elements required for accurate stellar models and present ALCHEMY, a simple and fast tool to compute [$α$/Fe]$_{\rm ev}$ for general $α$-element abundance patterns.

We study the existence of gravitational radiation at infinity for pure-radiation Robinson-Trautman metrics with one spacelike Killing vector and a cosmological constant $Λ$ of arbitrary sign. These metrics describe "photon rockets" with point, string, and sheet sources moving through spacetime while emitting null radiation. For $Λ\neq 0$, we use criteria for the existence of gravitational radiation based on the asymptotic super-Poynting vector. For point sources, we extend to $Λ\neq 0$ the known $Λ=0$ result that the Kinnersley rocket is the only rocket without gravitational radiation. However, for string and sheet sources, new possibilities without gravitational radiation arise. For $Λ>0$, we show that the vanishing of the canonical asymptotic super-Poynting vector---computed with respect to the unit normal to scri---exactly characterizes the absence of radiation. On the other hand, for $Λ<0$, we show that the appropriate criterion is the vanishing of the components normal to scri of the asymptotic super-Poynting vectors associated with any unit timelike vector tangent to scri or, equivalently, the proportionality between the Cotton-York tensor and the holographic stress tensor at scri. In particular, we provide explicit examples of metrics for which the Cotton-York and holographic stress tensors commute, yet gravitational radiation is present because the two tensors are not proportional. We also determine the principal null directions (PNDs) of the rescaled Weyl tensor at scri for both signs of $Λ$ and relate their geometry relative to the normal to scri to the tensorial criteria for gravitational radiation.

We introduce a family of effective theories and use them to define a specific type of coarse-grained models for canonical loop quantum gravity. Each effective theory is characterized by two parameters and it consists mainly of a Hilbert space of coarse states and an effective Hamiltonian operator. The construction of the coarse Hilbert spaces relies on a systematic coarse-graining procedure for spin network states. The effective Hamiltonians are then obtained from an analysis of the interplay between this coarse-graining procedure and the action of various Hamiltonian operators defined in loop quantum gravity. Finally, we provide a prescription for implementing the Hamiltonian non-perturbative renormalization framework for the coarse-grained models, and we explicitly write down the renormalization flow equations. The aim of this work is to build an arena for studying the emergence of the continuum limit and the derivation of phenomenological models in the context of canonical loop quantum gravity.