高能暂现源 · 每日文献综述

Solar extreme-ultraviolet (EUV) waves are large-scale disturbances that manifest as bright wavefronts, often during coronal mass ejections (CMEs). According to the magnetic field line stretching model, this phenomenon comprises two components: a fast-mode CME piston-driven shock wave and a slower, nonwave component. They are often associated with solar type II radio bursts. It is expected the radio source and the fast-mode EUV wave should come from different parts of the same shock, i.e., the CME piston-driven shock, and their speeds should be strongly correlated. To investigate this relationship, we utilized high spatiotemporal resolution observations from the Solar Dynamics Observatory in conjunction with radio data from the Radio Solar Telescope Network. Our analysis reveals that there exists a linear correlation between the EUV fast-mode speeds ($v_{euv}$) and the shock speeds derived from metric (m) type II radio bursts ($v_{radio}$), which is $v_{radio}=0.89v_{euv}+51$ kms$^{-1}$, with a correlation coefficient of 0.77. This strong correlation suggests that original coronal EIT waves, which are about three times slower than type II radio bursts, are not fast-mode waves, and it is misleading to map type II radio bursts to EIT waves in the literature.

Neutron star radius measurements, particularly using X-ray data collected with the Neutron star Interior Composition Explorer (NICER), have provided invaluable information for models of cold, catalyzed matter at densities above that of nuclear saturation. Here we present an analysis of NICER data on the 318-Hz pulsar PSR J0614-3329, which has a mass ~1.4-1.5 solar masses determined from radio observations. The best-fitting model we explore has three uniform-temperature circular hot spots and yields a symmetric 68% credible range for the equatorial circumferential radius of 9.88-12.77 km. We also explore joint fits to the NICER data and the X-ray Multi-Mirror (XMM-Newton) data on this pulsar, but find that the models that best fit both data sets systematically underpredict the XMM-Newton data when, as is standard, it is assumed that the XMM-Newton background is known from observations of surrounding fields. Finally, we discuss the implications of our results, combined with data on other neutron stars, for the properties of the dense matter in neutron star cores.

We study the scattering of massless scalar waves by static black holes embedded in dark matter halos. The halo is modelled by means of a Hernquist profile, for which the Einstein equations admit an exact solution. We analyse the scattering using null geodesics, the glory approximation, the partial wave expansion, and the complex angular momentum (CAM) method. The geometric analysis shows that the presence of the halo changes the light ring radius weakly but shifts the critical and glory impact parameters. The wave analysis shows that the characteristic black hole interference pattern is preserved, with halo compactness providing the leading correction and the halo scale radius playing a secondary role. For sufficiently compact halos, the environment also induces a sizeable gravitational redshift. Most of the displacement of the interference extrema can be reproduced by a vacuum Schwarzschild solution with an appropriately chosen $ωM_{\rm BH}$. A non-vanishing residual, however, reveals a genuine halo contribution that cannot be absorbed into such an effective frequency shift. Finally, we perform the CAM reconstruction of the scattering cross section and find that only a few Regge poles are required to achieve high accuracy at large angles.

Hard X-ray emission from Cas A has been attributed to jitter radiation, implying magnetic turbulence on scales near or below the ion Larmor radius. We propose these fields arise from ion-scale micro-instabilities (e.g., mirror and firehose) in the shock downstream, and use high-resolution hybrid simulations to demonstrate the generation of such small-scale turbulence. Its spectral index, once numerical dissipation is accounted for, is consistent with that inferred for Cas A, suggesting that jitter radiation is a direct probe of ion-scale turbulence in supernova remnants.

The observed merging binary black hole population is increasingly consistent with being composed of a mixture of subpopulations, each likely the result of different formation mechanisms. In particular, the low-mass subpopulation, with primary black hole masses below $\approxeq 15\,M_{\odot}$, has been attributed to mergers formed through isolated binary evolution. We use the binary population synthesis code POSYDON to study the mass ratio $(q)$ distribution of binary black hole mergers from isolated binary evolution and compare to the observed low-mass subpopulation. We explore variations in supernova remnant prescriptions, common-envelope efficiency, and black hole accretion efficiency. We find that our models have a preference for asymmetric $q$, most with a broad peak near $q\approxeq0.5-0.7$, and a near-equal-mass component whose relative strength varies across models. This resultant $q$ distribution is consistent with the $q$ distribution of the low-mass subpopulation observed with gravitational waves. We find that for the majority of models these features arise from physically distinct formation subchannels: the asymmetric peak reflects contributions from common-envelope and stable mass-transfer systems, while the near-equal-mass component traces double-core common envelope and contact systems. We conclude that the features in the $q$ distribution of the observed low-mass subpopulation emerge naturally from isolated binary evolution across a range of model assumptions. As the gravitational-wave catalog continues to grow, the relative strength of these $q$ features will provide an increasingly powerful diagnostic of isolated binary evolution and its formation subchannels.

Space-based gravitational-wave detectors such as LISA, Taiji, and TianQin employ time-delay interferometry (TDI) to cancel laser-frequency noise for unequal-arm constellations. Since different TDI observables exhibit distinct sky responses, a linear combination of candidate channels can enhance the average response over one sky region while suppressing that of another. We construct a frequency-domain response matrix for TDI combinations, average it across target and suppressed sky regions, and derive the optimal weights via a generalized eigenvalue problem that maximizes the ratio between these two regional responses. At millihertz frequencies, examples with the $A$, $E$, and $T$ channels, the Sagnac combinations $α$, $β$, and $γ$, and 16-links TDI show that a sky-region null and a large regional contrast are possible near the chosen frequency, with eigenvalues $ρ$ ranging from $\mathcal{O}(10)$ for small bases to $\mathcal{O}(10^2)$ for the larger set. The method is therefore expected to be well suited to nearly monochromatic sources such as the resolved Galactic double white dwarf binaries in the millihertz band. The Target-to-Suppression Ratio (TSR) peaks near the design frequency and falls quickly away from it, so the optimized weight vector is inherently narrowband and suited to targeted searches around a chosen frequency and sky direction.

Huntsman systems are a recently identified and rare subclass of millisecond pulsar (MSP) binaries, characterized by a detached neutron star and an evolved giant companion in relatively wide orbits. Their formation has been proposed to involve red-bump-induced detachment, whereas the influence of MSP-driven evaporation during this evolutionary stage has not yet been quantitatively assessed. We quantify the influence of MSP-driven evaporation on the formation and evolution of Huntsman systems and assess its effects on their observable properties. We performed detailed binary evolution calculations including MSP-driven evaporation over a wide range of initial binary parameters and combined them with binary population synthesis to predict the observable population of Huntsman systems. We find that Huntsman systems originate primarily from binaries undergoing Case B mass transfer and red-bump-induced detachment, with initial donor masses of $1.0-2.5\ M_\odot$ and orbital periods above the bifurcation period. Evaporation has a secondary effect, slightly modifying the orbital evolution and the duration of the detached phase, but does not significantly alter the formation parameter space or the expected population, which contains about 10 Huntsman systems. We further show that evaporation can produce systematic shifts in the white dwarf mass-orbital period relation at the low-mass end, leading to systematically wider final orbits for a given white dwarf mass.

Space-based gravitational-wave detectors can observe stellar-mass binary black holes (BBHs) long before merger, allowing weak environmental perturbations to accumulate. For binaries embedded in active galactic nucleus (AGN) disks, the local gas density characterizes the environment of the supermassive black hole (SMBH) and compact-object migration. We study whether such signals can constrain this density when a stellar-mass BBH orbits a Kerr SMBH. We evolve the outer orbit with relativistic corrections and gaseous dynamical friction (DF), and construct the detector-frame waveform including BBH inspiral, de Sitter precession, DF phase correction, and moving-source effects. Using Fisher-matrix calculations for sampled systems, we estimate statistical uncertainties and systematic errors. Larger gas densities generally improve the statistical precision of several source and outer-orbit parameters, but also increase systematic errors when DF is omitted. For favorable GW190521-like systems observed by LISA for one year, the disk density can be constrained at the level of $σ_ρ\sim10^{-12}\text{--}10^{-10}\,{\rm g\,cm^{-3}}$. Such constraints would connect BBH merger environments to the gas structure of galactic nuclei and the conditions that support black hole growth. These results indicate that hierarchical BBH inspirals can probe AGN disk environments, provided that gas effects are modeled consistently.

Neutron stars contain several forms of quantum condensed matter whose microscopic properties control macroscopic rotational dynamics and magnetic behavior of these fascinating objects. This review surveys superfluidity and superconductivity in compact stars, with emphasis on phenomena associated with quantized vorticity and magnetic-flux structures, and the possible connections to observed phenomena. We first summarize the microphysics of nucleonic pairing, including spin-singlet $^1S_0$ neutron pairing in the inner crust, proton superconductivity in the outer core, and spin-triplet $^3P_2$--$^3F_2$ neutron pairing at higher densities, together with the principal many-body uncertainties affecting the corresponding pairing gaps. We then discuss the dynamics of neutron vortices, including pinning, vortex creep, and dissipative motion, and the role of vortex dynamics in angular-momentum exchange between the superfluid and the observable crustal component. We give special attention to proton flux tubes in type-II superconducting cores, the possible realization of type-I superconductivity, and vortex--flux-tube interactions. We also review collective rotational phenomena, including Tkachenko oscillations of the vortex lattice and free precession, and their possible relation to long-term variability in pulsar timing. Finally, we discuss the possible deconfinement of hadronic matter into quark matter, the formation of color-superconducting phases, and the topological defects associated with these phases, together with their possible observational consequences. Throughout the review, we identify key open questions connecting microscopic pairing, mesoscopic defect dynamics, and observable neutron-star phenomena.

High-frequency gravitational waves in the MHz--GHz range require detection strategies beyond conventional interferometers. We study the response of a SQUID-terminated superconducting microwave cavity as a narrowband parametric transducer. The cavity boundary conditions and the flux dependence of the Josephson inductance are used to derive the quarter-wave mode spectrum and the first-order eigenfrequency response to changes in the physical line length, phase velocity, and SQUID inductive length. By projecting the perturbed dynamics onto the static cavity modes, we show that the resonance-frequency response and the photon-pair-production response are generally distinct. We therefore introduce two independent kernels, $R_n^ω$ and $R_n^{\rm pair}$, which coincide only when changes in mode normalization and spatial profiles can be neglected. Near $Ω_{\rm GW}\simeq 2ω_n$, the isolated-mode dynamics reduce to a Mathieu-type parametric amplifier, allowing the photon number, quadrature variances, gain, and instability threshold to be obtained in the presence of dissipation. Spontaneous photon production scales quadratically with the gravitational-wave strain and is extremely small for representative parameters, whereas phase-sensitive responses with a coherent probe can scale linearly with strain. The framework therefore provides a theoretical description of narrowband gravitational-wave transduction, while a quantitative sensitivity estimate requires device-specific calibration of the mechanical--electromagnetic response, verification of mode isolation, and a complete treatment of loss and noise.

The jet may compress an interstellar medium and soft X ray outside the jet may be absorbed by a compressed interstellar medium and thermal emission heated by a shock is expected inside the jet. Thermal emission was found for HST-1 and knot A of M87 in X ray energy spectra analysis by Chandra (Osone, 2017). The X ray image of the surrounding of the jet of M87 was studied by Chandra (Osone 2024). I find a soft X ray dip in a south region outside knot A. Therefore, by taking only a north region outside knot A as a background, where there is no soft X ray dip, I analyze X ray energy spectra for knot A by Chandra and confirm thermal emission with a high significance.

The 21 cm hyperfine transition of neutral hydrogen provides one of the few direct probes of the early cosmic history. High-redshift detections of this signal could shine light on the poorly understood epochs of the Dark Ages and Cosmic Dawn, periods that remain among the least understood in the Universe's history. However, this signal is masked by bright foregrounds and is distorted by the chromaticity of the antenna used to detect it. Correcting for the chromaticity requires an accurate representation of the radio sky across relevant frequencies. However, base sky maps used for this correction, such as instances of the Global Sky Model (GSM), are limited by resolution, calibration and extrapolation uncertainties, especially when scaled to lower frequencies relevant for Cosmic Dawn studies. This work quantifies how accurately the base map must represent the true sky to produce a reliable beam correction. Using simulated sky data, we generate beam chromaticity corrections generated from progressively degraded versions of the base map, and compare how well they do in comparison to a correction based on the full-resolution map. We find that degradation in map resolution of $\sim 1^\circ$ does not introduce measurable increases in the amplitude of the residuals when correcting for the chromaticity and subtracting three different foreground models (two polynomials and a power law expansion). These results provide practical constraints on the required resolution and accuracy of sky models used in beam correction pipelines, informing future design and calibration strategies for global 21 cm experiments, and future efforts to map the low frequency sky.

Future pulsar timing observations near Sgr~A* offer a unique probe of gravitational physics in the vicinity of a supermassive black hole. We forecast the ability of such measurements to constrain a Buchdahl-inspired $R^2$ gravity, parameterized by a single deviation parameter $ε$, using a timing framework that self-consistently integrates orbital dynamics with light-propagation delays and preserves the full timing solution across the observing span. Through Fisher-matrix forecasts for a representative pulsar, we systematically isolate how the precision on $ε$ depends on orbital geometry. We find that shorter orbital periods and higher eccentricities significantly enhance sensitivity, consistent with a substantial contribution from observations near periastron. As a benchmark comparison, we further consider a hypothetical pulsar on an S2-like orbit ($P_b=16~{\rm yr}$, $e=0.88$) and obtain a statistical sensitivity of $σ_ε\sim 10^{-4}$ within the adopted weak-field, static, and spherically symmetric timing model. This sensitivity is comparable to the natural order-of-magnitude truncation scale of the 1PN expansion and should not be interpreted as a complete forecast for the real Sgr~A* system. Under the adopted idealized assumptions, the characteristic statistical scale is several orders of magnitude below the current S2 95\% confidence interval half-width ($|ε|_{\rm S2}^{\rm 95\%}\approx 0.56$), though this comparison is heuristic given the differing confidence levels. These trends provide quantitative guidance for target selection and campaign design in future Galactic-center pulsar searches.

Large primordial curvature and tensor perturbations on small scales can generate second-order tensor-scalar induced gravitational waves (TSIGWs) through scalar-scalar, tensor-scalar, and tensor-tensor source terms. TSIGWs are recognized as one of the principal contributors to the stochastic gravitational wave background (SGWB) observations. We explore the energy density spectrum of second-order TSIGWs in the presence of non-Gaussian primordial curvature perturbations. Furthermore, we present the first calculation of the anisotropic angular power spectrum associated with second-order TSIGWs, which provides a promising tool to discriminate them from other SGWB sources.

We investigate the quasar clustering in the QuCatS photometric catalog, constructed from the fourth data release of the Southern Photometric Local Universe Survey (S-PLUS). The quasar sample for this study consists of $23,402$ quasars, spanning the redshift interval $1.1 \leq z_{\rm phot} \leq 2.6$, which we divided into four bins for our tomographic analyses. In each bin, we measured the two-point angular correlation function and compared it with theoretical predictions for the clustering of dark matter in the flat-$Λ$CDM cosmological model. We then estimate the effective linear bias in each bin that best fits the data, obtaining $b_{Q}(z_{\rm eff}=1.26)=2.17^{+0.30}_{-0.35}$, $b_{Q}(z_{\rm eff}=1.63)=2.67^{+0.36}_{-0.42}$, $b_{Q}(z_{\rm eff}=2.04)=3.29^{+0.52}_{-0.62}$, and $b_{Q}(z_{\rm eff}=2.38)=4.05^{+0.71}_{-0.86}$. These measurements are consistent with previous analyses in the literature. Moreover, the evolution of the bias agrees well with the $b(z)$ parameterization proposed by \cite{laurent2017}. Our measurements constitute the first cosmological study of the tomographic clustering of photometric quasars provided by the S-PLUS dataset, contributing to the mapping of the evolution of linear bias and paving the way for future analyses of data releases with larger datasets. In addition, our study also serves as a consistency test for the calibration procedure of the photometric redshift probability distributions of the quasars in the QuCatS catalog.

Primordial black holes (PBHs) are expected to be born essentially non-spinning and, if the primordial curvature fluctuations possess non-Gaussian tails, strongly clustered. Any spin measured in a PBH population must therefore be dynamically generated. Using direct $N$-body simulations with \textsc{nbody6++gpu}, modified to treat nearly parabolic dynamical-capture mergers, we quantify the conditions under which an initially non-spinning PBH cluster develops the spin, mass and stochastic-background signatures that gravitational-wave observations are now sensitive to. We find a sharp tension: producing a root-mean-square spin $χ_{\rm rms}\sim0.1 - 0.2$ in the $30 - 50\,M_\odot$ range requires initial Plummer radii of order $10^{-5}\,{\rm pc}$, whereas survival over cosmological times requires parsec-scale clusters. This tension is resolved naturally if PBHs form with a compact, short-lived core embedded in an extended halo, and we therefore simulate the two regimes as independent blocks. The core block ($4000$ PBHs, Plummer radii $3\times10^{-6} - 10^{-4}\,{\rm pc}$) collapses in days to years, producing a burst of mergers whose orbits are strongly non-circular ($e\to1$) and of low dimensionless orbital angular momentum, so that remnant spins are systematically below the quasi-circular value $χ\simeq0.7$. Redshifted from their formation epoch, the core mergers deposit a stochastic background peaking in the $10^{-6}$--$10^{-4}\,{\rm Hz}$ band accessible to LISA. The picture predicts a specific division of labour between observables, spins set in the primordial collapse, detectable mergers set by the long-term halo, and a two-component stochastic background, and, in particular, that both the spin and the mass data favour a primordial mass function truncated near $50\,M_\odot$.

Binary black holes (BBHs) formed in dense stellar environments or in hierarchical triples can coalesce on eccentric orbits and carry spins of arbitrary orientation, leaving distinctive imprints on their gravitational-wave (GW) emission. We present SEOBNRv6EPHM: the first generic-orbit, spin-precessing model in the effective-one-body SEOBNR family, whose waveforms have underpinned LIGO-Virgo GW analyses since 2011. The model describes the dynamics and multipolar GW signal of generic BBHs, covering the inspiral-merger-ringdown of coalescing binaries and extending to dynamical captures and scattering encounters. We perform the first systematic accuracy assessment of a generic-orbit model against numerical relativity (NR) waveforms of spin-precessing BBHs, using 1437 quasi-circular (QC) and 87 eccentric simulations: median waveform mismatches remain below $1 \%$, matching the accuracy of the QC model SEOBNRv5PHM, and improving on the state-of-the-art generic-orbit model TEOBResumS-Dalí by a median factor of $ 4 $. The model also reproduces the non-perturbative phenomenology observed in NR simulations of generic-spin BBH scattering. It is $\sim 2 - 3$ times faster than SEOBNRv5PHM in the QC limit, and up to an order of magnitude faster than TEOBResumS-Dalí, bringing eccentric inference to the cost of current QC analyses. As a proof of principle, we analyze eleven GW events and focus on GW200129, strengthening its evidence for eccentricity $-$ a result supported by injection-recovery studies with synthetic NR signals of eccentric, spin-precessing BBHs. SEOBNRv6EPHM thus enables, for the first time, accurate and efficient GW analyses that jointly account for eccentricity and spin precession.

We present JWST/NIRSpec PRISM and G395M grating spectroscopy for AzTEC-1, a massive sub-mm bright galaxy at $z=4.34$ in the COSMOS extragalactic field. The PRISM spectrum reveals strong H$α$, a significant Balmer break, and no H$β$ detection, indicating a $100-400$ Myr-old stellar population and high dust attenuation. BPT line ratios indicate the presence of an Active Galactic Nucleus (AGN). Decomposing narrow and broad line components, we recover broad, blueshifted H$α$ with a velocity offset of $1245{\,\rm km\,s^{-1}}$ from the systemic narrow line velocity and with FWHM$\,\sim2500\,{\rm km\,s^{-1}}$. AzTEC-1's smooth morphology and stellar age is suggestive of a past merger-induced starburst period that would have brought in a second supermassive black hole, raising the possibility for a binary supermassive black hole system. In this scenario, we assume that the lower mass black hole hosts a broad line region orbiting a quiescent primary. Evidence for an extended outflow is not found in the 2D spectrum, NIRCam imaging, resolved ALMA observations of dust continuum, or CO, [C II]$_{157\,μ\rm m}$ and [N II]$_{\rm 205\,μm}$ kinematics. AzTEC-1's high central gas mass surface density and dynamically unstable gas disk indicates that massive gas clouds external to the candidate binary SMBH's orbit might have played a role in stalling infall from $\sim10$ Myr to $\sim100$ Myr through dynamical torques, which has been theorized to occur in the nuclei of massive galaxies like AzTEC-1. If the supermassive black hole binary is confirmed, AzTEC-1 would be an excellent laboratory into the astrophysics driving low-frequency gravitational wave detections.

We derive the one-cycle first Magnusian for nonspinning compact binaries on planar, bound eccentric orbits through relative first post-Newtonian (1PN) order and linear order in radiation reaction, and construct the associated first-order periastron return map. Combining the conservative 1PN dynamics and its Jacobi transport with the 2.5PN and 3.5PN radiation-reaction forces, we obtain all four components in closed form for \(0<e<1\), without expanding in eccentricity. The dependence on all eight Iyer--Will radiation-reaction gauge parameters reduces to periodic coboundaries and therefore cancels over a radial cycle. The result reproduces the averaged energy and angular-momentum losses, their circular limit, and the secular evolution of the 1PN radial orbital elements. The two remaining components encode the dissipative angle-sector information. Projecting the resulting phase-space update onto the perturbed periastron return section yields the corrections to the return time and apsidal phase. We then compare the strict first-order map with a partially exponentiated map built from the same Magnusian. The comparison is observable dependent: at fixed periastron index, the strict map gives smaller residuals for a representative evolution over 40 radial cycles, whereas partial exponentiation reduces the accumulated periastron-timing residual by about an order of magnitude. Across a representative one-cycle grid at equal masses, partial exponentiation improves the radial-action and energy updates at every sampled point.

[Abridged] Investigating substellar populations in young massive clusters offers crucial insights into the formation of brown dwarfs (BDs) and the role of environmental conditions in shaping their properties. Westerlund 2 (Wd2), as one of the nearest dense and massive clusters in the Milky Way, represents an ideal laboratory for studying the effects of high stellar density and ionizing radiation from massive stars on BD formation. This paper presents deep JWST/NIRCam observations of Wd2 in a large number of filters between 1.15 and 4.1 $μm$. Our analysis focuses on identifying and characterizing the BD population within the cluster. We carried out PSF photometry on deep JWST/NIRCam data obtained in 4 wide and 6 medium-band filters, using DOLPHOT. The resulting catalog was used to identify BD candidates in Wd2 through spectral energy distribution (SED) fitting with atmospheric models. The 50\% detection limit of our NIRCam catalog is $\sim$0.015-0.02 $M_\odot$, at the distance, age, and extinction of Wd2, providing the deepest view of a supermassive star cluster to date. We identify 353 substellar candidates. Most candidates (301) lie above the 10 Myr isochrone in the Hertzsprung--Russell diagram consistent with cluster membership, which are defined as strong candidates. Comparison with a control field indicates a contamination level of $\lesssim$5\% for the strong candidate sample down to masses of $\sim$0.01--0.015~$M_\odot$. We identify 73 candidates exhibiting infrared excess indicative of circumstellar disks. These objects occupy the expected infrared-excess locus in de-reddened color diagrams and represent $27.7^{+3.4}_{-3.2}$\% of the candidates detected in F410M. The resulting catalog provides a well-characterized sample for future spectroscopic confirmation and subsequent studies of the substellar population of Wd2.

Theoretical models suggest that the adiabatic growth of a black hole immersed in dark matter can lead to the formation of high density regions of dark matter, known as ``spikes'', near the black hole event horizon. The density of these spikes is determined theoretically and observationally to be a power law of the form $ρ(r) \propto r^{-γ_\text{sp}}$. It has been shown that the spike can potentially have a detectable impact on the emitted gravitational waves and shadow radius of the central black hole. In this work, we model the dark matter spike using a real scalar field with a non-standard potential. More specifically we ``reverse engineer'' the equations of motion to find a potential for the scalar field that permits a solution to the equations of motion with desired energy density and reasonable background geometry. We show that the emerging geometry is testable. In addition, the fact that the solution is derived from a covariant action makes it possible to study gravitational perturbations of the black hole in the presence of a spike including the backreaction of the spike.

Quantum imaginarity is a fundamental quantum resource essential for quantum information processing. In this paper, we investigate the dynamical evolution behavior of quantum imaginarity for tripartite quantum mixed states in Schwarzschild spacetime. We find that Hawking radiation degrades the quantum resource of imaginarity, consistent with the behavior of entanglement and coherence under the Hawking effect. Interestingly, imaginarity exhibits a sharp change in the early stage of Hawking radiation, after which it varies slowly and asymptotically approaches a steady value. We further derive several trade-off relations that characterize the nonlocal redistribution of imaginarity across Rindler horizons. The findings of this study contribute to a deeper understanding of quantum resource behaviors in black hole spacetimes.

This paper presents the visual discovery of the first-ever recorded fading event of the Wolf-Rayet star WR 59. Historically documented as a stable star with an approximate magnitude of 13.9, the star underwent a sudden major decline during high-cadence visual monitoring in May 2021. On 11 May 2021 (JD 2459346), I observed the star plunge 1.3 magnitudes to a deep minimum of magnitude 15.2. It remained in this faded state for roughly 1 day before undergoing a structured 14-day recovery back to its baseline. This episode was independently verified by NASA's Transiting Exoplanet Survey Satellite (TESS) during Sector 38. The satellite's calibrated data stream confirms that the timing, structure, and recovery of the fade matched the ground-based observations. While a close 11.7 V companion star masked the true depth of the drop for automated large-pixel survey pipelines, this event firmly establishes WR 59 as an active dust-producing system. It demonstrates how high-magnification visual monitoring can successfully resolve crowded stellar fields.

We derive the background equations and complete odd- and even-parity quadratic actions for static, spherically symmetric black holes with radial scalar hair in general quartic-quintic Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories, including Horndeski. On regular, nondegenerate branches, the formulation applies across Killing horizons and yields local no-ghost conditions and radial and angular eikonal characteristics. Tensor modes in both parity sectors share the same squared radial speed. When the radial coordinate is timelike, generic antisymmetric mixing induces nonstandard large-multipole scaling for both even-parity angular branches. Requiring both branches to have finite, nonzero eikonal phase speeds selects the Horndeski-related compatibility condition between the quartic and quintic beyond-Horndeski functions. This condition aligns the covariant degeneracy directions and permits a local disformal map to Horndeski when regular and invertible. For a finite, nonzero scalar kinetic term at the horizon, every nontrivial branch of the exact quadratic GLPV black hole is locally unstable or has a degenerate tensor cone near a simple outer horizon. Apart from identified exceptions, this obstruction extends to general shift- and reflection-symmetric quadratic GLPV theories and the regular Horndeski-related branch of the quartic-quintic class. Finally, for scalar-Gauss-Bonnet black holes with a vanishing horizon scalar kinetic term, we construct analytic power-law quartic beyond-Horndeski deformations whose associated quintic function is fixed by the same condition. At sufficiently small coupling, all local no-ghost and high-frequency gradient-stability conditions hold throughout the exterior. For a linear Gauss-Bonnet coupling, we estimate an interior scale below which the background and stability expansions lose perturbative control; this does not imply a physical instability.

We quantify the impact of coupled instrumental systematics on next-generation CMB polarization experiments targeting primordial $B$-mode polarization, with a focus on the forthcoming \textit{LiteBIRD} satellite mission. We study the interplay between the non-linear response of Transition-Edge Sensor (TES) bolometers and Half-Wave Plate (HWP) non-idealities, in particular synchronous signals arising from differential emissivity. We develop a map-based formalism that captures the resulting intensity-to-polarization leakage by explicitly solving the binning map-making equations, avoiding the need for computationally expensive time-ordered data simulations. We apply this framework to \textit{LiteBIRD}, adopting its baseline scanning strategy and frequency configuration, and perform analyses at both single- and multi-frequency levels, including Galactic foregrounds and blind component separation. We find that while detector non-linearity and HWP non-idealities individually induce negligible bias on the tensor-to-scalar ratio $r$, their coupling can generate non-trivial contamination, driven by large signals such as the solar dipole and amplified in high-frequency channels by foreground leakage. From these results, we derive joint requirements on detector non-linearity and HWP differential emission, and discuss their implications for the instrument design and calibration strategy of \textit{LiteBIRD} and future CMB polarization missions targeting $r \lesssim 10^{-3}$.

A spectroscopic study of Regulus (late B-type rapidly-rotating star) was conducted with an aim of investigating its photospheric chemical abundances (especially for light elements), which has barely been challenged so far because of the considerable difficulty of abundance determination for such a very fast rotator (>~300 km/s). The atmospheric parameters were determined to be T_eff = 12345K (effective temperature) and log g = 3.58 (surface gravity) based on the spectral energy distribution, while the microturbulence was estimated as v_t = 0.5 km/s. The abundances of 14 elements (He, C, N, O, Ne, Mg, Si, S, Ca, Ti, Cr, Mn, Fe, and Ni) were derived by applying the spectrum-fitting technique, where the non-LTE effect was taken into account for lighter elements from He to Ca. The resulting relative-to-the-Sun abundances ([X/H]) revealed a remarkable trend that, while most elements indicate near-solar abundances (within +/-<~0.3dex), only C shows a marked deficiency ([C/H]~ -1.4) which is hard to explain. For example, a simple scenario of C underabundance caused by mixing of CN-cycled product (e.g., due to rapid rotation or binary mass transfer) is unlikely because any N enrichment is not observed. This problem remains yet to be further investigated.

We present a homogeneous VLT/X-Shooter study of accretion in young stellar objects spanning the entire Orion A complex. Our sample includes 91 pre-main-sequence stars hosting a protoplanetary disk according to Spitzer photometry, of which 34 have complementary ALMA dust mass measurements. We derived stellar and accretion properties using a self-consistent multi-component fitting procedure. Our sample encompasses spectral types from K3 down to M5, corresponding to stellar masses within $\sim$0.8-0.1 $M_{\odot}$. The accretion-stellar luminosity ($L_{acc}-L_{\star}$) and the mass accretion rate-stellar mass ($\dot{M}_{acc}-M_{\star}$) scaling relations in Orion A are consistent with those of other star-forming regions (SFRs) that span a range of stellar densities, far-ultraviolet (FUV) irradiation fields, and ages, with all regions occupying the same locus in parameter space. For the 34 sources with complementary dust mass measurements, we present the first investigation of the $\dot{M}_{acc}$ and disk mass ($M_{disk}$) correlation in Orion A, recovering a spread consistent with that reported for other regions. Despite our sample spanning nearly five orders of magnitude in local FUV field strength, we find no statistically significant correlation between $\dot{M}_{acc}$ and FUV irradiation. However, by combining our sample with literature measurements in Lupus, the Orion Nebula Cluster, and $σ$ Orionis, we find a tentative population-level decrease of the inferred disk lifetime $t_{\rm disk} =M_{disk}/\dot{M}_{acc}$ toward stronger FUV environments, though large intrinsic scatter and limited sample sizes at intermediate and high FUV fields prevent firm conclusions. The homogeneous $\dot{M}_{acc}$ measurements reported here provide a solid foundation for future studies of accretion and disk evolution across the diverse environments of Orion A and other SFRs.

Pole-skipping occurs at special complex frequencies and momenta where the retarded Green function of a black-hole or black-brane background is not uniquely defined. The local near-horizon mechanism is well known: at resonance, a Frobenius recurrence matrix loses rank and the space of smooth horizon solutions enlarges. We address the global question of how two boundary-normalized solutions enter this resonant horizon solution space. For a general second-order scalar radial equation on a nonextremal background analytic near the horizon, the Frobenius recurrence at the resonant order yields a solvability condition. We prove that its vanishing is equivalent to singularity of the horizon recurrence matrix, absence of the logarithmic Frobenius term, and existence of two independent smooth horizon solutions. Away from resonance, the source zero is equivalent to horizon smoothness of the response-normalized solution, while the response zero is equivalent to horizon smoothness of the source-normalized solution. We then analyze the parameter-dependent simple pole of the nonresonant ingoing solution as resonance is approached. After removing this singularity, its resonant limit is proportional to the larger-root Frobenius solution, with proportionality factor given by the same solvability function. Continuing to the boundary shows that the same condition is equivalent to simultaneous vanishing of the two regularized boundary connection coefficients. This establishes a horizon-to-boundary dictionary between local Fuchsian resonance and the boundary source-response 0/0 structure of pole-skipping. Finally, different directions of approach can select different resonant solutions, with the selection governed by the first parameter variation of the same solvability function.

In this work, we develop a perturbative framework for inflation driven by a complex inflaton with non-minimal gravitational coupling and a non-Hermitian potential. During the observable cosmic microwave background radiation era, the dynamics reduce to an effectively conservative two-field model, preserving the predictions of the $α$-attractor class and satisfying Planck 2018 and BICEP/Keck constraints on $n_s$, $r$, and $f_{\mathrm{NL}}$. Near the end of inflation, trajectory bending activates the non-Hermitian sector, triggering geometric reheating. The resulting non-unitary evolution modifies the curvature spectrum and stochastic gravitational-wave background through a calculable damping factor determined by the complex mass eigenvalues. While cosmic microwave background-scale observables remain essentially unchanged, a distinctive suppression emerges in the high-frequency gravitational-wave spectrum ($f > 10^2$ Hz), potentially testable by future detectors such as the Einstein Telescope and the Big Bang Observer.

We analyzed photometric and spectroscopic data for 11 candidates for non-pulsating stars located in the Cepheid instability strip (IS) of the Large Magellanic Cloud (LMC) in order to investigate the reasons for the lack of pulsations. We used available temperature calibrations based on photometric colors to estimate the effective temperatures of the candidates, which served as initial parameters for the spectroscopic analysis. We also applied surface brightness-color relations calibrated for Cepheid variables, giants, and supergiants to estimate stellar radii. The spectral analysis was performed using the spectral synthesis method to determine the atmospheric parameters; namely, the effective temperature, metallicity, surface gravity, microturbulent velocity, projected rotational velocity, and chemical abundances for up to ~30 elements. For most objects, only a single spectrum was available. However, no significant variations in radial velocities were detected among the stars with repeat observations; therefore, all stars were treated as single object in the analysis. Two stars exhibit broad spectral lines, which may indicate high rotational velocities or possible binarity; however, additional spectra are required to confirm this interpretation. One of these objects also shows asymmetric line profiles, which might be related to the presence of non-radial pulsation modes causing line-shape variations. A common feature among all analyzed candidates is an enhancement of barium-peak s-process elements compared to solar values. This may indicate past mass transfer from a companion during its post-asymptotic giant branch phase. This study provides an insight into the physical parameters of candidates for non-pulsating stars residing within the Cepheid IS in the LMC, although the lack of pulsations remains a mystery and challenges pulsation theory.

Large-scale spectroscopic surveys will need suitable benchmark stars that can be used to verify the performance of automatic pipelines. A promising type of object for this purpose is the detached eclipsing binary (DEB) containing an FG-star and a low temperature companion. For flux ratios $\lesssim1$~per~cent, the spectra obtained for the binary will be almost identical to a single star. As the methods for obtaining accurate parameters for binaries are well established, they would be excellent benchmark candidates. We analyse a group of DEBs with M-dwarf companions using TESS light curves and high resolution spectroscopy from NIRPS and HARPS on the ESO 3.6-m telescope. We obtain accurate fundamental parameters for the stellar components. The secondary component is visible with cross-correlation, allowing them to be characterised as well. With the stellar parameters obtained from the analysis, we can measure precise effective temperatures from Gaia parallaxes and archival magnitude data. Chemical compositions of the primary stars are also extracted from the stellar spectra. In this analysis, the secondary components have minimal impact on determined spectroscopic parameters. Our radii and masses are characterised to within sub per~cent precision as well as our primary effective temperatures. Beyond a new set of stellar benchmarks, the secondary components analysed in this work represent a well characterised sample of M-dwarf stars which will be useful to improve our understanding of low mass structure and evolution.

Mass loss in low-mass stars during the red giant branch (RGB) and early asymptotic giant branch (EAGB) phases plays a key role in shaping stellar evolution, yet its dependence on stellar parameters such as metallicity remains poorly constrained, with observational studies yielding conflicting trends. We present the first asteroseismic analysis of RGB and EAGB stars in NGC 5897, the most distant and metal-poor globular cluster observed by the Kepler space telescope during the K2 mission. We detected solar-like oscillations and derived the frequency of maximum power excess, $ν_{\rm max}$, for 20 RGB and 6 EAGB stars. Using asteroseismic scaling relations, we derived mean masses of $\overline{M}_{\rm RGB} = 0.74\pm0.01\,M_{\odot}$ and $\overline{M}_{\rm EAGB}=0.65\pm 0.03\,M_{\odot}$. The inferred integrated mass loss between the two phases is $ΔM_{\rm RGB-EAGB}=0.08\pm 0.03 \,M_{\odot}$. We present an updated mass-loss--metallicity relation for Type I globular clusters, extending it to the very metal-poor regime and supporting decreasing integrated RGB mass loss with decreasing metallicity.

We show that the relative phase primarily controls the survival, rather than the initial formation, of the common bridge in head-on collisions of radially excited boson stars. We vary the relative phase and track the post-contact bridge evolution across different boson-star configurations and scalar potentials. In the benchmark, all sampled phases form a common bridge, while larger phase offsets reduce its persistence; the same suppression persists across the configurations and potentials studied.

We develop a covariant framework for Josephson transport, superconducting interference, and shunt noise in the scale-dependent exterior generated by an Oppenheimer--Snyder-like collapse. Static Josephson frequencies and transported currents referred to Killing time acquire one lapse factor, whereas power acquires two. For a junction comoving with the collapsing surface, the coordinate-time phase rate differs from the frequency received at infinity because of null propagation and Doppler effects. We derive the exact radial-null travel-time kernel and show that its local near-extremal logarithmic enhancement crosses over, at fixed emission offset, to pole-controlled extremal behavior. We also obtain the redshifted resistively and capacitively shunted-junction equation and the dc and microwave-driven two-junction interference envelopes. In the negligible-total-inductance limit, static lapse imbalance modifies lobe amplitudes without shifting their centers, whereas microwave-induced translations require dynamical fluxoid closure. In a Hartle--Hawking state, Tolman redshift produces a superconducting exclusion layer and a lapse-independent asymptotic shunt-noise spectrum; its low-frequency limit obeys a parameter-free fluctuation--delay relation. Finally, we derive a shadow--Josephson consistency relation and sensitivity bounds on the running parameter.

The propagation of Solar Energetic Particles (SEPs) through the heliosphere is strongly influenced by solar-wind magnetic turbulence, which governs particle scattering, field-line wandering, and cross-field transport. These processes shape SEP intensity profiles, anisotropies, and arrival times. Because heliospheric turbulence spans a vast range of scales, direct numerical simulations cannot capture its full spectrum. Synthetic turbulence models provide an efficient alternative by generating fields with prescribed statistical and spectral properties, enabling realistic studies of SEP transport. This work presents a numerical model able to generate synthetic magnetic turbulence in the heliosphere with the goal of studying field line and particle diffusion. The model is inspired by in situ solar wind observations, indicating that solar wind turbulence properties vary with the distance from the Sun. We extend the Cartesian wavelet-based Synthetic Turbulence Model (STM), presented in \cite{Malara2016PhRvE..94e3109M}, to the non-homogeneous expanding solar wind. This is achieved by finding a suitable change of coordinates that allows one to pass from a space in which the turbulence correlation length is homogeneous to one in which it is not. We present the analytical derivation, the numerical implementation, and testing. We obtain an improved and computationally efficient synthetic turbulence model characterized by a background Parker spiral, a broad inertial range and tunable radial scalings for both the correlation length and the magnetic-field fluctuation amplitude, as well as a controllable level of intermittency. The model capability of reproducing solar wind turbulence up to the particle Larmor scale and to take into account solar wind radial evolution makes it a powerful tool to study the propagation of SEPs throughout the heliosphere.

Black-hole critical curves and photon rings provide complementary probes of strong-field geometry, motivating a unified analytic description of these observables beyond Kerr and a direct comparison with the Kerr predictions. We develop such a description for polar observers in a radial class of stationary, axisymmetric spacetimes with separable null geodesics. The spacetime dependence is organized through natural optical combinations selected by the null dynamics and a Kerr-relative representation suited to weak deviations from Kerr. We derive compact exact expressions for the polar critical radius, Lyapunov exponent, time delay, and rotation parameter, together with general first-order formulas that can be applied once the deformation functions of a specific metric are supplied. The weak-deviation analysis shows that the combined polar observables probe only a finite set of local deformation values and radial derivatives at the critical orbit, rather than the full radial profiles.

Double-bump showers are a surprising class of extensive air showers (EAS) predicted by Monte Carlo simulations, which, so far, no experiment has been able to directly detect. They occur when a high-energy secondary particle, the leading particle, travels significantly farther than the rest, creating a distinct double-peaked longitudinal profile. The unique radio footprint of double-bump showers, characterized by multiple pulses in the signals and interference patterns in the frequency spectra, enables reconstruction of longitudinal profiles from radio observations. With its dense antenna array and broad frequency range, SKA-Low will be the first observatory capable of detecting these features, offering a new opportunity to probe hadronic interactions and use the distinctive signatures of elements to provide new mass composition measurements. The goal of this analysis is to take the first steps toward using these radio signatures to reconstruct the relevant parameters of the longitudinal profile of a double-bump shower. We will start by explaining the radio signal of double-bump}showers compared to that of average showers. Then we will create a simple 2-point emission model to explain the interference patterns in the frequency spectra, which can be inverted to obtain rudimentary estimates of atmospheric depth of both peaks. Lastly, we implement a brute-force approach to reconstruct multiple parameters of the double bump.

Galaxy groups show entropy excesses $ΔS$ with respect to theoretical expectations from models and simulations with purely gravitational heating. We determine the heat $Q_{\rm heat}\simeq TΔS$ deposited by non-gravitational sources into the hot gas of elliptical galaxies, groups and clusters, and to compare it with the energy output of their central black holes (BHs). We adopt a simple model for the hot gas with only one free parameter: the core entropy. We calibrate the core entropy on the observed relation between X-ray luminosity and halo mass, and we use it to determine the entropy $S$ of the hot gas. We determine $ΔS=S-S_0$ by taking the difference between $S$ and the entropy $S_0$ found in cosmological adiabatic simulations for haloes of the same mass. The temperature $T$ of the hot gas during the heating phase is determined from semi-analytic/semi-empirical modelling by assuming that heat absorption traces the accretion histories of supermassive BHs. Our findings suggest that supermassive BHs thermalise 1 to $3\%$ of their energy output in the surrounding gas. Our results suggest two regimes: (i) in elliptical galaxies and groups, active galactic nuclei (AGN) heat the gas much more rapidly than it can cool, generating the observed entropy excesses and quenching star formation when the accumulated heat is large enough to unbind the gas reservoir in the host halo; (ii) in galaxy clusters (at $M_{200}>10^{14}{\rm\,M}_\odot$), heating and cooling are in self-regulated equilibrium.

We study gravitational-wave production during perturbative reheating without assuming instantaneous thermalization of the inflaton decay products. The injected energetic particles thermalize through an in-medium cascade of nearly collinear splittings subject to the Landau-Pomeranchuk-Migdal effect and are ultimately isotropized by elastic scatterings near the thermal scale. The non-thermal hard population present before complete thermalization produces an additional gravitational-wave component through hard-soft scatterings, with $Ω_{\mathrm{GW}}\propto f^{1/2}$ below the injection-scale turnover. The same isotropization erases the directional information underlying the vacuum $1/k$ bremsstrahlung soft pole, changing the deep-infrared spectrum from $Ω_{\mathrm{GW}}\propto f$ to $Ω_{\mathrm{GW}}\propto f^3$.

We propose Higgsino dark matter as a potential interpretation of the $248~\mathrm{keV}$ nuclear-recoil event of interest reported by the LUX-ZEPLIN (LZ) experiment. LZ studied several rare background processes and detector effects in detail, but did not identify any as a likely explanation of the event. A nearly pure Higgsino with mass $m_{\widetilde H}\sim1~\mathrm{TeV}$ naturally realizes inelastic dark matter through the off-diagonal $Z$ coupling of two nearly degenerate neutral Majorana states separated by a mass splitting $δ$. The same electroweak interaction fixes the inelastic Higgsino-nucleon scattering cross section, rather than leaving it as a free parameter. We show that the predicted Higgsino inelastic scattering cross section approaches the published LZ two-sided 90% confidence interval for $δ\sim350~\mathrm{keV}$.

Molecular line lists disagree at a level that measurably shifts retrieved C/O, so retrievals conditioned on a single list omit a dominant systematic from their error bars. Classical marginalization re-runs a full retrieval under K opacity realizations per object. We move that cost into simulation: while generating the training set we randomize opacities (smooth multiplicative Fourier fields in $\logν$ plus a discrete line-list mixture, under a deliberately broad prior informed by measured inter-list differences), so a neural posterior estimator learns an already-marginalized posterior. Conceptually, this is the amortized analogue of repeating a conventional retrieval under many plausible opacity realizations and averaging the resulting posteriors. On perturbed held-out spectra (n=2048) a standard NPE covers nominal 90% C/O intervals 43.3% of the time against 82.4% for a compute-matched marginalized network; three-seed control ensembles reach 93.2% on clean data but 61.4% under perturbation, against 89.4% marginalized, isolating the deficit as opacity-induced (TARP joint expected-coverage deviation 0.005 against 0.035). An axis ablation traces the gain to the continuous field (45.4% for the discrete swaps alone, 79.3% for the field alone). Applying the 105 real bad-pixel masks with median filling then collapsed the ensemble's C/O coverage from 0.901 to 0.479; retraining on the same mask distribution and pooling three such seeds returns a nominal 0.905 C/O and 0.891 overall under the full deployment path, still in simulation (n=1024, same 105 masks), at 0.21 to 0.31 of the prior width. On 105 JWST/G395H spectral products of 13 late-T/Y dwarfs, single marginalized networks bracket the Hood et al. (2024) T8 benchmark C/O where the control excludes it, a consistency check rather than a validation, at 1.6-2.6x wider intervals.

We investigate the effects of perfect fluid dark matter (PFDM) and a dark-energy field on the phase structure of a nonlinear magnetically charged Anti--de Sitter (AdS) black hole. We find that the small--large black hole (SBH/LBH) phase transition is driven by the nonlinear magnetic sector, while the dark sector does not generate additional transitions. In particular, increasing the magnitude of the PFDM parameter $λ$ suppresses this phase transition, eventually driving the system toward a single-phase regime. Moreover, a nonzero $λ$ prevents the formation of a regular black hole core. The effect of the dark-energy field depends on its equation-of-state parameter: in the quintessence regime, increasing its intensity strengthens the first-order phase transition, increasing the Gibbs construction area and latent heat while reducing the critical regime; in the phantom regime, the system exhibits spinodal behavior without phase coexistence. Finally, geometrothermodynamics (GTD) shows that the curvature singularities of the thermodynamic equilibrium manifold reproduce the phase structure of the black hole, while the associated power-law scaling near criticality is consistent with previous results for black holes, cosmological horizons, and real fluids, suggesting a universal thermodynamic behavior across these systems.

Accurate stellar ages are fundamental to interpreting the evolutionary histories of habitable zone (HZ) planets. Because stellar luminosity evolves over time, HZ boundaries migrate outward, meaning that present-day HZ planets may have experienced different irradiation environments earlier in their evolution. Accurate ages are therefore required to estimate HZ residence times and place planetary habitability in an evolutionary context. We use the Bayesian Analysis of Stellar Evolution with nine parameters (BASE-9) code to constrain ages and masses for exoplanet host stars with planets located in the HZ. Our sample includes single stars with effective temperatures of 4475-7200 K that host planets within their calculated HZ boundaries. We fit isochrones to broadband photometry from Gaia DR3, Pan-STARRS, and 2MASS jointly with Gaia parallaxes, spectroscopic metallicities, and extinction estimates, and assess the resulting age posterior distributions. Using these age constraints, we track HZ migration along stellar evolutionary sequences to estimate continuous HZ residence times, allowing us to identify ideal targets for followup high resolution characterization. Because isochrones separate most strongly near and beyond the main-sequence turnoff, our analysis emphasizes evolved and turnoff hosts, where BASE-9 produces the tightest constraints. We quantify age precision across the sample, yielding highly precise ages for subgiants and evolved main-sequence or turnoff stars, and less precise but measurable ages for lower main-sequence hosts. The final catalog provides our age constraints for 149 HZ planets around 146 host stars and supports evolutionary interpretations of planetary histories.

Dark Matter halos exhibit slow tumbling known as `figure rotation'. Figure rotation occurs in roughly $80\%$ of isolated $Λ$CDM halos and is relatively unaffected by baryonic feedback, making it an attractive and relatively unexplored test for $Λ$CDM. However, galaxy mergers are capable of exerting strong torques on a host halo's quadrupole, warranting an investigation of whether such interactions are capable of influencing figure rotation. Using isolated $N-$body simulations and 6 TNG50 halos containing MW analog galaxies, we investigate figure rotation in the context of massive mergers. For isolated galaxies we find that massive mergers elicit rotation of the host halo in both a rapid transient phase during the satellite infall with pattern speeds between $10^\circ-60^\circ$ Gyr$^{-1}$, and post-merger as a steady tumbling with pattern speeds between $2^\circ-40^\circ$ Gyr$^{-1}$ lasting for at least $6-8$ Gyr. Both transient and long-lived tumbling depend on the trajectory of the infalling satellite. We find that figure rotation can be induced by radial mergers with no orbital angular momentum, suggesting that tidal torques from the satellite are a driving mechanism. Meanwhile, TNG50 halos show quadrupole tumbling modified during major mergers in both pattern speed (3/6 halos) and rotation axis orientation (6/6 halos). Quadrupole tumbling remains stable after the last major merger in 5 of our 6 halos. Our results suggest that, rather than tracing the early tidal shear, figure rotation at present day may instead retain a dynamical memory of a halo's last major merger.

Motivated by the recent extension of Herrera's gravitational complexity to arbitrary higher-dimensional spacetimes, we investigate exact compact-star models that satisfy the vanishing-complexity condition within the Finch--Skea geometry in $(n+2)$-dimensional Einstein gravity. By combining the higher-dimensional Einstein field equations with the generalized complexity formalism, we obtain a new class of exact interior solutions describing anisotropic fluid spheres with zero complexity. The physical properties of these models are evaluated by analyzing the behavior of the matter variables, pressure anisotropy, and equilibrium conditions, alongside the standard requirements of regularity, energy conditions, causality, and stability. We further explore the influence of spacetime dimensionality on the structural characteristics of the stellar configurations, demonstrating that the presence of extra dimensions significantly modifies the internal matter distribution while preserving physical viability. The solutions presented here represent the first exact higher-dimensional Finch--Skea compact-star models constructed within this recently developed generalized complexity framework \cite{choudas}. These results provide a natural extension of zero-complexity stellar configurations beyond four-dimensional General Relativity and offer a robust framework for investigating self-gravitating systems in higher- dimensional gravity.

Upcoming large-scale structure surveys require accurate theoretical predictions for angular power spectra on the largest angular scales, where the commonly used Limber approximation breaks down and multiple relativistic and observational effects become relevant. At the same time, modern cosmological analyses increasingly rely on gradient-based inference techniques, motivating the development of fast, fully differentiable algorithms. In this work, we present a major extension of Blast.jl, a numerical toolkit for the efficient computation of non-Limber angular power spectra. Building on the Chebyshev-polynomial decomposition of the original framework, the updated algorithm incorporates redshift-space distortions, magnification bias, primordial non-Gaussianity, intrinsic alignments, CMB lensing, and the integrated Sachs-Wolfe effect, while remaining fully differentiable through custom automatic differentiation rules. Despite the increased physical complexity, the algorithm retains favorable scaling by precomputing all cosmology-independent quantities. We validate the expanded framework against brute-force integration and established cosmological codes, and provide a detailed analysis of the trade-off between computational speed and precision as a function of the algorithm hyperparameters. We demonstrate the readiness of Blast.jl for gradient-based inference through a simulated likelihood analysis with LSST Y10-like mock data, recovering unbiased cosmological and nuisance parameter constraints from a 35-parameter model using gradient-based samplers.

We study a phenomenological fixed-ADM prescription for an extended-uncertainty-principle (EUP) correction to the Schwarzschild exterior. Rather than treat mass constancy as a consequence of the EUP, we hold the charge measured at spatial infinity fixed so that we can compare exteriors at the same physical mass. We impose the EUP-shifted horizon radius and Hawking temperature and select the slowest admissible inverse-power representative. Its Einstein tensor defines an effective anisotropic tensor, but we do not infer an independent matter model, quantum state, or perturbation theory from that definition. For a positive EUP parameter, the effective energy density is negative throughout the exterior, while the transverse null and strong energy conditions fail over an extended radial region. The area entropy and the formal entropy obtained from the reduced relation $\mathrm{d}M=T\,\mathrm{d}S$ disagree at leading order; we interpret this mismatch as evidence that the thermodynamic description lacks work terms or an action-based entropy law, not as a definite EUP entropy correction. An explicit one-parameter family with the same mass, horizon, and temperature shows that the orbit, lensing, and test-field eikonal shifts depend on the chosen representative. Our results therefore characterize the minimal member of a phenomenological family rather than universal consequences of the EUP.

The strong $CP$ problem remains one of the major open questions in the Standard Model of particle physics. Its best-known solution is the Peccei--Quinn mechanism, which predicts a new pseudoscalar boson, the QCD axion. In recent years, alternative solutions and new perspectives on the foundations of the strong $CP$ problem have also received renewed attention. In this review, we provide a pedagogical account of the underlying physics and summarise the current theoretical and phenomenological status of the problem.

Temporal sparsity compares the mean interval between emitted quanta with a characteristic single-quantum timescale. We study this operational quantity for the rotating draining-bathtub acoustic horizon in two spatial dimensions. The Hawking temperature is fixed by the radial drain and does not depend on circulation, while the geometric capture width and the transmission spectrum do. A geometric black-body benchmark therefore predicts reduced temporal separation as circulation increases. We then solve the radial scattering problem and compute converged greybody-corrected number and energy fluxes, including the superradiant sector. At a circulation-to-drain ratio of unity, the thermal-clock sparsity is 0.44 whereas the spectrum-based sparsity is 1.82. The former crosses the temporal-overlap benchmark near a ratio of 0.40, while the latter remains above unity at all sampled circulation ratios. We also show that the binned sparsity definition is logarithmically infrared sensitive in two spatial dimensions. Rotation therefore enhances the number flux while hardening the spectrum, making temporal overlap intrinsically dependent on the operational clock used to resolve the emitted quanta.

We construct the electric and magnetic Carroll limits of the $\mathcal{O}(F^2)$-truncated $\text{D}_p$-brane via the Polyakov--KK route, which combines a single-mode Kaluza--Klein-like reduction at fixed light-cone momentum with a Dirac classification that keeps the auxiliary worldvolume frame. Unlike the $U(1)$-free ILST string, for $p\geq2$ the Carrollian D$_{p}$-brane cannot be treated as a consistent fixed-frame constrained system after the Dirac classification. In the electric family the obstruction is directly produced by the worldvolume $U(1)$ matter sector, while in the magnetic family the frame retention is forced by the scalar kinetic's density-weight structure rather than by the $U(1)$ currents. The frame must therefore be retained through the classification and eliminated afterwards by Dirac brackets. Freezing it beforehand is not a legitimate step in the Dirac procedure. The embedding scalar sector inherits the Carroll--Weyl $χ$ structure at the level of the ILST kinetic density, which is $χ$-invariant, whereas the full scalar action is only $χ$-covariant. The local extension of $χ$ to the full matter sector is obstructed by the $U(1)$ sector through the Gauss, circle and $A_-$-gradient brackets. The electric family keeps the global rescaling as a weak symmetry, while the magnetic family fails even for a global parameter. For $P_{-}\neq0$ the electric and magnetic families have $d-2$ and $d-3$ degrees of freedom, and the restored local circle at $P_{-}=0$ removes one further degree of freedom in each family. These features identify the resulting theories as constrained systems distinct from both the null string and the parent $\mathcal{O}(F^2)$ DBI theory, and we also discuss their on-shell interpretation and relation to tensionless/null strings.

Baryonic feedback can suppress matter clustering by $\sim 10\%$ at $k\sim 1h$/Mpc and $z\sim 1$, and is therefore a major source of systematic errors in weak lensing cosmology. We investigate this effect through the ratio $S(k,z)\equiv P_{\rm hydro}(k,z)/P_{\rm DMO}(k,z)$ measured in the FLAMINGO, IllustrisTNG, and Illustris hydrodynamical simulation suites, together with the one-parameter-at-a-time (1P) variation runs of CAMELS-TNG and CAMELS-SIMBA. We present a three-parameter fitting formula that reproduces all but one of these runs with maximum error less than $0.03$ (and typical error less than $0.01$) at $k\leq 3h/$Mpc and $z\leq 2$; the only exception is a run with unrealistically low $Ω_m=0.1$. Each of the three parameters ($B_0$, $n$, and $a$) has a clear physical interpretation: $B_0$ sets the characteristic scale of the suppression at $z=0$, corresponding to a gas particle displacement scale of $B_0^{1/2}$; $n$ sets the suppression floor $(1-Ω_b/Ω_m)^n$; and $a$ sets the redshift $z_B$ at which the suppression peaks. Furthermore, we find that $B_0$ and $z_B$ are significantly correlated for most runs. Also, $n\simeq 1$ for FLAMINGO, TNG and CAMELS-TNG. For these simulations, the description reduces to a single parameter formula with maximum error less than $0.03$. The formulas remain accurate at max$(|ΔS|)<0.03$ (and typical error less than $0.01$) for cosmologies well away from the calibration cosmology, spanning the range $Ω_m\in [0.2,0.5]$, $Ω_b\in [0.029,0.069]$ and $σ_8\in [0.6,1.0]$. These results imply that, despite the diversity of baryonic physics implementations, an accurate description of $S(k,z)$ requires at most three effective degrees of freedom. Therefore the impact of feedback on weak lensing cosmology can in principle be mitigated internally without significant loss of cosmological constraining power.

The magnetic Reissner-Nordstrom black hole embedded into the Bertotti-Robinson magnetic field is presented. Then it is used, as a seed, to generate, through the Harrison transformation of the Ersnt's equations, the Reissner-Nordstrom metric in the Bertotti-Robinson-Bonnor-Melvin magnetic field. Special cases generalising, the vacuum hairy type I Schwarzschild solution is discussed. The local equivalence between various forms of the Schwarzschild-Bertotti-Robinson is shown by exhibiting the explicit diffeomorphism.

We investigate strong cosmic censorship (SCC) for massless scalar perturbations of electrically neutral black holes immersed in a Chaplygin-like dark fluid (CDF). The matter distribution produces an asymptotically de Sitter exterior while supporting an inner Cauchy horizon. We derive a closed-form parametrization of the extremal and Nariai horizon boundaries. This analytic control yields explicit near-extremal asymptotics for the horizon splitting and Cauchy-horizon surface gravity, together with an analytic expression for the leading near-extremal scalar quasinormal spectrum. The fundamental near-extremal damping rate approaches the Cauchy-horizon surface gravity, whereas higher angular multipoles retain explicit dependence on the CDF extremal geometry. Combining these analytic results with global quasinormal-mode calculations, we determine the spectral gap and assess the Christodoulou formulation of SCC throughout the three-horizon domain. Potential SCC violation is confined to a narrow region near extremality. As the effective cosmological scale increases, the lower boundary of this region is controlled successively by de Sitter, photon-sphere, and de Sitter modes, while its normalized width varies nonmonotonically.

We construct exact solutions for single-field inflaton dynamics without invoking the slow-roll approximation. A suitable change of variables reduces the background equation to an Abel equation of the first kind. Although a generic Abel equation is not analytically solvable, we identify a class of inflaton potentials for which the transformed equation admits exact solutions. The resulting framework contains constant-roll inflation as a special case and also accommodates solutions with a constant second Hubble-flow parameter. We analyze the linear local attractor behavior and superhorizon evolution of these rolling backgrounds. Using the public joint CMB likelihood contours in the $(n_s,r)$ plane, we identify compatible parameter regions and show that one rolling branch can also yield $50\leq N_*<60$. Direct numerical evolution of the scalar and tensor modes at representative points validates the local-index predictions to better than $7\times10^{-4}$ in $n_s$ and $2\times10^{-6}$ in $r$. The exact family extends beyond slow roll, although the observationally selected regions displayed here lie close to the slow-roll regime.

We explore the construction of higher-dimensional Einstein-Maxwell(-Chern-Simons) solutions from vacuum seeds by means of a generalized Kerr-Schild transformation along a geodesic null vector field $\mathbf{k}$. Assuming the vector potential $\mathbf{A}$ to be aligned with $\mathbf{k}$, and $\mathbf{k}$ to be a Weyl aligned null direction satisfying the ``optical constraint'', we arrive at three distinct branches of solutions. If $\mathbf{k}$ is expanding and twisting, then its shear must vanish -- this branch includes certain charged Taub-NUT metrics. If $\mathbf{k}$ is expanding and twistfree, one finds two subfamilies: Robinson-Trautman electrovac solutions with a non-null Maxwell field if the shear is zero, or shearing solutions with a null field. Finally, the case when $\mathbf{k}$ is non-expanding reduces to a subset of the known Kundt solutions. In all cases, the Chern-Simons term turns out to be identically zero on-shell. In passing, by relaxing the alignment assumption on $\mathbf{A}$, we also obtain a six-dimensional extension of a charged Taub-NUT metric for which the magnetic part of the field strength is a linear combination of two distinct Kähler 2-forms, as opposed to the previously known examples in more than four dimensions.

The field of exoplanetary research is rapidly evolving, thanks to TESS and Kepler/K2. With the latest data release, Gaia DR3, Gaia has transformed the study of star clusters. By combining the known properties of exoplanets and those of star clusters, in which they are found, it is possible to study the planets in greater detail and test theories of planetary evolution. We aim to create a catalogue of Gaia IDs for known exoplanets and use it to link the planets to a catalogue of star clusters. We utilised the NASA Exoplanet Archive and the Extrasolar Planets Encyclopaedia to compile a catalogue of known exoplanets. We then cross-matched the data with Gaia DR3 sources to obtain the Gaia IDs of the exoplanets. Using this information, we inferred the potential association of these exoplanets with star clusters. We described the statistical properties of these exoplanets. We compiled a catalogue of Gaia IDs for known exoplanets and identified those associated with star clusters. This resource facilitates detailed studies of exoplanet properties and their evolutionary contexts within stellar clusters.

An interesting feature of quantum corrections to the Bekenstein--Hawking entropy is the appearance of logarithmic area terms, whose coefficients are governed by the spectrum of massless fields. For near-extremal black holes, the entropy also receives a logarithmic temperature corrections, whose coefficient is determined by the zero modes of the corresponding extremal black holes. In this paper, we study near-extremal rotating black holes in three, four, and five dimensions with an important focus on rotational zero modes. For three-dimensional BTZ black holes, our results are in agreement with the microscopic description. Furthermore, by treating the cosmological constant scale \(\ell\) as an independent parameter, we find an additional \(\log \ell\) correction to the entropy at extremality. For the five-dimensional BMPV black hole, we explicitly construct all the extremal zero modes and use them to evaluate the log temperature corrections to the entropy.

We investigate asymptotically Weyl-invariant gravity (AWIG) in the Palatini formulation, defined by an exponent n that interpolates between an Einstein-like infrared regime, where n goes to one, and a Weyl-invariant ultraviolet regime, where n goes to two. In four dimensions, we show that exact Weyl invariance within the minimal scalar Palatini f(R) sector uniquely selects the R^2 action as the ultraviolet endpoint. Interpreting the exponent as an effective curvature-dependent quantity, we constrain a phenomenological class of smooth autonomous flows compatible with the required infrared and ultraviolet endpoints. We then analyse the strict ultraviolet theory. On the regular branch R not equal to zero, and within a restricted torsionless, parity-even sector constructed purely from curvature, all admissible divergent on-shell counterterms reduce at arbitrary loop order to the original \sqrt{-g}R^2 term plus a topological Euler density. Although this conditional result does not establish full off-shell perturbative renormalizability, it provides nontrivial evidence for improved ultraviolet behaviour relative to Einstein gravity and identifies a concrete target for a future first-principles renormalization-group calculation.

Stress-tensor fluctuations carry information that is absent from the mean semiclassical Einstein equation, but their observable effect depends as much on the response of the geometry as on the noise itself. We formulate an effective, quasistationary spherical model organized by the response--noise structure of a quantum Langevin equation. A prescribed mean dressing and a horizon-localized colored source are varied independently. For every source realization we reconstruct the lapse, locate its outer trapping horizon, and evaluate the adiabatic Hayward--Kodama temperature from the slope at that same root. As the mean lapse approaches an inner--outer root merger, its inverse slope acts as a geometric susceptibility: a fixed source covariance produces enhanced horizon fluctuations, horizon--temperature covariance, and a positively skewed, greybody-filtered luminosity. The specific advance is a single-realization map from colored metric noise to correlated geometric, thermal, and radiative statistics, together with an explicit separation of reservoir strength from near-critical amplification. The model is a stochastic-semiclassical testbed, not a microscopic evaluation of Unruh-state response and noise kernels.

Some of the properties of the Szekeres solutions which have never been used in a cosmological context are known for long. In this letter, the total and unique decomposition of its matter energy density into a monopole and dipole moment is recalled and specialized to the axially symmetric quasi-spherical subclass of the model. All the model special features -- axial symmetry, spherical quasi-symmetry, location of the observer -- are observationally justified. Then, a consistency test of the model involving its no-high-multipole-in-mass-density property is proposed.

We construct a two-scalar hairy planar black hole in four-dimensional Einstein gravity coupled to two scalars whose potential descends from the ABJM consistent truncation of eleven-dimensional supergravity. Starting from the known single-scalar hairy black brane, we switch on the second scalar $\phim$ perturbatively in its amplitude $\eps$ and solve the coupled Einstein-scalar system to order $\eps^{2}$. The linearized $\phim$ profile is an exact hypergeometric function, independent of the $\pp$ hair, whose horizon-regular branch always carries a source, so there is no spontaneous $\phim$ hair. Because the dual operator $\mathcal{O}_{-}$ is irrelevant ($Δ=4$), the second-order response develops a logarithmically running condensate with a closed-form, scheme-independent slope $\tfrac{\sqrt{21}}{70}C_{s}^{2}$. The renormalized free energy is scheme dependent, but the geometric temperature shift $δT/T_{0}\approx-0.345\,\eps^{2}$ at fixed entropy is not. The full metric and $\pp$ back-reaction is obtained in closed form, diagonalizing into two Pöschl-Teller problems with $δ\pp=\tfrac{6}{\sqrt7}\,δH$. Three transport coefficients of the dual fluid remain exactly conformal to this order, while the sound speed, like the free energy, is scheme dependent.

In some occasions, it would appear that classical electromagnetic fields could be able to coexist with strong curvature, naked singularities, in the sense that the electromagnetic power flux would be bounded in any open neighborhood of them. We illustrate this rare behavior by considering the naked singularity present in Kasner spacetimes. There, using the Plebanski--Tamm map between Maxwell theory in curved spacetime and the associated description corresponding to an effective anisotropic medium in flat space, we found not only some regular electrostatic field configurations, but also electromagnetic waves whose amplitudes lead to a well defined, bounded power flux as they approach the singularity. Sometimes, in these unusual situations, the singularity resembles a mirror, perfectly reflecting its environs; in other occasions, the existence of a non-null, finite power flux as the waves travel to or from the singular plane, offers a very simple explanation as to how the singularity might absorb or create radiation fields.

We investigate the geodesic structure and thermodynamics of a $κ$-deformed Schwarzschild-anti-de Sitter black hole in a Kiselev quintessence field, where dynamics are governed by a mass-dependent lapse deformation. This term produces an inner Cauchy horizon without requiring charge or spin, yet it fails to resolve the central singularity; instead, the Kretschmann scalar diverges more strongly as $r^{-10}$. Because the deformation amplitude couples to the mass, the standard Bekenstein-Hawking area law violates the first law of thermodynamics. We resolve this by either deriving a modified entropy or rescaling the mass, both of which restore the first law and yield a consistent Smarr relation. Optically, an increasing deformation parameter shrinks both the photon sphere and the critical impact parameter. We also derive a closed-form Joule-Thomson coefficient, revealing that the $κ$-deformation triggers an inversion curve a feature absent in standard neutral SAdS. Notably, this occurs without generating a van der Waals critical point, demonstrating that Joule-Thomson inversion and van der Waals criticality can be cleanly decoupled. Finally, the deformation suppresses peak Hawking emission by a factor of roughly four and increases flux sparsity, an effect driven almost entirely by a drop in temperature rather than changes to the black hole shadow.

We construct an algebra of observables associated to a cut of null infinity in asymptotically flat spacetimes. The Bondi mass associated with a sharp cut of future null infinity is not a well-defined quantum operator: its fluctuations diverge even after smearing in retarded time. We instead introduce a finite-radius, time-smeared version of the Bondi mass and adjoin this operator to the matter and graviton observables in an arbitrarily small asymptotic neighborhood of the cut. We separately analyze spacetimes with and without black holes and find, in both cases, Type III$_1$ von Neumann algebras that satisfy non-trivial nesting relations. In Minkowski spacetime, the resulting algebra reconstructs the spacelike wedge associated with the cut. In a stationary black hole spacetime, it reconstructs the region bounded by the cut and the black hole bifurcation surface, providing an asymptotically flat analogue of an entanglement wedge. In the limit as the cut is moved to past infinity, we recover a Type I$_{\infty}$ algebra for spacetimes without black holes and a Type II$_{\infty}$ algebra for black hole spacetimes. For algebras at finite cuts of retarded time, we construct a Type II$_\infty$ regularization of the black hole algebra whose renormalized von Neumann entropy agrees with the generalized entropy. In appendices, we prove two technical results about quantum fields, in a Schwarzschild spacetime, that asymptote to the Minkowski vacuum at infinity: a split property for unbounded, spacelike separated regions and the construction of a faithful, normal, and semifinite Hartle-Hawking weight whose modular flow is Schwarzschild time evolution.

A discrete, anomaly-free $\mathbb Z_9$ gauge symmetry may persist to the deep infrared, exactly forbidding proton decay. This $\mathbb Z_9$ can emerge from Higgsing a lepton-flavour non-universal $U(1)_X$ that generates realistic neutrino masses and mixings through a high-scale seesaw and predicts an additional light Goldstone. Adding an anomaly-free chiral heavy-quark sector turns this mode into the QCD axion. The same selection rules that ban proton decay also forbid PQ-violating operators below a suitably high dimension, $d_{\rm PQ}\gtrsim10$, including operators involving the heavy quarks that radiatively match onto the scalar potential. We construct explicit models viable when PQ breaking occurs before or after inflation; in the latter case, avoiding stable heavy relics and eliminating the string-wall network tightly constrain the heavy-quark spectrum. We identify restricted regions of parameter space where thermal leptogenesis remains viable and, for $d_{\rm PQ}\geq13$, can coexist with a high-quality axion constituting all of the dark matter.

We derive a set of on-shell recursion relations for amplitudes in worldline quantum field theory (WQFT), an effective theory of gravity coupled to a massive worldline which is relevant for computing classical gravitational observables. We overcome the poor large-$z$ falloff of amplitudes under an all-line complex momentum deformation by deriving and exploiting a new soft-graviton theorem in the presence of a worldline. This theorem generalizes the leading (Weinberg) and subleading soft theorems with additional contributions due to soft emission from the worldline. Our main result is a $d$-dimensional recursion formula, expressing any $n$-graviton rational amplitude in terms of lower-point amplitudes from WQFT and pure gravity. Using the soft-worldline theorem, we can obtain amplitudes with any number of external worldline fluctuations from the corresponding all-graviton amplitudes, making the recursion sufficient to construct any rational amplitude of the theory. We verify our results by explicitly computing two-graviton and three-graviton amplitudes.

Dirac leptogenesis offers a qualitatively different route to the baryon asymmetry: total lepton number is conserved, but equal and opposite asymmetries are stored in the Standard Model and right handed neutrino sectors, with only the visible component processed by electroweak sphalerons. We present the first dedicated study of how evaporating primordial black holes (PBHs) modify this mechanism. In a minimal charged-scalar mediator setup, we solve the coupled Boltzmann system including thermal production, Hawking emission of the mediator $X$ and of right handed neutrinos, the PBH contribution to the expansion rate, and entropy injection. We find that Hawking emission can populate $X$ in regions where thermal production is inefficient, allowing its subsequent CP-violating decays to enhance the baryon asymmetry. For representative benchmarks, PBHs extend the successful region from mediator masses around $10^9\,{\rm GeV}$ down to about $10^6\,{\rm GeV}$ and can compensate for smaller effective CP asymmetries. This effect is not universal: where thermal Dirac leptogenesis is already efficient, PBHs can instead reduce the final asymmetry. Their evaporation also deposits energy in the right handed neutrino sector and contributes to $ΔN_{\rm eff}$. In the PBH parameter scan, part of the region that reproduces the observed baryon asymmetry lies below the Planck reference level $ΔN_{\rm eff}=0.284$ and above the projected CMB-S4 sensitivity $ΔN_{\rm eff}=0.06$.

Building on Jacobson's thermodynamics derivation of Einstein field equations, the "generalized entropy and varying-G" (GEVAG) framework was proposed to consistently incorporate generalized horizon entropy $S=f(A)/4G$ into both the thermodynamics and the geometry of spacetime. This leads to an effective gravitational coupling $G_\text{eff}=G/f'(A)$. A related "entropy-gravity correspondence" (EGC) instead is equivalent to promoting this horizon relation to a radially varying bulk coupling $G_\text{eff}(r)$. We clarify the similarities and fundamental distinctions between these approaches. Although they share the same horizon consistency relation, their global causal structures and asymptotic geometries can differ substantially. In addition, the radial prescription of EGC introduces an additional ambiguity for multi-center configurations. We further examine a near-horizon extension of GEVAG, which restores the equivalence between thermodynamic and ADM masses that is absent in the horizon-only formulation. We then discuss the implications of these different prescriptions for the Bekenstein bound. The Bekenstein bound provides a surprising link between $G_\text{eff}$ in near horizon GEVAG, EGC, and the one obtained in the recent $f(R)$-reconstruction approach of generalized entropy geometry via Wald entropy. Finally, we raise the most important question: what exactly is the $G$ measured in laboratories?

Pauli exclusion is often regarded as imposing a model-independent lower bound on the mass of fermionic dark matter in galaxies. We show that dark-sector interactions can substantially weaken this conclusion. In particular, eV-scale fermions can form bound structures with the characteristic sizes and densities of dwarf galaxies, thereby circumventing the conventional Tremaine-Gunn mass constraint. Within these objects, the degeneracy pressure is balanced by an attractive finite-range scalar Yukawa force that is significantly stronger than gravity. The interaction acts on dwarf-galaxy scales while remaining screened on larger scales. We derive the evolution of the resulting dark-matter fluid and identify a viable cosmological history in which structures first form gravitationally, with the new interaction becoming active only at late times. As a proof of concept, we construct a model in which a single late-time phase transition generates the required dynamics. These results provide a new route to exceptionally light fermionic dark matter and demonstrate that dark-sector interactions can qualitatively alter conventional phase-space limits.

The study of the dynamics of regular black holes is an emergent area of research. Recent works have discussed how to deform the Einstein field equations to regularize spherically symmetric black hole solutions due to the introduction of a new physics scale acting as regulator. In this exploratory paper, we consider for the first time the problem of constructing field equations in which the regularization scale is a dynamical field. Such field equations may provide an effective description of the evolution of the cores of regular black holes due to the backreaction of matter, and a novel avenue for constructing alternative dynamical solutions of theoretical and phenomenological interest. We discuss a general family of field equations describing spherically symmetric gravity coupled to a scalar field, and study whether the sector with a constant scalar field contains solutions describing static regular black holes with no additional physics scales aside from the ones provided by the scalar field. We show that this question can be reduced to solving a linear partial differential equation for the coupling functions between the scalar and the metric degrees of freedom.

The formation of the Galactic bulge remains incompletely understood, with evidence pointing to different stellar populations, including a bar-driven component, an inner-disk population, and an older spheroidal component. Chemical abundances provide critical constraints on the origin of these populations, particularly for odd-Z elements such as Na and Al, as well as Mg, whose behaviour at high metallicity is still a matter of debate. We aim to investigate the presence of overabundances of Na, Mg, and Al in Galactic bulge stars, with particular emphasis on the metal-rich regime, and to evaluate their consistency with predictions from chemical evolution models. We re-derived the abundances of Na, Mg, and Al for a sample of 55 bulge red giants previously analysed in the literature. Our study is based on high-resolution UVES spectra obtained with the ESO Very Large Telescope and employs spectrum synthesis using the Turbospectrum code, with updated atomic and molecular line lists. We find somewhat lower abundances of Mg and Al at the metal-rich end than previous studies, while a fraction of the metal-rich stars still exhibit significant Na enhancements. These enhancements persist when different sets of stellar parameters are adopted, indicating that they are robust. The presence of Na-enhanced stars at high metallicity is difficult to reconcile with standard chemical evolution models and suggests additional enrichment processes in the bulge, or a particular behaviour of stellar yields with metallicity. The Na enhancement could be due to metallicity-dependent yields from massive stars, not taken into account in available models, and/or enrichment by asymptotic giant branch stars, or due to second-generation stars evaporated from globular clusters, the latter option arising because for the metal-rich ([Fe/H]>0) stars a Na-O anti-correlation appears to occur.

Stellar multiplicity at different orbital periods is probed by different techniques: radial velocities at the shortest periods, direct imaging at the longest, and astrometry in between. Gaia DR3 provides unprecedented astrometric information to constrain binary populations with periods of tens to thousands of days. Beyond the small fraction of direct orbit solutions, Gaia publishes coarser astrometric diagnostics for all objects, such as on-sky accelerations, jerks, or the single-star goodness-of-fit measure, RUWE. We show that these diagnostics together are sensitive to a far wider range of orbital periods than orbit solutions alone. Built on the Gaiamock emulator, we develop a forward-modelling framework to constrain rates of multiplicity from Gaia data, using all astrometric solution types. We apply this framework to $366~027$ primaries of $0.2$--$0.75\,M_\odot$ between $50$ and $200$ pc, including vastly more M-dwarfs than previous multiplicity studies. For fiducial models of the period and mass-ratio distributions, the inferred multiplicity fraction is approximately constant at ${\sim}45\%$ from the solar-type regime down to $0.4\,M_\odot$, only then dropping to ${\sim}15\%$ by $0.2\,M_\odot$. This mass-multiplicity relationship revises the conventional picture of a monotonically rising mass--multiplicity relation, and aligns the upper M-dwarf regime with solar-type stars rather than placing it on a continuous decline.