高能暂现源 · 每日文献综述

The origin and evolution of massive stars in active galactic nucleus (AGN) discs remain uncertain. We develop a semi-analytical model that follows the evolution of an embedded core-collapse supernova (CCSN) remnant and the subsequent formation and growth of a compact gas cloud. In the dense disc environment, efficient radiative cooling can strongly compress or bypass the Sedov-Taylor stage and drive the remnant rapidly into radiative snowplow evolution. After the remnant loses its interior pressure support, partial backflow of cooled shell fragments and refilling gas may initialize a pressure-confined and tidally limited seed cloud. The cloud then grows through shear-limited Hill capture until the gravitational, tidal, shear, photoionization, and magnetic conditions for collapse are simultaneously satisfied. The outcome depends strongly on the supermassive black-hole (SMBH) mass and explosion radius. Models with the lowest SMBH mass yield fewer than one massive star per event on average, whereas the most massive SMBH models can produce from several to several hundred. For a top-heavy initial mass function, massive stars dominate the resulting stellar mass and feedback budget. Embedded supernovae may therefore provide a localized gas-recycling channel for second-generation massive-star formation in AGN discs.

The discovery of more than 300 $γ$-ray pulsars by the Fermi Large Area Telescope (Fermi-LAT) has revealed a rich diversity of light-curve morphologies that remains challenging to reproduce within purely magnetospheric emission models, suggesting that particle acceleration and radiation may occur, at least in part, in the striped-wind current sheet. We compute a comprehensive atlas of pulsar $γ$-ray light curves based on the split-monopole current sheet geometry, with the goal of quantifying the role of pair plasma loading in shaping the observed pulse morphology. The current-sheet surface is described analytically and assumed to be the dominant site of high-energy photon emission. Spatially dependent emissivity prescriptions are introduced through a minimal set of parameters that explicitly break the north-south and azimuthal symmetries of the emitting plasma. With only a few physically motivated parameters, the model is able to reproduce a broad range of the observed $γ$-ray light-curve morphologies, including asymmetric, multi-peaked, and highly structured profiles. The results show that asymmetric emissivity, possibly related to pair-plasma loading, provides a natural and economical mechanism capable of reproducing a substantial fraction of the observed diversity of $γ$-ray pulse profiles. The current-sheet scenario therefore appears to provide a promising and physically motivated framework for high-energy pulsar emission.

After two decades of observations, pulsar timing array collaborations have reported strong evidence for a stochastic gravitational wave background, most likely sourced by an inspiraling population of supermassive black hole binaries. Because that population is finite, anisotropy in the background is inevitable, producing hotspots on the sky that track the loudest binaries. Building on the Fisher formalism for anisotropic backgrounds, we recast the directional Fisher information as effective sensitivity curves on the sky, distinguishing the radiometer and full-Fisher estimators, along with a sky-weighted curve that reduces the anisotropic sky to a single spectrum and recovers the standard isotropic curve in the isotropic limit. We implement five sky-decomposition bases: pixel, spherical harmonic, square-root spherical harmonic, radiometer, and principal-map. We demonstrate the framework on an IPTA-like pulsar timing array: characterizing the angular response, analyzing the Fisher structure, recovering injected anisotropic hotspots, and forecasting future-array sensitivity. The framework is released as an extension to the sensitivity software package hasasia.

Dipole-radiationlike deviations from general relativity are most prominent during the early inspiral of compact binaries, making space-ground multiband observations a potential probe of such effects. In the same regime, orbital eccentricity can leave a significant imprint on the waveform and is therefore essential for robust dipole-radiation constraints. For the first time we present a multiband Bayesian inference pipeline for stellar-mass binary black holes that simultaneously incorporates eccentricity and a theory-agnostic dipole-radiation correction. We find strong degeneracies among the dipole parameter, chirp mass, and eccentricity, showing that eccentricity can broaden the inferred dipole posterior by opening an additional degeneracy direction. Even so, for a GW231123-like source, one year of TianQin or LISA observation with ground-informed priors from a next-generation detector network can still constrain the dipole parameter to <inline-formula><mml:math><mml:mrow><mml:mo>|</mml:mo><mml:mi>b</mml:mi><mml:mo>|</mml:mo><mml:mo>≲</mml:mo><mml:mi>O</mml:mi><mml:mo>(</mml:mo><mml:msup><mml:mrow><mml:mn>10</mml:mn></mml:mrow><mml:mrow><mml:mo>-</mml:mo><mml:mn>7</mml:mn></mml:mrow></mml:msup><mml:mo>)</mml:mo></mml:mrow></mml:math></inline-formula> under inference with noisy data. Our results show that multiband binary black hole observations provide a promising and distinct channel for testing theory-agnostic dipole radiation, while also highlighting the need for more complete waveform modeling in future precision tests of gravity.

Surveys such as DESI release data in stages, and each release invites a fresh assessment of whether dark energy is consistent with a cosmological constant. Standard Wilks-based $σ$ values are interpreted as if the test were performed only once, yet revisiting the same question at DR1, DR2, DR3, and beyond inflates the chance of an apparently significant fluctuation. We reanalyse the DESI BAO evidence for dynamical dark energy using an e-process, a likelihood-ratio-based measure of evidence that remains valid under repeated looks at accumulating data: it controls the false-detection probability under continued testing across releases with no trials-factor penalty. Applied to the DESI DR1$\to$DR2 BAO sequence, the result depends strongly on which departures from $Λ$CDM the test is designed to detect. For a pre-specified alternative aligned with the DR2-preferred direction, the running evidence reaches $M_{DR2} = 33.97$, crossing an illustrative 5% threshold of 20. The evidence is concentrated almost entirely in the LRG2 redshift bin, and removing that bin reduces the running e-value to $M = 0.49$, mildly favouring $Λ$CDM. When allowing any of the seven bins to have produced the excess, the signal does not survive a look-elsewhere correction. Other physically agnostic alternatives also fail to reject $Λ$CDM, while a physically motivated thawing-quintessence alternative rejects more strongly than any agnostic choice. The concentration of evidence in LRG2 specifically is difficult to reconcile with a smoothly evolving equation of state. The data therefore points to a fragile, single-bin, specification-dependent signal rather than robust evidence for dynamical dark energy. We recommend that future DESI, Euclid, Roman, and LSST data releases report an anytime-valid e-process value with its test specification stated alongside conventional $σ$ significances.

Theoretical spectral line shapes describe the distribution of opacity due to bound electronic transitions in hot dense plasmas and are used to fit emergent spectra from many astrophysical sources. Deficiencies in line broadening theory have been proposed as a possible explanation for unresolved discrepancies between theoretical and observed spectra in white dwarf star atmospheres and laboratory experiments at white dwarf star photosphere conditions. One possible source of these discrepancies is the formation of quasi-molecules. Quasi-molecules are close (unbound) collisions between atoms, which broaden line shapes and create additional satellite lines. Quasi-molecules are challenging to implement into traditional line shape codes and have historically required a number of physical approximations beyond what is used in standard Stark broadening models. Here we present a new approach to calculating line shapes with quasi-molecular resonances, using a novel multiple-basis method that considers both atomic and molecular states. We implement this approach into a simulation line shape code, present hydrogen Lyman-series line shapes with quasi-H$_2^+$ resonances, and demonstrate the impact our new line shapes have on hydrogen-atmosphere white dwarf star model spectra. We find that our new approach leads to broader quasi-molecular features that agree well with observed spectra in initial comparisons.

Young, forming planetary-mass objects often exhibit clear signatures of ongoing mass accretion and are thought to accrete material through processes analogous to those operating in young stars. In this study, we present high-spectral-resolution observations of asymmetric and time-variable H$α$ line profiles from the planetary-mass companion SR~12~c. The H$α$ line was observed at a resolving power of $R \sim 49,000$--40{,}000 (corresponding to 6.1--7.5~km~s$^{-1}$) using the High Dispersion Spectrograph (HDS) on the 8.2 m Subaru Telescope. Strong H$α$ emission is clearly detected, while higher-order Balmer lines (H$β$, H$γ$, and H$δ$) are not detected due to their faintness. The H$α$ line profiles are well spectrally resolved and exhibit blueshifted emission peaks, which can be interpreted as arising from either (a) emission partially absorbed by redshifted accreting material along the line of sight and/or (b) geometric occultation by the inner circumplanetary disk. Moreover, the H$α$ flux shows significant variability at 43.6~$\pm$~6.4~\% relative to the peak flux on hourly timescales. During a continuous 2.5-hour observing sequence, the emission component peaking at approximately $-30$~km~s$^{-1}$ weakened over the first hour. Subsequently, an emission component centered near $-10$~km~s$^{-1}$ became dominant and remained stable for the remaining 1.5 hours. We discuss possible interpretations of this behavior. Overall, these results support that magnetospheric accretion is operating in the planetary-mass object SR~12~c while a scenario combining boundary-layer accretion with a failed wind cannot be ruled out.

We investigate the excitation region of black hole quasinormal modes (QNMs) from both analytical and numerical perspectives. On the analytical side, we propose that the QNM excitation radius is identified by the dominance switching of WKB solutions across an anti-Stokes line. Based on this picture, we derive the condition for the QNM excitation radius in Kerr spacetime. In the Schwarzschild limit with mass $M$, we reproduce the previously known value $r=2.556929 M$, which differs from the light ring radius $r=3M$. We also show that the excitation radius is independent of the angular mode $\ell$ in the high-overtone limit. As an independent approach, we employ the numerical convergence test of QNM-plus-tail expansion and obtain values consistent with the Stokes geometry in the high-overtone limit at low and intermediate spins. In the extremal limit, the QNM convergence radius approaches the outer horizon, which is captured by the Stokes geometry of the zero-damping modes, rather than the high-overtone limit. This is consistent with the fact that the ringdown is dominated by zero-damping modes in the extremal limit. Based on the complementary analysis of Stokes geometry and the convergence test, we argue that in general, the QNM excitation radius depends on the QNM overtone number, giving rise to an effective QNM convergence region.

We study oscillon formation and gravitational wave production in a generalized exponential plateau inflationary potential. Using Floquet analysis, we identify parametric instability bands consistent with oscillon formation, and solve numerically for the oscillon profile, finding quasi-breather solutions with lifetimes $τ_{\rm osc} \cdot m_{\rm eff} \sim 10^3$ --- $6\times10^4$. Applying the poltergeist mechanism, we compute the induced gravitational wave spectrum and find a peak at $f_{\rm peak} \approx 2.5\times10^{10}$~Hz with amplitude $Ω_{\rm GW,0}\,h^2 \sim 10^{-9}$--$10^{-8}$ for the benchmark parameter $β_{\rm pot} = 5\times10^{-6}$. This is far below the region forbidden by big bang nucleosynthesis. For $β_{\rm pot} = 5\times10^{-5}$ the signal exceeds the big bang nucleosynthesis bound for all considered oscillon energy fractions, constraining the parameter space of the model. The signal falls in the GHz regime, potentially accessible to future resonant cavity experiments.

The Milky Way Mapper program in the fifth generation of the Sloan Digital Sky Survey (SDSS-V/MWM) has observed millions of stars, thousands of them in open clusters. The Open Cluster Chemical Abundances and Mapping (OCCAM) survey continues to create comprehensive datasets of open clusters and their members in order to constrain Galactic parameters. This eleventh contribution from the OCCAM survey is the first to use stellar parameters from stars observed with the optical Baryon Oscillation Spectroscopic Survey (BOSS) spectrograph to determine cluster membership. We use data from SDSS-V/MWM's 20th Data Release (DR20) and curate a sample of 1883 stars in 111 open clusters, including 95 not in previous OCCAM samples based on infrared data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectrograph. The sample includes 16 clusters with stars observed using both the BOSS and APOGEE spectrographs, and we find consistent agreement in measurements of both [Fe/H] and [$α/M$]. The BOSS sample includes the majority of the clusters at young ages (Age $< 150$ Myr) that complement the APOGEE sample of primarily older clusters. We use the combined BOSS+APOGEE OCCAM sample to constrain the radial metallicity gradient with respect to $R_{guide}$ ($-0.079 \pm 0.005 \text{ dex kpc}^{-1}$) and $R_{gc}$ ($-0.082 \pm 0.006 \text{ dex kpc}^{-1}$), which agree well with results from previous OCCAM papers using only APOGEE data. Finally, the inclusion of the primarily young BOSS clusters has not changed that the OCCAM open cluster sample indicates no significant evolution of this gradient in different mono-age populations.

In this paper, we investigate scattering of a scalar field near a Schwarzschild black hole through its $S$-matrix. Within this framework, we obtain a novel derivation of Hawking radiation by computing the emission rate, which yields a Bose--Einstein distribution with temperature $T_H=(8πGM)^{-1}$, the Hawking temperature. In addition to Hawking radiation, the S-matrix exhibits antibound states, corresponding to excitations at the threshold of becoming scattering (bound) states if the potential is decreased (increased). We interpret these excitations as constituents of the black-hole quantum atmosphere: a thermalised region outside of the event horizon, which is the source of the Hawking radiation. Using the spectrum of antibound states, we found the atmospheric radius, $r_{\text{Atm}} \approx 2.77 r_{s}$, which is in good agreement with previous results in the literature obtained through other methods. Our results indicate that, at the macroscopic level, the quantum atmosphere behaves like an ordinary thermalised gas at the Hawking temperature.

This work examines the observational signatures of rotating black holes with tidal charge in the Randall--Sundrum braneworld scenario. Combining an elliptic-integral-based analytical treatment with numerical ray tracing, we characterize photon motion around braneworld black holes in detail. For small observer inclinations, secondary images remain embedded inside the primary emission rings. As the inclination becomes larger, the primary and secondary images gradually separate and produce a strongly asymmetric image morphology. We show that the image asymmetry and the deformation of the inner shadow are jointly controlled by the black hole spin, the tidal charge, and the observer inclination. To analyze the frequency shifts across the accretion disk, we extend the emitting region from the ISCO down to the event horizon by including the plunging flow. The results indicate that the observer inclination is the dominant factor governing the frequency-shift distribution. In addition, we reconstruct braneworld black hole images using a fisheye-lens ray-tracing model. The optical morphology and brightness distribution show a clear dependence on the observing frequency, especially when comparing 230~GHz with 86~GHz. We also contrast the brightness distributions of prograde and retrograde disks, finding that both the total intensity and the peak intensity at 86~GHz are higher than those at 230~GHz. For negative values of the tidal charge, we further investigate the corresponding frequency-shift behavior and 230~GHz intensity profiles, which may provide useful theoretical guidance for future studies of extra-dimensional gravity models.

Weak gravitational lensing (WL) peaks probe non-Gaussian information of the large-scale distribution of matter that is not captured by two-point lensing statistics. We study the cosmological potential of the height distribution, redshift distribution, and angular clustering of high-valued WL peaks using a Bayesian inference approach that mimics a $\textit{Euclid}$ analysis. We use a forthcoming dark-matter-only hypercube, which varies cosmology in a ten-dimensional space, including evolving dark energy, neutrino mass, decaying dark matter, and the running of the scalar spectral index. We find the individual WL peak statistics to be complementary, as the redshift distribution best constrains the matter density, $Ω_\mathrm{m}$, and the dark energy equation-of-state parameters, $w_0$, and $w_a$; the height distribution and angular clustering are most sensitive to the amplitude of the primordial power spectrum, $\ln(10^{10}A_\mathrm{s})$; while combining the three statistics allows us to also probe the baryon density, $Ω_\mathrm{b}$, and the Hubble parameter, $h$. A comparison to the shear two-point correlation function demonstrates that WL peaks alone outperform the commonly used statistics, while even tighter constraints are obtained when combining all. Considering the 2-dimensional $Ω_\mathrm{m}-\ln(10^{10}A_\mathrm{s})$ and $w_0-w_a$ parameter planes, we find that the redshift distribution outperforms the angular clustering and peak-height distributions. We study the impact of the smoothing scale and find that, typically, the smallest scales yield the best results and the figure of merit improves by a factor $\approx2$ when combining multiple scales.

We study tidal flows in the convective envelopes of rotating, magnetised fluid bodies, such as low-mass stars and giant planets. In well-mixed convective regions, (magneto-)inertial waves are linearly excited by tidal forcing, and their dissipation can dominantly drive spin and orbital evolution in many close star-planet and binary star systems. We perform linear magnetohydrodynamic calculations of wavelike tides in spherical-shell geometry of a tidally-forced, rotating, incompressible, viscous and non-ideal magnetised fluid. Our calculations consider the widest range of magnetic field configurations to date (including both aligned and misaligned dipole fields, free-decay dipole and quadrupole fields, azimuthal "Malkus fields" and mixed poloidal-toroidal "Prendergast fields") to analyse the effects of magnetic fields on the wavelike response and dissipation. We find that the tidal response at a given frequency depends strongly on both magnetic field strength and geometry. Magnetic fields with strong poloidal components modify the flow more efficiently and introduce high-frequency Alfvénic resonances associated with weakly damped eigenmodes. When an enhanced (turbulent) viscosity is adopted, we find that viscous dissipation remains comparable to Ohmic dissipation for strong fields, in contrast to previous studies in which Ohmic dissipation was argued to dominate. We also explore the variation in magnetic effects as the shell thickness, magnetic Prandtl and Ekman numbers are varied. Finally, the frequency-averaged tidal power is found to be largely insensitive to the magnetic field in most cases, though significant deviations are found for free-decay fields. Our results have important implications for the tidal evolution of magnetised, rotating stars and planets.

The Hubble tension is usually formulated as a disagreement between two determinations of a single scalar parameter, $H_0$, within an isotropic FLRW model. We develop a quantitative framework treating the tension as a consistency test of the scalar FLRW compression of cosmological data in a homogeneous, anisotropically expanding Bianchi type I background. Beyond synthesizing established results on Bianchi I kinematics, null geodesics, and optical propagation, our original contribution is a worked weak-shear, axisymmetric calculation mapping a specified shear history into a low-redshift luminosity-distance quadrupole. The calculation explicitly separates the direction-dependent redshift--affine-parameter mapping from the Jacobi-focusing contribution, propagating the resulting distance quadrupole through an analytic polar-cap toy window. For freely decaying shear, we obtain $A_D(z) = -B_{H0} + (2q_0-1)B_{H0}z/2 + (5-q_0-18q_0^2+6j_0)B_{H0}z^2/12 + O(z^3, B_{H0}^2)$, where $B_{H0}=(H_{\parallel 0}-H_{\perp 0})/H_0$ and $j_0$ is the mean jerk parameter. A representative BBN limit, $Ω_{σ0} \le 10^{-23}$, implies $\vert{}B_{H0}\vert{} \le 9.5 \times 10^{-12}$ and a distance-modulus quadrupole below $2.4 \times 10^{-11}$ mag at $z=0.15$. The early-Universe bound used is adopted from prior work; the novelty lies in propagating it through the derived Sachs--Jacobi mapping into limits on the luminosity-distance quadrupole and catalogue-window bias. By contrast, a 1% directional shift requires $Ω_{σ0} \approx 2.5 \times 10^{-5}$, while matching the Planck 2018--SH0ES 2022 separation requires $Ω_{σ0} \approx 1.8 \times 10^{-3}$. Thus, the minimal shear-only model cannot resolve the tension, though the framework supplies a falsifiable programme for testing late-time anisotropy with SNe, BAO, and standard sirens.

This work investigates the brachistochrone problem for a traveler with constant local velocity within static and spherically symmetric (SSS) spacetimes. The brachistochrone trajectory (BT) equations for ultra-relativistic travelers are derived for general SSS metrics, and the solution is formally obtained in an integral form. We then apply the result to two representative spacetimes corresponding to the singular isothermal sphere (SIS) with a finite boundary and the relativistic Plummer mass profile, respectively. For the SIS spacetime, the BT inside the boundary is solved analytically and found always to bend. As the equation of state index $w$ increases, the turning radius $r_0$ of the BT, and consequently the total time, also increase. For the BT outside the boundary, it is found that the heavier the central object, the larger the $r_0$ and the total travel time. For the relativistic Plummer model, the BT will be a straight line passing through the origin when the initial and final points' radii are comparable or smaller than the size of the core region of the mass distribution. When the end points lie well outside the core region, the BT bends, exhibiting a larger turning radius for a more concentrated core. We then extend the consideration to travelers with subluminal constant velocity $v$ and show through the generalized Fermat's principle that the BT will be the same geodesic in the optical metric as ultra-relativistic travelers, with the total travel time scaled by a factor of $1/v$.

We present a framework for studying high Rayleigh number turbulent convection to better understand stellar and planetary convection zones. Utilizing the statistical symmetries of the fully developed turbulent state of Boussinesq convection, we identify relevant mean and fluctuating quantities. After validating these symmetry assumptions through numerical simulations, we formulate the governing equations. Vertical profiles of key physical quantities in the saturated turbulent state are explored in the simulations. To develop a modal theory, we use Fourier expansions, review linear theory, and use the Craya-Herring velocity decomposition. The modal equations we derive describe high Rayleigh-number turbulent convection dynamics self-consistently in terms of nonlinear interactions between three mode types: growing gravity modes, decaying gravity modes, and horizontal modes. Energy extracted by the growing modes from the superadiabatic background subsequently follows multiple pathways toward dissipation, enabled by the mode couplings. Among these, the traditionally dominant pathway is the turbulent cascade of the growing modes themselves. Reduced modal equations capture this pathway, precisely describing (i) mutual interactions between growing modes, and (ii) the excitation of decaying and horizontal modes, which are subordinate to the growing modes. Determining the relative efficiency of the pathways requires investigating their modal spectra using numerical simulations and kinetic models.

Turbulence within the intracluster medium (ICM) influences galaxy cluster thermodynamics and virialisation, contributing to non-thermal pressure support and impacting hydrostatic mass estimates. Characterising this turbulence through thermodynamic fluctuations remains observationally challenging due to the non-linear relationships between observables such as density and pressure, and the underlying velocity field. This study aims to constrain the properties of ICM turbulence by performing a comprehensive reanalysis of the Sunyaev-Zel'dovich (SZ) surface brightness fluctuations based on Planck survey observations of the Coma cluster. We analyse the 2D power spectrum of SZ fluctuations, modelling the underlying 3D pressure fluctuation power spectrum assuming Kolmogorov-type turbulence. We infer key parameters from a simulation-based inference framework relying on normalizing flows to accurately recover posterior distributions. By constraining the pressure fluctuation power spectrum, we are able to infer the properties of turbulence in the Coma cluster, finding a large injection scale of $l_{\text{inj}} = 540^{+450}_{-200}$ kpc, a slope of $α= 3.50_{-0.46}^{+0.50}$ (under Gaussian prior), and a substantial 3D Mach number of $\mathcal{M}_{3D} = 0.60^{+0.13}_{-0.09}$. These values correspond to turbulent velocities in the range $σ_{v,\text{ }3D} = 357-1095$ km/s and a non thermal pressure fraction of $P_{\text{turb}}/P_{\text{tot}} = 0.17_{-0.04}^{+0.06}$. Our results are consistent with recent direct velocity measurements from XRISM, supporting a scenario of significant turbulence in the Coma cluster and highlighting the complex interplay of dynamical processes within its ICM. Our simulation-based inference approach applied to SZ fluctuations paves the way for systematic multi-probe studies combining SZ and X-ray data, as well as direct and indirect observations.

Context: Modern cosmological simulations rely on sophisticated assumptions and generate rich, highly complex datasets. Interpreting their results in order to extract new scientific insights remains challenging. Existing visualisation tools offer powerful capabilities but often come with a relatively high barrier for entry, and are not designed with a focus on knowledge discovery through real-time, intuitive visual analytics. This stands in contrast to other research domains, such as bioinformatics, where visual analytics tools have become deeply embedded in scientific discovery workflows. Aim: Our goal is to complement the existing ecosystem of cosmological visualisation tools with a lightweight, user-friendly application that supports visual analytics and frictionless dissemination of results to the scientific community. Methods: We developed ARGOS, an open-source, web-based environment for real-time visual analytics, tailored to cosmological simulation outputs and designed with an emphasis on user experience. ARGOS combines GPU-accelerated browser rendering for interactive exploration of large datasets with a template-driven approach that enables rapid adaptation to other types of data and analysis workflows. Importantly, ARGOS combines catalogue-level and object-level exploration, allowing users to move seamlessly from large ensembles of objects to snapshots of individual objects. Results: We demonstrate how ARGOS can support intuitive visual data exploration through example dashboards for multiple cosmological particle datasets, and illustrate broader applicability with dashboards for SKIRT synthetic multi-band imaging data products. Source code is freely available at https://github.com/pvaut/skirt-argos under the MIT licence. A reference deployment, including sample data, is available at https://skirt-argos.ugent.be.

Faculae are a dominant source of stellar activity noise in radial velocity measurements, yet their low contrast and broad surface distribution make them difficult to track in disc-integrated observations. We apply Spectral Ratio Analysis (SRA) to HARPS-N Sun-as-a-star observations to isolate and characterize the spectral imprint of facular regions over rotational timescales. The resulting SRA spectra show coherent, line-dependent variability sensitive to surface magnetic activity, with the Fe I 4377 Angstrom line exhibiting a particularly strong diagnostic response to facular coverage. We interpret the observed signatures using two complementary synthetic frameworks: composite PHOENIX spectra, from which we derive best-fit facular temperature contrasts in the range 200-400 K, and MPS-ATLAS spectra synthesized using MURaM simulations of the quiet Sun including a small-scale dynamo and magnetically-enhanced facular analogues with initial mean vertical magnetic fields of 100G, 200G, and 300G. Both approaches are benchmarked against facular filling factors measured from Solar Dynamics Observatory (SDO) disc-resolved images. We find good agreement between SDO-measured and SRA-inferred filling factors using the Fe I 4377 Angstrom line, with Pearson R coefficients of 0.587-0.927 across models and timescales. The estimated filling factors track the solar activity cycle, rising from ~1.5% at lower activity to ~5.5% at higher activity, consistent with SDO-measured filling factors. These results demonstrate that SRA offers a means to reliably track surface magnetic activity in disc-resolved spectra, which is necessary for mitigating the effects of activity on RV characterization of exoplanet masses and atmospheres at modern precision.

We report on a coordinated campaign by amateur astronomers using a combination of high and low resolution spectroscopy to observe the 2025 eclipse of the symbiotic binary V1413 Aql shortly after a probable Z And-type symbiotic outburst. We measured the eclipse time of minimum and computed an updated eclipse ephemeris. Our spectra were calibrated in absolute flux and multi-Gaussian fits were used to resolve and quantify components of the Hα emission line. We measured the radial velocity curve of the white dwarf and determined the semi-amplitude as 25.7 km/s and the systemic radial velocity as 95.1 km/s. We found the spectral continuum was consistent with that of a late F or early G type giant star.

We construct an explicit model where dark matter consists of 't Hooft-Polyakov monopoles. The dark sector is in thermal contact with the Standard Model, and dark monopoles are created by a thermal phase transition in the early Universe. Generically, the abundance of monopoles is negligible with respect to that of stable dark elementary particles. We show how to avoid this by taking the lightest stable particle, a dark fermion, sufficiently light for its abundance to be suppressed, yet heavy enough to satisfy constraints on dark radiation. In this specific window of parameters, dark matter is composed of monopoles with a mass of about $10^8$ GeV or larger, depending on the nature of the phase transition. This candidate lies beyond the reach of present, conventional dark-matter detection experiments. However, the model necessarily predicts dark radiation, with $ΔN_{\rm eff}$ close to present-day bounds. In addition, if the dark phase transition is strongly first order, we find that the corresponding gravitational wave spectrum lies close to the region probed by future interferometers.

Mapping Calabi-Yau geometry to early Universe cosmology remains a primary goal in string phenomenology. We present an inflationary mechanism where flux stationarity shifts the field dynamics, driving inflation along the volume-controlling saxion direction near a Hodge boundary. In this region, the internal geometry strictly dictates the scalar potential. This setup stabilizes the field against heavy moduli corrections without consuming extra flux tadpoles. As a result, the properties of the geometric boundary translate directly into primordial tensor perturbations, creating a clear physical link from string compactifications to measurable data. The resulting geometric predictions match current cosmic microwave background limits and provide specific, testable targets for upcoming LiteBIRD and CMB-S4 observations.

The traditional distance ladder measures the standardized peak absolute magnitude M^B of Type Ia supernovae (SNIa). According to the SH0ES collaboration, the distance ladder value of M^B is highly discrepant with the value inferred from the cosmic microwave background (CMB) assuming the LCDM cosmology. This CMB-distance ladder tension is insensitive to the actual late time expansion history of the Universe. To derive a value of the Hubble constant H_0, from M^B requires a cosmological model. However, the magnitude-redshift relation of SNIa provides tight constrains the expansion history. As a consequence, uncertainties in the conversion of M^B into H_0 have no significant impact on the CMB-distance ladder tension. The tentative claim by the Dark Energy Spectroscopic Instrument collaboration for late time evolution of the dark energy equation of state does not alter this conclusion.

We introduce the data reduction pipeline for the Tartu Observatory Fiber-fed Echelle Spectrograph (TOFES). TOFES is installed in the Coudé room and will be connected to the 1.5 m Tartu Observatory AZT-12 telescope through a four-channel instrument adapter to be mounted at the Cassegrain focus of the telescope. The spectrograph has an average spectral resolution of 30,000 and covers the 390 to 900 nm wavelength band in a single exposure. The data reduction pipeline, based on the PyReduce package, was tested on spectra of the Sun. We also present the Spectroscopy-Toolbox package, which was developed to provide additional tools for diagnostics and spectral line identification for radial velocity measurements. The spectrograph will address a range of scientific questions, including the stellar characterisation of Herbig AeBe stars to measure accretion contamination from their protoplanetary disks, the stellar characterisation of exoplanet host-stars including the Ariel space mission targets, and radial velocity monitoring of large-scale atmospheric variability in massive stars.

HD 156424 is a hot magnetic star in the Sco OB4 association and has previously been identified as part of a binary system. Spectropolarimetric results show that the companion star is also strongly magnetic, and thus this is a rare example of a doubly magnetic hot binary. In this work, we aim to present a more detailed analysis of Transiting Exoplanet Survey Satellite data including phase variation. We find short-term phase variation consistent with an oblique magnetic rotator, as well as long-term phase variation consistent with the third element proposed previously. We performed asteroseismic modelling of the star and determined that the pulsations are most likely associated with the primary of the system. Our best-fit models are universally young, and we find that the star is well fitted by a model with $M$=7.5 M$_{\odot}$.

We present the largest and most homogeneous catalog of radial velocity (RV) measurements for field RR Lyrae (RRL) variables, based on both proprietary and publicly available spectroscopic data. The sample includes 17,563 RRLs pulsating in the fundamental mode (12,353 RRab), in the first overtone (5,011 RRc), and in double-mode (199 RRd). The RV curve (RVC) templates for metallic and Balmer lines were used to derive RV amplitudes and $V_γ$ velocities, defined as the RV of the stellar barycenter with respect to the Sun. The typical accuracy across the catalog is on average 3.8 km s$^{-1}$ for well-sampled RVCs, 6.5 km s$^{-1}$ for RVCs with 3-7 phase points and 11.3 km s$^{-1}$ for RVCs with fewer than three phase points. The use of different spectroscopic diagnostics and RVC templates provides, within the errors, very similar $V_γ$ velocities. We found that the metallicity dependence of RV amplitudes is vanishing for metallic lines, but becomes increasingly significant for H$γ$ and H$δ$. Moreover, the scaling relations between photometric (V, $G_{BP}$, G, $G_{RP}$) and RV amplitudes are linear for RRc and nonlinear for RRab variables, independently of the adopted diagnostic. This circumstantial evidence indicates that convection affects more luminosity than RV amplitudes when moving from the blue (hot) to the red (cool) edge of the instability strip. The spectroscopic Bailey diagram (RV amplitude versus period) shows a smooth transition and a reduced spread at a fixed period, when moving from metal-poor to metal-rich RRLs. Finally, we also found evidence that the metallicity distribution function of Blazhko RRLs is skewed toward the metal-intermediate and metal-rich regimes.

In gravity theories with torsion, inflation can be driven by the dynamical torsion. Since it naturally has a derivative coupling to the axial current consisting of Standard Model particles, the reheating dynamics should be much different from conventional inflation models like Starobinsky inflation. We calculate the inflaton decay rate in detail and find that, although the 2 body decay into the fermion pair is vanishing in the massless fermion limit, the anomaly-induced 2 body decay into the gauge bosons and 3 body decay involving the Higgs boson are non-vanishing and they give sizable contributions to the total decay width of the inflaton. This gives a natural lower bound on the reheating temperature in the inflation model with dynamical torsion.

Massive stars play a fundamental role in the evolution of the Universe. Yet, several physical processes governing their evolution remain poorly constrained. Notably, the main-sequence width is sensitive to the convective boundary mixing efficiency; it becomes necessary to account for binary interactions to explain some observed properties of massive-star populations. We constrain single-star models using recent observations of massive Galactic stars from the IACOB database. We use the latest proposed empirical location of the TAMS to calibrate the convective boundary mixing efficiency, and use this calibration to test single-star evolution by comparing various model predictions to the observed populations of the IACOB sample. We compute several GENEC grids with various overshoot calibrations, angular momentum transport (AMT) treatments, initial masses and velocities. Finally, we generate synthetic populations from the tracks with SYCLIST and perform a direct comparison with the observed population. The calibrated models at slow rotation reproduce the empirical TAMS location. We find that a mass-dependent overshoot efficiency is required to fit the observational constraints. The overall rotational properties of the observed populations are well reproduced with single-star models, independently of the AMT assumptions. Models accounting only for hydrodynamical instabilities are successful at reproducing the rotational properties, unlike previous genec grids, which we attribute to the choice of winds prescription. Although the empirical TAMS of slow rotators is well reproduced, we find that models are unsuccessful at explaining the velocity dependence of the TAMS location observed in the IACOB sample. Finally, we find that single-star models fail at explaining the population of blue supergiants to the right of the TAMS location.

The pseudo-$C_\ell$ estimator recovers the true cosmic shear power spectrum by correcting for the survey window convolution while employing inverse-variance weighting based on intrinsic shape noise of source galaxies. However, this weighting scheme is optimal only on small angular scales where shape noise dominates. In this paper, we derive a quadratic estimator for the unwindowed cosmic shear power spectrum by maximizing the Gaussian likelihood of the pixelized galaxy-shape field using the full covariance matrix, which accounts for both sample variance and shape noise. By combining FFTs in the flat-sky approximation, the conjugate-gradient method, and Monte Carlo realizations of Gaussian ancillary fields, we substantially reduce the computational cost of estimating the Fisher matrix, a key ingredient of the estimator that requires repeated inverse-covariance matrix operations. Using Gaussian simulations of shape fields, we validate the method and demonstrate that it can recover the input $E$-mode power spectrum with statistically optimal precision across all angular scales. We then apply the method to shape fields generated from ray-tracing simulations for a $Λ$CDM cosmology and show that, compared with the pseudo-$C_\ell$ method, it reduces the statistical uncertainties in the $E$-mode power spectrum by 5--15\% at multipoles of $\ell \lesssim 500$. We further demonstrate that the method significantly suppresses $E$- to $B$-mode leakage across the full multipole range. Our estimator therefore provides a statistically optimal approach for measuring cosmic shear power spectra from wide-area galaxy survey data.

We reconsider the production of dark photons $A'$ as dark matter, from the perturbative decay of a dark Higgs field $h$, that is stochastically misaligned from the minimum of its potential during inflation. This is a simple and predictive framework for generating the $A'$ relic abundance. It is constrained by structure formation, since the $A'$ are initially boosted, and inflationary isocurvature fluctuations, which require small quartic couplings $λh^4$. We identify $A'$ masses between 100 eV and 1 GeV and gauge couplings $g\sim 10^{-15}-10^{-10}$ that are consistent in this scenario, and which become more tightly constrained if a generic level of kinetic mixing is present. The favored parameter region could be tested through future CMB or Lyman-$α$ observations, and, in the presence of kinetic mixing, by direct detection experiments or diffuse soft gamma-ray searches.

Including nonlinear information from modified gravity (MG) brings more constraining power to the model-independent reconstruction of MG functions. However, the calculation of the nonlinear matter power spectrum with MGCAMB+ReACT is expensive in repeated likelihood evaluations, which limits the exploration of the high-dimensional parameter space. In this work, we construct a neural-network emulator for the nonlinear correction $R_{\mathrm{MG}}(k,z)=P_{\mathrm{MG}}^{\mathrm{NL}}(k,z)/P_{\mathrm{MG}}^{\mathrm{L}}(k,z)$, which is trained with \texttt{CosmoPower} on approximately $9\times10^5$ samples and validated with representative spectra, an independent validation set, and MCMC tests with synthetic data. For $Λ$CDM and moderate MG nonlinear corrections, the emulated power spectra agree with the reference predictions to within $1.5\%$ over the full scale range considered. For the extreme nonlinear case, the same accuracy is retained for $k<0.8\,\mathrm{Mpc}^{-1}$. Over the independent validation set, the mean residual is close to zero, with the $2σ$ scatter below $1\%$ for $k<0.5\,\mathrm{Mpc}^{-1}$ and about $2\%$ on smaller scales. The synthetic data MCMC analyses recover the input $Λ$CDM cosmology and the GR limits of the reconstructed MG functions within the posterior uncertainties, showing the accuracy and reliability of the emulator for Stage-IV-like surveys. We also demonstrate three applications: using $R_{\mathrm{MG}}$ to distinguish models with nearly degenerate linear power spectra, using the emulator for theory predictions for current photometric-survey $3\times2$pt likelihoods, and forecasting DESI+CSST constraints with principal component analysis.

Compact objects with the same exterior metric are locally indistinguishable to test particles, yet observables built from retarded fields can retain information about the spacetime outside the particle's immediate neighbourhood. The self-force acting on a particle in curved spacetime provides a unique probe of both the local geometry and the global structure of the background spacetime. We calculate the static, conservative self-force on minimally coupled scalar and electric charges in the simplest thin-shell gravastar: a de Sitter core matched to a Schwarzschild exterior. Weak-field expansions in the compactness $M/R$ are obtained analytically and summed in closed form. For a scalar charge outside the gravastar the self-force is nonzero---in contrast to the exactly vanishing result for a Schwarzschild black hole of the same mass---and behaves as $\tfrac{2}{5}q^2 M R^2/r_0^5$ at large distances, while for an electric charge the universal Smith--Will force $e^2M/r_0^3$ is corrected by a structure-dependent term $\tfrac{4}{5}e^2 M R^2/r_0^5$. Inside the gravastar the scalar self-force is directed toward the center at leading order in $M/R$, vanishes linearly at the center, and produces harmonic oscillations of the charge about the center; the electromagnetic self-force inside the gravastar behaves similarly. The results demonstrate explicitly that the self-force depends not only on the local curvature surrounding the particle but also on the global structure of spacetime: although the exterior geometry of a gravastar is identical to that of a Schwarzschild black hole, the interior boundary conditions modify the regular field and therefore produce distinct self-forces.

The Hubble Space Telescope (HST) has advanced our knowledge of stellar evolution thanks to its unique high-spectral resolution and high-sensitivity capabilities in the UV region, especially for hot massive stars. Within the field of red supergiants (RSGs), it has led to several major insights as well, such as, for example, characterizing the embedded hot companion in the VV Cephei system, the detection of surface mass ejection from Betelgeuse, and unveiling the rich population of RSG+B binaries in the Magellanic Clouds. We demonstrate that nowadays (and in the decade to come) we need HST more than ever, as for the first time, thanks to the significant advances of high-angular-resolution interferometric and astrometric techniques, we can resolve the orbital motion of stellar components in RSG systems. However, the long wavelengths are dominated by the cool RSGs. Thus, observing such companions in the UV with HST is the only way to constrain the properties and velocity of the hot companions, adding the required missing piece of information for constraining the orbital solution and evolutionary status of RSG systems. Such observations are critical for understanding the interaction and mass transfer in massive binary systems and their connection to the observed population of supernovae.

We study the realization of the chemical potential mechanism in cosmological collider physics in a robust class of inflationary models arising from multiple higher-dimensional gauge fields. The rolling inflaton background corresponds to an electric field in the extra dimension in which charged particles are produced analogously to the Schwinger mechanism, while neutral particles can be produced through non-minimal interactions. We show that particles heavier than the inflationary Hubble scale can be created without Boltzmann suppression in both cases. In particular, charged Kaluza-Klein excitations can be created through minimal gauge interactions. We construct realistic models along these lines consistent with both theoretical and experimental constraints.

Cosmological simulations have recently begun to quantify the halo-to-halo variance in the phase-space distribution of dark matter around the Sun. We use a sample of nearly one hundred Milky Way-like galaxies from the TNG50 simulation to determine what aspects of this variance control the predictions for dark matter direct detection. Contrary to the isotropy assumed in the standard halo model, we find the dark matter median azimuthal velocity is nonzero and preferentially corotating, i.e., in the direction of the baryonic disk's rotation, ranging from 6-70 km/s (16th-84th percentile). This corotation suppresses predicted scattering rates in laboratory experiments searching for dark matter lighter than 50 GeV and significantly affects the expected daily modulation amplitude for directional detectors. In particular, this induces a 21% uncertainty on the upper limit of the dark matter-nucleon interaction cross section at peak sensitivity for a typical isotropic ton-scale experiment. This uncertainty is not irreducible, however: it is strongly correlated with the rotational velocity. If studies of the Milky Way's formation history determine the rotation speed, this astrophysical uncertainty is reduced to 7%.

Measurements of the thermal Sunyaev-Zel'dovich (tSZ) effect have yet to form a consistent picture of the thermodynamic state of the gas in the intracluster medium: their interpretation is complicated by foreground contamination and uncertain halo masses. We present new measurements of the tSZ effect around the Dark Energy Spectroscopic Instrument (DESI) Luminous Red Galaxy (LRG) sample, together with galaxy-galaxy lensing (GGL) measurements that enable a like-with-like comparison to state-of-the-art hydrodynamical simulations. We robustly isolate the tSZ signal by directly modeling the dust and radio emission of the target galaxies using the Atacama Cosmology Telescope (ACT) single-channel temperature maps, substantially reducing uncertainties from astrophysical foregrounds. Across halo masses $M_{500}=10^{13}-10^{14}~M_\odot$ and redshifts $0.4<z<1$, we find that the fiducial 1 Gpc$^3$ FLAMINGO simulation significantly overpredicts the observed tSZ signal at $\lesssim3'$ (i.e., $\lesssim 4\,R_{500}$ at $z=0.7$). Even the simulation with the strongest gas expulsion---which successfully reproduces the gas density inferred from kinetic SZ measurements of the same galaxy sample---overpredicts the thermal pressure. Because the strongest feedback model already reproduces the observed gas density, the remaining discrepancy is difficult to explain with additional gas depletion alone. Instead, current hydrodynamical simulations appear to overpredict the thermal pressure of galaxy groups by a factor of two, pointing toward missing non-thermal pressure support or significant departures from hydrostatic equilibrium.

The ubiquity of free-floating planets inferred from microlensing and direct imaging surveys suggests that planetary ejection---a process in which planets initially born encircling a stellar host become gravitationally unbound---is common. Four overarching mechanisms have been proposed to induce planetary ejection: close approaches of neighboring planets, instabilities in binary or multi-star systems, stellar and planetary flybys, and post-main-sequence stellar evolution. Here we review the mechanisms underlying planetary ejection, as well as predictions derived from each. Current and upcoming microlensing surveys offer the potential to test existing models and distinguish between planetary ejection mechanisms, offering further insight into the demographic-level architectures of exoplanets across stellar environments.

We investigate the null geodesic structure, photon sphere dynamics, and high-energy particle collisions within a class of static, spherically symmetric hairy Horndeski black holes. Characterized by an invariant metric root at $r = 2M$ and a scalar hair parameter $Q$, the spacetime maps onto four distinct geometric domains dictated by the surface gravity $κ|_{2M}$. We derive exact analytical expressions for the photon sphere radius $r_{\text{ph}}$ and its dynamic stability criterion, showing that external circular null orbits remain dynamically unstable across non-extremal regimes. Crucially, we prove that a stable photon sphere arises exclusively in the extremal configuration ($Q = -2M$), where it coincides precisely with the degenerate horizon ($r = 2M$). We argue that this horizon-bound stable photon orbit acts as an infinitely redshifted bound state for light and ultra-relativistic particles. Finally, we analyze the Bañados-Silk-West (BSW) effect for infalling timelike test particles, demonstrating that the center-of-mass energy $E_{\text{cm}}$ for critical collisions diverges as $E_{\text{cm}} \propto (r - r_h)^{-1/2}$ strictly at the extremal threshold $Q = -2M$.

Chemical mixing during stellar mergers can significantly influence the subsequent evolution of the merger remnant. We perform a suite of three-dimensional hydrodynamical simulations of stellar mergers, each evolved for $\sim100$ stellar dynamical times until the remnant reaches a quasi-hydrostatic equilibrium. The simulations incorporate subgrid-scale diffusion models to capture the turbulent mixing of chemical elements. Starting with an idealized polytropic equation of state (EOS), we first identify the dominant mixing mechanisms and investigate how the merger outcome depends on the mass ratio, relative velocity, impact parameter, and stellar structure. We then extend our simulations to the context of stars embedded in active galactic nucleus (AGN) disks, using a realistic, composition-dependent EOS and AGN stellar models generated with the stellar evolution code MESA. We find that mergers with both younger metamorphic stars and H-rich accreting AGN stars can substantially rejuvenate old metamorphic stars through efficient core mixing after thermal relaxation. The merger remnants are nitrogen-enriched, with ${\rm N/O}\sim1$--3 and ${\rm N/C}\gtrsim5$, comparable to the abundances observed in the nebula surrounding SN 1987A. During subsequent stellar evolution, the remnants may converge onto the main sequence of isolated metamorphic AGN stars once they reach accretion--wind equilibrium. They may also deposit a significant amount of chemically enriched material into the AGN disk. This work provides a physical framework for connecting hydrodynamical stellar mergers with the long-term evolution of AGN stars and their observational and chemical signatures.

The entropy of the observable Universe is dominated, by fifteen orders of magnitude, by the horizons of supermassive black holes, and gravitational collapse into black holes has often been proposed as the Universe's preferred channel of entropy production. We examine this suggestion quantitatively, and the analysis largely refutes it. Three results are presented. First, an entropy production history: the rate $dS/dt(z)$ resolved by channel, from the star formation history and a Soltan-normalized accretion history. Black hole horizon growth exceeds all radiative channels by a factor $\sim 10^{16-17}$ after the first seeds; the total rate peaked near $z\approx 1$--$2$ and has since declined; the late peak is structural, because horizon entropy production weights accretion by the accretor's mass and the most massive accretors are assembled last. Second, a causal-hydrodynamic envelope: the fastest entropy-producing trajectory permitted by causality and gas dynamics, $\dot M \sim c_s^3/G$ in atomic-cooling halos, which reaches $10^{7\pm1}\,M_\odot$ by $z\approx 8$--$10$ without radiative throttling, and whose phenomenology (obscured, radiatively inefficient, X-ray weak, red) closely resembles the JWST little red dots. The realized-to-envelope ratio defines an efficiency $F(z)$, which remains between $10^{-7}$ and $10^{-4}$ throughout $4\le z\le 12$, even under the most generous JWST-era bracket. Third, order-of-magnitude no-go results: Boltzmann weighting of collapse channels by entropy gain, dissipative adaptation applied to self-gravitating systems, and any strong maximum-entropy-production principle in cosmology all fail at leading order, by factors of up to $10^{16}$. The Universe produces entropy overwhelmingly through black holes, yet remains far below its own envelope at all times. Whatever selects cosmic structure, it does not maximize entropy production.

We study a massive scalar field on the rotating Kalb-Ramond black hole of Kumar, Ghosh and Wang, in the (near-)extremal corner of its three-parameter family $(a,γ,λ)$. We verify by direct substitution that the Klein-Gordon-Fock equation separates on this background, with radial and angular separation constants related by $Λ_{rad}=Λ_{ang}+a^2ω^2-2amω$. At exact extremality the horizon polynomial and the function $K(r)$ share a zero, rendering $K^2/Δ$ regular there and reducing the radial problem to Whittaker form on the Kerr line $(γ=0)$ and the Kerr-Newman line $(λ=1)$. The stationary resonances saturate $ω=mΩ_H$ and satisfy the bound-state condition $μ>mΩ_H$, with overtones accumulating at the threshold from above; in the genuinely Kalb-Ramond interior we solve the exact radial equation as a two-point boundary value problem. Moving off extremality, the clouds continue onto the co-rotating zero-damped branch $ω_n=mΩ_H-iκ(n+1/2+β)$, governed by the same near-horizon exponent $β$; the photon-sphere family is a distinct observable. Greybody factors and superradiant amplification are obtained by direct integration, recovering the classical scalar amplification on Kerr. Strong-field lensing is treated in the Bozza-Tsukamoto limit with rotating photon orbits of both senses, where the prograde logarithmic coefficient departs strongly from its Schwarzschild value. The shadow contour follows from the Carter-Hamilton-Jacobi separation. Crossing the Event Horizon Telescope window of Zubair, Raza and Maqsood with the cloud-existence region yields a narrower bound on the Lorentz-violating parameters $(γ,λ)$ than either constraint alone.

We consider a massive vector-field perturbation on a Kerr black hole background. We fix the field's density at the edge of the black hole sphere of influence to model a bath of wave cold dark matter, from which the black hole can accrete endlessly. We employ the approach of Lunin, Frolov, Krtouš, Kubizňák, and Santos to separate the equations, and solve them with a mix of analytical and numerical techniques. We find that the field forms a density spike around the black hole with profile $ρ\sim r^{-3/2}$, consistent with dark matter spikes studied in the literature, which is not significantly distorted by spacetime rotation, except near the black hole's ergoregion. For any nonzero spin, an additional superradiant regime appears, in which co-rotating modes extract mass and angular momentum from the black hole. We find a mass \textit{extraction} rate as high as $10\, M_\odot/\text{yr}$ in the superradiant regime for a $10^9\, M_\odot$ black hole. For large field masses, the rate at which the black-hole mass grows behaves similarly to the Schwarzschild case, reaching $\sim 100\, M_\odot/\text{yr}$ for a $10^9\, M_\odot$ black hole. We compare these results to their scalar-field counterparts and discuss how they mix with the superradiant instability.

The spectrum of the white dwarf WD J091405.30+191412.25 displays the absorption and double-peaked emission lines of the volatiles hydrogen, oxygen, and sulfur. This unique characteristic has been interpreted as evidence of this white dwarf accreting mass from a circumstellar disk that had formed from atmospheric material evaporating off a close-in Neptune-like or super-puff mass planet. Thus far, however, the orbital separation of the planet and its mass-loss rate have only been estimated using simple analytical approximations. We investigate this scenario using 3D radiative-hydrodynamic simulations of irradiated hydrogen atmospheres together with 1D viscous disk evolution models. We compute atmospheric escape from Neptune-like and super-puff planets exposed to extreme ultraviolet (XUV) radiation of the white dwarf at different orbital separations and follow the evolution of the escaping gas after it forms a circumstellar disk. The simulations yield planetary mass-loss rates of $(1.8-4)x10^{12}$ g/s. The injected material forms a gaseous disk that reaches a quasi-steady state in less than $10^5$ through the balance between continuous mass supply and viscous accretion onto the white dwarf. The resulting accretion rates are consistent with observational estimates. In contrast to previous interpretations, our models predict that the disk extends beyond the planetary orbit. We conclude that a gas-rich planet orbiting at 15 solar radii undergoes sustained photoevaporation and naturally produces a circumstellar disk capable of reproducing the observed accretion rates and spectral signatures of WD J0914+1914. These results provide strong support for the evaporating-planet scenario and offer new constraints on the structure and extent of the circumstellar disk.

We present cosmological constraints on spin-1 ultralight dark matter, described by a vector field (VFDM) with mass $m_{\rm A}$, using Planck CMB data and geometrical probes from BAO and SNIa. A key theoretical result is the derivation of the full CMB temperature covariance matrix, including both diagonal and off-diagonal anisotropic contributions induced by the preferred direction of the background vector field. We first constrain the model using the diagonal part of the covariance, together with CMB lensing; the off-diagonal terms, which couple multipoles with $Δ\ell\in\{2,4\}$, could bias lensing reconstruction, but only at very low multipoles ($L=\{2,4\}$) not included in the Planck likelihood. We consider both a pure VFDM scenario and a mixed VFDM+CDM scenario, characterized by the fraction $f=Ω_{\rm A}/(Ω_{\rm A}+Ω_{\rm cdm})$, obtaining $\log_{10}(m_{\rm A}/\mathrm{eV})>-24.07$ (95\% C.L.) in the pure case, and a clear correlation between $f$ and $m_{\rm A}$ in the mixed case, with smaller fractions allowing lighter masses; standard cosmological parameters remain fully consistent with $Λ$CDM. For the off-diagonal contributions, we derive the corresponding Bipolar Spherical Harmonic (BipoSH) coefficients and predict their amplitude using our best-fit and bounds. While the anisotropic signal is difficult to detect in the pure VFDM scenario with current Planck data, mixed VFDM+CDM models can produce signals at, or above, Planck sensitivity over a range of multipoles, motivating dedicated searches for this characteristic signature.

We use a $Λ$-type three-level Maxwell--Bloch model to test whether an inverted molecular transition in an astronomical maser source can produce maser amplification or superradiance when its upper level also decays through a second radiative pathway with a much larger spontaneous decay rate. Such shared-upper-level configurations occur in multilevel, radiatively pumped molecules, including Class II methanol masers and several OH maser transitions. The model follows the coupled evolution of level populations, molecular coherences, radiation fields, and phenomenological relaxation and dephasing, separating population leakage from coherence loss. We focus on the mixed configuration in which the observed transition is inverted while the faster pathway is non-inverted and acts as a leakage channel. We find that rapid spontaneous decay through the competing pathway does not, by itself, suppress maser amplification or superradiant emission from the inverted transition. The response is controlled by the shared upper-level population reservoir, the available initial coherence, and the relaxation and dephasing timescales. For small effective coherence in the leakage pathway, its radiative output remains weak, while the inverted transition either amplifies a seed field in the quasi-steady maser regime or develops macroscopic coherence and produces a transient superradiant burst. A larger inversion does not necessarily produce a stronger burst if it is accompanied by a weaker initial coherence seed. As a benchmark, we apply the model to the 6.7 GHz methanol flare in S255IR-NIRS3, whose upper level also decays through the 239.7 GHz transition at a spontaneous rate more than four orders of magnitude larger. The calculated flare remains compatible with a transient-superradiance interpretation when this fast leakage pathway is included explicitly.

Spontaneous scalarization provides a dynamical mechanism to evade the no-hair paradigm, but it has been argued to generically eliminate the Cauchy horizon in charged black holes. We show that this obstruction is not universal, but instead follows from the sign-definite structure of the Einstein-Maxwell source term. Within the $P$-dual formulation of nonlinear electrodynamics, we derive a general condition under which the effective scalar source changes sign between the horizons, allowing the integral constraint to be satisfied without destroying the Cauchy horizon. This establishes that the fate of the Cauchy horizon depends on the electromagnetic coupling and identifies candidate theories where scalarized horizons may persist. The resulting framework opens the possibility of studying scalarization in the interhorizon region and its interplay with mass inflation.

We study chiral symmetry breaking in the Nambu-Jona-Lasinio model on a de Sitter background, treating it as a non-renormalizable effective field theory with a physical ultraviolet cutoff. Using exponential proper-time regularization, we obtain an exact solution for the constituent fermion mass in the strong-curvature regime via the Lambert $W$ function. The consistency condition for real-valued solutions leads to an upper bound on the cosmological constant, indicating a limitation of the mean-field description rather than a fundamental physical constraint on the spacetime geometry.

Baryonic feedback redistributes gas within and around dark matter haloes, suppressing the small-scale matter power spectrum at a level that is now the leading systematic for upcoming weak-lensing surveys. The kinetic Sunyaev-Zeldovich (kSZ) effect directly probes this redistributed gas, but existing measurements around galaxies are either tied to the properties of the chosen galaxy sample or are susceptible to biases from other extragalactic foregrounds. We address both by cross-correlating a kSZ template constructed from the tomographic weak-lensing convergence maps and the radial velocity maps reconstructed from galaxy surveys via the continuity equation, with the observed CMB temperature. We forecast the detectability for Rubin LSST Y10 and Roman kinematic lensing samples combined with ACT, SO, and CMB-HD, finding signal-to-noise ratios of $\sim$ 5-15 for current and upcoming CMB data and $\gtrsim 100$ for CMB-HD, corresponding to few-per-cent and sub-per-cent constraints, respectively, on the baryonic suppression of the matter power spectrum. This method should thus achieve sufficient statistical precision to model baryonic feedback effects for Rubin, without the systematic challenge of modeling any galaxy-matter connection.

We present a detailed investigation of scenarios in which dark-photon dark matter is produced from quantum fluctuations during inflation. In particular, we focus on inflationary models that necessarily involve a Weyl transformation, dependent on the inflaton amplitude, in order to move to the Einstein frame. In such models, the kinetic function of the longitudinal mode of the dark photon varies throughout, and even after, the inflationary period. We show that this variation of the kinetic function has a substantial impact on the resulting relic abundance of dark photons. As a representative and phenomenologically important example, we analyze the Starobinsky inflation model, for which we perform an accurate computation of the relic dark-photon abundance. By imposing the relevant observational constraints, we find that, in order to reproduce the observed dark-matter density in the present Universe, the dark-photon mass must lie in the range $5.6 < m < 7.4\,μ\mathrm{eV}$ within the framework considered in this work.

In three preceding articles, we studied the relation between the light curves of Mira variables and their stellar properties. The analysis was restricted to a sample of stars offering high density and quality of observations in the visible, allowing for the definition of simple parameterizations of the light curves. Clear relations were revealed between the evolution of the stars along the AGB and parameters such as the width of the light pulse or the deviation of its ascending branch from a sine wave. However, the restriction to Mira variables was found to be a major drawback preventing a complete picture to be drawn. The present article overcomes this deficiency by reviewing a large sample of semi-regular and irregular variables. It gives evidence for two families of stars having different progenies. The first family enters the AGB already pulsating with amplitudes at the scale of one unit of magnitude. It keeps cooling down and expanding, while pulsating with increasing amplitudes and periods and decreasing width of the light pulse; its progeny is dominated by some of the Mira variables studied in the three preceding articles. The second family enters the AGB before displaying significant pulsations; some of its progeny may leave the AGB without entering the Thermally Pulsing Branch and experiencing strong TDU events; others may instead become Mira variables studied in the three preceding articles and pulsating with a broader light pulse. The possible transition of both families from oxygen-rich to carbon-rich is studied and described. Comments on the interpretation of these results in the context of current state-of-the-art knowledge are presented. While the stars of the first family tend to have larger initial masses than the stars of the second family, details of the properties of the convective envelope seem also to play a role in defining which families a star belongs to.

The entanglement entropy of quantum systems typically exhibits both ultraviolet and infrared (IR) divergences. In the low-frequency limit, the IR divergence is intimately tied to the unbounded spatial delocalization of zero-modes, a pathological feature common to both coupled harmonic oscillators and massless scalar fields. In this work, we demonstrate that this infinite growth is naturally resolved by invoking the Extended Uncertainty Principle (EUP), which introduces large-length-scale geometric corrections to the canonical commutation relations. By exactly solving the simple harmonic oscillator under the EUP framework, we establish the existence of an intrinsic geometric confinement that enforces a strict upper bound on the position variance, limits spatial delocalization, and introduces an intrinsic localization length scale related to the background Ricci scalar. We extend this regularizing mechanism to many-body systems by evaluating the entanglement entropy and entanglement spectrum of a one-dimensional harmonic chain and a massless scalar field. We show that the EUP-induced spatial bounds prevent the accumulation of low-lying long-wavelength modes, keeping the entanglement spectrum discrete and evenly gapped even in the strictly massless limit. This non-vanishing modular gap effectively caps the local entanglement temperature of the vacuum. Consequently, the entanglement entropy saturates to a finite value, providing a robust, geometric resolution to the zero-mode IR divergence problem in quantum field theory.

We derive a first law of proto-area entropy in the CCKLP--Witten framework for approximate holographic entanglement wedge reconstruction. The central spectral function admits a modular Hamiltonian representation with kernel $L(x)=x\coth(x/2)$. For near-maximally-mixed bulk states, and within the unstructured Gaussian-unitary-ensemble (GUE) model of the encoding perturbation, the ensemble-averaged proto-area entropy varies linearly with bulk entropy to leading order, with a response coefficient containing a universal factor~$1/3$, traced to $L''(0)/2=1/6$ and independent of the bulk spectrum's detailed shape within this model. Imposing the gravitational-scaling condition required for nonzero backreaction, the first-law coefficient is $O(1)$, parametrically matching the semi-classical relation $δ({\rm Area}/4G_N)=δS_{\rm bulk}$.

We prove the Penrose inequality with charge under the 2-convexity condition recently introduced by Dong. More precisely, given a complete, connected and asymptotically flat Einstein-Maxwell initial data set $(M,g,k; E,B)$ satisfying the charged dominant energy and the 2-convexity conditions, with divergence-free electromagnetic vector fields $(E,B)$ and a connected outermost past apparent horizon $Σ$ that satisfies $|Σ| \geq 4πq^2$ - where $q$ is the total charge - we show that the following inequality for the ADM mass $m$ holds: $m\geq \sqrt{\frac{|Σ|}{16π}} + q^2 \sqrt{\fracπ{|Σ|}}$, with equality if and only if $k \equiv 0$ and $(M,g;E,B)$ is isometric to a canonical slice of sub-extremal Reissner-Nordström spacetime. Building on Dong's proof of the uncharged case, we use his $\mathbf{P}$-inverse mean curvature flow and its weak formulation, which only depends on $(g,\mathbf{P})$ and hence applies to the charged setting unchanged. The novelty of our work is the modification of the monotonicity formula to account for the additional charge term. For time-symmetric data ($k \equiv 0$), the flow reduces to the classical inverse mean curvature flow and our monotonicity formula to Jang's monotonicity of the charged Hawking mass, recovering the charged Riemannian Penrose inequality.

We propose a holographic map from the semiclassical Hilbert space of pure general relativity in $\text{AdS}_{3}$ to that of $\text{CFT}_{2}$. We define the bulk Hilbert space by semiclassically quantising the phase space in the basis of a fixed-area network on a Cauchy slice $Σ$. A fixed-area network is a maximal non-intersecting set of geodesics on $Σ$ whose lengths and angular momenta have been fixed. Our holographic map differentiates between `external' geodesics that are homotopic to a connected component of $\partial Σ$, and `internal' geodesics which are not. The lengths and angular momenta of external geodesics become conformal weights of primaries in the Hilbert space of the CFT living on the corresponding component of $\partial Σ$. The fixed-area network determines the wave function, which is given by a network of OPE coefficients of primaries whose weights are determined by the corresponding lengths. For sufficiently semiclassical states, there is an agreement between bulk and boundary inner products. We apply this proposal to various physics questions. The boundary dual of a bulk gauge turns out to be an emergent basis for sufficiently semiclassical states. We also define boundary operators that measure the lengths of geodesics behind the horizon, again in semiclassical states. Finally, we apply our map to closed universes and find a failure of semiclassicality in simple cases, which can be partially alleviated by the addition of a massive probe.

It is widely believed that Coleman--De Luccia (CDL) instantons characterize tunneling transitions in a de Sitter multiverse. Their most naive interpretation uses analytic continuation to Lorentzian de Sitter at the minimal size of the spatial three-sphere. However, what one really wants is a geometry where a small bubble of new vacuum forms within the huge spatial sphere of an old parent de Sitter. Even by applying de Sitter isometries to the original CDL solutions, this cannot in general be achieved. In particular, it fails in the gravity-dominated regime, i.e. for up-tunneling and for transitions with heavy domain walls. These cases remain pathological in that the whole multiverse is in the causal future of every single up-tunneling event. To solve this problem, we develop a Hamiltonian description of how a small off-shell bubble grows and eventually goes on shell within the large spatial sphere of late-time de Sitter. We provide the corresponding WKB analysis, recovering the CDL rate. We explain that our tunneling process and that of CDL are described by two different analytic continuations of a unique on-shell trajectory in the Hamiltonian treatment. Our analysis has crucial implications for the Larfors--Johnson problem, which questions the standard mechanism for populating the string-theoretic flux landscape on the basis of an instability of the relevant domain walls.