高能暂现源 · 每日文献综述

In this paper, we present observations of an eruptive young star in the Rosette Nebula, identified by the Gaia Science Alerts system using Gaia time series data. We aim to investigate the evolution of the brightness and mass accretion rate of V557 Mon throughout its outburst and subsequent decline. In addition, we trace the evolution of the inner accretion disk during the outburst by monitoring molecular emission features. We compiled multi-band photometric time series from Gaia, ZTF, and several 1 m-class ground-based telescopes and obtained optical and near-infrared spectra at multiple epochs covering the outburst and fading phases. Stellar parameters were derived from quiescent colour/spectra and spectral energy distribution (SED) fitting. We also measured the mass accretion rate and fit models to molecular emission bands. Since late 2024, V557 Mon has undergone a year-long outburst consistent with EXor variability. Based on quiescent photometry, V557 Mon has a spectral type of M1 with an extinction of AV = 1.8+_0.3 mag, consistent with a 0.4-0.5 M_sol star at an age of 2 Myr. Our multi-epoch spectra and u-band photometry indicate a peak accretion rate of 6.3x10^(-7)M_sol/yr during the outburst, roughly 70 times higher than in quiescence. We report the detection of hot water vapour emission bands, together with TiO, VO, and CO emission features. Using ExoMol models, we measured the inner-disk temperature changed from 3000 K to 2000 K during the fading phase of the outburst. We report a recent EXor outburst in a low-mass Class II YSO. Our observations reveal the transient formation of a hot molecular inner disk, traced by variable water vapour emission during the EXor event. A positive correlation is found between the molecular excitation temperature and the overall stellar brightness.

The fluorescent iron line and its broadening due to relativistic effects are excellent probes to study the inner part of an accretion disk and the space-time geometry near the compact object. We investigate the iron K$α$ line profile within the extended RAR model, which describes a fermionic dark matter distribution on galaxy scales. The most general solutions are characterized by a compact and highly degenerate core able to mimic the central black hole, transitioning into an extended halo composed of the same particles. We aim to contrast the resulting line morphologies in this scenario with those predicted by the standard Kerr black hole paradigm. Special attention will be given to MCG-06-30-15 galaxy. We compute the line profile using the numerical ray-tracing code, Skylight. We consider two distinct configurations for the emissivity of the cold accretion disk: an irradiation profile based on the lamp-post corona prescription, and a phenomenological power-law profile. The resulting profiles exhibit a diverse phenomenology. In particular, the most compact fermion cores produce a line broadening comparable to that observed in rapidly rotating black holes. The presence of emitting matter at radii smaller than a gravitational radius yields distinctive spectral features that are entirely absent in the black hole scenario. For MCG-06-30-15 galaxy, we find a good agreement with the observed broad features of the iron line profile, provided the compactness of the fermion core is close to critical. These results reinforce the need for independent black hole spin measurements. Combined with such constraints, iron-line spectroscopy may provide a powerful observational tool to distinguish black holes from alternative compact solutions, in particular compact fermionic dark-matter cores.

We present the selection and identification of high-z radio quasars from a combination of X-ray (eROSITA All-Sky Survey), optical/NIR (DECam Local Volume Exploration), and radio (Rapid ASKAP Continuum Survey) surveys. After building a sample of 68 new high-z quasar candidates, we performed follow-up spectroscopic observations on 46 sources, confirming 39 to have redshifts z>3.5. For the subset of radio quasars at z>4, the 14 new sources identified here represent an increase of $\sim$65% in the known population of objects above the same flux limits in the same area. Using X-ray-to-optical relative intensity, we identified blazars in our sample, which we then used to compare the total number of z>4, X-ray selected blazars to the predictions of a fractional IC/CMB model previously proposed in the literature. Overall we find a relatively good agreement, even considering the potential biases in the redshift distribution from the incompleteness of the spectroscopic follow-up and the blazar classification criteria. The sources presented in this work represent a sample well suited for investigating the evolution of the most extreme systems in the early Universe, including their relativistic jets and accretion properties

Long-term instabilities in astrophysical fluids are inherently nonlinear, where even small-amplitude perturbations can trigger dramatic instability. However, owing to the complex interactions among non-normal modes, the perturbation structures responsible for the greatest growth remain poorly understood. In this paper, we employ the nonlinear optimization method known as the conditional nonlinear optimal perturbation (CNOP) to identify the most dangerous initial velocity perturbation, i.e., the perturbation that maximizes the kinetic energy growth in the two-dimensional compressible Rayleigh-Taylor instability in astrophysical hydrodynamics. Compared with random perturbations, the optimal perturbation forms a coherent wave-packet structure localized around the density interface. We investigate its dependence on spatial resolution and optimization time horizon through two sets of numerical experiments. For a fixed optimization time, increasing the spatial resolution produces a more sharply localized wave packet, whereas for a fixed spatial resolution, increasing the optimization time causes the wave packet to become progressively more dispersed. Furthermore, we analyze the optimal perturbations in Fourier space using the fast Fourier transform (FFT), which provides a clearer characterization of the spectral distribution. Higher-resolution simulations concentrate most of the perturbation energy into only a few dominant modes, while longer optimization times distribute the energy over a broader range of modes. These results indicate that short optimization time horizons involve relatively weak modal interactions and remain closer to the linear regime, whereas longer optimization times enhance nonlinear modal interactions, broaden the spectral distribution, and reduce the predictive capability of linear stability theory.

The assumption of long-term pulse-profile stability underpins high-precision pulsar timing and forms the basis of pulsar timing array experiments. However, several millisecond pulsars exhibit temporal profile variability that can introduce systematic biases in pulse time of arrival measurements and compromise timing precision. We present a profile-domain analysis of PSR J1713+0747 at low radio frequencies, in the 300-500 MHz band, using upgraded GMRT observations for the Indian Pulsar Timing Array experiment. We model frequency-resolved pulse profiles using a Bayesian Gaussian decomposition framework in which individual Gaussian components are associated with persistent emission regions through informative phase priors that permit modest temporal variations. By tracking the evolution of the decomposed components across observing epochs and frequency sub-bands, we identify central Gaussian components that remain precisely localized despite changes in the integrated pulse morphology. We then reconstruct pulse profiles with realistic noise using these central components and perform timing analysis. Our approach provides a physically motivated framework for mitigating pulse-profile variability and offers a generic methodology for recovering robust timing information from pulsars exhibiting profile evolution.

We study the minimal classically scale-invariant extension of the Standard Model, containing a single $\mathbb Z_2$-stabilised real scalar singlet whose mass is not an independent input but is generated dynamically through the quantum effective potential and linked to radiative electroweak symmetry breaking through the Higgs portal. We construct the full two-field one-loop effective potential and introduce a modified on-shell renormalisation scheme that fixes the electroweak vacuum, the Higgs mass, the vanishing Higgs--singlet mixing and the singlet curvature at the physical point, yielding predictions stable under renormalisation-scale variation. Since thermal freeze-out is excluded by direct-detection limits, we identify a highly predictive freeze-in realisation of this model. Imposing perturbativity, vacuum stability and the observed relic abundance leads to a freeze-in solution with a dark-matter mass of around $2~{\rm MeV}$. The predicted electron-scattering cross section for this solution lies far below the current sensitivity of DAMIC-M. Current direct-detection experiments therefore do not constrain this scenario. The minimal scale-invariant singlet model thus provides a robust and highly predictive framework connecting radiative electroweak symmetry breaking and freeze-in dark-matter genesis.

We present the characterization of HIP 61637 b (TOI-5401 b), a brown dwarf discovered by TESS to transit an A-type star. HIP 61637 is the most massive and the brightest star known to host a transiting brown dwarf to date. The companion lies in the middle of the "brown dwarf desert". We perform a joint analysis of light curves from NASA's TESS mission and our high-resolution spectroscopy from the Tillinghast Reflector Echelle Spectrograph. We determine that HIP 61637 b has a radius of $R_{BD} = 1.149^{+0.049}_{-0.038}$ $R_J$, a mass of $M_{BD} = 47.8^{+1.5}_{-1.4}$ $M_J$, and transits its host star every $6.829104 \pm 0.000011$ days in a near-circular orbit ($e = 0.054 \pm 0.013$). The host star has a mass of $2.86\pm 0.12\,M_\odot$, a radius of $4.33 \pm 0.17\, R_\odot$, and an effective temperature of $T_{\text{eff}} = 9180^{+240}_{-230}$ K. We find that the host is nearing the end of its time on the main sequence and has begun to evolve, allowing for a precise age estimation of $396 \pm 46$ Myr for the system using stellar evolution models. This adds an important data point to the handful of well-characterized transiting brown dwarfs with reliable age estimates, allowing us to test the latest substellar evolution models. Theory of tidal evolution predicts that tidal dissipation mechanisms have circularized the orbit, consistent with the observed near-zero eccentricity.

We present an overview of our ongoing GASTRONOMI project, which investigates the coevolution of the Milky Way (MW), its satellite dwarf galaxies, and their star clusters through chemo-dynamical analysis. We derive precise chemical abundances for stars in five classical dwarf galaxies, which reveal mass-dependent chemical evolution, particularly in alpha elements, such as [Si/Fe]. A distinct dichotomy in [Al/Fe] is found between metal-rich ([Fe/H]>-1.5) stars formed in-situ in the MW and those originating in dwarf galaxies. Star clusters act as sensitive environmental probes. The presence of multiple populations correlates with galactic evolution, and nitrogen-rich stars in Fornax are likely relics of disrupted globular clusters (GCs). We developed a chemical classification for Galactic GCs, isolating primordial populations by their low [Al/Fe]. This places in-situ and accreted GCs in distinct regions of the [Al/Fe]-[Fe/H] plane, providing a new tool to reconstruct the Galaxy's accretion history.

The photospheric abundance pattern of the components is a sensitive probe of mass and angular momentum transfer in Algols. With the aim to trace the evolutionary history and disclosed efficiency of mass transfer in Algols we collected new high-resolution spectra for about a dozen Algols with the {\sc hermes} spectrograph at the Mercator Telescope on La Palma, Canary Islands. In the present paper, which is the first in the series, we present the results of a comprehensive analysis of Z Vul, a hot Algol-type system. We derived the absolute stellar quantities and elemental abundances for the components. The carbon-to-nitrogen (C/N) ratio is the most sensitive tracer of thermonuclear processing and mass transfer. It is found to be within expected value for gainer but donor lacks the severe C/N inversion traditionally expected for a deeply stripped star. An extensive grid of over three million evolutionary models was calculated with the Cambridge \texttt{STARS} code which allows determination of the best-fitting and all surviving models. Constraints from the He and CNO abundances indicate that Z Vul underwent an episode of nearly conservative mass transfer during the Main Sequence life-time of the originally more massive component (Case A). Our detailed chemical tagging confirms that the surface abundances of the mass-losing component represent the delicately stripped outer layers still not reaching the CNO-rich core. This underscores the need of coupling high-resolution spectroscopic abundances with interior stellar profiles to accurately reconstruct the evolutionary history of interacting binaries.

A wide range of variability mechanisms exist among intermediate mass and massive stars, which are not yet fully understood. Using complementary data sources for a large population of B- and O-type stars, we aim to study the prevalence and interplay of different types of variability, including binarity, pulsation, and rotation, to prepare for future modelling. To this end, we analyse high-resolution HERMES spectra and 2-min cadence TESS photometry and characterise the diverse variability observed within a population of 873 O- and B-type stars. The spectroscopic data were normalised using machine-learning techniques, compared to a grid of synthetic TLUSTY spectra to determine stellar parameters, and used to identify radial velocity variability. Photometric time series were analysed using standard frequency analysis methods to detect pulsations and rotational modulation signatures. We find that more than 93 per cent of the sample exhibits photometric variability. Photometric variability caused by pulsations is identified in 82 per cent of the sample, with dominant contributions from $β$ Cep and slowly pulsating B-type stars, as well as stochastic low-frequency variability. Based on a limited number of spectroscopic epochs, at least 14 per cent of the stars show evidence of binarity, including both eclipsing and spectroscopic systems. This work represents one of the largest homogeneous surveys of variability for intermediate-mass and massive stars in the Northern hemisphere, and complementing similar efforts in the Southern hemisphere. It provides a statistical framework for future studies of stellar structure and evolution, particularly in the context of asteroseismology.

These lecture notes provide an introduction to the generation of initial conditions for cosmological N-body simulations. Starting from the definition and properties of Gaussian random fields, we discuss their role in cosmology and the efficient generation of such fields using Fourier methods. The Vlasov-Poisson system is introduced as the governing framework for cold collisionless matter, and its solution via characteristics and Lagrangian perturbation theory (LPT) is detailed. We discuss the use of LPT for initializing N-body simulations, emphasizing the importance of high-order LPT and late-time starts to minimize truncation and discreteness errors. Finally, we discuss time integration schemes, including PT-informed integrators, and their role in accurately evolving the system. These notes aim to bridge the gap between theoretical perturbation methods and practical simulation techniques.

Redshift information is central to nearly every extragalactic and cosmological application of sky surveys, yet only a small fraction of cataloged sources, and none of the photons forming diffuse backgrounds, have spectroscopic redshifts. Clustering-based redshift inference estimates the redshift distribution of an arbitrary dataset through spatial cross-correlation with a reference sample of known redshifts. It relies only on positional information, making it applicable to any tracer of large-scale structure, including source populations and diffuse intensity maps. Its broader adoption, however, has been limited by technical barriers: assembling and characterizing spectroscopic references, expensive pair-counting computations, theoretical corrections, and systematic control. To remove these barriers, we introduce Tomographer, an end-to-end clustering-redshift framework. The key design feature is a set of precomputed "activation maps" encoding the spatial pair information of 3 million SDSS spectroscopic galaxies and quasars up to $z\sim4$ over $10{,}000\,{\rm deg}^2$. This eliminates user-end pair counting, reducing computational scaling from $O(N\log N)$ to $O(1)$ map multiplications. Given a source catalog or intensity map, Tomographer returns the bias-weighted redshift distribution, $b(z)\,{\rm d}N/{\rm d}z(z)$ or $b(z)\,{\rm d}I/{\rm d}z(z)$. We validate the framework against samples with known redshifts, demonstrate accurate uncertainty estimates, and show robustness to survey footprint, spatially varying selection functions, beam smoothing, and foreground contamination. We showcase applications to source catalogs selected by flux, color, photometric redshift, morphology, or variability, and to intensity maps from radio to X-rays. Future Tomographer releases will incorporate additional wide-field spectroscopic reference samples as they become available.

Irregularities in electron density within the interplanetary medium (IPM) can cause fluctuations in the Doppler frequency of spacecraft radio signals. The amplitude of these fluctuations depends on factors such as the carrier frequency, propagation geometry, and link configuration. However, quantitative characterization of these effects across different frequencies in various occultation experiments is currently limited. We analyze five complementary datasets: two-way S-band observations from Chandrayaan-3 outside the lunar ionosphere, two-way S-band data from Chandrayaan-2 during lunar occultation, one-way S/X band measurements from the Venus Express Radio Science (VeRa)/Akatsuki Radio Science (Akatsuki) under IPM-only conditions, and one-way X-band Akatsuki data during solar occultation. The Chandrayaan-3 and Akatsuki IPM observations isolate IPM effects by excluding contributions from planetary atmospheres, the lunar ionosphere, and, except during solar occultation, the solar corona. Chandrayaan-3 data sample dynamically evolving Earth-Moon geometries and exhibit weak, mHz-level Doppler fluctuations, while Chandrayaan-2 observations provide near-lunar plasma benchmarks with higher amplitudes, during quiet time solar and geomagnetic conditions. Akatsuki and VeRa's IPM-only measurements capture long-path interplanetary effects, whereas Akatsuki solar occultation data reveal strong coronal signatures. Power spectral density analysis indicates Kolmogorov-like turbulence for lunar occultation and solar occultation cases, while IPM-only spectra show low-amplitude fluctuations. These results quantify the IPM contribution to Doppler noise, demonstrate the enhanced plasma sensitivity of two-way coherent links, and provide constraints relevant to turbulence modelling, precision spacecraft tracking, and the interpretation of radio occultation experiments.

Recent James Webb Space Telescope (JWST) observations suggest an unexpectedly high abundance of luminous galaxies at $z \gtrsim 10$, challenging traditional models of star formation. The 21-cm signal of neutral hydrogen offers a complementary, volume-averaged probe of these early epochs. In this work, we present a major extension to the explicitly photon-conserving semi-numerical framework SCRIPT, enabling the self-consistent calculation of spin temperature fluctuations driven by inhomogeneous Lyman-$α$ coupling and X-ray heating during the Cosmic Dawn. Using this framework, we compare a JWST-informed fiducial galaxy model, featuring a redshift-evolving star-formation efficiency, against a static baseline model. We demonstrate that the global 21-cm signal is highly degenerate: a static galaxy population can replicate the absorption trough of an evolving population if a steep, mass-dependent X-ray efficiency is invoked to shift intergalactic medium heating toward highly abundant, low-mass halos. However, this degeneracy is definitively broken by the 21-cm power spectrum. Because spatial fluctuations retain a structural memory of the clustering bias of the source halos, the tuned static model predicts a substantially lower power spectrum amplitude across all characteristic peaks. We conclude that combining global and fluctuation measurements is essential to robustly constrain the redshift evolution of high-redshift galaxies.

Motivated by the proposed relation between 3D gravity and the doubled Virasoro TQFT, and by the associated program of ensemble holography, we ask whether ensemble holography in AdS$_3$/CFT$_2$ can be understood as an average over absolute 2D CFTs obtained by varying the topological boundary condition of the doubled Virasoro TQFT. We show that, at genus one and in the ordinary nondegenerate sector, every vacuum-normalized, modular-invariant genus-one pairing that acts boundedly on the auxiliary $L^2$ label space is diagonal. Under the ordinary block-diagonal vacuum--continuum ansatz, the same conclusion holds for entrywise-positive, modular-invariant Borel-measure pairings satisfying the two vacuum marginals, even if they are initially singular or unbounded. Consequently, within these analytic classes, the Virasoro TQFT does not admit a Narain-like ensemble mechanism based on averaging distinct nontrivial torus pairings from ordinary topological boundaries. Any nontrivial ensemble interpretation must instead involve information invisible at genus one, additional sectors, or genuinely generalized boundary conditions. Technically, the proof identifies the Virasoro $S$ and $T$ transformations with the even Weil representation of the metaplectic group and applies the Cowling--Steger lattice-restriction theorem. We also give elementary proofs for several explicit classes of candidate boundary conditions and perform numerical checks of the general result.

Recent James Webb Space Telescope (JWST) observations favor an earlier and more efficient reionization history, leading to Thomson-scattering optical depths larger than those inferred from the cosmic microwave background (CMB). We investigate whether this tension can be alleviated within the framework of self-interaction (SI) gravity by modifying the cosmological expansion history while retaining the standard astrophysical description of reionization. The SI gravity parameters are constrained through a Bayesian MCMC analysis of the Union3 Type Ia supernova and DESI DR2 Baryon Acoustic Oscillations (BAO) data. The resulting expansion history is then used to predict the ionization history and Thomson optical depth. We find that the predicted optical depth decreases from $τ_{\rm{CMB}}\simeq0.076$ in $Λ$CDM to $τ_{\rm{CMB}}\simeq0.061$, consistent with the Planck PR4 measurement within $1σ$, thereby substantially reducing the optical-depth tension.

Context. Granular collapse is an ubiquitous process of granular evolution on the solar surface, but it is hard to analyze in sufficient spatial, temporal, and spectral detail. Aims. We analyze the change in physical conditions in the photosphere during a specific granular collapse event and the subsequent atmospheric response. Methods. We contrast a high-resolution radiative magneto-hydrodynamic simulation of a granular collapse performed using the CO5BOLD code with the recent integral field unit observations carried out using the MiHI instrument at the Swedish 1-m Solar Telescope. Results. Our analysis shows that the observed and simulated granular collapse show remarkable similarity. Specifically, they both exhibit the signature of a wave pulse excited in the deep photosphere and visible up to the temperature minimum. This wave is detectable through a blue-wing emission in the observed and synthetic Na i D1 line. We also estimate the acoustic energy flux carried by the wave and analyze its initiation. Conclusions. Combining high-resolution IFU spectropolarimetry and state-of-the-art simulations of the solar lower atmosphere, this study showcases our current capabilities in identifying specific physical processes taking place during the granular collapse and their impact on the atmosphere above.

The Large-Scale Structure (LSS) of the Universe forms a complex network of nodes, filaments, sheets, and voids known as the Cosmic Web. As current and upcoming galaxy surveys increasingly probe the quasi-linear and non-linear regimes of structure formation, understanding its geometry and dynamics is essential for precision cosmology. In particular, cosmic filaments, which channel matter across the web, are central to these dynamical processes. This thesis develops numerical tools to study the non-linear cosmic web. First, the Sahyadri suite of high-resolution cosmological $N$-body simulations is introduced, providing a framework for precision studies of LSS and its cosmological dependence. A calibration framework for filament reconstruction is then developed using controlled filament realizations, enabling systematic investigation of reconstruction biases. The effects of filament curvature and reconstruction noise on inferred filament properties are quantified, and a novel Fourier-space smoothing approach is introduced to improve profile recovery. The thesis further presents Skeletor, a Voronoi-based filament finder that identifies filamentary structures directly from discrete tracers while explicitly incorporating the hierarchical nature of the cosmic web. A novel framework for classifying sub-filamentary structure is developed. Applying these tools to cosmological simulations reveals distinct properties of filament substructure and provides a detailed view of filament phase space, including coherent inflows, multistreaming, and caustic-like features. Together, these developments provide a framework for studying the geometry, hierarchy, and dynamics of the non-linear cosmic web. More broadly, they contribute to the ongoing effort to build a physically motivated understanding of the non-linear cosmic web beyond traditional measures of clustering.

Recent numerical studies of semiclassical gravity suggest that, in spherically symmetric black holes with both outer and inner horizons, the semiclassical instability of the inner horizon can drive the complete evaporation of the trapped region on timescales shorter than the standard Hawking evaporation time. Independent simulations further indicate that the disappearance of the trapped region is followed by the formation of an anti-trapped region, i.e.~a dynamical white hole. In this work, we develop an analytic treatment of quantum effects in trapped and anti-trapped regions, showing how these numerical results can be understood within simplified two-dimensional models. We consider collapse models describing the formation of charged and regular black holes and compute the renormalized stress-energy tensor of the $|\textit{in}\rangle$ vacuum state. We show that, within this framework, the emergence of an anti-trapped region is a generic consequence of the amplification of negative energy fluxes propagating along the outgoing direction inside the initial trapped region. This provides an analytic explanation for the black-hole-to-white-hole transition observed in numerical simulations. Our analysis further suggests that the fluxes generated by the subsequent anti-trapped region, now propagating along the ingoing direction, may trigger the formation of a new trapped region. This raises the possibility of a cascade of black-to-white-hole transitions, potentially ending in a horizon-free, bouncing spacetime without invoking additional quantum-gravitational dynamics. Although establishing the complete evolution requires a self-consistent treatment of semiclassical backreaction, our framework identifies which features of the mechanism are universal and which depend on the geometry, laying the groundwork for a systematic investigation of semiclassical black-hole-to-white-hole transitions.

We develop a general-relativistic framework for two-component quantum dark fermion stars: equilibrium configurations of two degenerate fermion species governed by gravity, a Yukawa-mediated dark fifth force and a globally relevant Bohm quantum-pressure correction. The treatment retains the full covariant form of the nonlinear Klein--Gordon equation in the Schwarzschild interior, with closure relations valid at arbitrary compactness, from the ultralight baseline up to densities of order $0.16\,\mathrm{fm}^{-3}$ at which relativistic scalar densities and self-consistent effective fermion masses become unavoidable. Two Lagrangian parameters, the dark-fermion mass and the dimensionless ratio between the Yukawa channel and gravity, together fix the equilibrium structure; a joint measurement of mass and radius therefore constrains the dark-sector microphysics directly from gravitational-wave observables. For particle masses in the band $10^{-11}$--$10^{-10}$ eV, the configurations exhibit radii of $3$--$24\,\mathrm{km}$ and compactness in the range $0.14$--$0.34$, behaving as dual mimickers: at moderate compactness they overlap with neutron stars in mass, radius, and inspiral frequency; at the most compact end ($κ\sim 0.34$, $R_T/R_S\simeq 1.5$) they cross the photon sphere and could masquerade as low-mass black holes in the mass-gap region. Tidal-deformability measurements discriminate against both populations: the dimensionless tidal deformability is measurably smaller than the neutron-star value yet remains non-zero, unlike that of a genuine black hole. These objects populate the sensitivity bands of LISA, the Einstein Telescope, and Cosmic Explorer, producing astrometric microlensing signatures individually resolvable by \textit{Gaia}. The framework thus provides a reproducible and falsifiable template for constraining dark-sector properties through multi-messenger observations.

Two-dimensional fluids conserve energy and enstrophy, driving inverse energy cascades via Fjørtoft's argument. We show General Relativity admits an analogous structure: for linear radiative perturbations of Petrov type D backgrounds (Kerr, Kerr--AdS), the gravitational-wave energy $W = \sum_k W_k$ and magnetic Weyl enstrophy $\mathcal{Z} = \int B_{ab} B^{ab} \sqrtγ \, d^3x \approx \sum_k ω_k^2 W_k$ are approximately conserved in the zero-angular momentum frame, where vorticity coupling vanishes identically and curl exchange cancels mode-by-mode. This yields a gravitational Fjørtoft constraint implying nonlinear energy transfer proceeds preferentially toward lower frequencies. The constraint is dynamically active in near-extremal Kerr ($τ_{\text{damp}} \gg τ_{\text{nl}}$) and confined geometries (AdS), but suppressed in generic ringdown. In AdS, $\mathcal{Z}$ maps holographically to the boundary fluid enstrophy.

Departures from standard slow-roll (SR) inflation have attracted increasing interest in recent years. In particular, scenarios that strongly enhance the power spectrum of the curvature perturbation are often proposed as a mechanism for producing primordial black holes, which could account for part or the totality of dark matter. An ongoing debate in these models is whether non-linear interactions of cosmological perturbations on small scales, namely loop corrections, can become sufficiently large to backreact on CMB scales. In this work, we adopt a non-linear framework, dropping spatial-gradient terms, to study loop corrections at super-Hubble scales. Our focus is to clarify the role of spatial-diffeomorphism invariance, especially dilatation invariance, which is the symmetry under overall rescaling of spatial coordinates, in demonstrating the suppression of loop corrections to the CMB power spectrum. This analysis is valid for any inflaton potential, both with smooth and sharp transitions, and at any loop order, as long as the CMB scales cross the horizon during an SR phase. We compare this result with the different explanations proposed in the literature using various gauge choices, and show our analysis is consistent both in the comoving and in the spatially-flat gauges. In particular, we show that in the spatially-flat gauge, the cubic interaction contains a term that diverges in the sharp transition limit. However, this contribution is exactly cancelled by the quartic interaction.

Gravitational-wave (GW) cosmology is currently bottlenecked by the scarcity of electromagnetic counterparts for bright sirens and the systematic uncertainties of galaxy catalogs for dark sirens. We propose a purely gravitational resolution using the Integrated Cosmological Memory (ICM)-the cumulative GW strain encoded in the spacetime geometry of an expanding Universe. While the GW transient emitted by the source provides the luminosity distance, the ICM accumulates a mathematically distinct integral of the cosmic expansion history. We demonstrate that extracting both observables from a single binary merger completely breaks the distance-redshift degeneracy within the gravitational sector. This establishes a novel, catalog-free dark siren framework for third-generation GW detector networks. Crucially, the resulting constraints on late-time dark energy are only weakly sensitive to the local expansion rate, providing a robust cosmological probe that can potentially mitigate the impact of the H0 tension.

We derive the leading logarithmic soft-photon theorem in $d>4$ spacetime dimensions and its classical radiative counterpart. A direct one-loop analysis in massive scalar quantum electrodynamics (QED) yields a factorizing soft term of order $ω^{d-4}\lnω$, although the charged-particle S-matrix is infrared finite. The logarithm is generated by the scale-invariant loop-momentum region $ω\ll|\ell|\llΛ$, where $Λ$ denotes a characteristic hard-particle energy scale. At leading radiative order, the corresponding logarithmic contribution to the classical electromagnetic waveform arises from the long-range acceleration of the asymptotic charged particles. In even $d\geq6$, the straight-line waveform at this radiative order is distributionally supported in retarded time within an interval whose width is set by the characteristic size of the hard-scattering region, whereas the logarithmic acceleration term produces universal early- and late-time radiative tails proportional to $|u|^{-(3d-10)/2}$. In odd $d\geq5$, straight-line motion already gives a late-time tail at the same radiative order proportional to $u^{-(d-4)/2}$. The acceleration correction adds universal late- and early-time terms proportional, respectively, to $\ln u/u^{(3d-10)/2}$ and $|u|^{-(3d-10)/2}$. A comparison of Feynman and retarded boundary conditions separates the classically radiative contribution from the intrinsically quantum part of the logarithmic soft factor.

The relative prevalence of horizontal and vertical magnetic fields in the quiet-Sun internetwork remains debated, owing to the weak linear polarisation signals that make the inferred magnetic inclination distributions sensitive to observational quality and inversion methodology. We investigate the magnetic topology of the quiet-Sun internetwork in {\sc Sunrise~iii} observations by independently applying transformer-based and traditional inversion techniques to the same spectropolarimetric dataset. We analyse observations obtained with the Sunrise Chromospheric Infrared spectroPolarimeter (SCIP). Transformer-based inversions (SINN), trained exclusively on synthetic Stokes profiles generated from a large radiative magnetohydrodynamic simulation, are compared with independent inversions performed using the \textsc{DeSIRe} code. Both inversion methods recover a quiet-Sun magnetic topology in which internetwork fields are strongly dominated by the horizontal component, whereas network fields exhibit a substantially more balanced topology. At $\logτ=-1.2$, the median horizontal and unsigned line-of-sight field components in the internetwork are 64 and 7G with \textsc{DeSIRe}, and 71 and 8G with SINN, respectively, corresponding to a horizontal-to-line-of-sight ratio of approximately nine for both methods. The agreement between the two fundamentally different inversion methodologies indicates that the quiet-Sun internetwork is characterised by a substantially stronger horizontal than vertical magnetic field component. These results demonstrate that transformer-based inversions can be successfully transferred from synthetic training data to real spectropolarimetric observations, while providing inference orders of magnitude faster than traditional inversion techniques.

We present high-resolution multi-line spectropolarimetric observations of a quiet-Sun network element obtained with the {\sc Sunrise~iii} Chromospheric Infrared SpectroPolarimeter. The observations combine photospheric, upper-photospheric, and chromospheric diagnostics at a spatial resolution and polarimetric sensitivity that allow the transverse magnetic structure of the network boundary to be examined directly. We find that the strongest linear polarisation is concentrated in a narrow ridge around the edge of the magnetic element, co-spatial with enhanced transverse magnetic field inferred from multiline inversions. The magnetic azimuth exhibits a coherent, predominantly radial organisation around a more vertical core, consistent with an expanding magnetic canopy. An azimuth proxy derived directly from the observed Fe~\textsc{i} and K~\textsc{i} linear polarisation reproduces the same large-scale organisation, showing that this structure is encoded in the Stokes profiles rather than imposed by the inversion. Response functions and a MURaM-based forward-synthesis test indicate that the Fe~\textsc{i}~8468~Å linear polarisation is sensitive to magnetic azimuth in the upper photosphere, with the closest proxy agreement occurring near $\logτ\approx-3$. We find no evidence for strong azimuthal shear between the Fe- and K-sensitive diagnostics. At the network boundary, we also identify localised parasitic-polarity patches associated with complex, multi-lobed Stokes $V$ profiles, and one case in which the Stokes $V$ polarity reverses between photospheric Fe~\textsc{i} and chromospheric Ca~\textsc{ii} lines. These results demonstrate that quiet-Sun network boundaries contain organised upper-photospheric canopy fields together with small-scale mixed-polarity structure, providing new constraints on the three-dimensional magnetic structure of network elements.

Axion-like particles (ALPs) provide a well-motivated dark matter candidate whose interactions with Standard Model particles may generate observable cosmological signatures. We investigate the diffuse $γ$-ray emission produced by the scattering process between ALP dark matter and cosmic-ray (CR) protons inside dark matter halos, and explore its detectability through the cross-correlation between the unresolved $γ$-ray background (UGRB) measured by \textit{Fermi} Large Area Telescope (LAT) and the Two Micron All Sky Survey Redshift Survey (2MRS) galaxy catalog in the local Universe ($z\leq0.1$). To model the cosmological $\mathrm{GeV}$-$\mathrm{PeV}$ CR proton population, we develop a phenomenological bottom-up prescription that links CR injection to the star formation rate through the supernova rate, while the steady-state CR density is determined by diffusive escape. Our forecasts indicate that UGRB-galaxy cross-correlation measurements can probe previously unexplored regions of the ALP parameter space over a broad range of ALP masses. More generally, this work presents a general framework for cosmological observables generated by interactions between dark matter and an additional astrophysical field, opening a new avenue for indirect dark matter searches using large-scale structure observations.

We calculate the vacuum polarization energy (VPE) of a scalar field in the background of a nonsingular cosmic string in $2+1$ spacetime dimensions. Our calculation expresses the VPE as a renormalized sum and integral over scattering data, which can be expressed in terms of Legendre and Bessel functions for the "ballpoint pen" model, analogous to a square well in curvature, and which can be obtained numerically for a generic string profile. We show how relationships between the local density of states, expressed in terms of the Green's function, and the global density of states, expressed in terms of the Jost function, extend to this curved spacetime background and allow for precise implementation of perturbative renormalization conditions.

The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) has begun its ten-year survey of the entire visible southern hemisphere. To ensure robust cosmological measurements, computationally inexpensive investigations of modeling choices must be made to gauge the performance of proposed cosmological analyses. In this paper, we introduce the $\texttt{Augur}$ tool of the Dark Energy Science Collaboration (DESC), which provides Fisher forecasts for cosmological inference for the LSST using software frameworks designed for DESC science. We test the pipeline by comparing it to forecasts produced by external code and direct sampling of the posterior via nested sampling methods, finding good agreement between all methods. We additionally investigate a range of modeling and hyperparameter choices for a 3$\times$2pt investigation in harmonic space, providing users with diagnostics to obtain reliable forecasts. $\texttt{Augur}$ will be continually updated to be compatible with the other tools in the DESC software ecosystem as additional probes and functionality become available.

$Λ$CDM provides a remarkably successful description of the Universe, yet it suffers from persistent discrepancies, with one of the most prominent being the $σ_8$ tension between early-Universe Cosmic Microwave Background (CMB) measurements and late-time structure growth probes. To address this mismatch, we investigate generalized interacting dark sector models governed by a quintessence field coupled to dark matter via conformal and disformal transformations. By generically engineering a quintessence potential that ensures the combined evolution of dark matter and dark energy exactly mimics $Λ$CDM, our models satisfy all background constraints while signaling modified gravity effects within the linear perturbation sector. We perform a statistical analysis using late-time structure growth data anchored to Planck 2018 constraints. Furthermore, we address the initial conditions problem inherent to purely disformal models, demonstrating the necessity of a non-zero initial kinetic energy to initiate dynamical evolution. Our results indicate that purely conformal couplings efficiently transfer energy from dark matter to the quintessence field, suppressing late-time structure formation and successfully accommodating CMB data within late-time modified structure growth. This purely conformal limit yields a strong statistical preference over the $Λ$CDM baseline according to both the Akaike and Bayesian Information Criteria. Conversely, while non-zero disformal couplings introduce a kinetic friction that dampens the dark sector energy exchange, their expanded parameter space incurs heavy statistical penalties without providing a decisive improvement over the purely conformal scenario.

We point out that the asymptotically Bertotti-Robinson multi-black hole solutions of Einstein-Maxwell theory can be constructed using only three-dimensional sigma-model techniques, without resorting to the monodromy-matrix approach.

Being agnostic about the field content of a gravitational system, we consider a general disformal transformation of the metric, $g_{μν}=Ch_{μν}+Dt_{μν}$, on a four-dimensional Lorentzian manifold. Using the Cayley-Hamilton theorem, we derive an explicit formula for the inverse disformed metric. Implementing the Hawking-Ellis classification, we categorize disformal transformations into four types: Type I, II, III, and IV, based on possible Jordan block structures. By examining the eigenvalues, we further classify each type into its corresponding Segre subclasses. We find explicit links between the Cayley-Hamilton degree of the disformal tensor $t_{μν}$, its Hawking-Ellis type, and its Segre subclass, which can restrict the possible Hawking-Ellis types once only the Cayley-Hamilton degree is known. In some cases, the type can be determined without even performing a full Jordan decomposition. For singular transformations, when new dynamical degrees of freedom emerge, we obtain the general form of their corresponding mimetic energy-momentum tensor $T^\star_{μν}$. We show that the Hawking-Ellis types of $t_{μν}$ and $T^\star_{μν}$ always coincide for Type I. For Types II and III it can differ, while Type IV is preserved generically but can reduce to Type I when the complex pair is mapped to a repeated real eigenvalue. This makes it possible to infer physical properties of $T^\star_{μν}$ directly from the Hawking-Ellis type of $t_{μν}$. We apply our setup to two specific cases: $t_{μν}=\partial_μφ\partial_νφ$ and $t_{μν}=F^α{}_μF_{αν}$, where $φ$ is a scalar field and $F_{μν}$ is the field-strength tensor of a gauge field. This general framework can be used to systematically study the kinematical and dynamical properties of various invertible and non-invertible disformal transformations with different field content.

We apply the two-particle irreducible (2PI) formalism as a framework for a consistent thermal resummation in studies of cosmological phase transitions. Considering a model with two mixing real scalar fields, we work within the Hartree approximation and renormalize the 2PI effective action, while introducing a connection to physical parameters. This yields the Hartree-resummed finite-temperature effective potential, which is valid for all temperatures and avoids the limitations of conventional methods based on the high-temperature approximation. With this potential, we study one- and two-step transitions within the model, and compare our results with those obtained using resummation schemes widely employed in the literature. Finally, we evaluate the gravitational wave spectrum generated from first-order phase transitions, demonstrating the impact of the choice of resummation scheme on the predicted spectrum.

Pre-inflationary axion cosmologies admit a broad range of initial velocities and angles that generate a landscape of misalignment histories, whose nonlinear fate and small-scale structure remain uncertain. We use lattice simulations to follow the QCD axion in the kinetic misalignment scenario through the QCD crossover into the non-relativistic regime, towards matter-radiation equality. In the meV mass range, this landscape contains a continuum of ''summit-landing" solutions sensitive to both the initial angle and velocity. Nonlinear fragmentation reduces the comoving axion number and modifies the relation between the misalignment history and present relic abundance. For sufficiently large axion masses, strong self-interactions drive the small-scale spectrum towards the attractor found for post-inflationary axions, so that distinct early histories can lead to similar late-time structures.

Understanding how the Milky Way disc assembled and evolved requires tracing the coupled evolution of stellar chemistry and orbital structure over time. Open clusters, as coeval stellar populations with well-constrained ages, distances, and chemical properties, provide powerful benchmarks for this purpose. We aim to characterise the age-dependent chemo-dynamical structure of the Galactic disc and to investigate how open clusters populate dynamical phase space as a function of age. We analysed a sample of Galactic open clusters using homogeneous chemical abundances from the Gaia-ESO Survey together with Gaia DR3 phase-space information. Combining cluster ages with orbital parameters and actions, we examined how clusters populate dynamical phase space over the last ~4 Gyr. We find that clusters with similar chemical properties occupy coherent regions of action space, while their orbital structure shows a clear dependence on age. Radial excursions and orbital eccentricities broaden systematically toward older ages, indicating increasingly diverse orbital configurations in the older cluster population. The dispersion in the [Fe/H]-Rg relation also increases with age, consistent with a combination of secular redistribution, survival bias, and dynamically distinct outer-disc populations. In addition, older clusters reach larger vertical amplitudes and vertical actions, revealing a coupled but anisotropic evolution between in-plane and vertical orbital structure. Open clusters provide precise, age-resolved tracers of the chemo-dynamical structure of the Galactic disc. Our results reveal systematic age-dependent variations in the orbital and chemical properties of the cluster population, consistent with the combined effects of secular evolution, orbital redistribution, and environmentally dependent cluster survival over the last few Gyr.

The distinct stellar populations of the Galactic bulge can be disentangled through detailed analysis of their chemical abundances and kinematical properties. Recent studies have suggested that globular clusters located in the Galactic bulge with metallicities around $\rm [Fe/H] \approx -0.7$, may represent some of the oldest systems in the Milky Way, potentially tracing the early spheroidal bulge. The coincidence of a metallicity peak at $\rm [Fe/H] \approx -0.7$ in both field stars and globular clusters, together with the presence of phosphorus-rich (P-rich) stars, may provide important clues to the nature of the first generations of stars formed in the Galaxy. In this work, we investigate the odd-Z elements Na, Al and particularly P in the bulge globular clusters NGC~6539 ($\rm[Fe/H] \sim -0.75$) and NGC~6569 ($\rm [Fe/H] \sim -0.85$) using APOGEE spectra. We also examine the clusters Tonantzintla-1 and NGC~6316, which exhibit evidence of phosphorus enhancement. Our analysis confirms that NGC~6539 is a cluster of interest, with one clearly P-rich star, whereas NGC~6569 shows a lower level of P-enhancement. This again suggests that there might have been an early bulge building block with the metallicity of $\rm[Fe/H] \sim-0.75$, of which NGC~6539 would be part of. The observed abundance patterns indicate that the production of Na and Al is consistent with nucleosynthesis in massive stars. However, the origin of the phosphorus enrichment remains uncertain, suggesting that additional nucleosynthetic channels may be required to explain the observed abundances. These findings provide new constraints on the chemical evolution of the Galactic bulge and the nature of its earliest stellar populations.

Stellar evolution simulations predict physical quantities such as luminosity, whereas broadband photometric observations measure flux in specific bandpasses; converting the predicted stellar state to magnitudes requires interpolating a stellar atmosphere model at the surface parameters, convolving the resulting spectral energy distribution (SED) with filter transmission curves, and applying a photometric zero-point correction. We introduce Custom Colors, which performs this conversion from the stellar model. It is integrated into MESA as MESA Custom Colors, and available as the Python package SED_Model for external applications. At each timestep, the module interpolates a user-specified atmosphere grid at the current T_eff, log g, [M/H], applies geometric dilution at a user-specified distance, convolves the SED with each requested filter transmission curve, and appends observer-frame magnitudes to standard MESA output files. We demonstrate the module across six diverse use cases: TP-AGB evolution, nonlinear RR Lyrae pulsation, starspot-modified photospheres, white dwarf cooling, blue-loop evolution, and rotational spot modulation based on an external YREC SPOTS grid. These cases draw on Kurucz/ATLAS9, BT-Settl, and Koester DA atmosphere grids and filter systems including Roman WFI, LSST ugrizy, Gaia, and extended Johnson UBVRIJHKLMN. Two of these demonstrations compare the module directly with observational data: a 0.6M_dot DA white dwarf cooling track follows the broad Gaia DR3 cooling locus from M_G ~ 8.5 to 15mag without intermediate color transformation, and an RSP model recovers the Kepler light curve of FN Lyr (KIC6936115) to 1.1% in period and 0.2% in amplitude.

In this study, we investigate higher-dimensional static and stationary Bianchi-type solutions in an $R^2$ gravity theory using the formalism of exterior differential forms. We construct a broad class of exact higher-dimensional Bianchi-type solutions in an $R^{2}$-corrected gravity theory. It is shown that the theory admits hyperscaling violating black hole solutions associated with homogeneous but anisotropic horizon geometries, encompassing both static and stationary configurations. We further analyze some thermodynamic properties of these backgrounds and demonstrate that higher-curvature corrections give rise to unconventional features. In particular, we show that within the critical sector, the solutions possess a finite Hawking temperature despite an identically vanishing Wald entropy, signaling an unusual thermodynamic regime. These configurations arise at the critical point of the theory, where the effective gravitational coupling vanishes and the space of admissible constant-curvature geometries is enlarged.

In this study, we developed a unified geometric and relativistic framework for a new family of traversable wormholes constructed from a super-hyperbolic deformation of the classical catenoid, whose geometric embedding combines an explicit local curvature parameter $κ$, which secures a regular throat, with the Mittag-Leffler-based super-hyperboloid deformation function ${\mathfrak{S}C}_α (v)$, where the deformation parameter $α>1$ governs the radial onset and far-field growth of the embedding beyond the throat, continuously approaching the classical catenoidal geometry in the boundary limit $α\rightarrow1^{+}$. Allowing a non-constant redshift $Φ(r)$, we systematically evaluate closed analytical expressions for the shape function, curvature tensors, matter sources, and junction conditions, culminating in an exact thin-shell equation of motion and stability criterion. This work establishes a mathematically consistent and physically viable framework for the extension of wormhole theory, providing a new avenue for exploring exotic geometries within general relativity and identifying the conditions under which traversable configurations remain locally stable.

The predominant fusion chain in stellar nucleosynthesis produces positron and neutrino byproducts in equal amounts. An extremely high neutrino flux can be directly measured, but the unobservable, yet equally high flux of positrons is traditionally considered to be short-lived antimatter that annihilates upon contact with electrons. The electrons are traditionally assumed to be populated in such excess that their annihilation with positrons could be sustained indefinitely. This paper posits that, considering the extremely high positron and neutrino flux within a stellar core, there is an opportunity for localized positron populations and accumulation. As there are no existing methods to directly observe a positron accumulation within the solar core, evidence must rely largely on observations of the surface and above. The difficulties of direct observation into internal stellar processes introduces a chance to overlook critical components such as a theoretical positron accumulation, thus exacerbating unresolved stellar questions surrounding observed coronal signatures and high-energy emission channels. This investigation examines the potential for stellar positron accumulation, its consequences for core dynamics, and observational signatures that could support the existence of long-lived positrons. The framework is applied to problems in stellar and galactic physics, solar weather forecasting, and high-energy-density plasma systems.

Numerical studies of critical phenomena in gravitational collapse have provided key insights into the nonlinear dynamics of Einstein's field equations in the strong-field regime. However, most prior investigations have been restricted to highly symmetric models, limiting our understanding of the universality of critical behavior. Extending these studies to more general systems poses substantial computational challenges, as resolving the fine-scale structure near the black hole threshold requires extremely high spatial and temporal resolution. In this work, we present the first direct comparison between the discontinuous Galerkin (DG) and finite-difference methods applied to critical phenomena. For the case study, we used the classical example of spherically symmetric gravitational collapse of massless scalar fields. The DG method, which combines the high-order accuracy of spectral techniques with the flexibility and locality of finite-difference schemes, demonstrates significant computational advantages: Near criticality, it achieves comparable accuracy with fewer degrees of freedom, approximately half the number of computational steps, and a third of the run-time required by finite-difference methods. These improvements mitigate the run-time and resolution limitations characteristic of finite-difference simulations in higher dimensions and complex field systems. A detailed extension of the DG framework to the collapse of nonlinear, axisymmetric gravitational waves will be reported in future work.

We develop a quantitative Fredenhagen--Haag like approach for describing Hawking radiation using massless scalar fields on controlled spherically symmetric Vaidya space-times. The local thermal character of the system is supplied by the universal scaling limit of Hadamard two-point functions at an outer trapping horizon \cite{KurpiczPinamontiVerch2021}. On regular detector--horizon windows, we construct globally hyperbolic developments and compare the nonautonomous Vaidya evolution with a frozen Schwarzschild propagator on Sobolev energy spaces. We derive an explicit Duhamel estimate that is uniform in angular momentum, calculate the exact linear null-peeling coefficient, and bound the quadratic remainder of the ray map. Combining these estimates with positivity gives a two-sided detector-response inequality relative to the local thermal reference. Its error terms quantify operator variation, stationary scattering tails, finite Hadamard scaling, horizon localisation, and the outgoing channel. The inequality is valid at finite parameters because each of these contributions is retained. Under the decay hypotheses, the detector response converges to the corresponding Fredenhagen--Haag form for asymptotically stationary accretion and for evaporation--accretion turnaround profiles. We also construct a Hadamard state by Cauchy transport from an eventually stationary Unruh covariance and show that a finite evaporating slab does not determine a late-time response without a prescribed future extension. For asymptotic evaporation with $m(u)>0$ at every finite time and $m(u)\to0$, a mass-rescaled conformal formulation yields a scale-covariant finite-window estimate for scale-following detectors.

Recently, an order completeness property has attracted attention in some low regularity spacetime geometry literature, where it was named `chronocompleteness'. In this work we prove that, in the framework of standard Lorentzian geometry, this property is equivalent to global hyperbolicity. The equivalence of global hyperbolicity with other more traditional forms of order completeness is also established.

We present an exact gravitational instanton solution on a five-dimensional, conformally invariant, Kerr-like warped Riemannian brane-world manifold. The geometry can be described as the Kähler manifold $\mathbb{C}^1\times\mathbb{C}^1\times \mathbb{R}$. By applying a double cover of $S^3$ through stereographic projection onto $\mathbb{C}P^1\times \mathbb{C}P^1$ of the effective four-dimensional manifold, together with the Klein surface construction, we exploit the underlying $\mathbb{Z}_2$ symmetry. The instanton is then obtained by fibering over the antipodal $S^2$. The metric is determined by a first-order differential equation containing an integer parameter, while the equation governing the angular momentum component decouples from the remaining field equations. Finally, we show that our solution admits an analytic complex transformation to a locally conformally related Kähler manifold possessing a Kähler potential, thereby making the self-dual structure manifest.

The gravitational frequency shift of light is well understood in the theory of classical electromagnetism. Nevertheless, its description in quantum theory is not yet fully developed. Recent work pointed out inconsistencies in previously developed models aimed at describing the gravitational redshift as an effective multi-mode mixer (MMM) acting on modes of light, but so far a complete solution of these issues was not obtained. Here, we identify the root cause of the MMM model's inconsistency and provide two complementary approaches to correct it: a "natural" one from a field-theoretic perspective, and another adapted to the language of quantum mechanics of finite-dimensional systems. We show that the second approach allows for modeling of the redshift in a multi-mode transmission setup as a quantum channel that can be characterized using standard quantum information-theoretic techniques when restricting the input states to Gaussian states of light.

We study the entanglement entropy of a conformally coupled scalar field at its ground state in $(3+1)$-dimensional AdS space in global coordinates. We consider spherical entangling surfaces centered at the origin of AdS and allow for general boundary conditions at the conformal boundary. Through numerical and analytical means, we show that the UV-divergent part of the entropy has a universal form, while the UV-finite part is sensitive to the boundary conditions. We determine the dependence of the latter part on mixed boundary conditions that interpolate between Dirichlet and Neumann.

We extend the Lee-Yang phase transition framework to charged anti-de Sitter (AdS) black holes in four-dimensional trace anomaly gravity. By treating the horizon radius as a complex variable, we derive a fully resolved complex phase diagram that uncovers novel supercritical phenomena within this modified gravity setting. Relative to the standard Reissner-Nordström-AdS black hole, the trace anomaly shifts the location of the critical point: for a representative set of anomaly parameters, both the critical pressure and critical temperature are suppressed. The Widom line is rigorously identified as the projection of the complex Lee-Yang zeros onto the real physical phase plane, a trajectory that demarcates the small-black-hole-like and large-black-hole-like phases throughout the supercritical regime. We also independently recover this same Widom line via the thermodynamic response function method, demonstrating that the two definitions are in excellent quantitative agreement in the near-critical region and share identical universal scaling behavior. Furthermore, our analysis reveals a smooth, continuous crossover across the Widom line as probed by thermodynamic response functions--a behavior fundamentally distinct from the discontinuous first-order phase transitions that occur below the critical point. These results offer new, physically concrete insights into the thermodynamics of quantum-corrected black holes.