高能暂现源 · 每日文献综述

Classical gravitational waves (GWs) are stable in vacuum. We show that treated as coherent graviton states, they decay into photon pairs, a quantum process forbidden classically and semiclassically and enhanced by the graviton number squared $N^2$. We estimate the resulting rates for compact binaries and a stochastic background, including the effect from stimulated decay to the CMB. In theories with light degrees of freedom, an analogous decay into them is also possible, and more relevant for ultralight dark matter, as it can entail huge occupation numbers. We derive first constraints on cosmological GW sources by the corresponding injection of photons from CMB spectral distortions, extragalactic backgrounds, and light-nuclei photofission. In summary, the decay of GWs into photons offers a new (challenging) handle into the detection of GW sources, with the extra appealing feature of being only possible by the quantum nature of the gravitational field.

We present a neural network surrogate model that emulates the NRSur7dq4 gravitational waveform model for precessing binary black hole mergers. The surrogate decomposes the waveform into constituent quantities and trains an independent multilayer perceptron (MLP) for each. We validate the surrogate against NRSur7dq4 on 10,000 waveforms spanning its full parameter space ($1 \leq q \leq 4$, $|χ_{A,B}| \leq 0.8$). For representative total masses between 60 and 300 $M_\odot$, median sky-averaged frequency-domain mismatches range from $8.0 \times 10^{-5}$ to $1.7 \times 10^{-4}$, with 95th percentiles below $10^{-3}$. On an NVIDIA L40S GPU the JAX surrogate evaluates a single waveform in about 1 ms end-to-end, roughly 10 times faster than the LALSimulation C implementation of NRSur7dq4, and sustains about 140 times the LALSimulation throughput at batch size 64, making it well suited for both low-latency parameter-estimation samplers and large-scale waveform generation. The full NRSur7dq4 NN waveform-to-likelihood pipeline is implemented in JAX and is differentiable. This is the first neural-network surrogate of a precessing numerical-relativity waveform model to combine validated NR-faithful accuracy with a fully differentiable, GPU-accelerated inference pipeline, enabling gradient-based inference approaches via automatic differentiation including Fisher information matrices, GPU-accelerated nested sampling, gradient-based MCMC and importance sampling.

We consider how a class of morphological descriptors, the Minkowski Tensors (MTs), can be used to test the statistical isotropy of random fields on the sphere. The definition of the MTs involves an integral of a tensor, which is an ambiguous operation on a curved manifold. We find that existing estimators in the literature, when applied to fields on the two-sphere, either explicitly break covariance or artificially isotropize the MT due to a geometric rotation of tangent spaces. To evade these issues, we construct the MTs of individual connected components and use them to build correlation functions $ξ_{\pm}(θ,ν)$ of their relative orientations. These correlation functions are built from scalars and are therefore covariant, and can be used to search for alignment of structures as a function of scale (angular separation). We generate four sets of random fields on $S^{2}$ -- isotropic, dipole modulated, globally-sheared and locally-sheared, and show how the connected component correlation functions can distinguish scale dependent alignments. For the sheared fields, the decay scale of $ξ_{+}$ measures the angular coherence of the alignment, and the amplitude of $ξ_{-}$ at large separations measures its globally coherent fraction, distinguishing the two shear models. In contrast, dipole modulation generates no significant signal in the orientation statistics. We show analytically that its effect on the traceless component of the Minkowski tensor is second order in the modulation amplitude $λ\ll 1$.

In this work, we study the gravitational lensing of gravitational waves (GWs) by extending the geometric-optics approximation to higher order. With the help of the Newman-Penrose formalism, we reexpress the GW propagation equations as a series of scalar equations and present explicit expressions for the Weyl scalars that describe the GW polarizations. By combining the approaches of solving geodesic deviation and transport equations, we construct a solvable system of equations that describes the evolution of GW polarization along null geodesics. This framework fills the gap left by the leading-order geometric optics and the Kirchhoff diffraction integral, neither of which captures the polarization characteristics of GWs during the lensing process. This work applies the above framework to a Schwarzschild lensing configuration. Through a rigorous theoretical formulation and detailed numerical analysis, our results reveal the emergence of apparent vector and scalar modes in lensed GW signals, which originate from the smearing of the polarization plane and distortion of the wavefront and do not represent genuine dynamical degrees of freedom but rather arise as the propagation effects imposed by gravitational lensing.

We study a Schwarzschild-like black hole embedded in an exponential-sphere (ESM) dark matter halo, characterized by a halo mass $M_0$ and a scale radius $r_0$. We first show that the halo's effect on the marginally bound orbit (MBO) and innermost stable circular orbit (ISCO) is richer than a simple shift: the characteristic radii and energies vary non-monotonically with $r_0$, dipping below their Schwarzschild values before recovering, while the angular momenta decrease monotonically; as a function of $M_0$, the response can even reverse sign depending on how extended the halo is, with only the ISCO energy remaining monotonic throughout. We classify periodic orbits by the rational frequency ratio $q=ω_φ/ω_r-1=w+v/z$ and find that $r_0$ and $M_0$ leave clearly distinguishable imprints on the orbit spectrum. Using the numerical kludge framework, we compute the corresponding extreme-mass-ratio-inspiral (EMRI) waveforms and show that varying $r_0$ produces a strong, monotonic effect enlarging the orbits, lengthening the radial period, and introducing a clear dephasing while comparable variations in $M_0$ leave the signal nearly unchanged unless $M_0$ becomes a sizable fraction of the black hole mass. Together, these results indicate that EMRI waveforms can, in principle, disentangle the total mass of a dark matter halo from its spatial extent, offering a strong-field probe of the dark matter distribution around supermassive black holes.

An intermediate-mass black hole (IMBH) hidden in our Galactic Center (GC) may explain the puzzling observations of the stellar distribution around Sagittarius A* (Sgr A*), the supermassive black hole (SMBH) in the GC. Future observations with the next-generation radio telescopes, such as the SKA, are promising to discover pulsars orbiting around Sgr A*, and thus provide the possibility of constraining the hidden IMBH with pulsar timing. We study the detectability of a third-body, the IMBH, in the pulsar-SMBH system based on radio timing observation. We find that the pulsar-SMBH system is very sensitive to such a third-body perturbation and can be used to put stringent constraints on the existence of the IMBH. Even under strong perturbations caused by the complex GC astrophysical environments, timing observation will still complement the existing observational constraints.

Plasma streaming instabilities excited by relativistic charged particle beams play a pivotal role in astrophysical and laboratory environments. Their numerical study, however, is challenged by the disparity in spatiotemporal scales between the background plasma and beam particles, which can differ by several orders of magnitude for tenuous, ultrarelativistic beams. Here, we exploit the quasistatic approximation (QSA) to develop a new theoretical framework capable of capturing the full unstable spectrum in the spatiotemporal regime relevant for beams that continuously encounter unperturbed plasma at their leading edge. Within this linear, fully electromagnetic model, we uncover a previously unreported spatiotemporal evolution of the current filamentation instability and elucidate its interplay with the oblique two-stream instability, predicting the dominance of filamentation in the vicinity of the beam front. The good agreement between theory, kinetic particle-in-cell (PIC) simulations, and QSA-based PIC simulations validates the robustness of the approach. By pushing QSA-based PIC simulations to extremely dilute electron-positron beams, such as those found in blazar jets, we demonstrate their unique ability to capture the rich nonlinear dynamics of streaming instabilities in parameter regimes previously inaccessible to kinetic simulations.

The Magnusian is a phase-space function that generates finite-time evolution through nested Poisson brackets. It is related to several familiar generators of classical dynamics, including the radial action, the eikonal phase and related quantities. In this work, we extend the Magnusian framework to systems with dissipation and nonlocal-in-time interactions using the in-in formalism, also known as the Schwinger-Keldysh or Galley formalism. This framework is particularly natural for binary dynamics, where integrating out the mediating gravitational field can produce both dissipative radiation-reaction effects and hereditary, nonlocal-in-time interactions. We derive the generalized Magnusian and show that it continues to generate finite-time evolution. As an application, we construct the Magnusian for Newtonian bound motion subject to the leading 2.5PN radiation-reaction force. The resulting generator defines a discrete evolution map from one cycle to the next and describes the evolution of the system in agreement with numerical solutions.

The radio halo in the cool-core galaxy cluster A1795 has recently been proposed to be of hadronic origin, because it extends on a scale of the order of Mpc, where no turbulence is expected to be injected in a relaxed cluster. In this paper we aim to constrain the properties of the non-thermal protons and the cluster magnetic field strength under the hypothesis of a hadronic origin of the radio halo at the light of the available gamma ray upper limit in this cluster. We assume a radial profile and several values of the central intensity of the magnetic field, and derive the corresponding properties of the non-thermal protons necessary to reproduce the flux density and the surface brightness profile of the radio halo. For the obtained results, we calculate the corresponding gamma ray emission and compare it with the Fermi-LAT upper limit. We obtain that, for a magnetic field energy radial profile following the thermal one, magnetic field central intensities $B_0<5\,μ$G imply a gamma ray emission similar to or above the Fermi-LAT upper limit. Therefore larger values of the magnetic field are necessary in the hadronic scenario. For these values the radial profile of non-thermal protons needs to be slightly decreasing with radius, although more slowly than the thermal one. For smaller values of the magnetic field different mechanisms for producing or accelerating the non-thermal electrons are necessary.

We develop a new method for simulating pressureless fluids of neutral dust coupled to magnetohydrodynamic gas through dust-gas drag. It has been pointed out that, in the strong-coupling regime, dust-gas multifluid methods suffer from artificial variations in the dust-to-gas mass ratio when the dust and gas are evolved with independent numerical fluxes. This problem arises from inconsistencies between the dust and gas mass fluxes. In the strong-coupling limit, the dust-to-gas mass ratio is advected with the local gas velocity. Recently, a new method based on the Harten-Lax-van Leer (HLL) solver was proposed. This method constructs the dust mass flux so that it is consistent with the gas mass flux, and successfully reduces artificial variations in the dust-to-gas mass ratio. Here, we develop a Split-Flux method that can be coupled to an HLLD gas solver. Through various numerical experiments, we show that the Split-Flux method suppresses artificial variations in the dust-to-gas mass ratio, while preserving the low numerical diffusivity of the HLLD solver.

We perform three-dimensional, high-resolution, general-relativistic magnetohydrodynamics (GRMHD) simulations of the magnetorotational instability (MRI) in differentially rotating neutron stars. We consider both high-mass models which collapse either promptly, or due to the outward transport of angular momentum removing rotational support, and lower-mass models, which remain stable even after solid-body rotation has been achieved. We measure effective transport coefficients of the resulting turbulent flow, shear-viscosity $α_{\rm vis}$, mixing-length $\ell_{\rm mix}$, and mean-field dynamo $α_{\rm DYN}$-parameter, and their correlations with mean-flow parameters, such as rest-mass density $ρ$, characteristic wavelength of the MRI $λ_{\rm MRI}$, and vertical Alfvén velocity $v_A$. At saturation, $\ell_{\rm mix}$ and $α_{\rm DYN}$ correlate with $λ_{\rm MRI}$ and $v_A$ respectively, as expected from dimensional analysis. However, both quantities show deviations of roughly an order of magnitude from the values predicted on the basis of these correlations. They are also highly intermittent in space and time. The mixing length is found to be largely independent of density, calling into question the $\ell_{\rm mix}(ρ)$ ansatz used in many general-relativistic large-eddy simulations. Our results show that, while the effects of MRI-induced turbulence might be qualitatively reproduced by simulations that employ transport coefficients chosen using dimensional-analysis considerations, fully-resolved GRMHD simulations are needed to make quantitative predictions.

Recent observations have demonstrated the presence of cosmic rays (CRs) in cosmic-web filaments. Cold streams supply gas inflows from these filaments into massive galaxies during the cosmic noon. As these streams are expected to be magnetised, external cosmic-web CRs may become entrained with this inflowing gas. We aim to determine whether this externally-supplied CR population can deposit energy to alter or disrupt the supply of cold gas to galaxies. We couple a spectrally-resolved CR transport calculation to a redshift-dependent analytical model of magnetised cold streams in galaxy haloes and investigate whether externally-supplied CRs can modify gas supply through this channel. We find CR energy deposition can alter the thermal state of cold streams. Dense stream cores remain largely resilient and only experience weak heating. Their temperature is raised by less than a factor of 10, which is insufficient to overcome radiative cooling at the stream-CGM interface. In more diffuse streams, and in partially mixed interface gas of the most massive haloes near the virial radius, CR heating becomes strong enough that radiative cooling can no longer balance it, and the gas is heated toward or above the mixing-layer temperature. This weakens the stability of the stream, making it more susceptible to disruption. Complete evaporation is possible only in extreme cases. Cold streams are therefore more vulnerable to CR heating at larger galactocentric radii, higher halo masses, and in more diffuse or partially-mixed stream material. By preferentially heating diffuse gas, externally supplied CRs may introduce additional selectivity into cold-gas accretion that modifies the gas supply and growth of massive galaxies. These CRs weaken fragile streams and erode their cold envelope, and may cause surviving cold flow components to appear thinner and more sharply confined far into galaxy haloes.

Automated solar filament detection using deep learning faces several challenges. Semantic segmentation of solar filaments is a complicated multiscale feature extraction task with long-tail distribution. Furthermore, a large-scale, highly complete, and finely detailed dataset has become mandatory for providing abundant information. To address these challenges, we present a series of machine learning approaches to develop a solar filament detection workflow that performs superbly. First, we manually annotated a small-scale solar filament dataset based on H$α$ spectra called MHAS. Next, we developed the Multiscale ORiented DENdritic (MORDEN) model, a semantic segmentation model focusing on multiscale feature extraction. We also introduced the Dense Conditional Random Field (DenseCRF) and Density-Based Spatial Clustering of Applications with Noise (DBSCAN) methods for post-processing. Using the proposed workflow, we generated a large-scale, high-quality dataset called AHAS. Experimental results demonstrate that MORDEN outperforms several existing solar filament semantic segmentation models with open access. DenseCRF has been demonstrated to effectively capture fine edge details. We also evaluated the effects of data scaling and the reliability of DBSCAN and found that both approaches yield satisfactory performance. Multiple visualization results substantiate our quantitative findings. Our work provides a foundation for maximizing the potential of deep learning models for solar filament detection.

We investigate phenomenological effects induced by a noncommutative deformation of Einstein--Rosen gravitational-waves within the framework of the Riemannian geometry of noncommutative surfaces developed by Chaichian et al. Considering a noncommutative structure between the radial and axial coordinates, we study perturbatively the motion of nonrelativistic test particles in the corresponding deformed geometry. We show that the deformation generates a coupling between the radial and longitudinal sectors, while the radial dynamics remains unaffected by the noncommutative deformation at the perturbative order considered. The induced longitudinal response is governed by a spectrally weighted functional of the gravitational-wave profile, implying that longitudinal observables depend on higher-order spectral moments than their commutative radial counterparts. As a consequence, noncommutative effects exhibit enhanced sensitivity to the ultraviolet structure of the gravitational configuration. We analyze separately monochromatic Einstein--Rosen waves and the localized Weber--Wheeler pulse. In the monochromatic case, the noncommutative correction induces a quasi-periodic longitudinal motion, whereas for the Weber--Wheeler pulse it produces an impulsive longitudinal response analogous to a gravitational velocity memory effect. In addition, we derive an explicit analytical expression in commutative General Relativity for the residual radial velocity generated by the Weber--Wheeler pulse at large radial distances in the perturbative regime.

We consider a cosmological first-order phase transition in which bubbles of true vacuum nucleate during inflation but do not collide and percolate until the Universe has entered the radiation-dominated era. If the collisions take place soon after the end of inflation, the size of these bubbles can be significantly greater than the Hubble length. This has two important consequences for the gravitational waves produced by the bubble collisions: First, as the peak frequency is determined by the comoving bubble radius, it can be well below the MHz frequencies typical for bubble collisions at the end of inflation. Second, when comparing collisions beginning at the same time, the amplitude of the gravitational waves is greatly enhanced relative to Hubble-sized and smaller bubbles. Together, these two effects mean that gravitational waves produced by super-Hubble bubbles soon after the end of inflation can be within the observable frequency and amplitude ranges of LIGO and NANOGrav, as well as LISA and other future gravitational wave experiments. We demonstrate this with a simple illustrative model.

The discovery of S301 (GRAVITY Collaboration et al., 2026) with pericenter distance rp= 280rg and eccentricity e=0.9825, opens the prospect of measuring the spin parameter of Sgr A* through Lense--Thirring (LT) nodal precession. A major obstacle is Newtonian confusion: any non-spherical extended mass distribution can also induce nodal precession. We aim to separate the LT spin signal of S301 from the Newtonian nodal precession. We compare the secular Newtonian torque exerted by a disk or flattened mass distribution on the orbits of S301 and of the apocenter-matched reference stars S2, S55, and S38, using analytic estimates validated by numerical orbit-averaged torque calculations. For a disk or flattened distribution extending beyond the stellar pericenters, the secular Newtonian torque on a highly eccentric orbit is controlled mainly by the apocenter, whereas the LT signal is controlled mainly by the pericenter. Thus stars with apocenters comparable to S301's but much larger pericenters, in particular S2, but also S55, and S38, experience comparable Newtonian torques while having ~ 30 times smaller LT signals (for S2). Their measured precessions, or upper limits on them, can therefore calibrate the mass and orientation of the Newtonian background for subtraction from S301's precession. The Schwarzschild apsidal advance of S301 further rotates the orbit's pericenter relative to any disk, producing a systematic time dependence in the Newtonian contribution, while the LT signal remains fixed by the spin vector. Granularity of the perturber population sets a stochastic floor on this subtraction, which orbit- and star-averaging suppress. With continued GRAVITY+ astrometry and Extremely Large Telescope (ELT) spectroscopy, the in-plane spin projection may be within near-term reach; the full spin vector requires a much longer-term accumulation of the LT apsidal signal.

In recent years, Gaia has been the primary driver of the expansion of the white dwarf (WD) initial-final mass relation (IFMR) in open clusters. The increased sample size has highlighted a pronounced observational gap at progenitor masses of $\simeq2$--$2.7\,M_\odot$, with no spectroscopically confirmed cluster-member WDs in this range. Analysis of the Milky Way open cluster census shows that this absence is primarily driven by the scarcity of appropriately aged, nearby clusters capable of hosting Gaia-detectable WDs, implying that deeper, targeted photometry will be required to build a substantial sample in this progenitor mass range. We further searched for previously unexamined Gaia WD candidates in clusters with ages consistent with producing gap progenitors and identified two viable targets, which we observed spectroscopically with Gemini GMOS-N. Both targets yield inferred progenitor masses within the observational gap, making them the first spectroscopically confirmed cluster-member WDs in this progenitor mass range. The NGC 6991 candidate, in particular, is confirmed as a DA WD with an inferred progenitor mass of $2.12^{+0.04}_{-0.15}\,M_\odot$, providing further support for a non-monotonic trend in the IFMR.

We investigate the end stages of circular white-dwarf--compact-object binaries by developing a novel integrator implementing mass transfer and 2.5-order Post-Newtonian kinematics. White-dwarf--compact-object binaries are subject to two phases: a slow inspiral during which binary evolution is dominated by weak-gravity radiation reaction and a quicker ``outspiral" dominated by mass transfer. These systems have unique gravitational waveforms with several characteristic features including an accumulation of signal near the maximum cutoff frequency set by the transition between in- and outspiral. We investigate trends in gravitational wave parameters based on component masses. In particular, maximum cutoff frequency depends strongly on white dwarf mass and compactness. It is unlikely that extragalactic binaries will be measured by LISA or current or future terrestrial detectors. However, white-dwarf--compact-object binary end stages will be an important source for future decihertz detectors such as DECIGO and LGWA: The final inspiral of tens of white-dwarf--neutron-star binaries will be detected annually by LGWA, and millions of inspirals along with thousands of outspirals will be detected by DECIGO. The ultimate fates of these binaries are diverse and dependent upon the intricacies of angular momentum loss. In particular, we show that white dwarfs with partners of sufficiently low/high mass can end their lives in common envelopes/mergers, while white dwarfs do not enter contact with partners of intermediate mass. The highest frequencies produced by white-dwarf--compact-object binaries in our tests are 10--20 Hz---incapable of mimicking sub-solar-mass compact object signals in terrestrial detectors or explaining S251112cm-like signals.

We study equilibrium sequences of magnetized strange dwarfs composed of a self bound MIT bag strange matter core, with \(B_{\rm bag}^{1/4}=145\,{\rm MeV}\), and an ordinary crystalline crust. The aim is to determine how nuclear composition changes and magnetic pressure anisotropy in the crust modify the mass radius relation. The strange core is kept isotropic, while the crust is described either by pure nuclei stopped at the first inverse beta threshold or by electron capture sequences extended to neutron drip for C, O, Ne, and Mg compositions; selected mixed crusts are also considered up to the first instability. The stellar structure is solved with the radial pressure as the integrated pressure and with the anisotropic contribution \(2(P_t-P_r)/r\) restricted to the crust. This treatment is compared with ordinary white dwarf sequences and with scalar pressure branch calculations. We find that extending the crust to neutron drip produces more compact strange dwarf branches than stopping at the inverse beta threshold, because the evolved crust is softer and the core crust transition occurs at higher pressure. Magnetic anisotropy further shifts the selected branches toward smaller radii, with the effect visible across the compositions studied and clearer at fixed stellar mass. The comparison with compact objects from the Montreal White Dwarf Database is used only as an observational reference plane, but it indicates that compact white dwarf candidates are a relevant region for testing small core strange dwarf scenarios.

Colliding winds in massive-star binaries generate non-thermal radio emission and an increased X-ray emission. We study the radio emission of the non-thermal emitter 9 Sgr, which is a long-period and highly eccentric binary. We conducted a monitoring campaign of 9 Sgr around its 2013 - 2014 periastron passage, obtaining radio, X-ray and optical spectroscopy data. In this paper, we analyse the radio data. The radio data at 3.6, 6 and 20 cm show a maximum near periastron. Other non-thermal radio emitters among O-type binaries have a minimum flux near periastron, because the synchrotron emission is absorbed by the free-free absorption in the two stellar winds. This is not the case for 9 Sgr, because even at periastron the orbital separation is sufficient to maintain the wind-wind collision and its associated synchrotron emission outside the effective free-free radius of both stars. Our standard modelling with a local magnetic field that decreases inversely proportional to the distance from the stars (1/r) fails to explain the observed fluxes. Instead, we need to adopt a local magnetic field that decreases faster than 1/r. While our model provides an acceptably good fit to the data, there is clearly still room for improvement. More advanced modelling should include magnetohydrodynamics and more detailed physics of the injection, acceleration and cooling of the relativistic electrons. Radio observations at orbital phases away from periastron can put further constraints on the models.

Supergranulation is one of the dominant scales of near-surface solar convection and provides an important diagnostic for studying the interaction between convective flows, rotation, and magnetic activity. We develop an automated framework to identify and characterize supergranular structures using subsurface horizontal-velocity maps inferred from time-distance helioseismology. The method applies Laplacian-of-Gaussian detection to horizontal velocity divergence maps and combines this with magnetic-field masking, divergence-based filtering, and multi-peak rejection to isolate supergranular cells under both quiet-Sun and active conditions. Using this approach, we analyze 16 years of SDO/HMI observations spanning Solar Cycles 24 and 25 and investigate temporal and latitudinal variations of supergranular properties. The results reveal a clear solar-cycle dependence: the mean supergranular diameter decreases near solar maxima and increases around solar minima, with systematically larger supergranules in the weaker Solar Cycle 24 than in the stronger Solar Cycle 25. The width of the diameter distribution increases during high magnetic activity, whereas the number of detected supergranules shows only weak cycle dependence. The mean velocity divergence within detected supergranules is strongly anticorrelated with sunspot number, indicating magnetic suppression of divergent convective flows. Time-latitude distributions of supergranular diameter and divergence closely follow the migration of solar activity belts, while the curl of the horizontal velocity shows weak cycle dependence but pronounced hemispheric asymmetry. These results establish supergranulation as a sensitive tracer of solar-cycle-related changes in near-surface convection.

Pulsar timing arrays (PTAs) are sensitive to ultralight dark matter (ULDM) in the $10^{-24}$-$10^{-20}\,\mathrm{eV}$ mass range, with existing datasets already probing otherwise open parameter space and future PTAs promising substantial improvements in reach. Thus far, however, PTA searches for ULDM have typically been formulated using limiting descriptions. Analyses are performed in either the fully correlated limit, in which the local ULDM amplitude is shared across the array, or the fully uncorrelated limit, in which each pulsar has an independent local amplitude. Because the transition between these regimes occurs within the PTA-sensitive mass range, projected sensitivities and data-derived constraints can depend on which limiting description is assumed. For the first time, we develop a self-consistent analysis that treats the ULDM field as a Gaussian random field with finite spatial correlations, allowing the amplitude prior used in PTA signal models to interpolate continuously between the fully correlated and fully uncorrelated limits. We apply the framework to both linearly and quadratically coupled scalar ULDM, the latter including the universal gravitational signal sourced by the oscillating ULDM pressure. Pulsar-distance uncertainties are incorporated through an augmented latent-field prior, and the resulting distance-marginalized latent-amplitude distribution is represented with a normalizing-flow surrogate. We validate the method on mock PTA datasets, including blinded signal injection tests.

Context. Gamma-Loud Protostars (GLPs) have been recently reported as Galactic hadronic accelerators whose acceleration site is situated in their protostellar jets. Theoretical and observational analysis situate radio cm luminosity as a thermal tracer of jet activity, presenting an unique opportunity to study jet properties as accelerators. Aims. We aim to develop a way to estimate the kinetic power of protostellar jets and compare their energetics with those extracted from the non-thermal gamma-ray side of GLPs. Methods. We combine theoretical and phenomenological relations to estimate the jet mechanical luminosity based on the radio cm luminosity. We relate the resulting values to the non-thermal contribution of GLPs, studying its behaviour and efficiency. Results. The derivation of the jet power successfully reproduces infrared and radio observations. The cosmic-ray energy correlates to the injected mechanical energy, implying an acceleration efficiency of 1--10%. Future radio observations are needed to find the definite accelerators and obtain reliable efficiencies.

We study the rotational Unruh effect by identifying the pseudodynamics which emerges when fundamental spacetime symmetries are violated. We show that there is, fundamentally, no rotational Unruh effect, in agreement with the first explicit calculations of the literature, and that, when such an effect has been claimed to exist in later articles, its origin traces back to the derivation of the standard Unruh effect involving linear acceleration. Such a linear Unruh effect intrudes because the chosen reference frames do not respect the cylindrical symmetry of the system, and thus the analyses require Lorentz boosts. Our study also confirms previous findings that the Unruh effect is a consequence of the pseudodynamics which arises because Instant-Form dynamics explicitly breaks a fundamental symmetry of spacetime: Poincaré invariance.

Numerical simulations of gravitational waves (GW) production during violent evolution of matter inhomogeneities in the early Universe yield highly wiggle infrared parts of the spectra. Obtained directly from the two-point correlation function, these wiggles are nonphysical, corresponding to the parasitic, double frequency terms in naively averaged squared oscillation amplitudes of GW, and hence must be washed out. The deep infrared behavior can be predicted on general grounds, e.g. fixed by causality considerations. However, what matters for real observations, e.g. like that of NANOGrav, and what can be only inferred from numerical simulations, is the infrared slope near the maximum of the spectrum. It reflects the dynamics responsible for the GW production in its heyday, and hence must be accurately predicted. We illustrate the problem with numerical simulations of the Domain Wall network performed with the help of code CosmoLattice. We suggest a numerical procedure to smooth out these parasitic wiggles, which allows us to recover the true spectrum. Being quite generic, it may be applied to numerical simulations of other hypothetical sources of GW possibly operating in the early Universe. The procedure requires to extend the simulation by a few Hubble times after termination of the GW production. We checked with numerical simulations, that the technically natural long-time extension of simulations, which becomes available via artificial scaling of different parts in the scalar sector equations provided by PRS prescription, gives wrong GW spectra even if the source terms are properly rescaled.

Strong magnetic fields modify the thermodynamics of white dwarf (WD) matter by quantizing the transverse motion of degenerate electrons into Landau levels and splitting the pressure into components parallel and perpendicular to the magnetic field. We investigate how this microscopic pressure anisotropy affects ultra-dense WD sequences when Coulomb lattice contributions, electron capture thresholds, neutron drip limits, and nuclear composition are treated consistently in the equation of state (EoS). The stellar equilibrium structure is obtained by solving an anisotropic extension of the Tolman--Oppenheimer--Volkoff (TOV) equations, where $P_r = P_\parallel$ and $P_t = P_\perp$ denote the radial and tangential pressures, respectively. We compare the post-electron-capture branches with their corresponding pre-capture sequences for pure $^{12}\rm{C}$, $^{16}\rm{O}$, $^{20}\rm{Ne}$, and $^{24}\rm{Mg}$ compositions, as well as for fixed 50/50 C/O, Ne/O, and Mg/Ne mixtures. The EoS predicts $P_\perp < P_\parallel$ in density ranges where only a few Landau levels are occupied. Consequently, pressure anisotropy shifts the stellar sequences toward smaller radii, with only minor changes in the maximum masses. We also find that post-capture configurations cannot be interpreted from the mass--radius plane alone, since the corresponding $M(ρ_c)$ curves reveal unstable portions after the maximum mass is reached. Our results show that strong magnetic fields significantly reduce the radii of low-mass WDs, yielding better agreement with the observational data available in the Montreal White Dwarf Database and suggesting that future high-precision observations of massive magnetic WDs could help assess the role of magnetic pressure anisotropy in determining their masses and radii.

We obtain explicit formulas for the expected number and height distribution of critical points of smooth isotropic Gaussian random fields on $\mathbb{R}^d$. The expected number density formula is expressed in terms of at most one-dimensional integrals, regardless of the dimension $d$. To obtain the formulas, we provide a variant of de Bruijn's theorem, as well as Weierstrass' convolution formula with a Gaussian random variable and its inversion.

Cosmological stasis, a surprising phenomenon in which the abundances of different energy components in the universe with different equations of state remain constant despite cosmological expansion, has been a focus of recent attention. This behavior emerges as the consequence of an attractor that governs the dynamics of the corresponding cosmological system and pulls it towards stasis even if the system is not initially in this state. However, while some systems actually reach stasis in finite time, it is also possible for such systems to spend considerable time under the influence of this attractor, continually heading towards stasis without ever quite reaching it. This too represents behavior that is entirely unexpected within standard cosmological scenarios. In this paper, we present an explicit model which realizes both of these behaviors in a thermal context while satisfying all relevant phenomenological and cosmological constraints. Within this model, we then examine how the attractor influences the cosmological dynamics and explore the potential consequences for the early universe.

As the nearest protoplanetary disk to Earth ($d = 60.14$ pc), TW Hya is one of the most studied protoplanetary disks and a critical benchmark for testing planet formation theories. We present high-contrast coronagraphic imaging of the TW Hya disk from JWST/NIRCam across four filters (F187N, F200W, F356W, and F444W). We detect the disk's scattered-light emission in F200W, F356W, and F444W. An elliptical fit to the disk image yields an average inclination of $i = 8.74^{+1.03}_{-0.94}$ degrees and a position angle of $\mathrm{PA} = 75.62^{+7.86}_{-6.56}$ degrees. We find tentative evidence for radial variations in these parameters, a trend consistent with a disk warp. Our companion search yields no new detections, placing the lowest mass limits yet on companions that might be responsible for carving out the dust gap. Assuming no local extinction and a system age of 10 Myr, the F444W data are sensitive to masses down to $\sim 0.4\,M_{\rm Jup}$ at separations of $1$ arcsec ($\sim 60$ AU). Accounting for local disk extinction analogous to the AS 209 system, our limits reach sub-Jupiter masses beyond $2$ arcsec. Furthermore, our analysis provides a detailed view of a previously detected feature in the outer disk at $\sim 120$ AU, confirming its morphology as a distinct bifurcation structure. This feature may indicate the presence of complex substructures arising from dynamical planet-disk interactions. These results demonstrate JWST's ability to characterize the architecture of protoplanetary disks and constrain the properties of forming worlds.

We investigate the quasinormal modes (QNMs) of scalar perturbations and strong cosmic censorship (SCC) in regular Ayón-Beato-García-Bronnikov-de Sitter (ABGB-dS) black hole spacetime. The main motivation of this work is to clarify whether the regularization of black hole core, which removes the central singularity, can also change the fate of SCC connected to the Cauchy horizon. We first study the dependence of the scalar QNM frequency (QNF) on the scalar mass and black hole parameters. For angular number $l=0$, a small scalar mass can give rise to a slowly decaying mode which is purely imaginary. We also find that the black hole charge and cosmological constant affect the QNM spectrum in qualitatively opposite ways. We then examine SCC under massless and massive scalar perturbations. For massless perturbations, the QNMs spectrum can be organized into photon sphere (PS), de Sitter (dS) and near-extremal (NE) families. Compared with the SCC in the Reissner-Nordström-de Sitter (RN-dS) case, SCC is generally more easily violated in the ABGB-dS spacetime, although this tendency is reversed for sufficiently large cosmological constant. For massive scalar perturbations, we find that the scalar mass does not restore SCC. Instead, it can enhance the violation by driving the system into the regime $β>1$. At last, we discuss what we may expect from the violation of SCC in a regular black hole spacetime.

Modern stellar surveys measure millions of spectra, yet one self-consistent atmosphere and spectrum can require tens of minutes. This cost has motivated grids, spectral emulators, and data-driven models. We present Payne Zero, which reorganizes one-dimensional LTE Kurucz calculations for GPU-native synthesis and multicore atmosphere iteration, and validate it against the original Fortran programs. A 300--1000 nm solar spectrum sampled at $R_{\rm grid}=300{,}000$ takes about 14 s on an NVIDIA H100 GPU, while the APOGEE 1500--1700 nm interval takes about 1 s. Physical atmosphere iterations take 2--5 s on 16 AMD CPU threads, and learned initializers reduce the iterations required for convergence. Final spectra remain in practical parity across the tested dwarf and giant regimes. These speeds place direct synthesis inside an optimizer without a label-to-flux spectral emulator. We demonstrate direct many-element fitting of reduced APOGEE spectra and recover multi-element abundance trends broadly consistent with the survey catalog. GPU-resident velocity shifts, broadening, line-spread-function convolution, and detector sampling add negligible cost relative to synthesis. The direct-synthesis search takes less than one minute per star on an H100, while atmosphere verification runs independently on multicore CPUs. The same computational graph calibrates more than $10^5$ oscillator-strength and damping corrections jointly against the Sun and Arcturus in about one minute on an H100. Payne Zero therefore brings direct physical fitting and atomic-data calibration to survey scale. The code is available at https://github.com/tingyuansen/payne-zero.

We investigate gravitational wave (GW) emission from periodic timelike orbits of a test particle around a magnetized Ernst black hole and the gravitational waveforms generated by their orbital dynamics. The bound geodesics are systematically classified using the zoom-whirl representation labeled with three integers $(z,w,v)$. Gravitational waveforms are computed within a numerical framework that combines exact geodesic motion with the quadrupole approximation, which is well-suited to extreme mass-ratio inspirals (EMRIs). This analysis is particularly relevant for assessing the capability of future gravitational-wave observations to detect the effects of magnetic fields. Our results show that an intrinsic magnetic field imprints characteristic features on the GW signal, highlighting GW astronomy as a promising avenue for probing magnetized black hole spacetimes.

Relativistic particle beams propagating through dense ambient plasmas are susceptible to streaming instabilities that can govern the system dynamics in various astrophysical and laboratory settings. For an unmagnetized, collisionless plasma pervaded by a dilute, cold relativistic beam, the dominant instabilities are the quasielectrostatic, oblique two-stream (OTSI) and the essentially magnetic, current filamentation instability (CFI). While their linear and nonlinear properties have been researched for decades, most treatments assume unbounded, uniform systems and thus predict purely temporal instability growth. This assumption, however, is questionable for realistic configurations where a bounded beam continuously encounters fresh plasma. This feature causes instabilities to grow in a spatiotemporal manner. Whereas spatiotemporal perturbative treatments of streaming instabilities were derived as early as the 1960s, only recently have the spatiotemporal regimes of OTSI and CFI been addressed theoretically. Yet these models are restricted to a specific instability class, and hence cannot describe the competition between spatiotemporal OTSI and CFI. In this work, we present a unified, fully electromagnetic quasi-static model of all unstable modes arising throughout the beam. By not adopting the slowly varying envelope approximation (SVEA), we find that a previously unreported spatiotemporal CFI actually prevails near the front, precisely where the SVEA fails, and is only superseded by OTSI further back in the beam. Furthermore, we demonstrate that our model also captures the growth of the self-modulation and hosing instabilities excited by long, narrow beams. Comparisons with particle-in-cell simulations confirm the validity of the quasistatic approach for modeling streaming plasma instabilities triggered by relativistic dilute beams.

We show that retarded correlators in conformal field theories of scalar primary operators evaluated at finite temperature using $AdS/CFT$ scale anomalously at large light like momenta. The anomalous scaling depends on the curvature of the horizon. Setting the momenta equal to the frequency $ω$, the retarded correlator for black holes with planar horizons scales as $ω^{\frac{2}{d+2} (2Δ- d) }$ as opposed to the scaling behaviour of $ω^{2Δ- d}$ expected by dimensional analysis at generic fixed momenta and large frequencies. $Δ$ is the dimension of the primary and $d$, the number of space-time dimensions. For black holes with spherical and hyperbolic horizons when the frequency squared equals the Casimir along the horizon, the retarded correlator scales as $ω^{\frac{2Δ-d}{2} }$. We establish this using exact results in $d=2$, and a numerical analysis of the Heun equation for the $AdS_5$ planar black hole and finally using the WKB approximation in general $d$. The exact result for black holes with hyperbolic horizon as well as the analysis at large $d$ provides additional checks for the anomalous scaling behaviour. Finally we evaluate the anomalous scaling exponent for the stress tensor correlator in all its 3 channels.

We establish exact analytical thresholds and present a unified thermodynamic state-space representation for the regular Hayward black hole, resolving the full phase structure without reliance on numerical approximations. By evaluating the Hawking temperature, Helmholtz free energy, and heat capacity against the classical Schwarzschild baseline, we derive the exact geometric watershed for the zero-temperature extremal remnant at $r_h = \sqrt3l$, along with the exact Davies critical transition at $r_h = 3l$. Within the intermediate regime $\sqrt{3}l < r_h < 3l$, we uncover a distinct horizon bistability where two distinct horizon radii share identical free energy and temperature profiles. We demonstrate that the Davies singularity acts as a precise thermodynamic divide, separating a locally stable ($C_V > 0$) quantum Small Black Hole branch from an unstable ($C_V < 0$) Large Black Hole branch. Furthermore, we evaluate the exact integrated non-area law entropy at the critical turning point, yielding $S_{turn} = πl^2 \left[ \frac{63}{8} + 2\ln(8l^2) \right]$. Finally, we introduce a compact, 3-parameter thermodynamic state-space diagnostic that tracks the continuous evolution of regular black holes from classical thermal evaporation to cold remnant lock, offering a quantitative framework for quantum-gravity phenomenology.

We study the inflationary primordial perturbations in $κ$-Minkowski non-commutative space-time, a Lie-algebraic type deformation of canonical space-time motivated by quantum gravity scenarios. Employing the $κ$-deformed star product formalism, we construct the bilinear action for curvature perturbations and derive the $κ$-deformed Mukhanov-Sasaki equation and obtain the perturbative solutions. Further, we compute the primordial power spectrum and spectral index, showing that the leading order corrections to the power spectrum induces scale-dependent term proportional to $(\ln k)^2$. The spectral index also exhibits an explicit $\ln k$ dependence, which persists even when the slow-roll parameters are constant. We also perform a Bayesian MCMC analysis using ACT DR6 data and constrain the $κ$-deformation length scale to $λ=6.32^{+6.00}_{-4.30}\times10^{-30}m$ at $1σ$ CL, approximately four orders of magnitude larger than the Planck scale, demonstrating that the $κ$-deformed space-time offers a potential window into quantum gravity phenomenology through precision cosmology.

The Planck all-sky surveys at (sub)millimeter wavelengths enable us to accurately determine the corresponding local luminosity functions up to the highest luminosities. The detected galaxies are strictly local, so evolutionary effects, which are known to be particularly strong at these wavelengths, are not a problem. However, previous studies have so far relied only on the Planck Early Release Compact Source Catalog (ERCSC) for this purpose. Another important improvement over earlier estimates is the availability of complete all-sky catalogs of galaxies within hundreds of megaparsecs, with redshift-independent distances for nearby objects, for which redshifts are not reliable distance estimators. In this paper we re-estimate the (sub)millimeter local luminosity functions using data from the Second Planck Catalog of Compact Sources, which supersedes the previously used ERCSC and contains far more sources and more accurate photometry. We computed the luminosity functions using both the classical $1/V_{\rm max}$ and the nonparametric kernel density estimation (KDE) method, which overcomes limitations of binning techniques. Our implementation of the KDE uses the $1/V_{\max}$ weighting to account for survey selection effects. We obtain Planck-based local luminosity functions at 857, 545, 353, and 217 GHz, as well as the total IR luminosity function and the dust mass function. We find significant differences from earlier estimates and discuss their possible origins.

The origin of black hole entropy remains one of the deepest mysteries in modern physics. Two recent developments offer complementary perspectives on this puzzle: the entropy release from regular Schwarzschild black holes with a de Sitter core (the OCK construction), and the local thermodynamics of the de Sitter vacuum (Volovik). In the OCK framework, the inner horizon carries positive Bekenstein-Hawking entropy $S_{\rm inner}=πh_c^2$ that is gradually released as the core shrinks, until a classical Minkowski breaking obstructs the evolution at $n=0$. In Volovik's framework, the total entropy of a homogeneous de Sitter region is $S_{\rm dS}= \operatorname{sgn}(H)\,π/H^{2} = \operatorname{sgn}(H)\,A/4$: expanding de Sitter ($H>0$) carries positive entropy, while contracting de Sitter ($H<0$) carries negative entropy. We show that the sign of the Hubble parameter is the unifying element linking the two pictures. The OCK core is de~Sitter only for $n>2$; the Minkowski breaking is a classical kinematic obstruction, not a dynamical transition to a contracting de Sitter phase. Any connection between the expanding and contracting regimes would require a quantum mechanism that remains speculative. Nevertheless, both frameworks embody the same thermodynamic principle, the shrinking of the interior drives the system toward increased total entropy, and together they provide a consistent picture of entropy flow during gravitational collapse. The integer nature of the OCK parameter suggests a quantized entropy spectrum and a statistical interpretation of black hole entropy, while the generalized second law is satisfied in both frameworks, and in the speculated quantum connection provided the environmental entropy is properly accounted for.

Massive stars have a major impact on their environment in their host galaxy. Observational determinations of their physical parameters are required to better constrain evolutionary models. In this context, the binary system WR 25 whose dominant spectral type is that of a nitrogen sequence Wolf-Rayet star, is of particular interest. It exhibits the highest known hydrogen content among the Milky Way Wolf-Rayet stars, as well as additional absorption lines. It is most probably an object still on the main-sequence or close to leaving it. We acquired new high-resolution spectra of this extremely interesting object. We present an improved version of the SB1 orbital solution for the motion of the WN component. We confirm the detection of the previously reported probable O companion and definitively prove that it is indeed gravitationally bound to the WN star. A first SB2 solution is presented, and a mass-ratio WN/O of 2.02 +/- 0.36 is derived. Following a spectral disentangling procedure, we identify the companion as an O5(f^+) star belonging to either the main-sequence (V) or giant (III) luminosity classes. The spectral type of the companion, together with the above-mentioned mass ratio, points to a very massive primary WN star of at least 55 solar masses. This confirms that WR 25 belongs to the family of very massive WNLh objects, a very poorly populated class in the Milky Way. We demonstrate that the absorption component in the P-Cygni profile of the He II lambda 4859 line of WR 25 is mainly due to the O-type companion, and we propose to adopt a WN6ha spectral type for the WN component of the system. On the basis of the extracted disentangled spectra, we derive approximate physical parameters through a detailed CMFGEN analysis, given the difficulty in constraining both the extinction towards WR 25 and the definitive brightness ratio between the components.

We present a compact and unified framework for quantum-information diagnostics of time-dependent two-mode bosonic systems based on the Bogoliubov ratio $λ_k(η) \equiv β_k(η)/α_k(η)$. For a general time-dependent quadratic two-mode Hamiltonian, the state dynamics is exactly reduced to a single complex Riccati equation for $λ_k$. Upon tracing out one partner mode, the spectrum of the one-mode reduced density matrix is determined entirely by the squared magnitude $q_k(η) = \vert{}λ_k(η)\vert{}^2$. Consequently, we could construct the explicit, model-independent formula for the for the reduced-state purity, linear entropy, Rényi-2 entropy, and von Neumann entropy without reconstructing and diagonalizing the reduced density matrix on a model-by-model basis using coupled squeezing parameters ($r_k, φ_k$). We demonstrate the utility of this framework in two distinct non-stationary setups: primordial cosmological perturbations and a chirped-pulse nondegenerate optical parametric amplifier. In the cosmological context, our formulation clarifies how background-induced phase rotation and frequency softening regulate squeezing growth and state mixedness; in the optical domain, it captures the delayed onset, suppression of squeezing accumulation, and late-time entropy saturation induced by finite pump duration and frequency chirp. By cleanly factorizing model-dependent driving protocols from universal information-theoretic metrics, this framework offers an efficient, standardized diagnostic tool for a broad class of parametrically driven quadratic bosonic systems.

We update the Hubble constant measurement with corrected Pantheon+ and DES-DOVEKIE supernovae. The use of DES-DOVEKIE here is the first application of DES-DOVEKIE to a distance-ladder $H_0$ determination. Recent reanalyses of supernova datasets have put Pantheon+, DES-DOVEKIE, and Union3.1 samples on the same footing with regard to the evidence of dynamical dark energy ($3.2$--$3.4σ$), and thus an update on the Hubble constant is the next logical step. The $H_0$ Distance Network (H0DN) baseline is $73.499\pm0.809$ km s$^{-1}$ Mpc$^{-1}$, a $7.1σ$ tension with the cosmic microwave background (CMB) determination in a $Λ$ cold-dark-matter ($Λ$CDM) cosmology, $H_0^{\rm CMB,ΛCDM}=67.24\pm0.35$ km s$^{-1}$ Mpc$^{-1}$. A revised host-mass correction applied to the older Pantheon+ changes 114 of the total 1701 apparent-magnitude rows. The calibrator supernovae are not affected, but 52 of the 277 Hubble-flow rows are. Applying only these magnitude corrections, with the H0DN covariance, redshifts, and velocities unchanged, gives $H_0=73.264\pm0.806$ km s$^{-1}$ Mpc$^{-1}$ and a $6.85σ$ Hubble tension. This is our main baseline result and the update for the astrophysics community. Alternatively, replacing the complete Hubble-flow treatment with the corrected Pantheon+ data gives $73.139\pm0.791$ km s$^{-1}$ Mpc$^{-1}$ and $6.82σ$. For DES-DOVEKIE, 220 supernovae span $0.025\le z_{\rm HD}\le0.151$ in Hubble-diagram redshift, and 196 of them overlap with corrected Pantheon+. These overlaps determine the offset used to place the public DES-DOVEKIE distance moduli on the H0DN apparent-magnitude scale. Holding this offset fixed gives $H_0=73.267\pm0.828$ km s$^{-1}$ Mpc$^{-1}$ and a $6.70σ$ tension. Extending to $z_{\rm HD}\simeq0.3$ raises $H_0$. However, both rises are smaller than the H0DN uncertainty. Neither update resolves the Hubble tension. (abridged)

We investigate the influence of nonlinear longitudinal disturbances, triggered by an initial field-aligned velocity flow, on the damping of standing kink oscillations in fine-structured, cool coronal loop strands under isobaric conditions. Using two-dimensional ideal MHD simulations, we model different realistic flow geometries, bounded, unbounded, and external, and quantify their impact on wave excitation, damping, and energy leakage. Our modelled loop strand incorporates strong density contrasts ($d = 5$ and $d = 20$), providing a configuration consistent with cool-loop observations from Hinode/SOT and SDO/AIA. Our results show that while the nonlinear disturbances exert mild influence on the oscillation period, they substantially modify the damping time. Unbounded flows yield the strongest damping, reducing the damping time by up to $\sim 25\%$ compared to bounded flows, caused by enhanced wave-flow coupling and scattering. Longitudinally inhomogeneous flows further intensify the damping, with high-density strands exhibiting faster convergence toward the uniform-flow limit. In cases with supersonic internal flow, slow sausage-mode harmonics and weak slow shocks are additionally excited, indicating the generation of mixed-mode wave responses in flow-dominated loops. These findings demonstrate that realistic, spatially extended nonlinear disturbances play a significant role in the damping of kink oscillations and should be incorporated into forward modeling and coronal seismology diagnostics.

We present a homogeneous analysis of rotational variability and spot properties in young stellar objects across multiple star-forming regions observed by the Hunting Outbursting Young Stars (HOYS) project. From over 2000 candidate members, we identify 144 YSOs with robust periodic signals and well-constrained multi-band amplitudes. The sample has a median age of $\sim$1~Myr, effective temperatures of 3500--6500~K (masses $\sim$0.6--2~M$_\odot$), and is dominated by Class~2 objects, one third of which exhibit inner disc dust emission. The rotation period distribution is strongly bimodal, with 55 percent fast rotators ($P<5.5$~d) and 45 percent slow rotators. Fast rotators are predominantly inner disc-less, whereas slow rotators include both disc-bearing and disc-free systems, indicating that disc braking alone cannot explain the observed rotational states. We derive spot properties from multi-band amplitudes and find that, after correcting for observational biases, the intrinsic cold-spot coverage distribution of fast rotators is well described by an exponential function. This implies that small spot coverages are intrinsically much more common than large ones, consistent with stochastic magnetic flux emergence governing spot formation. In contrast, slow rotators show a pronounced deficit of small cold spots. After considering observational biases and alternative physical explanations, we conclude that small spots on slowly rotating YSOs have significantly shorter lifetimes. These results provide new evidence that magnetic surface structure and its evolution depend on stellar rotation, placing new empirical constraints on models of magnetic activity and angular momentum evolution in young stars.

Stellar binaries and multiples are common objects. Their identification and characterization are primarily limited by the angular resolution of current instrumentation, survey depth and dynamic range. Towards the Galactic plane, stellar crowding further complicates these studies. We aim to identify unresolved binaries with good astrometric solutions and M dwarf primaries in the b294 field from the Vista Variables in the Vía Láctea (VVV) survey using publicly available data. We examine the catalogue of M dwarfs within 500 pc in the b294 tile, employing binarity tracers based on statistical parameters from Gaia Data Release 3, multi-band photometry, and information in the literature. We reassess the astrometric and photometric parameters typically used for binary detection, establishing new boundaries and validating existing ones in the dense stellar field examined. We compare these results with those obtained in the solar vicinity. We present 990 unresolved binary candidates and 43 previously known binaries, including five possible triple systems. These represent the 13\% of the catalogue, rising to 14.9\% in well-covered regions. Binary-model SED fitting yields effective temperatures for 98 primary stars, with the properties of their secondary candidates indicating that nearly half may be substellar objects. We select 120 of the most promising binary candidates. Tangential velocities, where calculated, place 95\% of the studied binary candidates within the young disc population (tau <= 1 Ga). We demonstrate that the influence of nearby Gaia detections on the statistical parameters is small, allowing constraints similar to those that are applied in less crowded regions.

We present a refined astrometric and photometric analysis of the well-studied intermediate-age open clusters NGC 2266 and NGC 2324 using high-precision Gaia DR3 data, complemented by 2MASS and LAMOST DR7 catalogs. Probable cluster members are identified using unsupervised machine learning techniques. We apply both Gaussian Mixture Models (GMMs) and \texttt{pyUPMASK}. We find that the GMM-based membership sample yields a cleaner, more coherent cluster sequence in the Gaia CMDs than pyUPMASK. We identified 719 and 852 high-probability members ($P \geq 0.7$) for NGC 2266 and NGC 2324, respectively. Using the parallax method, we determine distances of 3.55 $\pm$ 0.23~kpc for NGC 2266 and 4.18 $\pm$ 0.24~kpc for NGC 2324. The radius estimates for both clusters are 7.23 $\pm$ 0.47 pc and 10.94 $\pm$ 0.63 pc. Isochrone fitting estimated ages of $1.1 \pm 0.1$~Gyr for NGC 2266 and $790 \pm 150$~Myr for NGC 2324. These age estimates were derived assuming metallicities of $Z = 0.0084$ and $Z = 0.0038$, respectively. The King profile fitting indicates that both clusters exhibit compact, well-defined radial structures. Their tidal radii are $8.84'$ (9.13 pc) for NGC 2266 and $10.97'$ (13.34 pc) for NGC 2324. The slopes of the present-day mass functions are $1.13\pm0.18$ for NGC 2266 and $1.24\pm0.19$ for NGC 2324, indicating a deficiency of low-mass stars. The derived mass-function slopes are consistent with dynamical evolution in both clusters. The clusters exhibit short relaxation times, while only NGC 2324 shows a mild indication of mass segregation. This study highlights the power of Gaia astrometry to resolve internal structures within open clusters and refine their dynamical parameters.

We revisit the derivation of the diffraction integral, which is an approximate evaluation of the Kirchhoff integral, widely used in the literature for phenomenological applications in gravitational lensing. We propose a systematic approach to evaluate the Kirchhoff integral within a beyond-eikonal expansion, carefully tracking all approximations involved in its standard derivation. In this framework, we recover the usual diffraction integral as the leading contribution, together with a correction term that is typically small in realistic lensing scenarios. We further show that our evaluation of the Kirchhoff integral is equivalent to a beyond-eikonal expansion of wave propagation, after summing over all geometric-optics images. This result clarifies the physical origin of diffraction in gravitational lensing and demonstrates that diffraction effects and beyond-eikonal corrections are not distinct phenomena, but rather different but equivalent descriptions of the same underlying physics.

Neutrino oscillations establish that neutrinos are massive, providing the only laboratory detection of physics beyond the Standard Model. Direct kinematic experiments bound the electron-neutrino mass to $m_{ν_e} < 0.45$ eV (KATRIN, 90% CL), implying $\sum m_ν\lesssim 1.3$ eV. Conversely, cosmology within $Λ$CDM is highly constraining: Planck CMB, CMB lensing, and DESI DR2 BAO yield $\sum m_ν< 0.056$ eV (95% CL), in 2-3$σ$ tension with the inverted-ordering floor (0.10 eV). However, this bound relies on $Λ$CDM, while data hint at an evolving dark energy. To determine the model dependence of cosmic neutrino mass bounds, we deconstruct each probe's sensitivity to late-time physics and pursue two robust routes to a $\sum m_ν$ bound: (i) The existing dark-energy-marginalized route, retaining all data and marginalizing over $(w_0, w_a)$, is shown to also be immune to flexible binned and cubic $w(a)$ histories, yielding $\sum m_ν< 0.152$ eV, sharpening to $σ(\sum m_ν) \approx 0.043$ eV with Simons Observatory lensing and Spec-S5 BAO. (ii) A new late-Universe-free route combines primary CMB, marginalizing over acoustic-peak smoothing via $A_{\rm lens}$, with the reconstructed lensing spectrum $C_L^{κκ}$, removing late-time expansion dependence by construction. This yields $\sum m_ν< 0.41$ eV today, tightening to 0.31 eV (Simons Observatory) and 0.28 eV (cosmic-variance limit) across all tested dark-energy models. These relaxed bounds trade statistical power for model independence. Interestingly, they land in the sensitivity range targeted by next-generation laboratory experiments like Project 8 ($m_{ν_e} \sim 0.1$ eV), motivating vital synergies between future cosmological and terrestrial neutrino measurements.

We present TempLat, a C++ framework for lattice field theory simulations in arbitrary dimensions. Its symbolic language, built on expression templates, translates mathematical expressions almost verbatim into C++ while compiling to highly optimized kernels, in contexts ranging from classical-statistical to Monte Carlo simulations. TempLat is performance-portable: building on Kokkos, it supports large CPU clusters, as well as NVIDIA and AMD GPUs. Its abstraction of hardware into a device concept makes TempLat extensible to future architectures. We demonstrate excellent strong and weak scaling on both CPUs and GPUs. We also present ParaFaFT, a standalone parallel discrete Fourier transform library supporting arbitrary dimensions on all of the above hardware, and benchmark its scaling. Both are open source and available on GitHub, and power a new release of CosmoLattice, a widely used early-universe simulation library now available on GPUs.

At microscopic scales the linear response of thermal states of large-$N$ CFTs is governed by a thermal operator product expansion (OPE), while at large scales response is governed by collective excitations known as quasinormal modes (QNM). We show that the OPE and QNM representations of the retarded correlator in mixed time and spatial momentum coordinates have an overlapping region of convergence in the complex time plane, giving a map between OPE and QNM data. We show that large-overtone QNM asymptotics are related to OPE singularities, while low-overtone QNM data appear in analytic continuation from short to large times. Using this approach we obtain new analytic results for QNM asymptotics, and numerically obtain low-overtone QNMs from OPE data for the Schwarzschild-AdS$_5$ black brane. We further show that the OPE spectrum is intimately related to QNM data through a set of sum rules which we derive in Mellin space. Finally, using the lightcone OPE, we argue that stress tensor correlators at large spatial momentum thermalise slower as the conformal collider bounds approach saturation. This work points to a new thermal bootstrap programme where OPE and QNM data constrain each other.

Line intensity mapping measures the combined emission of atomic and molecular lines from unresolved galaxies, offering a way to map cosmic structure across enormous volumes. A single observed frequency, however, contains emission from several spectral lines at different redshifts. These interlopers are usually removed before cosmological inference. We show that this removal is not always optimal. Once the possible emitting lines and their redshifts are included in the model, interlopers become additional tracers of large-scale structure at other epochs, projected into the coordinate system of the target line. We formulate interloper treatment as a Fisher decision problem, requiring both improved precision and parameter bias below a chosen tolerance. In SPHEREx forecasts for H$α$ with [O III], H$β$, and [O II] interlopers, and in FYST forecasts for [C II] with CO interlopers, $Ω_m h^2$ and baryon acoustic oscillation (BAO) distance measurements are comparatively robust to astrophysical calibration errors, whereas the clustering amplitude $σ_8$ and the dark energy parameters $w_0$ and $w_a$ are more sensitive to the adopted line model and priors. The BAO distance measurement gives a simple physical picture: modeling interlopers turns two observed bands into a transverse BAO distance ladder over $0.7\lesssim z\lesssim5.8$. Interlopers are therefore not only contaminants to remove, but a calibrated component of the cosmological signal model for future LIM surveys.

The initial conditions of our Universe contain a wealth of information about the particle physics of very high energies. One such class of signatures, called cosmological colliders, generates oscillations in the three-point correlations (or bispectra) of the primordial density field, and these imprint scale-dependent oscillations in the halo bias. We develop a new method for simulating cosmological collider models that foregoes traditional template-based basis-decomposition methods and can reproduce the scale-dependent signals of the input template at percent-level accuracy. Using this method, we produce simulations for one class of collider models and present the first measurements of oscillating halo bias in simulations. The amplitude and phase of the oscillations show a clear dependence on halo mass, with a factor of ten shift in halo mass causing a factor of two shift in the location of the oscillations. Increasing the frequency of the primordial bispectra model suppresses the signal in the halo bias, as the oscillations average down over the window function of the halo. The phase of the signal is also sensitive to assembly bias. In all cases, the scale-dependent halo bias can be accurately modeled using a simple peak background-split theory. The oscillations and their mass/selection-dependent phase offsets are a unique signature that is not easily mimicked by known observational systematics and is therefore a more robust target. Our simulations and underlying initial conditions code are both made publicly available.

While the standard $Λ$CDM paradigm is in excellent agreement with most current cosmological observations, theoretical challenges surrounding the cosmological constant ($Λ$) have strongly motivated the exploration of dynamical dark energy (DE) and modified gravity (MG) models. Investigating the physical nature of the cosmic acceleration requires N-body simulations to probe the non-linear growth of cosmic structure and prepare for the high-precision data from Stage-IV surveys. In this paper, we present EFT-RAMSES, a comprehensive extension of the ECOSMOG cosmological simulation code designed to explore non-linear structure formation in DE and MG scenarios. We embed the effective field theory of dark energy (EFTofDE) framework into this new numerical pipeline, utilising the $α$-basis parameterisation to provide a versatile, model-agnostic, computational engine. By consolidating diverse scalar and vector-tensor theories---including the normal and self-accelerating Dvali-Gabadadze-Porrati (DGP) models, cubic Galileons (cubic scalar Galileon (csG), cubic vector Galileon (cvG) and generalised cubic covariant Galileon (GCCG)), and generic effective field theory (EFT) parameterisation---into a single "master" Vainshtein equation, this pipeline bypasses the need for model-specific solvers and easily specialises to any particular model. As validations, we perform high-resolution N-body simulations for the normal-branch DGP (nDGP), csG, GCCG, and EFT models, comparing the resulting matter power spectra against dependent and independent codes such as legacy ECOSMOG and HiCOLA, as well as linear theory, and find excellent agreement. EFT-RAMSES provides a robust and versatile computational tool for precision cosmological tests of DE and MG using upcoming cosmological surveys. The code is available for download from the GitHub EFT-RAMSES repository.

Origins of globular clusters (GCs) are linked to the assembly of their host galaxies. We analyze star-cluster populations in two strongly lensed systems that bracket Cosmic Dawn and Cosmic Noon: the Cosmic Gems arc (GEMS) at z=9.625, among the first galaxies, and the Sparkler at z=1.378. New STARRED deconvolution photometry of GEMS provides SEDs for ten unique, doubly imaged cluster candidates, while a homogeneous Bayesian analysis places both populations on a common cosmological timeline. The GEMS clusters formed at $z_{\rm form}\approx 10$--$11$ (median $\simeq10.2$), consistent with halo assembly at or above the atomic-cooling scale. Their photometry requires low metallicities: individual clusters are consistent with $[Z/{\rm H}] \lesssim -1.2$, and the data exclude $[Z/{\rm H}]\geq-0.5$, though they cannot distinguish reliably below $[Z/{\rm H}] \simeq -1.5$. This conclusion is unchanged when using stellar-population models including binary evolution---important for ultraviolet emission at this age---yielding similarly low metallicities, $[Z/{\rm H}]=-2.2$ to $-2.7$. The formal estimate, $[Z/{\rm H}] = -2.3\pm0.3$, is consistent with the Milky Way GC metallicity floor, though its value remains prior-dependent. The Sparkler clusters formed $\sim2.5$ Gyr later, at $z_{\rm form}\approx 2$--$3.5$ in a Cosmic Noon dwarf galaxy, and are more enriched ($[Z/{\rm H}] \approx -0.5$). Comparison with Milky Way GCs places GEMS in an exceptionally early, metal-poor regime and the Sparkler among later, more enriched populations, though neither association uniquely determines an in-situ or ex-situ origin. Closed-box and gas-regulator calculations show both systems are compatible with limited pre-enrichment followed by rapid enrichment and accretion-regulated growth. Together, they probe distinct cluster-forming environments from Cosmic Dawn to Cosmic Noon.

To explore neutrino astronomy at high energies (> 10 PeV), the Radar Echo Telescope for Cosmic Rays (RET-CR) was developed to assess the feasibility of a radar technique for detecting particle cascades in ice, serving as a precursor to the Radar Echo Telescope for Neutrinos (RET-N). The main concept of RET-CR is that, as a high-energy cosmic-ray air-shower core propagates into the high-altitude ice sheet, a dense secondary-particle cascade is created, which is very similar to that of an in-ice high-energy neutrino-induced cascade. At RET-CR, the expected signal consists of three distinct components: radio emission from the in-air particle shower, Askaryan radio emission from the secondary in-ice cascade, and the radar signal itself arising from the reflection of the transmitted radio signal from the ionisation trail of the in-ice secondary cascade. In this work, we present the first combined simulation-based package and study aimed at characterising the combined radio and radar signals at the in-ice receivers at RET-CR. We describe the simulation framework and provide a detailed discussion of the salient features of the radio and radar signals, including their spatial footprints and temporal characteristics, as predicted for the shallow in-ice detectors.

This paper introduces $\tt {\mathcal C}osmo{\mathcal L}attice$ $\tt v2.0$, a major upgrade that substantially broadens the physical scope and computational capabilities of the code. It introduces lattice implementations of scalar fields non-minimally coupled to gravity through $φ^2R$, as well as axion-like fields coupled to Abelian gauge sectors as $φF_{μν}\widetilde F^{μν}$. It also provides new procedures for generating specialized initial conditions, including scaling networks of cosmic defects ($\it e.g.$ strings and domain walls), and fields with arbitrary power spectra. The release also incorporates low-storage Runge-Kutta integrators for non-symplectic systems (suitable $\it e.g.$ for non-minimal scalar kinetic terms as $\mathcal{G}_{ab}\partial_μφ^a\partial^μφ^b$), scalar-field simulations on reduced $(1+1)$- and $(2+1)$-dimensional lattices, new optimized gravitational-wave evolution, more flexible field and energy-density outputs, and GPU support that can accelerate simulations by a factor $\mathcal{O}(10)$ relative to CPU execution. Extensive documentation on the use of the code is provided on https://www.cosmolattice.com

We construct the exterior coupled gravitational and electromagnetic response of a magnetically supported generalized Hayward black hole within a specified nonlinear electrodynamic completion. Both parity sectors reduce to canonical two channel wave systems with explicit potentials and the correct Schwarzschild and effective Reissner--Nordström limits. We compute the quasinormal spectrum, metric and optical characteristics, extremal throat weights, quadrupolar wave conversion, finite bandwidth transfer, and coherent absorption eigenchannels while verifying exterior hyperbolicity and flux conservation. An effective charged operator captures the leading weak core geometry and mode mixing; after its subtraction, the residual hierarchy is consistent with cubic spectral corrections in the primarily electromagnetic branch and quartic corrections in the primarily gravitational branch and principal scattering observables. The fundamental quadrupolar branches become intrinsically linewidth separated near $χ\simeq0.70$, whereas parity splitting remains subleading. Metric and optical characteristic families separate monotonically toward extremality. At $χ=0.9$, positive parity reflected conversion reaches $45.8\%$ and remains $40.8\%$ after moderate bandwidth averaging, while coherent incident combinations yield $98.4\%$ bright and $1.3\%$ dark absorption. These independently evaluated observables provide mutually consistent diagnostics of the same nonlinear electrodynamic operator.

Blue asymmetries (``Blueshifts'') in the C IV 1550A emission line are common in luminous quasars. If they are formed in winds, how much energy, momentum and mass do those winds transport? We address this question by considering how much mass must be supplied through the line-forming region to maintain a given density and ionization state. Using a combination of 1D analytic and 2D numerical models, we find that for blueshifted C IV lines to form in a wind, the wind must have mass outflow rates of $\sim 50 f_V$ times the accretion rate, where $f_V \leq 1$ is the volume filling factor accounting for clumping. Our results therefore disfavour line formation in a smooth disc wind and point towards one of two scenarios: either the wind is clumpy, with required clumping factors suggestively close to those in hot star winds; alternatively, if the mass is instead swept up from the ambient medium, the wind need not be clumpy and MHD and radiative winds can provide the original source of momentum and energy. The power of the outflow depends on the square of the terminal velocity of the flow, $v_\infty$. If the wind is also the BAL outflow, with $v_\infty \sim10,000~{\rm km~s}^{-1}$, the wind power is significant and important for feedback. There are various caveats which moderate our conclusions, motivating i) a better theoretical understanding of wind driving and clump formation physics and ii) improved observational constraints on the physical conditions where the lines are formed.

The solar wind is characterized by turbulence, where a cascade produces intermittent current structures called current sheets (CS) that efficiently dissipate energy into the plasma. These have been studied with in situ spacecraft observations, but single-spacecraft techniques such as the partial variance of increments (PVI) are inherently limited since they lack spatial context. A combined analysis of in situ observations and numerical simulations can provide significant insight into the properties of intermittent structures forming in heliospheric turbulence. Understanding the size and distribution of these structures is crucial in tracing the pathways of energy dissipation and particle energization in space plasma. Using 3D fully kinetic simulations of magnetized turbulence, we identify CS via machine learning and find a complex broken-power-law distribution for the CS widths, where the power-law breaks separate ion-scale CS from electron-scale CS. Electron-scale CS dominate, with widths peaking near $2d_e$. Comparing simulations with MMS data, we test PVI as a CS detector and show it can infer CS scale, though oblique crossings inflate inferred sizes. The prevalence of electron-scale sheets suggests they may contribute to plasma heating in aggregate.

Dark matter deficient galaxies provide a direct way to test whether baryons and dark matter can become sufficiently separated during galaxy evolution. We formulate a Dark Matter-Baryon Separability condition based on the relative incorporation efficiencies of the two components, requiring the final dark matter to baryon ratio to fall below an observationally defined threshold. Applied to high speed collisions, this condition constrains dark matter baryon momentum transfer cross section, interacting dark matter fraction and the efficiency of gravitational recapture. The same framework gives us bounds on the abundance and cooling time of dissipative dark matter, and on the integrated escape rate of ultralight fuzzy dark matter from shallow or tidally disturbed potentials. These results show how dark matter deficient galaxies can complement cosmological and laboratory probes by constraining late time dark matter interactions, dissipation and halo stability.

We consider a spatially flat cosmological model containing a noninteracting barotropic fluid and holographic dark energy with the future event horizon as the infrared cutoff. We parametrize the deviation of the horizon entropy from the Bekenstein--Hawking form by a smooth positive function of the horizon radius. We reduce the background evolution to a closed autonomous system and analytically describe the crossing of the phantom divide, $w=-1$. For entropies growing more slowly than the fourth power of the radius, the crossing is unique, occurs at an extremum of the event-horizon radius, and proceeds from the quintessence regime into the phantom regime. The local Chevallier-Polarski-Linder coefficient $w_{a,\mathrm{loc}}$ at the crossing is then positive, and its sign directly constrains the local entropy-scaling dimension at the horizon scale. The crossing kinematics yields an exact expression for the local entropy-scaling dimension, and a local prescription for the scale-dependent Barrow exponent in the Barrow--Tsallis entropy enables an analytic reconstruction of the entropy function. The early-time asymptotics remain consistent with the standard matter- and radiation-dominated eras, while the event-horizon consistency criterion selects physically admissible late-time trajectories leading to de Sitter states, to Type III or Big Rip singularities, or, for $δ=1$, to accelerated power-law expansion. The analytic results are illustrated numerically. Within the adopted decomposition of the total entropy, the generalized second law of thermodynamics further requires an additional dark-energy entropy in the phantom regime: the equilibrium entropy evolution implied by the Gibbs relation fails to satisfy the law already at the crossing, where the purely barotropic adiabatic description of perturbations also breaks down.

We combine the axiverse with a negative cosmological constant $Λ$, both originating from the string landscape, and apply an observation-time-weighted anthropic argument. Adopting a uniform prior on $Λ$ and a typical string-motivated axion decay constant comparable to the reduced Planck scale, this framework predicts a $\sim 40\%$ probability of observing $0.1 < Ω_m < 0.9$, thereby naturally resolving the long-standing fine-tuning and coincidence problems of dark energy. Unlike many scalar-field dark energy models, the anthropic Lambda-axion universe (ALAverse) statistically disfavors slow-roll dynamics, as slow-roll requires fine-tuning of the initial field displacement. Moreover, the negative cosmological constant renders fast-roll scenarios anthropically unfavorable, since they typically yield only a very brief observational window with positive dark energy density. Having ruled out both extremes, the ALAverse characteristically predicts a moderate-roll dynamics. We derive a two-parameter parametrization in terms of $δ_Ω$ and $|\varepsilon_s|$ that covers ALAverse solutions as well as a broad class of canonical and phantom field models. Current observational data yield $δ_Ω= -0.0498 \pm 0.0186$, corresponding to a $2.7σ$ rejection of $Λ$CDM ($δ_Ω= 0$) and phantom models ($δ_Ω> 0$). The data also show a mild preference for the ALAverse over slow-roll quintessence, a trend that can be conclusively tested with future high-precision measurements of the Hubble diagram.

Under the assumption that black hole horizon area is quantized, each Hawking evaporation step, during which the black hole loses mass and transitions to a lower area level, is interpreted as the erasure of one bit of information. In this paper, by employing Landauer's principle, we test the consistency of various black hole entropy relations with this information-theoretic framework. For the Bekenstein-Hawking entropy, the energy emitted per step saturates the Landauer bound. We extend this analysis to a broad class of generalized entropy models, yielding three distinct outcomes. In the first category, Landauer's principle imposes constraints on the Hawking temperature and, consequently, on the black hole mass. In the second, it restricts the free parameters of the entropy model. The third category, exemplified by Kaniadakis entropy, proves incompatible with Landauer's principle. For all compatible models, we derive the area quantization parameter and the corresponding area spectrum. While this parameter is constant for Bekenstein-Hawking entropy, it becomes level-number-dependent for many generalized models. Nonetheless, the relative spacing between successive area levels vanishes in the classical limit. Our findings point to a deep link between information theory and black hole thermodynamics.

The Arches cluster, located in the Galactic Centre (GC) is one of the best astrophysical laboratories to study the properties of massive stars and young massive clusters (YMCs). However, several fundamental parameters of the Arches cluster remain uncertain. Our goal is to constrain key cluster parameters (cluster age, mass, and initial mass function, IMF) by comparing the observed stellar radio flux density distribution of the Arches cluster to those derived from a set of synthetic clusters. We use the deep X-band (10 GHz) Very Large Array data from our previous radio continuum study of the Arches cluster. We model each simulated cluster with three parameters: age, mass, and IMF slope. We use three different stellar evolutionary models: GENEC, PARSEC, and MIST at two different metallicities, solar ($Z=0.014$) and super-solar ($Z=0.020$). We run Markov-chain Monte-Carlo simulations for each model/metallicity combination in order to explore parameter space. All models and metallicities return preferred ages in the $2\lesssim t_{\rm age}/{\rm Myr}\lesssim 3$ range. We obtain an IMF slope of $α_{\rm IMF}=-1.85^{+0.28}_{-0.20}$, averaged over all models, where uncertainties are dominated by the degeneracy between cluster mass and IMF slope. If we use the IMF slope from previous infrared studies as prior, the cluster mass distributions peak at $\sim2.7\times10^4\, M_\odot$ and we can establish a lower limit at $\gtrsim2\times10^4 M_\odot$ for the Arches cluster mass. Radio continuum observations of their most massive stars can be used to constrain YMC parameters. In the case of the Arches cluster, age can be determined regardless of prior spectroscopic information, which can be useful to characterise newly discovered YMCs in the GC. Our results support the idea that a top-heavy IMF may be preferred in the GC or in YMCs in general.

We present CLASSIER-DDM, an extension of the Boltzmann solver CLASSIER that implements the decaying dark matter (DDM) model via its integral-equation approach. The code handles generic two-body decays of a dark matter particle into two lighter decay products with arbitrary masses, naturally encompassing both massless (dark radiation) and massive (warm) decay products, with their perturbations evaluated via integral equations solved iteratively. We describe the numerical implementation in detail, including the background evolution, the iterative perturbation evolution, and a small-scale analytic approximation. A modest number of iterations is sufficient to achieve sub-$0.1\%$ convergence in the matter power spectrum and the CMB lensing power spectrum across the observationally relevant parameter space. We find that a hundred momentum bins for the decay product perturbations are sufficient to achieve $\mathcal{O}(0.1\%)$ accuracy in the matter power spectrum today up to $k \sim 3\,{\rm Mpc}^{-1}$. The code achieves $\mathcal{O}(1\,{\rm min})$ runtimes per evaluation, requiring neither a Boltzmann hierarchy nor any fluid approximation, making parameter estimation with the DDM model numerically tractable. We also discuss the impact of DDM on cosmological observables, focusing on the case of two massive decay products. This work further establishes the integral-equation approach as a versatile and efficient framework for modeling non-cold relics in cosmological perturbation theory.

Recent studies have suggested a mismatch of up to 0.20 dex between iron abundances derived from Fe I and FeH lines in the H-band spectra of M dwarfs, and in this work we investigate the nature of this possible offset. We analyze near-infrared H-band APOGEE spectra of stars in 18 binaries composed of a G-dwarf primary and an M-dwarf secondary, together with four M-dwarf stars having measured angular diameters from the literature, and six M-dwarf members of the Hyades and Coma Berenices open clusters. These three families of benchmarks were used to evaluate the FeH line list and check for possible systematic uncertainties in the FeH $gf$-values. Our tests used 1-D LTE plane-parallel model atmospheres, a radiative transfer code, and the baseline APOGEE spectral line list to derive metallicities for the binary G-dwarf primaries using Fe I lines, while stellar parameters and metallicities for the M dwarfs used both FeH and Fe I lines. The mean metallicity obtained for the Hyades M-dwarfs was $\langle$[Fe/H]$\rangle$=+0.08$\pm$0.04, and for Coma Berenices $\langle$[Fe/H]$\rangle$=+0.02$\pm$0.08. The metallicities of the G- and M-dwarfs in binary systems showed excellent agreement (0.06 dex), and the mean metallicities for the open clusters were also consistent with literature values from high-resolution optical analyses. We investigated the consistency between the spectroscopic and interferometric $T_{\rm eff}$ scales, finding agreement within the uncertainties. Forcing full agreement between the spectroscopic and interferometric $T_{\rm eff}$ scales resulted in a poorer match for the metallicities in the binaries and the open clusters. We conclude that the best overall concordance is obtained when no adjustments are made to the FeH $gf$-values, which are based on the Hargreaves et al. (2010) line list.

We study the free Maxwell field on the planar patch of four-dimensional de Sitter spacetime ($dS_4$). We review its bulk canonical quantization in the Bunch-Davies vacuum, and we give a representation-theoretic viewpoint by studying the transformation properties of single-particle states under infinitesimal dS transformations. By taking the late-time limit, we identify two late-time operators with scaling dimensions $Δ=1$ (leading) and $Δ=2$ (subleading). We introduce CFT-inspired inner products invariant under the dS group ($SO(4,1)$) for states created by late-time operators acting on the Bunch-Davies vacuum. We explain how the unitary discrete series representations of $SO(4,1)$ associated with the photon are furnished by both operators, in contrast with the Maxwell field on $AdS$ where the $Δ=1$ operator corresponds to a non-normalizable mode. We also explain how the corresponding discrete series representations of $SO(4,1)$ split into a direct sum of representations corresponding to two helicities $+1$ and $-1$. This is achieved by taking advantage of the dS invariance of the self-dual and anti-self-dual sectors of the photon field strength. In our outlook, we draw inspiration from a recent proposal for the microscopic description of $dS_4$ higher-spin gravity where conformal gauge fields in 3 dimensions play a central role, and we investigate a possible connection of the $Δ=1$ late-time operator with a conformal spin-1 gauge field in 3 dimensions.

Bright-rimmed clouds (BRCs) are valuable laboratories for investigating how ionizing radiation from massive stars reshapes molecular clouds and influences star formation. We present a kinematic and dynamical study of the BRC SFO 25 using archival JCMT-HARP observations of the $^{12}$CO, $^{13}$CO, and C$^{18}$O ($J = 3-2$) transitions at an angular resolution of about 14-15 arcsec (0.051-0.054 pc). Gaia parallaxes of young stellar objects associated with the cloud yield a revised distance placing SFO 25 behind the ionizing O7V star HD 47839, implying that ultraviolet radiation can directly affect both the head and tail. The molecular gas exhibits a pronounced head-tail velocity gradient, with the tail systematically redshifted relative to the head, inconsistent with the expectations of classical radiation-driven implosion (RDI) and suggestive of an evolved phase dominated by radiative dispersal and photoevaporation. The head is moderately denser than the tail, while a compact C$^{18}$O clump associated with IRAS 06382+1017 reaches densities of $10^4~\mathrm{cm}^{-3}$. Virial and energy analyses indicate that the head, tail, and dense clump are gravitationally unbound, with kinetic energy exceeding both the gravitational binding energy and the external ionized gas pressure. Class II young stellar object candidates identified in the tail demonstrate that star formation is not confined to the dense head. Although RDI may have triggered earlier star formation in the head, it cannot readily explain the activity observed in the tail, pointing to a more complex evolutionary history than predicted by the classical RDI scenario.

We develop the cosmological framework for Hassan--Schmidt-May multi-gravity, a ghost-free extension of bimetric theory with genuinely non-pairwise interactions of multiple spin-2 fields. For metrics that are simultaneously homogeneous and isotropic, the background dynamics reduce to a modified Friedmann equation supplemented by a system of coupled quartic polynomial equations for the scale-factor ratios. The spin-2 interaction contributes to the Friedmann equation as an additional effective fluid. We identify a regular high-density branch that approaches the standard radiation- or matter-dominated Universe, while regular low-density branches approach proportional vacuum solutions, where the interaction acts as a cosmological constant and the leading correction to the effective spin-2 energy density provides an additional matter contribution. We also determine the relative null-cone structure: on the regular high-density branch, the additional null cones approach wider opening angles than the matter-coupled null cone, while all null cones coincide in the vacuum limit. At linear order, we solve the algebraic equations determining the non-metric vielbein perturbations, derive the first-order consistency equations and their scalar and vector projections, and obtain the complete system of coupled tensor perturbation equations. These results establish a framework for studying cosmological solutions and perturbations in ghost-free multi-gravity beyond bimetric theory and its pairwise-interacting extensions.

We constrain the $z \approx 1$ HI distribution by jointly modeling two independent, existing observations of the 21-cm signal, the HI density parameter $Ω_{\rm HI}$ measured using uGMRT by stacking the 21-cm emission from blue, star-forming galaxies, and the 21-cm autocorrelation power spectrum (PS) measured using CHIME. We assign HI to the dark matter halos in a cosmological simulation using an HI mass-halo mass (HIHM) relation with three free parameters whose values we estimate by performing a joint Bayesian inference comparing the simulated $Ω_{\rm HI}$ and 21-cm PS with the measurements. We use the inferred HIHM posterior to simulate the HI distribution and predict the $z \approx 1$ HI mass function (HIMF). We find that the HIMF remains nearly constant at low HI masses $( \lesssim 3.6 \times 10^9 M_\odot)$, and it declines rapidly for larger HI masses. Around $\sim 90$ percent of the total HI gas is contained in the mass range $M_{\rm HI} \in [2 \times 10^9, \, 4 \times 10^{11}] \, M_\odot$. Our estimates predict a larger abundance of high mass HI galaxies than predicted by earlier observations and hydrodynamical simulations. We expect these results to be useful in understanding galaxy evolution and star formation.

Solar neutrinos have been studied for over half a century to test both the Standard Solar Model and the electroweak sector of the Standard Model of particle physics. Contemporary experiments are now entering an era of high-precision measurements, demanding corresponding theoretical predictions with sub-percent accuracy to enable meaningful comparison. In this paper, we identify and analyze the essential physical and computational components required to compute solar neutrino fluxes with high fidelity, and present a unified, computationally efficient framework. This framework incorporates: (i) the time-varying Earth-Sun distance; (ii) Earth matter effects modeled using both one-dimensional (1D) and three-dimensional (3D) Earth electron-density profiles; and (iii) a fast, Strang-splitting-based implementation of the Mikheyev-Smirnov-Wolfenstein (MSW) neutrino propagation formalism, enabling rapid, large-scale scans over neutrino trajectories and energy grids. We deliver site-specific predictions for the China Jinping Underground Laboratory (CJPL) and other underground laboratories actively engaged in solar neutrino programs.

I investigate the behaviour of the Higgs field in Schwarzschild spacetime by introducing a Planck-suppressed coupling between the Higgs field and the Kretschmann scalar, the leading curvature invariant in Ricci-flat geometries. I show that spacetime curvature modifies the Higgs effective potential, causing the vacuum expectation value to decrease continuously with increasing curvature. A critical curvature is derived at which the Higgs vacuum expectation value vanishes, signalling a curvature-induced restoration of electroweak symmetry. For Schwarzschild black holes, we obtain analytical expressions for the critical curvature, the corresponding phase-transition radius, and the Planck-curvature radius that marks the onset of quantum-gravity effects. These results identify a self-consistent region inside the event horizon in which electroweak symmetry is restored while the effective description remains applicable. The model provides a simple analytical framework linking strong gravitational fields to the Higgs vacuum through a single dimensionless curvature-Higgs coupling.

Bow shocks (BSs) around massive stars are commonly identified in mid-infrared (MIR) surveys. In contrast, systematic optical investigations of these structures remain scarce with only a few possible detections reported so far. We performed a targeted Halpha imaging survey of 78 IR BS candidates compiled from literature catalogues. Observations were obtained with multiple ground-based facilities and complemented with archival MIR images from Spitzer and WISE. For the detected bow structures, geometrical parameters were measured, and the bows were classified based on the parameters of their central stars, the measured stand-off distances and adopted plausible ISM conditions Clear arc-shaped Halpha nebulae are detected in 15 objects, with one additional BS discovered serendipitously. A further 35 objects exhibit diffuse Halpha emission associated with complex background structures, while 28 show no detectable Halpha emission. The Halpha and IR morphologies generally trace the same large-scale structures, although most of the IR arcs lie slightly closer to the star and appear broader than their optical counterparts. We find that several systems are consistent with radiation-supported BSs, bow waves or dust waves, while others remain compatible with classical wind-supported BSs. This survey demonstrates that a fraction of IR BS candidates around OB stars also exhibit detectable ionised gas structures in Halpha, and both stellar wind momentum and radiation pressure can contribute to shaping these structures. No correlation is found between the detection of an Halpha BS and the stellar parameters, and the overlap in objects observed in Halpha and in the radio regime was too small for firm conclusions. Future spectroscopic observations will be required to determine the physical conditions and kinematics of the ionised gas and to further constrain the nature of these BS systems.

Hydrodynamics provides a universal description of many-body systems at long wavelengths. Its long-lived collective excitations, known as hydrodynamic modes, admit long-wavelength expansions whose convergence is encoded in the analytic structure of retarded correlators of conserved quantities in thermal equilibrium. We show that a boost can change which nonhydrodynamic singularity limits such an expansion. At large boost, the relevant singularity originates in the large-momentum, near-light-cone region of the rest-frame spectrum. After removing the Lorentz-factor growth, the rescaled convergence scale is controlled by the microscopic spectral structure of the theory. We explicitly demonstrate this in two examples: relaxation-time kinetic theory and holography.

We propose a geometric cosmological probe: the nodal line of the anisotropic galaxy correlation function --- the locus in the plane where the function changes sign. Because the nodal line depends only on this sign, it is invariant under any amplitude rescaling, and its information is mostly independent of and complementary to BAO. In a proof-of-concept analysis of DESI DR1 galaxies, the nodal line constrains $Ω_m h^{3/2}$ to 3\% at fixed galaxy bias, degrading to 4.8\% under a 10\% prior. Combined with BAO, it yields a 4.45\% sound-horizon-free constraint on $H_0$.

We study the island formula and Page curve for the asymptotically flat eternal and quasi-stationary evaporating black hole solutions within the dimensionally reduced Einstein-Hilbert (DREH) model. In this model, the four-dimensional Einstein-Hilbert action reduces to a two-dimensional dilaton gravity, on top of which the quantum corrections can be incorporated via the Polyakov-Liouville (PL) action for a two-dimensional conformal field theory with a large central charge $c$. This gravity model arises from the s-wave approximation of four-dimensional Einstein-Hilbert gravity and provides a fully gravitational setting in which we study the islands, i.e., we will not require a non-gravitational bath region to collect the radiation, instead it lives in the black hole spacetime itself. The fine-grained entropy of Hawking radiation in the eternal and evaporating black holes within the DREH model was derived using the island rule in \cite{djordjevic2022eternal, djordevic2025evaporating}. The island rule is based on the replica method using the Euclidean gravitational path integral. In this work, we complement the Euclidean approach by providing a Lorentzian prescription for the generalized entropy $S_{\text{gen}}$, in the island formula without invoking the replica trick to compute $S_{\text{gen}}$. The generalized entropy is shown to coincide with Wald-like Noether charge of the combined DREH-PL action. Using this generalized entropy, we determine the quantum extremal surface, the Page time, and the Page curve for the eternal and the evaporating black hole. We conclude with a discussion of the possible extension to the full four-dimensional geometry incorporating vacuum polarization corrections.

Limb darkening, the decrease in stellar intensity from the disk center to the limb, encodes the temperature structure and opacity of stellar atmospheres. Direct spatially resolved measurements of this center-to-limb variation remain scarce, especially in the near-infrared. We present interferometric limb-darkening measurements for 31 stars observed simultaneously in the $H$ and $K$ bands with the CHARA Array. The sample spans spectral types F--M and luminosity classes IV--I. The targets are well resolved in $H$ and, for most targets, also in $K$. This coverage constrains the visibility curvature associated with limb darkening in joint $H+K$ fits. We fit the combined $H{+}K$ squared visibilities with four analytic limb-darkening laws and compare the resulting coefficients with bandpass-matched predictions from five stellar-atmosphere grids (Kurucz, MPS1, MPS2, Stagger, and spherical SATLAS, with reported coefficients placed on the Rosseland-radius convention) spanning one-dimensional plane-parallel, three-dimensional radiation--hydrodynamic, and spherical low-gravity models. The associated limb-darkened angular diameters are measured with median formal precisions of $\simeq 0.2$--0.3\%. The CHARA results show expected weaker limb darkening at longer wavelengths and also with increasing $T_{\rm eff}$. The clearest discrepancy with the atmosphere grids is in the wavelength dependence: the median fractional decrease in the power-law coefficient from $H$ to $K$ is $\simeq 39\%$ in the CHARA sample, compared with only $\simeq 17$--$22\%$ with model predictions. Relative to the MPS2 comparison, the empirical coefficients are higher by $\simeq 21\%$ in $H$ and lower by $\simeq 5\%$ in $K$. These results provide multi-band interferometric limb darkening as a near-infrared benchmark for stellar-atmosphere models.

We generalize the notion of quantum reference frames (QRFs) to cases where the frame does not necessarily correspond to a tensor factor subsystem, but to a covariant quantum instrument. This unlocks a variety of physical applications: "frames of labeling" for indistinguishable particles, suggesting explanations for the symmetrization postulate and the absence of parastatistics, and yielding a transparent description of the entanglement of bosons and fermions; and relational clocks reproducing the Schrödinger equation exactly even when all subsystems are interacting or when there are frequency superselection sectors. Our work generalizes the perspective-neutral approach to QRFs pioneered by Höhn and co-authors, which we reconstruct from a simple operational scenario. We give a resource-theoretic grounding of this framework, and show how the notion of completely covariant operations explains the relevance of the charge-zero sector and the pure-state transformation behavior across perspectives. This also suggests operational clarifications of some aspects of constraint quantization, e.g. of the meaning of constraint equations such as $C|ψ\rangle=0$. Some of our results, such as our generalization of relationalization maps to instruments, apply more broadly to other QRF frameworks too, and they contribute to bridging the gap between operational quantum information theory and the internal QRF research program.

In this paper, we present the 1-loop calculation of the three-point function $\langle TJJ \rangle$ of the stress-energy tensor and two insertions of $SO(3)$ global currents, using a 3d toy model for holographic cosmology. By applying the holographic dictionary that relates these QFT $n$-point functions to cosmological correlators, together with the $Sl(2,\mathbb{Z})$ duality that maps the electric Noether current to a magnetic vortex current dual to cosmological magnetic monopoles, we relate the $\langle TJJ \rangle$ correlator to the cross-correlations between metric perturbations and the bulk magnetic monopole field, specifically mapping to the non-Gaussianities $\langle ξ\tilde{A} \tilde{A} \rangle$ and $\langle γ\tilde{A} \tilde{A} \rangle$. We calculate the semi-local contact terms necessary to achieve the exact factorization of the cosmological correlators in the squeezed limit, $p_1 \to 0$. Finally, we evaluate the effective non-linear parameters, showing that the scalar-monopole cross-correlation vanishes at leading order, $f_{NL}^{ξ\tilde{A} \tilde{A}} = 0$, while the tensor-monopole cross-correlation yields a non-zero $f_{NL}^{γ\tilde A\tilde A}$. These results respect the expected amplitude hierarchy of the non-Gaussian correlators, while pointing at new directions in which holographic cosmology can be tested experimentally.