高能暂现源 · 每日文献综述

We present the first sample-level search for supermassive black hole binaries (SMBHBs) requiring coherent quasi-periodicity at a common period in the X-ray and optical bands, over 1194 Swift-BAT hard X-ray AGN (Stage 1) and 175 4XMM-DR14 AGN (Stage 2). No source is a co-periodic candidate. Each light curve is modelled as a damped random walk (DRW) and searched with a Lomb-Scargle periodogram and a look-elsewhere-corrected Monte-Carlo significance. Because DRW red noise is largely independent between corona and disc, we require both bands individually significant with periods coincident within 5%, and gate the survivors with the model-independent null-signal-template test of Robnik et al. (2024). Over $P=100$-$900$ d the completeness-corrected 95% upper limit on the co-periodic fraction is amplitude-dependent: $\lesssim 3\%$ for hard-X-ray fractional modulation $\gtrsim 0.3$, $\approx 15\%$ (precision-limited) at 0.2, and uninformative below $\sim 0.15$ (the $ε=1$ floor is 0.25%). The sensitivity is set by the hard X-ray monitoring, not the optical photometry or the statistics, the opposite of the usual assumption. Daily MAXI and RXTE/ASM monitoring of the brightest AGN raises the X-ray completeness 5-8-fold, and the search remains null. Integrated over the BAT black-hole mass function, the expected all-amplitude co-periodic fraction is $\sim 3\times10^{-2}\, f_{\rm bin}\, δ_{\rm mod}$ (modulo a factor $g<1$), with $f_{\rm bin}$ the sub-pc binary fraction, $δ_{\rm mod}$ the modulating duty cycle, and $g$ the fraction reaching recoverable hard-X-ray amplitude, so a null is expected. We deliver a validated cross-band framework and the first completeness-corrected constraint on the co-periodic fraction, ready for the denser X-ray monitoring of Einstein Probe and eROSITA.

Radio detection of ultra-high energy particles ($\gtrsim10^{18}$ eV) depends on how broadband radio pulses reflect from natural media boundaries. We extend the spherical-wave (Sommerfeld--Weyl) treatment of a single homogeneous interface to stratified media by replacing the Fresnel coefficient of each plane-wave component with the characteristic-matrix reflection coefficient of a layered medium, evaluated in the local tangent plane on the spherical surface. The calculation reduces to the single-boundary result at machine precision when the layer contrast is removed and agrees with the published spherical-surface calculation to better than $1.1\%$ at ten HiCal-2 elevation angles, with a mean deviation of $0.6\%$. We apply the formalism to shallow firn stacks proposed as explanations for anomalous-polarity ANITA events. For realistic firn contrasts, layering changes the reflected amplitude but does not reverse the pulse polarity over $150$--$850$ MHz for the elevations studied. In a reference $s$-polarized two-layer model, a coefficient sign change requires buried refractive index $n_2\simeq2.56$, $2.04$, and $1.79$ at local elevations of $8^\circ$, $15^\circ$, and $25^\circ$, respectively. We also test the specular factorization used in fast propagation models, finding $0.2\%$ agreement with the full angular integral for high-altitude balloon geometries, while near-boundary sources require the full integral. The calculated reflected pulses reproduce the expected polarity inversion in $101$ of $106$ HiCal-1 direct/reflected pulse pairs. Because the medium enters through its complex refractive index, the framework applies to ice, lunar regolith, and conducting media.

In this paper, we examine the stellar properties of quark stars containing dark matter, focusing on both non-rotating and slowly rotating configurations. By employing a two-fluid framework, we formulate the generalized Tolman--Oppenheimer--Volkoff equations, treating dark matter and ordinary matter as independent perfect fluids that interact solely through gravitational forces. We model ordinary matter using the color-flavor-locked and the MIT bag model equation of state, while for dark matter, we apply a self-interacting bosonic condensate along with fermionic equation of state. By considering a dark matter fraction of $f_\x=5\%$ and varying the bag constant for ordinary matter, we investigate how dark matter accumulation affects global stellar features such as maximum gravitational mass, radius, and dimensionless tidal deformability. Further, we extend our analysis to first-order rotational effects, calculating the frame-dragging equation and the influence of moments of inertia on the two-fluid system. We also explore universal relations, particularly the connection between rotation and tidal effects, to understand how the inclusion of dark matter affects the relationship between rotational and the tidal deformability. Our findings indicate that a dark matter fraction of $f_\x=5\%$ can lead to notable deviations from the traditional single-fluid quark star characteristics in stellar radius, gravitational mass and tidal deformability. Moreover, the response to rotational and tidal forces remains consistent even in the inclusion of the dark matter component. Finally, we compare our theoretical results with current observational data from GW events and the NICER mission, thereby demonstrating that our developed two-fluid models are consistent with these observations.

Stellar flares are sudden releases of magnetic energy that can distort exoplanet transit photometry and transmission spectroscopy, biasing planet radius estimates, transit timings, and atmospheric characterization. Understanding flare activity in Ariel targets is therefore essential to identify stars where flares may compromise observations and to characterize the radiation environment affecting atmospheric escape and photochemistry. We analyzed 290 Ariel target stars using TESS light curves. Flares were identified via iterative Gaussian process detrending, and their energy distributions were modeled with two-segment power laws. We performed injection-recovery tests by adding synthetic flares to detrended light curves and running the full pipeline to quantify completeness and detection biases. We detected 15,857 flares across 1,638 TESS sectors, with 2-86 events per sector. We defined a normalized flare index GF.01 to compare activity across stellar luminosities. Near 3% of the sample exhibits enhanced flare activity (GF.01 > 1). AU Mic and HD 28109 show a high likelihood of flare contamination during transit observations. GF.01 correlates negatively with stellar bolometric luminosity, indicating higher relative flare output in lower-luminosity stars. AU Mic is an extreme case: four of five observed transits of AU Mic b are affected by flares, consistent with statistical expectations. We validate the framework by comparing predicted flare-contamination probabilities with observed flare occurrences in a representative subset of transits, finding agreement within uncertainties. These results confirm that energetic flares can significantly impact transit observations and provide quantitative guidance for Ariel target selection and analysis strategies.

We construct a charged Oppenheimer-Snyder-like collapse model in scale-dependent gravity by matching a spatially flat FLRW interior to a charged scale-dependent exterior across a timelike thin shell. The electric charge is confined to the stellar surface, preserving interior homogeneity and isotropy. The exterior geometry is supported by a phenomenological Bianchi-consistent effective source, while the shell dynamics follow from the Israel-Maxwell junction conditions. A barotropic surface equation of state closes the shell system, with a charged-dust shell as the minimal realization. For a negative scale-dependent parameter, $\tildeω<0$, the exterior contains a finite-radius boundary $x_s$ defined by $D(x_s)=0$. Charge separates the solutions into three regimes. For $0\le q^2<x_s$, the lapse develops a negative pole at a curvature singularity, the physical exterior contains one outer horizon, and a representative monotonic collapse crosses this horizon before reaching $x_s$; no future-directed locally outgoing radial null branch emerges from the singular boundary. At $q^2=x_s$, simultaneous zeros of the numerator and denominator cancel the curvature pole, although the prescribed running coupling remains singular. For $q^2>x_s$, the curvature singularity persists with a positive pole and locally outgoing radial null branches exist. Depending on the physical extremality condition $x_e>x_s$, the exterior may contain two simple horizons, one degenerate horizon, or no horizon. These results show that charge qualitatively changes the singular and horizon structure of scale-dependent collapse and provide model-level evidence for horizon shielding in the negative-pole regime.

Computational tomography is a tool for determining the internal structure of objects from a set of projections, typically taken along some regular path. In recent years, methods and GPU-accelerated libraries have emerged that allow for fast reconstruction from projections along more complicated paths. Most of these libraries rely on a Cartesian discretization of the object, which is not appropriate for all scenarios. We present TomoSphero, a differentiable tomographic projector over spherical grids which are often used in planetary and solar tomography. TomoSphero is designed to be used as a building block in reconstruction algorithms and includes common projection types such as cone-beam and parallel-beam, but is flexible enough to accommodate arbitrary projections. TomoSphero is implemented in PyTorch which allows for fast projection computation on GPUs, easy access to modern machine learning optimizers, and automatic differentiation for rapid prototyping of parametric models.

Relativistic jets launched by active galactic nuclei are fundamental for understanding the physics of accreting supermassive black holes and their immediate environments, yet the origin of these jets remains an open question. NRAO 150 is a blazar with a complex relativistic jet morphology that evolves on short timescales due to strong projection effects, enabling detailed kinematic analysis. In this study, we utilise data by the Very Long Baseline Array and the European VLBI Network from 2010 until 2019 at 43 GHz, to understand the formation and launching processes of the jet in NRAO 150. We study the $γ$-ray and radio light-curves, together with total intensity and linear polarisation information to probe the connection between flaring events, $γ$-ray emission, and the ejection of new jet features. Furthermore, we investigate the magnetic field configuration in the innermost jet region, as captured in polarised light, to gain insights about its configuration before, during, and after a $γ$-ray flare. Our results indicate a close temporal link between the $γ$-ray flaring activity and the ejection of new VLBI jet components, suggesting that the high-energy emission is produced downstream of the VLBI core. The combined kinematic and polarimetric evidence further points to a toroidal magnetic field in the inner jet, highlighting the key role of magnetic fields in governing both jet dynamics and high-energy emission in NRAO 150.

Gravitational waves from extreme mass ratio inspirals (EMRIs) are precise probes of the environment of the supermassive black holes (SMBHs) they orbit. If an SMBH is actively accreting, the surrounding gaseous disk can impart hydrodynamic torques on and assist the formation of EMRIs within it. Such disk-EMRI interactions could leave measurable imprints on future observations by the Laser Interferometer Space Antenna (LISA), and potentially provide a route to constrain disk properties using gravitational wave observations. We present herein a detailed relativistic analysis of these hydrodynamic interactions using linear theory. We first derive a Lagrangian governing the evolution of spiral density waves in the disk and use it to formulate a balance law for the transfer of angular momentum between the EMRI and disk. We then develop a stable numerical scheme which can be used to treat corotation resonances and find modal solutions in thin disks up to very large azimuthal numbers. Using this numerical scheme, we explore how SMBH spins, EMRI semi-major axes, disk scale heights, sound speed gradients, and surface density gradients affect the interaction between accretion disks and circular EMRIs. Our results show that relativistic effects substantially alter disk-EMRI interactions once the secondary orbit is within $\mathcal{O}(25)$ Schwarzschild radii from the SMBH. Comparing our numerical results with recent analytical models suggests that the impact of pressure gradients and softening of the gravitational potential is important for disks with finite thickness and cannot be captured by tuning the torque cutoff parameters in the analytical models. The framework provided here will help analyze the formation scenarios of EMRIs and build relativistically accurate waveform models of disk-EMRI interactions.

We analyze microlensing variability in 15 seasons of optical monitoring data and 4 epochs of new X-ray observations of the doubly-imaged gravitationally lensed quasar SDSS J133907.23+131038.6 to place empirical constraints on the size and structure of that system's X-ray and optical continuum emission regions. Employing a Bayesian Monte Carlo method, we analyzed ground-based optical light curves to constrain the half-light radius of the far-UV source $\log(r_{\rm 1/2, FUV}/{\rm cm})=15.78^{+0.26}_{-0.28}$ at 193 nm, the rest-frame center of the {\it r}-band, assuming a $60^\circ$ inclination angle. This size corresponds to $\sim100\,{\it r}_{\rm g}$ for a $4.0 \times 10^{8} \: {\rm M_{\odot}}$ black hole. We measured the half-light radius of the full band ($0.2-8.0 \: {\rm keV}$) X-ray continuum emission region $\log(r_{\rm 1/2, X_{full}}/{\rm cm})=14.32^{+0.23}_{-0.31}$, a size measurement that is consistent with the radius of the innermost stable circular orbit (ISCO) in the Schwarzschild metric.Two shifted Fe K$α$ lines caused by microlensing are detected in the stacked spectrum of image A at 5.9 and 8.9~keV at $>99\%$ significance.

Recent studies strongly suggest that the $Λ$CDM model may no longer serve as the definitive standard model in cosmology, given the increasing tensions between different cosmological observables. Some researchers have described this situation as a "crisis in cosmology." The $Λ$CDM model relies on two fundamental assumptions: the isotropy of the universe (supported by observational evidence) and the Copernican principle (a philosophical postulate). Together, these assumptions lead to the well-known Cosmological Principle, with the homogeneity of the universe emerging as a direct consequence. In this thesis, I review the cosmological consequences of relaxing some of these assumptions, exploring inhomogeneous and anisotropic universe models, as well as tilted cosmologies, which consider observers in motion relative to the Hubble flow. We examine methods to study these effects using existing cosmological data. First, we explore a variety of models that describe inhomogeneous and anisotropic universes, including different metric theories, perturbative analyses, averaging effects, tilted scenarios, and cosmographic approaches. We then apply this theoretical framework to analyze SNIA data and the local peculiar velocity field, aiming to constrain key parameters.

Extreme-mass-ratio inspirals (EMRIs) provide sensitive probes of the astrophysical environments surrounding massive black holes. We investigate the inference of dark-matter (DM) spikes with eccentric EMRI gravitational waves within the analytic-kludge waveform framework, including DM-induced dynamical friction and accretion in the secular orbital evolution. We perform Bayesian parameter estimation using Markov-chain Monte Carlo sampling, complemented by Fisher-matrix analyses. We find that steeper DM spikes produce stronger accumulated waveform modifications and substantially improve the measurement of the spike slope $α_{\rm DM}$. More importantly, the constraints exhibit a nonmonotonic dependence on orbital eccentricity. At moderate eccentricity, higher harmonics help break the degeneracy between $e_{\rm LSO}$ and $α_{\rm DM}$, whereas this correlation can persist or the parameter recovery can deteriorate for highly eccentric systems. These results demonstrate that the harmonic structure of eccentric EMRIs can provide valuable information for probing DM distributions around massive black holes with future LISA observations.

In this paper, we investigate the behavior of a vector field subject to a Lorentz-violating quartic potential on a fixed Schwarzschild background. We analyze the equilibrium configuration of the field and its linear perturbations. We show that the equilibrium solution and spherically symmetric perturbations are governed by a quadratic function whose properties determine their qualitative behavior. By requiring the background field to be real and finite, we derive bounds on the allowed parameters and identify critical cases in which the monopole perturbations become enhanced. We further derive asymptotic expressions for multipole perturbations near the event horizon and at spatial infinity.

Area metric theories have been proposed as effective descriptions in a number of quantum gravity approaches: as continuum limit of effective spin foams, as an effective description for string theory and in the context of holography. Area metric actions allow for non-topological parity violating terms, which opens the possibility of observationally determining the Barbero-Immirzi parameter. We consider the shift symmetric version of linearized area metric theory in Lorentzian signature, which arises in particular from spin foams and modified Plebanski theory, and avoids ghost and tachyonic instabilities in the graviton sector. We discuss the gravitational wave like solutions of this theory and through an analysis of the coupling to electro-magnetism, deduce the signals in gravitational wave detectors. Using polarized light in such interferometers allows in principle to measure area metric induced birefringence and to determine the Barbero-Immirzi parameter. Assuming Planck massive non-length excitations in the area metric the resulting signal is however extremely weak.

We use kinetic Monte Carlo (KMC) simulations to study molecular hydrogen formation on carbonaceous dust grain surfaces, validated against recent laboratory measurements of H$_2$ formation on coronene films at temperatures from 10 to 250 K. The model uses a three-dimensional amorphous carbon lattice with heterogeneous physisorption ($45 \pm 5$ meV) and chemisorption ($1.75 \pm 0.25$ eV) sites, and tracks both Langmuir--Hinshelwood (LH) and Eley--Rideal (ER) formation channels within a stochastic Gillespie event-driven framework. The model reproduces the measured efficiency curve within the experimental uncertainties, including the isothermal (constant surface temperature) measurements at 100 - 250 K. The simulations correctly describe the phase boundary between the LH and ER driven processes as functions of grain temperature and the observed crossover. Under interstellar medium conditions, 10 - 250 K and n = 10 - 10$^4$ cm$^3$, the model predicts three distinct regimes for the formation efficiency $ε$, the fraction of impinging H atoms released as H$_2$. At 10 K diffusion is slow and $ε\approx 0.06$. Between 20 K and 80 K, LH dominates and $ε\approx 0.28$. Above 150 K, an ER plateau at $ε= 0.19$ is sustained by chemisorption-trapped H atoms. The LH-to-ER crossover occurs between 100 and 120 K. At 100 K we observe a 16\% density-dependent stochastic enhancement, which rate-equation models cannot capture. At T$_{dust}$ = 60 K, n = 10$^3$ cm$^3$ we find the ratio of H$_2$ formation to free-fall time $t_{{\rm H}_2}/t_{\rm ff} \approx 0.93$, so dust-catalysed H$_2$ chemistry can keep pace with gravitational collapse in high-redshift star-forming environments.

Black-hole quasinormal modes (QNMs) may coalesce at exceptional points (EPs) in the frequency spectrum. We study EPs and their phenomenology for gravitational perturbations of a Schwarzschild black hole whose Regge-Wheeler potential is perturbed by a localized delta-function of amplitude $ε$ at radius $r_0$. For real $ε$, we find infinite families of discrete EPs. Each family approaches a distinct unperturbed QNM overtone frequency as $r_0$ grows large. Under perturbation at fixed $r_0$, we find that neighboring QNM overtones migrate in the complex plane to meet at these EPs, with the higher overtone moving further. We derive large-$r_0$ asymptotics, finding that EPs have (asymptotically) equal spacing in the tortoise coordinate, and that EP amplitudes $ε$ can be exceedingly small, decaying exponentially according to a rule governed by the complex frequency of the unperturbed QNM. Using quadratic approximations around EPs and high-precision numerical methods, we investigate a range of phenomena in the model: square-root splittings, avoided crossings and hyperbolae, hysteresis and geometric phases generated by encircling an EP, adiabatic invariants, deformed Cassini ovals and cusp-like trajectories, as well as the lemniscate geometry of the excitation factors. We then replace the delta-function perturbation by a finite-width Gaussian, verify the persistence of the EP structure, and show that varying the width extends isolated EPs into exceptional lines in parameter space. Finally, we study the response to initial data and find that, although a weak perturbation can substantially reconfigure the QNM spectrum, the corresponding time-domain response remains perturbative. This contrast is captured by a re-interpretation of the tale of The Princess and the Pea.

Protoclusters in the epoch of reionization provide key laboratories for investigating how environment shapes early galaxy formation and evolution, and may also have contributed to cosmic reionization. We analyze 23 member galaxies of A2744-z7p9OD, a protocluster at $z=7.88$, using JWST/NIRCam and NIRSpec to investigate their stellar population properties, rest-frame UV sizes, and ionized-gas properties. We also quantify the internal structure of A2744-z7p9OD using the projected distance to the most massive galaxy ($D_{\rm YD4}$), and to the nearest neighbor ($D_{\rm nei}$), as global and local environmental indicators, respectively. Stellar mass, SFR on a 100 Myr timescale, dust attenuation, and galaxy size show significant correlations ($p<0.05$) with $D_{\rm YD4}$, but not with $D_{\rm nei}$, suggesting that these properties are primarily linked to the global protocluster structure. The member galaxies also show a large galaxy-to-galaxy variation in R23 ($=\log{(([\mathrm{O}\text{\textsc{iii}}]λ\lambda4960,5008\rmÅ+[\mathrm{O}\text{\textsc{ii}}]λ\lambda3727,3730\rmÅ)/\rm{H}β)}$), implying inhomogeneous chemical enrichment in the protocluster environment. O32 ($=\log{([\mathrm{O}\text{\textsc{iii}}]\lambda5008\rmÅ/[\mathrm{O}\text{\textsc{ii}}]λ\lambda3727,3730\rmÅ)}$) correlates with $D_{\rm YD4}$, indicating that the core region is characterized by low-ionization gas. Together with the non-detection of Ly$α$ emission, the possible neutral-gas reservoir traced by ALMA [C{\sc ii}]~$158μ$m emission, and evidence for high-column-density neutral hydrogen in the core, this suggests a neutral-gas-rich protocluster core where the current escape of ionizing photons may be suppressed, even in a overdense environment during the EoR.

We study the gravitational collapse of a homogeneous dust sphere in higher-dimensional spacetime, with the loop quantum gravity correction entered through a modified Friedmann equation. Its most striking feature is an endpoint: at a finite horizon radius the temperature vanishes and evaporation stops, leaving a remnant. Reading \(α\) as an effective charge, we find behavior reminiscent of the Weak Gravity Conjecture (WGC), although no \(U(1)\) gauge field is present in the model. Solving the degeneracy conditions with the untruncated metric function, rather than with a mass expansion that is not uniform near the endpoint, we obtain closed-form expressions for the remnant radius and mass in \(D=4,5,6,7\). The unscaled ratio \(α/M_{\text{remnant}}^2\) is constant only in four dimensions and grows as \(α^{4-D}\) elsewhere, but it carries dimension \(L^{8-2D}\), so that growth is an artifact of the units. The dimensionless combination \(\tilde{\mathcal{R}} = (α/M^2) r_0^{2D-8}\) settles instead on a finite \(α\)-independent number in every dimension, decreasing from \(27/64\) in four dimensions to \(13824/(15625π^4)\) in seven. We also deform the quantum parameter, \(α\to α+ \varepsilon\), and evaluate \(-T(\partial S/\partial \varepsilon)_M\) in the remnant limit. Because \((\partial M/\partial r)_α\) vanishes there, the fixed-entropy derivative reduces exactly to a fixed-radius one, and the resulting combination \(\mathcal{U}\) is finite in each dimension but depends on \(\varepsilon\) except for \(D=5\). What is invariant is the product \(\mathcal{R}\,\mathcal{U}\,M_{\text{remnant}} = (D-3)/2\), which we verify numerically. Lastly, we study Bondi accretion onto the quantum-corrected black hole and obtain the Eddington luminosity for each dimension.

Gravitational microlensing surveys potentially discover isolated black holes (IBHs) at large distances through their gravitational effects on apparent brightness and motion of collinear stars. Here, we study detecting and characterizing IBHs within the mass range $[3,~5000]M_{\odot}$ with either stellar or dark matter origins in the upcoming observations by Vera~C.~Rubin Observatory towards the Large and Small Magellanic Clouds (LMC and SMC). We consider four lens mass functions (MFs:~$dN/dM\propto M^{-β}$ for $β=0,~0.5,~1,~2$), and generate long-duration microlensing events due to IBHs detectable by Rubin. By assuming the fraction of IBHs's mass in total Galactic mass as $\mathcal{F}$, Rubin potentially detects $\sim0.3,~\rm{and}~2$ microlensing events towards SMC and LMC due to IBHs if $β=1,~\rm{and}~\mathcal{F}=5\times10^{-3}$. These IBHs are inside our galaxy with the probability $\gtrsim70\%$. These events have on average $θ_{\rm{E}}\sim30-50~\rm{mas}$, so that the probabilities of resolving their lensing-induced images through the Rubin astrometric observations are $\sim1.4,~\rm{and}~16.3\%$ towards LMC and SMC. In $\sim1,~5.2\%$ of these events their astrometric deflections are realizable. The probabilities of discerning their parallax are $\sim40,~25\%$. We evaluate relative errors with simulating synthetic data points and by assuming the true models as the best-fitted ones. We conclude for a log-uniform MF for $\lesssim0.1,~\rm{and}~0.3\%$ of photometrically detectable microlensing events towards in LMC and SMC the relative errors in the lens mass, distance and velocity are $\lesssim3\%$. We calculate the number of detectable IBHs versus by assuming their complete contribution of compact objects in halos' darkmatter, and conclude Rubin specifies $95\%$~C.L. upper-limit on IBHs exclusion by masses $\lesssim208,~8M_{\odot}$ for $\mathcal{F}\simeq4\times10^{-3}$.

Context. Galaxy groups and clusters are widely used to probe the evolution of the cosmic web and cosmology, while assuming that they are relaxed. Aims. We identify the properties of the brightest halo galaxies (BHGs) that can be used to predict the most likely sample of dynamically relaxed host halos. Our work combines thoroughly studied galaxy clusters with less frequently analysed groups. Methods. Our analysis was based on data from the IllustrisTNG simulations. We considered several observationally motivated parameters, including the offset of the BHG from the potential well of the host system ($d_\text{off}$) and from the r-band luminosity centre ($d_\text{lum}$), the distance between the brightest and second-brightest galaxies ($d_{12}$), and the r-band magnitude gap between them ($Δm_{12}$). The primary analysis was performed at redshift $z=0$, with an additional investigation of the redshift evolution of halo relaxation up to $z=1$. The observable proxies were applied to construct a halo mass function (HMF), which was then compared to the HMF of the relaxed sample defined from 3D information commonly used in theoretical approaches. Results. We find that $d_\text{off}$ and $Δm_{12}$ are effective indicators of group and cluster relaxation, particularly when used in combination. The selection criteria of $d_\text{off}<0.05~R_{200}$ and $Δm_{12}>1.6$ mag allowed us to reproduce an HMF that closely matches that of the relaxed halo population. These criteria can be applied to observations up to $z\sim0.2$ within a mass range $\text M_{200}\geq10^{12.5}\text M_\odot$ ($\text M_\text{*, BHG}\gtrsim10^{10.9}\text M_\odot$), including groups and clusters in the selection. In this mass range, $15-23\%$ of the systems are considered fully relaxed at $z=0$. The fraction of relaxed haloes decreases with redshift up to $z\sim0.4$, after which the decrease is far slower.

We investigate how a surrounding dark-matter halo imprints itself on the QNM spectrum of a static, spherically symmetric black hole, considering two physically distinct density profiles: the Dehnen (1,4,5/2) and DC14 profiles. Both follow double-power-law forms, while the shape parameters of the DC14 profile are calibrated to galaxy-formation simulations and vary with the stellar-to-halo mass ratio $X=\log_{10}(M_*/M_{\rm halo})$, which controls the inner density structure of the halo. For both profiles, we compute the halo contribution to the metric function and the resulting effective potential governing axial gravitational ($s=2$) perturbations, and extract the fundamental QNM frequencies for the $\ell=2$ multipole. Our results show that the halo scale radius $r_s$ has the largest influence on the QNM spectrum among the halo parameters explored, reshaping the effective potential barrier near the light ring and shifting both the real and imaginary parts of the QNM frequencies. The density normalization, by contrast, plays a comparatively minor role for the Dehnen profile but is more consequential for DC14, reflecting the different inner structures associated with its varying $X$ values. The Prony-extracted frequencies show excellent agreement with the sixth-order WKB results, with relative differences remaining below $0.04\%$ across the parameter ranges considered. To our knowledge, this constitutes the first QNM analysis of a black hole embedded in a DC14 dark-matter halo. These results demonstrate the sensitivity of the QNM spectrum to the surrounding dark-matter environment and provide a consistent numerical framework for studying such environmental effects.

We present a clustering analysis of $\sim 3000$ ultraluminous infrared galaxies (ULIRGs) at $z\sim 2$, uniformly selected by $24μ{\rm m}$ flux and IRAC colors in the COSMOS and BOOTES fields. We measure the angular correlation functions of ULIRGs in both fields and fit them with galaxy clustering models. Linear theory modeling shows that these ULIRGs reside in dark matter halos with characteristic masses of $\log M_{\rm h} /({h^{-1}\rm M_{\odot}}) = 12.64\pm 0.50$ in COSMOS and $12.72\pm 0.13$ in BOOTES. The halo occupation distribution (HOD) modeling yields occupation-weighted effective halo masses of $\log M_{\rm eff} /({h^{-1}\rm M_{\odot}}) =12.50^{+0.26}_{-0.28}$ for COSMOS and $12.89^{+0.11}_{-0.12}$ for BOOTES. These host halos are expected to evolve into halos with masses of $\sim 10^{13.6-13.9}\ {h^{-1}\rm M_{\odot}}$ at $z=0$. The HOD fits allow for a non-negligible satellite contribution to the clustering of galaxies in the BOOTES field, but the satellite fraction derived in the COSMOS field appears nearly zero.

We investigate the unitarity of quantum evolution relative to an internal time defined by a local observer's clock. The observer is modeled as a relativistic particle carrying both a clock and a matter-field detector, analyzed first on a fixed curved background and subsequently within a fully diffeomorphism-invariant theory of dynamical gravity. In the former case, we find that evolution with respect to the internal clock time is generally nonunitary, implying a violation of the Einstein equivalence principle at the quantum level. In contrast, in the latter case, diffeomorphism invariance allows us to adopt observer-centric coordinates without loss of generality. On the resulting partially-reduced phase space, one of the diffeomorphism generators becomes linear in the clock Hamiltonian, generating a relational evolution that is consistent with the remaining diffeomorphism constraints. Assuming that an effective quantum field theory exists to be consistent with the diffeomorphism invariance, these features ensure unitary evolution relative to the internal clock, thereby preserving the equivalence principle even in the quantum regime. Our results highlight the fundamental role of diffeomorphism invariance in shaping relational unitary evolution from the perspective of a local observer.

The large amount of ground-based photometric measurements of $η$ Carinae obtained since 1940 have remained problematic for quantitative modeling due to the blending of flux from the stellar core and the surrounding circumstellar nebula. In the era of the Hubble Space Telescope, spatially resolved imaging & spectrophotometry have enabled disentanglement of these components, allowing recovery of the stellar core $V$-band brightness from ground-based observations. We isolate the $V$-band fluxes of the stellar core and nebula using 1999--2020 HST (ACS and STIS) observations, and use these to calibrate coeval ground-based photometry. The main finding is an orbital light curve with an amplitude $Δm \approx \pm 0.2\,$mag, many times higher than that modeled by ellipsoidal deformation of the primary. The observations suggest that Roche lobe overflow starts at $- 75$ days before periastron in coincidence with the start of rising in the orbital light curve, and remains for 150 days. An expanding (and afterwards dissipating) gas cloud reflecting the light from the primary would explain the observed large amplitude of the orbital light curve. A sharp periodic photometric peak occurs at $\sim -18$ days from the periastron. It is followed by a broad minimum around the superior conjunction of the secondary (T$_0+5.2$ days), which we interpret as a partial eclipse of the ejected material, in coincidence with the \emph{shallow minimum} in X-rays, which also has been attributed to an eclipse.

Recent Event Horizon Telescope results have demonstrated unique and transformative science in gravitational physics and black hole astrophysics enabled by event-horizon-scale imaging of supermassive black holes (SMBHs). Nevertheless, the angular resolution of current ground-based very long baseline interferometry (VLBI) arrays limits such studies to only two sources, precluding systematic investigations of horizon-scale emission across a nearby SMBH population. The proposed Black Hole Explorer (BHEX), a millimeter/submillimeter space VLBI mission, would overcome this limitation by delivering substantially higher angular resolution. Here, we present a series of simulated observations to assess a population of nearby horizon-scale targets accessible with BHEX. Based on a recently developed SMBH number density model, we find that BHEX could infer black hole masses for ~70-90 sources from size measurements, constrain magnetic field structures through linear polarization imaging for ~20-30 sources, and resolve black hole shadows for ~20-25 sources. Targeted observations of ~50 nearby SMBHs are expected to yield measurements for ~30 source sizes and ~10 shadows and linear-polarization patterns. These projections are supported by detailed imaging simulations of general relativistic magnetohydrodynamic (GRMHD) models for eleven nearby SMBHs. Together, our results highlight BHEX as a powerful facility for revealing the demographics of SMBH properties across diverse accretion states, radio loudness, host galaxy environments, and viewing geometries.

We present our chemical abundance analysis of ten new extremely metal-poor stars with $-4.05\leq\mbox{[Fe/H]}\leq-2.33$, based on high-resolution (R $\sim28,000$) Magellan/MIKE spectra. Eight of our stars have low heavy-element abundances of $\mbox{[Sr/H]}<-4.5$ and $\mbox{[Ba/H]}<-4.0$, making them Small Accreted Stellar System (SASS) stars. Four are hyper neutron-capture-element poor with $\mbox{[Sr/H]}<-5.0$, including Gaia DR3 5729400267359655680, which sets a new record for the lowest detected Sr abundance of $\mbox{[Sr/H]} =-6.4$. We identify four distinct [Sr/Ba] groups within the wider SASS star population which span a large range from $\mbox{[Sr/Ba]} =-2.0$ to +1.6, pointing to multiple types of progenitor events and different nucleosynthesis processes/sites. To explore the origins of this large [Sr/Ba] range, we adopt site-agnostic Sr yields of $\mbox{[Sr/H]}=-6$, $-5.75$, $-5.42$, and $-4.93$ for the four groups. Applying those yields suggests that the majority of SASS stars formed from gas enriched by $\sim$1-10 progenitor events, consistent with expectations from their extremely metal-poor nature. We thus attribute the [Sr/H] abundance scatter to intrinsic variations in the Sr yield per nucleosynthesis site/event. Our proposed Sr yields for each [Sr/Ba] group and associated nucleosynthesis origin are a reasonable and representative approximation, good to within a factor of a few, and can constrain future theoretical heavy element nucleosynthesis calculations in early core-collapse supernovae.

Stochastic gravitational-wave backgrounds from different primordial mechanisms can produce identical peak frequencies and amplitudes, obscuring their physical origin. We show that the broadband spectral shape breaks this degeneracy. Comparing scalar-induced and gauge-field-induced gravitational waves for identical primordial spectral profiles and cosmological evolution, we find that their spectra retain distinct source-dependent signatures even after matching both the peak frequency and amplitude. While the two mechanisms share a universal deep-infrared behavior, their tensor-source kernels generate different peak morphologies and ultraviolet asymptotic scalings. In particular, the ultraviolet spectrum provides a direct diagnostic of the underlying source mechanism that is insensitive to the overall normalization. Our analysis shows that broadband spectral information contains additional source-dependent signatures that are inaccessible from peak observables alone.

While localized astrophysical sources can generate macroscopic graviton squeezing, their observable quantum signatures at far-field detectors remain unresolved. In this work, we investigate the propagation dynamics of the squeezed states using spatial quantum optics methods to evaluate correlation functions accessible to a local observer. Crucially, we reveal a severe kinematic conflict in same-cone measurements, which highly suppresses local quantum coherence. Consequently, these macroscopically squeezed states appear classically thermal to a single detector. Our results demonstrate that global squeezing does not guarantee local observability, and the measurable quantum signatures may be significantly weaker than what would be expected from the overall squeezing parameter of the state.

The solar wind is a turbulent, weakly collisional plasma characterized by non-Gaussian fluctuations, long-range correlations, and multifractal dynamics. We investigate the long-term evolution of these properties using hourly proton density measurements obtained directly by the Wind spacecraft over 1995--2025. The use of a single-spacecraft dataset provides an independent test of previous results derived from the multi-spacecraft OMNI database. The three components of the nonextensive $q$-triplet are estimated within one-year sliding windows shifted monthly: $q_{stat}$ from the distribution of density increments, $q_{rel}$ from the decay of the autocorrelation function, and $q_{sens}$ from the multifractal spectrum. Their mean values, $q_{stat}=1.71\pm0.07$, $q_{rel}=4.62\pm0.52$, and $q_{sens}=-0.45\pm0.27$, confirm the persistent presence of heavy-tailed statistics, slow relaxation, and weakly chaotic multifractal dynamics. The parameters nevertheless exhibit distinct temporal variability and relationships with solar activity. The Fourier spectrum of $q_{stat}$ contains a dominant period of approximately $10.1$ years, while its correlation with the sunspot number is positive and moderate ($r=0.611$). Correlation and mutual-information analyses show that $q_{stat}$ is primarily associated with solar proxies, whereas $q_{sens}$ displays stronger relationships with geomagnetic indices and $q_{rel}$ exhibits weaker dependencies. An anomalous enhancement of $q_{stat}$ around 2004 coincides with a sequence of intense interplanetary disturbances, although possible effects related to Wind's orbital transition must also be considered. These findings demonstrate the robustness of the nonextensive description and show that the statistical and dynamical properties of solar wind proton density show evidence of modulation by solar activity.

We consider the $d\geq 4$ non-polynomial pure gravity theories defined so that their 2D reduction to spherical symmetry minimally modifies that of General Relativity at small distances. They satisfy Birkhoff theorem and admit exact black hole solutions for an arbitrary number of couplings. These solutions have a logarithmic leading correction to the entropy and a quantum-like correction to the Newtonian potential, both arising from the regularised critical order $d=2p$ theory, which is related in even dimensions to the Euler characteristic of the 2D orbit space. These black holes can be made regular, without the need for infinite towers of corrections, using invariants of any order $p>d/2$. In even dimensions, their smoothness is linear in the number of corrections and does not require fine-tuning. We construct a class of theories admitting as unique (massless) vacuum an extremal black hole deformation of (A)dS$_4$ or M$_4$ with vanishing entropy, so that Nernst's third law of thermodynamics is satisfied without discontinuity in the entropy. We show that a Maxwell field does not disrupt the regularity of the metric, and that simple non-minimal couplings in the action enable to regularise the electric field. Considering infinite towers of corrections, we construct quasi-regular black holes with one horizon as well as regular (A)dS-core ones with a near-extremal inner horizon for any mass. When charged, these two types of black holes prevent or tame the mass inflation provided the mass and charge satisfy an inequality of the form $M > α\ell + βQ^2 / \ell$, where $α$ and $β$ are numerical factors depending on the specific model, while $\ell$ is the length scale controlling the high-energy corrections. The quasi-regular black holes are sufficient to resolve the Coulomb singularity without the need for non-minimal couplings.

Early Dark Energy (EDE) models have been suggested as a possible solution to the so-called Hubble Tension, a discrepancy of the measurement of the Hubble constant at early and late times. In this paper, we investigate the effects of EDE on large-scale structure probes of cosmology via the EDENS (Early Dark Energy N-body Simulations) suite. The EDENS suite extends the reach of available EDE simulations considerably by adding volume and resolution. We derive several key metrics, such as the halo mass function, the nonlinear power spectrum, and the concentration-mass relation. Furthermore, we implement a halo occupation distribution model to populate the simulations with synthetic galaxies. This allows us to measure the galaxy-galaxy correlation function and galaxy bias. We choose an EDE model that is consistent with observations across several probes and allows for the increase of the present day value of the Hubble constant to resolve the Hubble tension. This model adds three more parameters to the standard $Λ$CDM model. Additionally, it requires small shifts in the best-fit $Λ$CDM cosmological parameters to accommodate existing observational constraints. We find significant differences between the standard $Λ$CDM model and the EDE model, suggesting that some of our chosen metrics may allow us to distinguish EDE from $Λ$CDM, and future observations should help further constrain possible cosmological models. We release outputs from our simulations via the OpenCosmo data portal.

An operating stellar engine that transfers momentum to its host star could produce an approximately persistent transverse acceleration during the Gaia Data Release 3 (DR3) observing epoch. We search for such accelerations among 406,984 quality-selected Gaia DR3 stars with nominal distances below 200 pc (about 650 light-years), using 8,890 published Acceleration7 solutions. Because long-period binaries and astrometric systematics can produce similar sky-plane curvature, we model these conventional explanations together with a broad component that can absorb any remaining persistent acceleration or model mismatch. At $a_0 = 2.60 \times 10^{-4}$ m s$^{-2}$, where essentially the entire parent sample is searchable, mapping the residual weights evaluated at the one-sided 95% profile-limit point gives a parent-population fraction limit of $1.21 \times 10^{-5}$. Multiplying this fraction by the parent-sample size gives a summed upper-limit weight of about five star-equivalents above the threshold. Toward the lowest acceleration thresholds, the searchable fraction declines rapidly, so the corresponding bounds primarily describe the reach of the search. No individual source is interpreted as a technological signal.

We establish the perturbative stability of the fuzzy-sphere black-hole horizon in the large-$N$ matrix quantum mechanics of \cite{Chu:2024qil}. Large-$N$ counting shows that the leading quantum correction to the fluctuation spectrum is the planar bosonic one-loop contribution, while higher-loop bosonic effects and the leading fermionic one-loop contribution are parametrically suppressed. The classical spectrum contains a tachyonic $(1,2)$ mode and a marginal $(2,3)$ mode; we show that both acquire positive quantum curvature and are stabilized. For the general spectrum, we find that a factorization structure of the Hessian controls the leading quantum curvature and renders it non-negative. Quantum effects dominate the stabilization of generic low-angular-momentum modes, whereas classical curvature dominates at high angular momentum. The two effects become comparable in the crossover regime $L \sim \sqrt{N}$, where both must be retained. Under smoothness and non-saturation assumptions supported by finite-$N$ numerical tests, positivity of the quantum fluctuation spectrum is thus established for sufficiently large but finite $N$. This local curvature stability is compatible with non-perturbative monopole tunneling. Intriguingly, the same $L\sim\sqrt{N}$ mesoscopic angular momentum range also dominates the tunneling process, suggesting a distinguished IR--UV crossover regime in the quantum dynamics of the black-hole horizon.

Stars of low and intermediate initial mass lose most of their stellar mass at the end of their lives during the asymptotic giant branch (AGB) phase. Determining their gas and dust mass-loss rates (MLRs) is crucial for quantifying the contribution of evolved stars to the life cycle of dust and gas in the Universe. The Atacama Large Millimeter/submillimeter Array was used to observe 38 carbon stars (C stars) in the large Magellanic cloud (LMC) and three C stars in the small Magellanic cloud (SMC) in the CO J= 2-1 line. Line profiles were fitted to derive stellar velocities and wind-expansion velocities (Vexp). CO emission is detected in two C stars in the SMC and 33 C stars in the LMC. This is the first detection of carbon monoxide around an AGB star in the SMC. One object in the LMC shows emission in $^{13}$CO. The wind-expansion velocity ranges from \sim7.5 to \sim30 km/s. Archival data were used to determine the pulsation periods as well as construct and model the spectral energy distributions using two dust radiative transfer codes. Mass-loss rates were independently derived from these two codes as well as from the intensity of the CO line, using a simple formula. On average, the dust-based MLRs higher than the MLRs based on the CO line by a factor of 1.6. Additional CO data in other transitions, combined with proper modelling, is required to further investigate this possible discrepancy. Mass-loss rates, pulsation periods, and expansion velocities were compared to a sample of Galactic C stars. There is a strong bias, as the Magellanic Cloud targets sample the highest MLRs and luminosities, yet they represent only a minority of stars in a Galactic sample. Comparing this sample with a similarly extreme set of Galactic stars with periods longer than 500 days, we identify no correlation between metallicity and either the MLR or Vexp.

In this paper we present a semi-analytical model for the velocity power spectrum in $\La$CDM cosmology for wave numbers $k<1/$Mpc. We mainly concentrate on the dominant divergence part but also present some results on the vorticity contribution. We divide cosmological parameters into evolution and shape parameters and model the dependence of the evolution parameter $h$ and of the shape parameter $\om_{\rm cdm}$ with an accuracy better than 2.5\%. A surprising finding of our study is that the velocity power spectrum becomes independent of $\om_{\rm cdm}$ on nonlinear scales. A python implementation of the model is publicly available.

We study the exceptional line (EL) in the quasinormal modes (QNMs) of Reissner-Nordström-de Sitter black hole surrounded by a static thin shell of matter. For a conformally scalar perturbation, we derive the QNM condition by matching the interior and exterior solutions across the shell and show that higher overtones are particularly sensitive to variations of the shell and background parameters. A mode permutation between two QNMs reveals an exceptional point (EP). After extending the parameter space, this degeneracy forms a continuous EL. We show that the spectral response near the line is intrinsically directional. For a perturbation in parameter space $ε\widehat{\mathbf u}$, the QNM splitting is $|ω_+-ω_-| =C_{\widehat{\mathbf u}}\sqrtε+o(\sqrtε)$, with $C_{\widehat{\mathbf u}}=(\widehat{\mathbf u}^{T}\mathbf{K}\widehat{\mathbf u})^{1/4}$ and $\mathbf{K}$ is so-called spectral sensitivity anisotropy matrix. The tangent direction of EL is a null direction of $\mathbf{K}$, so that the leading square-root splitting vanishes along the exceptional line, whereas the two principal directions in the normal plane exhibit different sensitivities. Furthermore, the square-root branch structure makes conventional linear QNM parametrizations singular near an EL. We therefore construct an EL adapted parametrization which incorporates both the local geometry of the line and the nonanalytic QNM splitting.

Quantum permutations, or magic unitaries, have in recent years been explored in the context of identifying `genuinely quantum' isometries of graphs. Here, we import this tool in physics, showing that quantum permutations yield a generalisation of quantum reference frames in a discrete setting that is reminiscent of the passage from special to general relativity. We show that the typical quantum reference frames framework corresponds to quantum permutations classified as `classical' in the mathematical literature, and which we demonstrate are quantum controlled transformations (superpositions of classical coordinate maps). Genuinely quantum permutations (i) allow to construct \emph{non--commuting} quantum reference frames (ii) correspond to \emph{local}, as opposed to global, superpositions of transformations. Strikingly, we find that the non-commutativity of quantum fields, when used as reference systems, is exactly what implies that the change of frame is achieved through a genuine quantum permutation. We illustrate the above with several examples in both first and second quantization formalism, which demonstrate (a) simultaneous control on non--commuting variables, (b) the existence of bipartite states that can be localized with a genuine quantum permutation and cannot be localized with the usual quantum reference frame transformations (without introducing additional degrees of freedom), (c) extension of the Ising model symmetries to genuinely quantum permutations, and (d) extension of the symmetries of a scalar field action on curved spacetime to genuinely quantum permutations. While we have in mind applications in quantum gravity, we expect our formalism to be of interest in a wide range of topics in quantum information.

Grounded in the covariant phase space approach of the Iyer-Wald formalism, we propose a quasi-local Hamiltonian for generalized Kerr-Schild (GKS) black holes. Evaluated for spherically symmetric spacetimes over a flat Minkowski background, our formulation recovers the Misner-Sharp mass. Because this framework relies solely on the GKS structure, it provides a straightforward extension of the Misner-Sharp mass to rotating geometries. We further extend our analysis to asymptotically anti-de Sitter (AdS) black holes, where a renormalization procedure to subtract the background AdS energy naturally emerges. By employing this technique, we establish a geometric quasi-local formulation of Kerr-AdS thermodynamics.

The process-matrix formalism describes quantum processes without assuming a fixed global causal order, but the physical meaning of indefinite causal order remains open. We address this question within histories theory, where temporal ordering and dynamical evolution are distinct structures. We show that the decoherence functional admits coherent superpositions of dynamics. In measurement settings, under suitable factorization conditions, these generate process matrices. Thus, we identify process-matrix indefinite causal order as an operationally restricted realization of the more general phenomenon of superposition of dynamics. Histories theory also admits a distinct kinematical notion of indefinite order, in which the ordering of physical events is itself a history observable. The resulting distinction between event order and intervention order clarifies the relation between indefinite causal order, quantum dynamics, and spacetime structure.

We investigate traversable wormhole solutions in five-dimensional Einstein-Chern-Simons (EChS) gravity, a gauge-theoretic extension of General Relativity that introduces a higher-curvature correction parametrized by the combination $αl^2$, where $α$ is a dimensionless coupling and $l$ is a length scale. Working with the Morris-Thorne metric and an anisotropic fluid, we derive exact expressions for the energy density, radial pressure, and lateral pressure at the wormhole throat. We show that the radial Null Energy Condition (NEC) is satisfied at the throat if and only if $αl^2\leq-r_0^2$, being saturated at $αl^2=-r_0^2$ and strictly satisfied for $αl^2<-r_0^2$, independently of the shape function. In the latter regime, the energy density is strictly positive and the full NEC, Weak, Strong, and Dominant Energy Conditions can be simultaneously satisfied. These results are established analytically for arbitrary shape functions and illustrated concretely for the power-law family $b(r)=r_0(r_0/r)^n$, $Φ=0$, for which all four standard energy conditions are satisfied at the throat for all $n>0$ when the EChS coupling is sufficiently negative. We further show that the radial pressure is negative and geometrically fixed at the throat, independently of $α$, $b(r)$, and $Φ(r)$. Using the Volume Integral Quantifier (VIQ), we establish that the EChS correction reduces the magnitude of the negative integrated NEC contribution relative to GR, and derive an exact closed-form critical coupling $αl^2_{\rm crit}$ at which the VIQ vanishes. The hierarchy $αl^2_{\rm crit}<-r_0^2<0$ shows that NEC satisfaction at the throat and a non-negative global VIQ are compatible but distinct conditions, both achievable within EChS gravity. All results reduce continuously to those of GR in the limit $l\to0$, confirming the consistency of the framework.

A warped extra dimension in a five-dimensional (5D) anti de Sitter (AdS) background was introduced in 1999 by Lisa Randall and Raman Sundrum to solve the gauge hierarchy problem in particle physics. As a bonus, a holographic interpretation in terms of four dimensional (4D) conformal field theories (CFT) was found. Interestingly enough, another 5D background, the linear dilaton (LD), was found to have a holographic interpretation in terms of Little String Theory. In this review we will show how a set of 5D backgrounds, parametrized in terms of a real parameter $ν$, generalizes both theories and gives rise, in particular, to AdS for $ν=0$ and to LD for $ν=1$. Furthermore, working in the 5D theory, we will consider applications of the LD background to: i) Particle Physics, so that the 5D Planck scale can be lowered to sub-Planckian values, ii) Brane World Cosmology (BWC), based on the appearance of an extra vacuum characterized by a 5D black hole. In all cases we find a gapped continuum for bulk propagating fields, which makes connection with unparticles. In the case of BWC we also point out on the existence of a pressureless holographic fluid which could play the role of dark matter (DM), with feeble (gravitational) interactions to the Standard Model (SM), decoupled from the thermal SM bath, and generated by a freeze-in mechanism after inflation. We also point out the additional possibility of identifying DM with a long-lived feebly interacting massive graviton, as an isolated resonance generated by radiative corrections to the continuum graviton propagator self-energy.

Traversable wormholes in general relativity require non-standard matter sources, making the identification of physically motivated equations of state particularly important. We investigate wormholes supported by a polytropic equation of state, considering homogeneous and inhomogeneous configurations within a unified framework. We derive the corresponding solutions and analyze the effects of the polytropic parameters on the geometry and energy conditions. In the homogeneous case, the polytropic construction yields a consistent wormhole interior whose geometry and matter content are governed by the constant polytropic parameters. For the inhomogeneous case, we obtain a general analytical expression showing that the geometry is completely determined by the radial polytropic coefficient $ω(r)$. For positive $ω(r)$, the requirement for physically meaningful solutions naturally restricts the polytropic exponent to odd integer values. Using a power-law profile, we construct explicit classes of solutions exhibiting distinct parameter regimes and finite radial support. Interestingly enough, for an exponent $α=2γ-3$, a generalized absurdly benign traversable wormhole-like configuration emerges naturally. Although the flare-out condition implies null-energy-condition violation at the throat, the inhomogeneous framework allows its radial distribution to be controlled. Our results establish a systematic connection between polytropic matter and wormhole geometry, providing a flexible framework for constructing compact wormholes with localized exotic matter.

Precise astrometric surveys and modern clustering algorithms are working in step to transform our view of star-forming regions. By revealing a much richer substructure than previously accessible, they pave the way for reconstructing star formation histories by accurately resolving and age-dating individual sub-populations. The Orion star-forming complex is the best-studied stellar nursery in the solar neighborhood and the nearest one currently forming massive stars. Even so, a comprehensive characterization of its substructure, including a homogeneous age mapping and extinction analysis, is still incomplete. Here, we present the most complete census of stellar populations across the Orion complex from the newest version of the SigMA algorithm and outline our additions and improvements to the algorithm that have extended its usage to distant (>300 pc) regions. We separate the Orion complex into 47 co-spatial and co-moving stellar groups comprising 11,996 reliable members, with ages ranging from 1.5 to 25 Myr. To evaluate the statistical robustness of each group, we derive cluster persistence values and individual membership probabilities for each source from 10 independent clustering repetitions. Our group memberships agree well with the literature, but SigMA consistently finds a factor of ~2-3 more members. In particular, it resolves more very young populations, such as NGC 2024, RV Orionis, B30, NGC 1977, NGC 2068, and NGC 2071, than previous algorithms. In addition to recovering 28 known clusters and three groups previously classified as substructures, we present 16 new co-eval substructure candidates of the Orion star-forming complex. This work builds up a new high-resolution time-resolved picture of Orion. This spatio-temporal map allows us to relate its stellar content to the surrounding ISM and paves the way for a detailed analysis of its star formation history in the future.

The discovery of cold structures around Sgr A* has challenged our understanding of the gas dynamics and thermodynamic state of the plasma in its vicinity. This work aims to constrain the conditions for the formation of such structures, namely the cold disc-like structure and the recently discovered G-1-2-3 complex. We conduct hydrodynamic simulations of the observed Wolf-Rayet stars feeding Sgr A*. Our simulations show that the plasma chemical composition is crucial for determining the medium properties. We demonstrate that the formation of a cold disc is possible for chemical compositions that are consistent with observational constraints. However, it is not possible to reproduce all the properties of the observed disc which might suggest the interaction with another structure. Additionally, we present our first results on the hydrodynamic modelling of IRS 16SW as a colliding-wind binary. This is the first step to develop a realistic model on the formation of the G-1-2-3 complex.

We define gravitational entropy as the manifestly integrable surface charge associated with local transverse Lorentz boosts, entirely bypassing the conventional reliance on spacetime diffeomorphisms. Any notion of entropy must satisfy the second law. To answer the question posed in the title, an analogy with Newtonian classical mechanics is instructive: Newton's second law of motion is written by inertial observers who are defined by the first law of mechanics. We show that the second law of gravitational thermodynamics is written by free-fall observers with path parameterization in which the non-affinity of the geodesics is equal to the expansion of their velocity vector field. We then provide a proof of the local second law by studying variations in entropy as viewed by this class of covariantly-defined causal free-fall observers. We show that the entropy variation is strictly non-decreasing, provided the matter sector satisfies the integrated strong energy condition along the observer path.

We present deep, SCExAO/CHARIS high-contrast integral field spectroscopy and archival imaging of four candidate Roman Coronagraph PSF reference stars within/near the Roman Continuous Viewing Zone and potentially suitable for the Coronagraph's key technology demonstration targets HIP 71618 and HIP 54515. For CHARIS data, we achieve 5-$σ$ contrasts down to $\sim$1.4$\times$10$^{-5}$, $\sim$6$\times$10$^{-6}$, and 10$^{-6}$ to 4$\times$10$^{-7}$ at 0\farcs{}16, 0\farcs{}25, and 0\farcs{}5 to 1\arcsec{}. Companion mass limits rule out brown dwarfs at $ρ$ $\sim$ 0\farcs{}15--0\farcs{}25 and massive planets at wider separations around all targets. More critically, for three of the four references our analysis disfavors companions with $V$ band contrasts brighter than 10$^{-8}$, 10$^{-9}$, and $10^{-10}$ at 0\farcs{}15, 0\farcs{}3, and 1$\arcsec{}$. Unless these targets have faint substellar companions within $ρ$ $\sim$ 0\farcs{}15, they likely lack background stars or companions that could corrupt the Roman Coronagraph's dark hole digging to preclude detecting reflected-light planets. For $α$ Cep, our limits are a factor of $\sim$10 worse but still meet the TTR5 limit of 10$^{-7}$ beyond $ρ$ $\sim$ 0\farcs{}25: beyond 0\farcs{}4, they exclude a Jupiter-twin reflected-light companion (10$^{-9}$). Archival Keck/NIRC2 data likewise find no substellar companions with $Δ$V $>$ 10$^{-8}$ at wider separations. Finally, we assess the observability of HIP 71618 and HIP 54515 -- updated for Roman's launch date of August 30, 2026. Adding $γ$ Boo -- not currently in the Roman CPP team reference-star list -- would improve schedulability for the tech demo's key targets.

The detection of the global 21-cm signal from the Cosmic Dawn and Epoch of Reionisation remains a challenge to experiments worldwide. Emitted at a rest-frame frequency of 1420.405~MHz, this signal from the early Universe is redshifted to 40-200~MHz with a maximum brightness temperature of a few 100~mK. Efforts to detect this sky-averaged signal include experiments such as the Shaped Antenna measurement of the background RAdio Spectrum (SARAS) and Probing ReionizATion of the Universe using Signal from Hydrogen (PRATUSH). Detecting this faint signal requires precise calibration of the antenna, which includes a high-precision measurement of its reflection coefficient. This measurement must be performed \textit{in situ} at the observation site, as the antenna characteristics vary significantly with the environment. PRATUSH, a space-based radiometer, faces the additional challenge of structural distortions induced by thermal cycling, necessitating multiple measurements of the reflection coefficient. This work highlights the development of an \textit{in situ} Vector Network Analyser, which utilises a novel noise source-based calibration scheme and a cross-correlation spectrometer to perform magnitude and phase measurements of the complex reflection coefficient of the antenna. Further, we demonstrate the performance of the designed network analyser using independent measurements from a precision network analyser and reflection coefficient modelling of the device under test. We find the level of non-smooth calibration systematics, which need critical control for 21-cm signal detection, to be about $10^{-5}$. Finally, we study the impact of reflection coefficient correction on sky measurements, highlighting its usability for precision 21-cm observations.

The Y dwarf WISE 1935 exhibits a thermal inversion in its radiative atmosphere, producing methane emission features in its JWST spectrum, but the physical mechanism responsible for this inversion remains unknown. Using the open-source radiative--convective equilibrium code PICASO, we model atmospheric heating with Chapman energy deposition profiles to reproduce the observed thermal inversion and methane emission feature. Our models require heating rates of approximately 10^5-10^6 erg cm^-2 s^-1. We show that the atmospheric response depends primarily on the integrated heating deposited in the observable atmosphere, revealing a degeneracy between heating magnitude, vertical extent, and emitting surface fraction. Disequilibrium chemistry lowers the required energy input by lowering CH$_4$ opacity and strengthening the inversion. Comparison with recent electron-beam heating models indicates that reproducing the thermal inversion in W1935 requires substantially greater energy deposition than currently predicted for brown dwarf auroral heating, while the observed methane emission favors energy deposition near 10^-3-10^-2 bar. Our models also predict a prominent methane emission feature near 7.8 microns, along with energy-sensitive ammonia features near 6 microns, implying a bolometric luminosity greater than that yet measured. Finally, we investigate potential sources of the inferred upper-atmospheric heating. We find that Joule heating would require a strong magnetic field and large electron densities, the latter supported by external ionization from an unidentified source. We also consider cometary impacts as a possible source of atmospheric heating.

The upcoming Roman Coronagraph will be the first high-contrast instrument in space capable of high-order wavefront sensing and control technologies, a critical technology demonstration for the proposed Habitable Worlds Observatory (HWO) that aims to directly image and characterize habitable exoEarths. The nominal Roman Coronagraph observing plan involves alternating observations of a science target and a bright, nearby reference star for both wavefront calibration and reference differential imaging post-processing. Reference star criteria for the most demanding coronagraph mode are restrictive, limiting the sample to only 40 candidates for which thorough observational vetting is needed to assess their suitability. Reference star properties such as resolved diameters, presence of circumstellar dust, and close point sources may also have more subtle impacts on post-processing efficacy that may inhibit final contrast performance. In this work, we describe the current progress of the CoronaGraph Instrument Reference stars for Exoplanets (CorGI-REx) observing campaign, a 300+-hour observing campaign that utilizes instruments from around the world to vet reference stars for high-order wavefront control suitability. We will present the pre-launch list of reference star candidates being utilized for the Roman Coronagraph Observation Phase constructed from a thorough analysis of high contrast and interferometric observations. We will also present the results of simulations investigating the impact of reference star resolved diameters and companions on post-processing performance. We conclude by discussing the importance of reference star selection for scheduling observations and optimizing contrast performance for the Roman Coronagraph along with implications for HWO coronagraph operations.

The absence of an algebraic relation between the Ricci scalar and the trace of the energy-momentum tensor in Non-Conservative Unimodular Gravity ($\mathrm{NUG}$) opens new possibilities for constructing spacetime geometries from prescribed curvature profiles. Exploiting this property, we develop a curvature reconstruction framework in which traversable wormhole geometries are generated directly from a prescribed curvature profile rather than from the matter sector or the metric functions. The reconstruction procedure is implemented for a power-law Ricci scalar combined with three different redshift functions, leading to distinct classes of static and spherically symmetric wormhole solutions. We investigate their geometrical properties, asymptotic behavior and null energy condition. Although the radial null energy condition remains necessarily violated at the throat, we show that the dimensionless curvature parameter controls the intensity of the exotic matter supporting the wormhole, while the curvature exponent determines the global asymptotic structure of the reconstructed spacetime. In particular, the critical configuration separating asymptotically flat solutions from geometries with residual asymptotic deformation naturally emerges from the reconstruction scheme. These results establish curvature reconstruction from prescribed Ricci scalar profiles as a viable geometrical framework for generating compact-object spacetimes within non-conservative unimodular gravity.

Galaxy shapes are unique tensor tracers of large-scale structure, providing a promising avenue to both enhance current cosmological programs and detect new physics beyond the scalar sector. We develop a general formalism to describe the full 3D structure of galaxy shapes and their statistics, including the breaking of isotropy by the line of sight and redshift space distortions. We constructively show that the redshift-space mapping generates a kinematic basis whose form factors are strictly polynomial in the line-of-sight angle $μ= \hat{k} \cdot \hat{n}$, and that parity selection rules restrict scalar-tensor and tensor-tensor correlators to 3 and 13 independent form factors, respectively, with the latter further reduced to 9 by exchange symmetry. We show that this polynomiality is preserved transforming into a total helicity basis denoted by total angular momentum $M$---sourced to be nonzero by powers of the line-of-sight $\hat{n}$---and that this is equivalent to the form factors having spin weights $(1 - μ^2)^{|M|/2}$ and described by associated Legendre polynomials $P^{|M|}_\ell$. We construct estimators for form factors in the normalized total-helicity basis that provide the optimal angular weighting to extract shape information, and connect the full tensor basis to projected shape statistics. To validate our formalism, we study the above tensor form factors within a toy model, showing that all allowed channels are generated even within simplified assumptions, and apply our estimators to halo shape statistics in N-body simulations wherein all channels up to total angular momentum $|M| \leq 2$ are detected. We anticipate that the methods developed here will have applications ranging from optimal extraction of intrinsic-alignments in hydrodynamical simulations to identifying new physics in tensor channels forbidden by selection rules in the standard model of cosmology.

Semi-Symmetric metric gravity extends general relativity by introducing a semi-symmetric connection with vectorial torsion. The modified field equations contain extra contributions from the torsion vector and its derivatives. Assuming a purely radial torsion vector consistent with spherical symmetry, we derive two exact vacuum solutions. The metric depends on two integration constants, defining the Schwarzschild radius and a new cosmological-type length scale. Classical Solar System tests, including perihelion precession, light deflection, and radar echo delay, are used to constrain the new length scale and the associated deviations from general relativity. The thermodynamic properties of the resulting black hole solutions are investigated, and it is shown that the vector perturbation sector is linearly stable.

We introduce a unified framework for dark energy diagnostics based on the joint phase space of the equation of state $w$ and the sound speed $c_s^2$. The resulting $w-c_s^2$ plane provides a minimal extension beyond background cosmology, capturing both the expansion history and perturbative properties within a single representation. Building on this framework, we define the microphysical flow parameter $F=dc_s^2/dw$, which encodes the dynamical relation between background evolution and perturbative response. We derive a direct connection between the present-day value $F_0$, $H_0$, and $σ_8$, and show that the microphysical flow parameter enables a hierarchy of increasingly stringent consistency tests that substantially reduce the viable dark energy theory space. We further demonstrate how trajectories in the $w-c_s^2$ plane distinguish models that are nearly degenerate at the level of $w(a)$, including canonical quintessence, Chaplygin gas models, and noncanonical scalar field realizations. This framework provides a compact phenomenological bridge between dark energy microphysics and future perturbation-sensitive observations, establishing $F_0$ as a useful discriminator of the kinetic structure underlying cosmic acceleration.

Radiative corrections at the percent level can shift the predictions of $α$-attractor and Starobinsky-like models into the region of the $(n_s,r)$ plane preferred by ACT DR6. We show that the decisive property is not the size of a correction but whether it is removable. In the slow-roll $N$-formalism the observables are functionals of $\eps(N)$, and equality of $\eps(N)$ on an interval reconstructs the potential up to an amplitude rescaling and a shift of the canonical field. A larger class, selected by $(V/V')Δ'={\rm const}$, preserves the leading predictions and provides a criterion for any proposed deformation. In weakly nonlocal completions of $R+R^{2}$ the improvement scale $μ=H(φ)$ makes the renormalization-group time one half of the logarithm of the tree potential, so the local one-loop flow passes the test and evolves the model onto the E-model family $V\propto(1-e^{-\sqrt{2/3}\,φ/\mpl})^{p}$ with $p=2+K$. Since the divergent local beta functions of these super-renormalizable completions are one-loop exact, no higher-loop local running modifies this picture. The induced shifts are $\ord(\ln N/N^{2})$ in $n_s$, obtained in closed form for the removable part and numerically for the rest. The number of $e$-folds, which the criterion does not protect, contributes at the \red{$22\%$} level with an opposite sign. Matter-induced corrections fail the same test at leading order, which is why they shift the predictions. Among the deformations proposed since ACT DR6, an $R^{n}$ term in $f(R)$ gives $(V/V')Δ'=\ord(N^{n-1})$, so only $n=2$ is removable, and no deformation that increases $n_s$ satisfies the criterion. For Standard Model matter, the removable channel is fixed by the Higgs nonminimal coupling alone and is $\ord(10^{-11})$, because the measured amplitude sets the coefficient of $R^{2}$ to $5.1\times10^{8}$.