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Due to their different nucleosynthetic origin, a stellar population produces oxygen (O) and iron (Fe) on different timescales, and their relative abundance can deviate strongly from solar. Galaxy formation models should treat these elements separately, as they play a distinct role in shaping physical phenomena. For example, oxygen mainly sets the gas cooling rate, while the iron abundance sets stellar atmosphere opacities impacting stellar evolution, spectra, and feedback. Observations of star-forming galaxies usually only constrain gas-phase oxygen abundance, vastly limiting our capabilities of separating the cosmic evolution of oxygen and iron. Here, we present an observationally motivated framework to scale the cosmic evolution of O and Fe abundances. We applied the relation between the α-enhancement and galaxies' specific star formation rate ([O/Fe]--sSFR) to derive the Fe and O-dependent cosmic star-formation history (cSFH). We find that star formation with near-solar O/Fe is rare: at least 70% of the integrated cosmic stellar mass forms at non-solar O/Fe. The cosmic average metallicity is generally lower in [Fe/H] than in [O/H] (by up to a factor 3), with the offset increasing from z = 0 to redshifts z ≈ 3 and then approaching the core-collapse O/Fe ratio. We validated our results against samples that probed the Fe-dependent cSFH in different regimes such as absorption-derived ⟨[Fe/H]⟩ from long gamma-ray bursts. Our results impact the interpretations of stellar and galaxy spectra and the predicted rates of transients, especially those linked to metal-poor progenitors (e.g. black hole mergers).

Transient X-ray obscuration in Seyfert 1 galaxies likely arises from clumpy accretion-disk winds near the broad-line region (BLR), but the wind structure and short-timescale variability are difficult to measure because high-resolution spectra are often suppressed during deep low states. We analyse a coordinated XMM-Newton + NuSTAR campaign on Mrk 335 in 2021 June, with long-term Neil Gehrels Swift Observatory monitoring, capturing the source in an intermediate-flux state with strong Reflection Grating Spectrometer (RGS) absorption features. We model the broadband spectral energy distribution to determine the ionizing continuum for self-consistent photoionization modelling of the RGS spectra. The stacked RGS spectrum requires three photoionized absorbers with <inline-formula> <mml:math><mml:mi>log</mml:mi><mml:mi>ξ</mml:mi><mml:mo>≃</mml:mo><mml:mn>3.69</mml:mn></mml:math> </inline-formula>, 2.97, and 1.91, outflowing at ∣v<SUB>out</SUB>∣ ≃ 5800, 3200, and 2100 km s<SUP>−1</SUP>, respectively. Their properties are consistent with the three-phase obscurer reported in 2009, indicating that a similar multiphase obscuring wind can persist over decade timescales. Using five consecutive RGS observations, we track the wind evolution on day timescales and find strong variability in column density and ionization in all phases, together with smaller but coherent velocity changes. During a flare, the low-ionization phase shows a significant drop in opacity, while in the subsequent epoch all phases show increased outflow velocities, suggesting a possible connection between continuum variability and changes in the line-of-sight absorber. The high-ionization phase responds most directly to changes in ionizing luminosity, while the lowest-ionization phase shows at most a delayed response. Order-of-magnitude constraints place the obscurer at BLR scales ∼ 10<SUP>3</SUP>─10<SUP>5</SUP>R<SUB>g</SUB>, with kinetic power potentially reaching the percent level of L<SUB>bol</SUB> for plausible assumptions on geometry and clumpiness.

GW231123 is the most massive binary black hole merger observed to date by the LIGO--Virgo--KAGRA detectors, with a reported total mass of 190--265 M<SUB>⊙</SUB>(90% confidence level, c.l.). Such a high observed mass can result from the combined effects of cosmological redshift and gravitational magnification if the source is gravitationally lensed. In addition, compact objects such as stellar remnants can induce wave-optics diffraction, imprinting characteristic distortions on the signal. We present a multiscale lensing analysis of GW231123 that incorporates diffraction by a compact microlens embedded in an external gravitational potential. The data favor a lensed interpretation with a conservative false-alarm probability of ≲1%. The inferred total source mass shifts to 100--180 M<SUB>⊙</SUB>, reducing the need for extreme spins and tensions between waveform models. We reconstruct both source and lens parameters, including the microlens mass (190--850 M<SUB>⊙</SUB>), its projected offset, and the amplitude and orientation of the external potential. Assuming a galaxy-scale macrolens modeled as a singular isothermal sphere, we infer external magnification that places the source at redshift z ~ 0.7--2 and predicts a ~55% probability of forming an additional detectable image. This analysis demonstrates how current gravitational-wave observations probe the wave-optics lensing regime, enabling joint inference of compact lenses and macroscopic gravitational potentials, including bounds on compact dark matter. Continued searches for additional macroimages and diffraction by stellar fields will further test GW231123 as a lensed event candidate.

Millisecond pulsars (MSPs) are the core of pulsar timing array (PTA) experiments for nanohertz gravitational wave (GW) detection, but rare abrupt profile variations in MSPs introduce unmodeled systematic biases that degrade timing precision. We report the detection of a new abrupt profile transition event in MSP J1547-5709 from the MeerKAT Pulsar Timing Array 4.5 yr data set, at MJD 59781(6). The event is characterized by an abrupt flux enhancement of the third peak component (P3) with no significant change of the phase difference between the second peak component (P2) and P3, followed by exponential decay with a characteristic timescale of τ ≈ 600 days. High-precision timing analysis reveals no significant change in the spin-down rate <inline-formula> <mml:math><mml:mover><mml:mrow><mml:mi>ν</mml:mi></mml:mrow><mml:mrow><mml:mo>̇</mml:mo></mml:mrow></mml:mover></mml:math> </inline-formula> or abrupt time of arrival (TOA) jumps, but a clear monotonic upward drift in timing residuals postevent, tracking the profile recovery. This component-specific, mild event with a long recovery timescale places new tight constraints on local pulsar magnetospheric dynamics, and highlights the impact of unmodeled profile variation on PTA experiments.

The production sites of high-energy neutrinos in blazar jets remain poorly constrained. In this work, we investigate the physical conditions required for efficient neutrino production by using radio-constrained jet properties to evaluate the radial evolution of the external-to-magnetic energy density ratio (Compton dominance Y). We identify Y ≫ 1 as the key physical condition for efficient neutrino production, as it simultaneously enhances photohadronic interactions and suppresses synchrotron radiation from secondary pairs, thereby avoiding an excess of hard X-ray emission. We find that such large values of Y are most readily achieved near or within the broad-line region. This large-Y condition is generally incompatible with reproducing the observed broadband spectral energy distribution within a single emission region, naturally indicating that the neutrino-emitting region is physically distinct from the dominant electromagnetic emission zone. We further show that such a scenario can be realized either if the jet completes its acceleration within subparsec scales or if the bulk Lorentz factor is intrinsically large, both of which appear uncommon based on current observations. These results offer a physically motivated framework for identifying neutrino production sites, provide a natural explanation for the rarity of blazar─neutrino associations, and underscore the importance of constraining jet property at subparsec scales in the search for neutrino-emitting blazars.

A decade after the first direct detection of gravitational waves, the growing catalog of hundreds of confirmed events is revealing new insights into the spins of stellar-mass black holes. Spin measurements have long been heralded as a promising tracer of compact-object binary formation and evolution, as different formation channels predict distinct spin signatures on a population level. In this review, we summarize the astrophysics, phenomenology, and current measurements of black hole spins. We begin with an overview of the predictions for black hole spin magnitudes and orientations from leading formation channels---isolated binary evolution, dynamical formation in clusters, formation in AGN disks, and hierarchical triples. We then describe the imprint of spin effects on the gravitational waveform and the measurability of spin in individual events. Finally, we review current population-level constraints on spin magnitudes, orientations, and effective spin parameters, including correlations with mass and redshift, and discuss their astrophysical implications. We conclude by highlighting open questions and future prospects, emphasizing how improved detector sensitivity will enable increasingly precise spin measurements for both individual events and the binary black hole population as a whole.

Detection of gravitational waves enables probes of environmental effects around compact binaries. Ultralight bosons, well motivated in particle physics and capable of forming core-like dark matter structures, induce environmental dynamics that differ qualitatively from those produced by stars or particle dark matter. For comparable-mass binaries, such bosons can form gravitationally bound states analogous to molecules once the binary separation falls below the characteristic wavelength of the bound states, with an inner region co-moving with the binary. We combine numerical simulations and a semi-analytic framework to characterize the structure and ionization of these gravitational molecules. We determine the extent of the co-moving region and compute the ionization flux driven by orbital motion over a range of eccentricities. Using these results, we estimate the backreaction on the binary orbital evolution and identify a new environmental effect: eccentricity-induced ionization of the co-moving component leads to efficient circularization. We further show that this molecular phase can be astrophysically viable and significantly modify the stochastic gravitational wave background from supermassive black hole binaries.

The rapidly accumulating discoveries of binary stellar-mass black-hole (sBH) coalescences, detected by LIGO, have opened a new window into the formation and evolution of compact binaries. In particular, residual orbital eccentricity may provide a distinctive signature of their formation channels. Here, we investigate a scenario in which high-eccentricity compact binaries form through the sequential capture of multiple sBHs by massive main-sequence stars, using a combination of hydrodynamical and semianalytic few-body simulations. We find that sBHs with $M_\bullet\lesssim 0.2\,M_{\star}$ can be captured by massive stars and settle into a quasi-hydrostatic black-hole star (BH*) through gas dynamical friction. A subsequent encounter with a second sBH can then produce a compact binary embedded within the stellar envelope. Our hydrodynamical simulations show that through captures with small impact parameter, some binaries are born with high eccentricity ($e\gtrsim 0.5$), with its orbital frequency already entering the LISA band. Our semianalytic models further demonstrate that gas dynamical friction can pump the eccentricity to $e_{\rm 10\,Hz}>0.9$ before gravitational-wave emission eventually circularizes the binary during the final stage of coalescence. Once formed, the binary can merge quickly in $\sim 10$ hours. This channel may operate in dense stellar environments, such as star clusters and active galactic nucleus (AGN) disks. The same mechanism can also be applied to Thorne-Żytkow objects. A high-eccentricity binary in the LIGO band could therefore provide a distinctive signature of this formation scenario.

We investigate the spherical accretion onto a static Konoplya Zhidenko black hole and examine how the deformation of the spacetime affects the dynamics of the accreting matter. By applying the conservation laws of particle number and energy-momentum, we formulate the accretion problem and derive the corresponding Hamiltonian describing the fluid motion. The critical points and sonic transitions are then analyzed for ultra stiff, ultra relativistic, radiation, and sub relativistic fluids. We study the dependence of the critical point structure and flow trajectories on the KZ deformation and compare the results with those obtained for asymptotically safe, Schwarzschild MOG, and Reissner Nordström black holes. The comparison shows that the location and behavior of the critical points vary significantly with the underlying BH geometry and the equation of state of the fluid. In particular, the KZ deformation produces noticeable changes in the radial structure of the accretion flow, with different effects observed for the considered fluid models. These results provide a comparative picture of spherical accretion in different black hole spacetimes and help clarify how modifications of the background geometry influence matter dynamics in the strong field region.

Sgr A<SUP>⋆</SUP>, the 4 × 10<SUP>6</SUP> M<SUB>⊙</SUB> supermassive black hole at the Galactic center, exhibits frequent flaring with X-ray luminosities of L<SUB>X</SUB> ∼ 10<SUP>35</SUP>─10<SUP>36</SUP> erg s<SUP>−1</SUP>, while its ultraviolet (UV) emission remains unconstrained due to extreme extinction (A<SUB>V</SUB> ∼ 30 mag). We use JWST/MIRI time-resolved spectroscopy of the central <inline-formula> <mml:math><mml:mn>0</mml:mn><mml:mover><mml:mrow><mml:mi>.</mml:mi></mml:mrow><mml:mrow><mml:mi>″</mml:mi></mml:mrow></mml:mover><mml:mn>3</mml:mn></mml:math> </inline-formula> region to search for mid-infrared emission line variability driven by Sgr A<SUP>⋆</SUP> flares, comparing the results to CLOUDY photoionization models spanning flare luminosities of L<SUB>UV</SUB> = 10<SUP>32</SUP>─10<SUP>39</SUP> erg s<SUP>−1</SUP>. We detect no continuum-correlated variability in any mid-infrared line, including [Fe II] (5.34 μm), [Ne II] (12.813 μm), [Fe II] (17.936 μm), and [S III] (18.713 μm) over lags of ∼1─8 hr. Despite expectations of a flare-driven response, we show that the lack of variability is consistent with the physical conditions in the spatially extended line-emitting gas, where light-crossing timescales of ∼0.1─10 days and recombination and cooling timescales much longer than the variability timescales suppress any observable response to individual flares. We further find that the modeled infrared spectra are dominated by continuum emission rather than isolated line emission. The brightest predicted lines are intrinsically weak (lower than 10<SUP>−5</SUP> mJy), and their detectability is further reduced by the large kinematic broadening expected at the CLOUDY-predicted emitting radii, reducing their contrast against the continuum. Extending the analysis to higher-ionization mid-infrared and near-infrared lines does not improve sensitivity. These results demonstrate that infrared emission lines trace a steady-state radiation field rather than individual flaring events, and therefore infrared line diagnostics cannot be used to constrain the instantaneous UV flux of Sgr A*.

The formation and evolution of galaxies during the Cosmic Dawn is a topic of current interest in extragalactic astrophysics. The physical processes involved are highly non-linear and multi-scale, and their understanding therefore requires numerical simulations. One such process is the energetic feedback from stellar systems on their surroundings, in particular that produced by X-ray binaries. With the aim of incorporating this feedback into simulations, the present work analyses the performance of the hydrodynamical cosmological code SWIFT, characterising its scalability and identifying an optimal configuration for its task-based parallelism. Using this configuration, we run a reference simulation employing the EAGLE physics model and study the properties of the resulting galaxies. The results are consistent with previous work and will be compared with those obtained once the new feedback process is included.

Astrophysical black holes exist within non-vacuum environments, and their motion through these environments generically result in a force on these black holes through processes such as dynamical friction and Bondi accretion. We explore these forces numerically for black holes moving through a complex scalar field of mass $m$ with constant acceleration $a$, while also revisiting the constant velocity case considered in the existing literature. The former is modeled by the C-metric, while we use Painlevé-Gullstrand metric with an additional divergence and vorticity free velocity field to mimic the constant velocity motion. Our simulations reveal several novel and interesting aspects of the drag force in both cases. For the constant velocity case, the force saturates at late times, with a value that depends on velocity in a manner distinct from known dependence. For the constant acceleration case, the force increases to a maximum value $F_\star$ and then reduces drastically, with $F_\star \approx 0.3~ m a$. Moreover, the density wake in this case shows revivals separated by decreasing time intervals.

Constraining the location and geometry of ultra-fast outflows (UFOs) is essential for identifying where they are launched and how they are accelerated. We investigate the soft X-ray variability of the luminous quasar PDS 456 using simultaneous March 2024 observations with XRISM/Xtend and NuSTAR. A model-independent comparison between the flare and quiescent phases reveals spectral variability around 1 keV in the rest frame, while the hard X-ray spectral shape remains nearly unchanged. Broadband spectral fitting shows that the soft X-ray structure is well described by a partial-covering low-ionization UFO with $\log (ξ/(\mathrm{erg~cm~s^{-1}})) \simeq 3.1$ and $v_{\mathrm{out}} \simeq 0.30c$. Time-sliced spectral analysis further reveals significant variability in the covering fraction of this absorber. Interpreting this variability as transverse motion across the X-ray source, we constrain the crossing velocity to be $v_{\mathrm{cross}} \lesssim 5 \times 10^{-3}c$ and derive a lower limit on the absorber distance of $r \gtrsim 4 \times 10^3 R_{\mathrm{g}}$. This location is substantially farther out than the high-ionization UFO previously inferred at ~200-600 $R_{\mathrm{g}}$, while the two phases have comparable outflow velocities. The resulting velocity-distance structure disfavors a self-similar magnetocentrifugal wind and instead suggests either radiation-pressure acceleration following a Castor-Abbott-Klein-like velocity law or compact magnetic acceleration through magnetic reconnection. These results demonstrate that soft X-ray partial-covering variability can provide a geometrical probe of UFOs and directly connect spectral variability to wind acceleration.

Pulsar glitches display diverse behaviors. They are commonly labeled as "Vela-like" or "Crab-like," yet these qualitative categories do not provide reproducible quantitative boundaries. We constructed an objective classification scheme based on the joint distribution of backward waiting time $Δt_{-}$ and fractional glitch amplitude $Δν/ν$. A sample of 349 glitches from 22 pulsars was compiled by cross-matching the Jodrell Bank and ATNF glitch databases. For each source, we used two-dimensional kernel density estimation (KDE) together with highest-density regions (HDRs) to derive geometric descriptors, including the HDR area, anisotropy ratio, and out-of-HDR fraction. Hierarchical clustering of the KDE--HDR descriptors revealed two morphology classes independent of visual inspection. In this convention, the Compact class is associated with small HDR areas, elevated anisotropy, and limited peripheral occupancy. The Extended class is associated with broader HDR occupancy and stronger low-density extensions. We found that bootstrap resampling and hyperparameter sensitivity tests confirmed this partition for most sources. Nevertheless, two prolific pulsars (PSR J0537-6910 and PSR J1341-6220) were found to occupy intermediate positions. Logistic regression identified the mean backward waiting time $\langleΔt_{-}\rangle$ as the strongest class predictor (in-sample $\mathrm{AUC}=0.88$; leave-one-out $\mathrm{AUC}_{\mathrm{CV}}=0.59$, reflecting the limited sample size). Additionally, a parallel analysis using $Δt_{+}$ recovered the same two-class structure but with reduced stability. The data suggest that the Compact class is consistent with near-complete reservoir depletion, whereas the Extended class reflects partial, avalanche-like releases. As a result, short-term measurements of $G$ in Extended-class pulsars may underestimate the true crustal superfluid fraction.

Research on dual AGNs (Active Galactic Nuclei) is crucial for understanding the formation, growth, and evolution of galaxies and supermassive black holes (SMBHs). However, the current number of identified dual AGNs remains scarce, which limits our understanding of galaxy mergers, the growth of SMBH pairs, and the prediction and detection of low-frequency gravitational waves. A total of 187 new dual AGNs, 4 triple AGN systems, and 1 quadruple AGN system were identified based on the Million Quasars Catalog. All of these multiple AGN systems have low redshifts ($z &lt;$ 0.5), with projected distance ($r_{\rm p}$) between members less than 100 kpc and line-of-sight velocity differences ($\Delta v$) smaller than 600 km/s. This sample complements existing low-redshift dual AGN samples and provides valuable insights into AGN triggering mechanisms and the evolution of SMBH pairs. A visual inspection of the optical and infrared images of the identified samples reveals that approximately 24% of the dual AGN systems exhibit clear tidal features. Statistical analysis of their redshift, projected distance, and line-of-sight velocity difference indicates that the number of dual AGN increases with decreasing redshift, and that most $\Delta v$ values are distributed below 400 km/s. The number of dual AGN systems with tidal features is relatively small in larger projected distances, with only one system found in (60$-$65) $ h^{-1}_{70} \; \text{kpc} $. As the projected separation decreases, the number of such systems increases, reaching a peak of 10 cases in (10$-$15) $ h^{-1}_{70} \; \text{kpc} $, and then gradually decreases in smaller scales.

The James Webb Space Telescope (JWST) discoveries of supermassive black holes (BHs) at z ≳ 5 may provide key insights into their seeding origins. Using new [18─72 Mpc]<SUP>3</SUP> BRAHMA cosmological simulations, we investigate how variations in heavy-seed prescriptions, coupled with a subgrid dynamical friction model, shape BH populations at z ∼ 5 and ∼ 0. We consider two "lenient" seed models, in which all halos containing sufficiently dense and metal-poor gas form ∼10<SUP>4</SUP> and ∼10<SUP>5</SUP> M<SUB>⊙</SUB> seeds, and a "strict" seed model, in which ∼10<SUP>5</SUP> M<SUB>⊙</SUB> seeds form only under additional constraints motivated by direct collapse BH formation. By z ∼ 5, all models produce M<SUB>*</SUB>─M<SUB>BH</SUB> relations broadly consistent with the observed local Universe for M<SUB>*</SUB> ≳ 10<SUP>9</SUP> M<SUB>⊙</SUB> galaxies, but only the lenient scenarios generate systems near the upper envelope of the observed local scatter. In galaxies hosting M<SUB>BH</SUB> ∼ 10<SUP>8</SUP>─10<SUP>9</SUP> M<SUB>⊙</SUB> BHs, lenient production of ∼10<SUP>5</SUP> M<SUB>⊙</SUB> seeds also produces multiple overmassive systems with M<SUB>BH</SUB>/M<SUB>*</SUB> ≳ 0.01. Although their growth is dominated by seeding and mergers, these systems reach luminosities of ∼10<SUP>43</SUP>─10<SUP>45</SUP> erg s<SUP>−1</SUP>, comparable to those inferred for JWST-detected BHs. As a key observational signature, the lenient seed models yield merger rates of ≳100 yr<SUP>−1</SUP> and near-unity local BH occupation fractions even in galaxies with M<SUB>*</SUB> ≲ 10<SUP>7</SUP> M<SUB>⊙</SUB>. In contrast, the strict seed model produces merger rates of only ∼1 yr<SUP>−1</SUP> and local occupation fractions of ≲10% for galaxies with M<SUB>*</SUB> ≲ 10<SUP>8</SUP> M<SUB>⊙</SUB>. Future gravitational-wave event rates and measurements of local BH occupation fractions will therefore provide strong constraints on the dominant pathways responsible for high-redshift BH assembly.

Severe space weather is caused by coronal mass ejections (CMEs). While the chain of CME activities from the Sun to Earth has been well tracked for some individual events, the statistical relations between the physical properties of CMEs near the Sun and those of their counterpart interplanetary CMEs (ICMEs) have not been well investigated. In this article, we provide a comprehensive study of a large set of properties for all 66 Earth-affecting CMEs during 2011─2013. Among them, 32 (48%) CMEs originated from compact and stronger magnetic field regions, i.e., active regions (ARs), while 34 (52%) CMEs originated from larger but weaker-field quiescent regions (QRs). The AR-CMEs are much faster than QR-CMEs near the Sun, with average true speeds of 1086 and 711 km s<SUP>−1</SUP>, respectively. We find that, at 1 au or near Earth, the differences between the two contrasting types are no longer prominent, but not fully diminished. While the charge states and velocities remain statistically different, other ICME properties, including magnetic field strength, plasma β, proton temperature, helium abundance, and others, do not differ with statistical significance. Interestingly, QR-CMEs and AR-CMEs have nearly equal chances of driving a forward shock at 1 au (68% versus 69%). These results indicate that the evolution of CMEs during their propagation from the Sun to Earth has significantly reduced many differences in properties near the Sun between the two types of events.

The Event Horizon Telescope (EHT) has provided images of the supermassive black holes Sgr A* and M87*, enabling direct tests of gravity. Any extended mass distribution, such as a dark matter halo, perturbs null geodesics in the photon-ring regime, making shadow measurements a probe of inner-halo structure. In this work, we investigate static, spherically symmetric black holes surrounded by Einasto-type dark matter halos and derive constraints from EHT shadow data. Starting from the Einasto density profile with parameters <inline-formula> <mml:math><mml:msub><mml:mrow><mml:mi>ϱ</mml:mi></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mover><mml:mrow><mml:mi>α</mml:mi></mml:mrow><mml:mrow><mml:mo>∼</mml:mo></mml:mrow></mml:mover><mml:mo>,</mml:mo><mml:mover><mml:mrow><mml:mi>ν</mml:mi></mml:mrow><mml:mrow><mml:mo>∼</mml:mo></mml:mrow></mml:mover></mml:math> </inline-formula>, we construct a metric function <inline-formula> <mml:math><mml:mi>f</mml:mi><mml:mo>(</mml:mo><mml:mi>r</mml:mi><mml:mo>)</mml:mo><mml:mo>=</mml:mo><mml:mn>1</mml:mn><mml:mo>-</mml:mo><mml:mn>2</mml:mn><mml:mi>M</mml:mi><mml:mo>/</mml:mo><mml:mi>r</mml:mi><mml:mo>+</mml:mo><mml:mn>2</mml:mn><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mi>∞</mml:mi></mml:mrow></mml:msub><mml:mover><mml:mrow><mml:mi>g</mml:mi></mml:mrow><mml:mrow><mml:mo>∼</mml:mo></mml:mrow></mml:mover><mml:mo>(</mml:mo><mml:mi>r</mml:mi><mml:mo>)</mml:mo></mml:math> </inline-formula> that interpolates between the black hole horizon and the asymptotic halo, following the approach of Xu et al. but adapted specifically to the Einasto scenario. We analyze the photon potential, null geodesics, and shadow radius as functions of black hole mass M in the nonspinning limit. Using the dimensionless shadow diameter d<SUB>sh</SUB> ≡ Dθ/M measured by the EHT---<inline-formula> <mml:math><mml:msubsup><mml:mi>d</mml:mi><mml:mrow><mml:mspace></mml:mspace><mml:mtext>sh</mml:mtext><mml:mspace></mml:mspace></mml:mrow><mml:mrow><mml:mi>M</mml:mi><mml:mn>87</mml:mn><mml:mo>*</mml:mo></mml:mrow></mml:msubsup><mml:mo>=</mml:mo><mml:mn>11.0</mml:mn><mml:mo>±</mml:mo><mml:mn>1.5</mml:mn></mml:math> </inline-formula> and <inline-formula> <mml:math><mml:msubsup><mml:mi>d</mml:mi><mml:mrow><mml:mspace></mml:mspace><mml:mtext>sh</mml:mtext><mml:mspace></mml:mspace></mml:mrow><mml:mrow><mml:mi>Sgr</mml:mi><mml:mspace></mml:mspace><mml:mi>A</mml:mi><mml:mo>*</mml:mo></mml:mrow></mml:msubsup><mml:mo>=</mml:mo><mml:mn>9.5</mml:mn><mml:mo>±</mml:mo><mml:mn>1.4</mml:mn></mml:math> </inline-formula>---we perform Bayesian parameter estimation to identify allowed regions in the Einasto parameter space. Combined with the independently measured black hole masses from stellar dynamics, our results place constraints on the inner dark matter distribution: for Sgr A*, adopting the stellar-orbit mass prior, we find ϱ<SUB>0</SUB> ≲ 10<SUP>-11</SUP> M<SUB>⊙</SUB> pc<SUP>-3</SUP> at 1σ confidence, while for M87*, the bounds are weaker due to distance uncertainties. The Einasto index <inline-formula> <mml:math><mml:mover><mml:mrow><mml:mi>ν</mml:mi></mml:mrow><mml:mrow><mml:mo>∼</mml:mo></mml:mrow></mml:mover></mml:math> </inline-formula> is weakly constrained, indicating that EHT precision primarily limits the mass enclosed near the photon sphere rather than the profile slope. These findings demonstrate that horizon-scale imaging can complement galactic-scale dynamics in probing dark matter models, including fuzzy dark matter scenarios with solitonic cores. Future EHT observations will refine these constraints and distinguish between competing dark matter descriptions.

Dual active galactic nuclei (DAGN) mark the observable stage of massive black hole (MBH) pairing during galaxy mergers and are the progenitors of the MBH binaries that generate low-frequency gravitational waves. Using the large-volume ASTRID cosmological simulation, we construct mock DAGN catalogs tailored to the selection functions of current (COSMOS-Web and DESI) and forthcoming (Nancy Grace Roman Space Telescope (Roman) and Lynx X-ray Observatory (Lynx)) surveys, enabling direct comparisons between simulations and observations. With realistic observational selections, ASTRID reproduces the observed dual fractions, projected separations, and host-galaxy properties across redshifts. We predict a substantial population of small-separation (&lt;5 kpc) duals that remain inaccessible to current surveys, demonstrating that the apparent paucity of subkiloparsec systems in COSMOS-Web is primarily a consequence of observational selection rather than an intrinsic absence. Following each simulated dual to coalescence, we show that DAGN are effective tracers of MBH mergers: ~30%--70% merge within ≲1 Gyr, and 20%--60% of these mergers produce gravitational-wave signals detectable by the Laser Interferometer Space Antenna (LISA). Duals observable with Roman and Lynx are the progenitors of ~10%--50% of low-redshift LISA sources and contribute ~30% of the PTA-band stochastic gravitational-wave background. We further identify massive green-valley galaxies hosting moderate-luminosity active galactic nuclei (AGN), together with massive star-forming galaxies containing bright quasars at z &gt; 1, as the environments most likely to host imminent MBH binaries. These results establish a unified cosmological framework connecting DAGN demographics, MBH binary evolution, and gravitational-wave sources, while identifying high-priority targets for coordinated electromagnetic and multimessenger observations in the coming decade.

Blazars constitute the main population of active galactic nuclei detected in $\gamma$-rays by the Fermi-LAT satellite. However, around 34\% of the sources in its catalog remain unidentified due to their large positional uncertainty, complicating the association with optical counterparts. To address this issue, a method has been proposed to identify BL Lac-type blazars based on their X-ray properties, using Swift-XRT observations and the analysis of light curves, spectra, and hardness ratios. In this work, we empirically evaluate the effectiveness of this method through comparisons with recent optical classifications. The results show that most candidates selected from their X-ray emission were confirmed as BL Lac blazars, representing 78,94\% of the analyzed sample. This value increases to 84,75\% when more restrictive positional criteria are applied. This study demonstrates that the X-ray band is an effective tool for identifying blazars among unclassified $\gamma$-ray sources and supports future spectroscopic follow-up campaigns.

Binary white dwarfs (BWDs) represent one of the most common systems of compact objects in the Universe and are expected to be the main sources of low-frequency gravitational waves (GW). The upcoming Laser Interferometer Space Antenna (LISA) mission will open a new observational window, by accessing a low-frequency ( $10^{-4}$ Hz to $10^{-1}$ Hz) regime invisible to ground-based detectors, including the signal from BWDs across the Milky Way (MW) and nearby galaxies. In this work, we use the rapid population synthesis code \textsc{sevn} to simulate BWD populations, exploring different evolutionary parameters, compositions, and metallicities. We characterize their properties including mass distribution, orbital periods, and formation timescales, and compare our results with observational data. We aim to study their detectability in a realistic galactic environment by integrating these populations into a MW-like galaxy model from \textsc{tng50} simulations, allowing us to build spatial distributions of these systems and identify regions with higher probabilities for GW detection. Our results provide a theoretical framework for interpreting LISA's future observations and for advancing our understanding of compact binary populations in the Universe.

Despite the small mass fraction typically observed for the interstellar medium, dust plays a significant role as a key component of galaxies, affecting a wide range of properties. This review focuses specifically on how dust grains influence interstellar chemical abundances and on the processes that regulate the evolution of the galactic dust budget. I describe the main physical processes regulating dust evolution, including production by stars and other sources, destruction in supernova shocks and interstellar growth, and the ways in which they are included in galactic chemical evolution models. I discuss the main effects of interstellar dust on the abundances measured in various high-redshift systems that include Damped Lyman <inline-formula><mml:math><mml:semantics><mml:mi>α</mml:mi></mml:semantics></mml:math></inline-formula> absorbers, detected along the lines of sight of distant quasars and in the absorption spectra of Gamma Ray Burst afterglows. I discuss the measure of dust masses in galaxies and review its global budget, evaluated through the study of the evolution of the comoving dust mass density, for which I present an up-to-date compilation of data chosen from the literature. Interstellar dust growth plays a critical role in regulating the dust budget, for which I present a list of evidence both in favour of it and against. The dust budget at high redshift is one aspect that requires attention to drive significant progress in the future, along with the investigation of the properties of dust in local, low-metallicity systems. Our poor theoretical knowledge of basic aspects related to dust evolution evidences the need for a new high-sensitivity space telescope operating in the far-infrared regime, still awaited by the community since the demise of Herschel.

As images of the supermassive black holes Messier 87* (M87*) and Sagittarius A* (Sgr A*) from the Event Horizon Telescope (EHT) grow in number, we gain a better understanding of the typical conditions of the near-horizon region of these objects, and slowly approach a converged time-average of the black hole image. In this article, we briefly review the signatures of black hole spin that manifest most apparently in these time-averaged images. We divide our discussion between coarse spatial features that are accessible with time averages from terrestrial very-long-baseline interferometry (VLBI) at 230 and 345 GHz, and fine spatial features which require either the extension of VLBI at these frequencies to space or the operation of global VLBI at much higher frequencies. We find that, while both coarse spatial features available from the ground and fine spatial features available only from space can both greatly inform spin, the primary difference is the degree of sensitivity to unknown astrophysical conditions, with photon ring-dominated observables benefitting from the exponential suppression of the details of the accretion disk. We conclude that spin measurements from resolved features of strong lensing are likely to provide sharp (~±10%) spin measurements of both M87* and Sgr A* in the near future.

We develop a coordinate invariant formalism which describes the mechanical and electromagnetic interaction of gravitational waves (GWs) with a wide class of resonant detectors. We solve the GW-modified equations of electrodynamics and elasticity with dynamic boundary conditions using an eigenmode expansion. Furthermore, we take damping effects and electromagnetic back-action on mechanical systems covariantly into account. The resulting coupling coefficients are particularly useful for high-frequency gravitational wave experiments using microwave cavities and allow a straightforward numerical implementation for arbitrary detector geometries.

Domain walls (DWs) can be produced when a discrete symmetry is spontaneously broken, and long-lived DWs can dominate the energy density of the universe. In this work, we explore the possibility that a ``domain wall dominant (DWD)'' phase existed in the early universe and ended with DW decay. During the DWD phase, the universe undergoes a power-law accelerated expansion of the scale factor and exhibits temporal superhorizon evolution of the relevant frequency modes. We show that this can lead to distinct features imprinted on the stochastic gravitational wave (GW) background including the independence of its amplitude from the wall tension. Our findings provide a comprehensive framework for evaluating GW emission associated with DWD, leading to distinguishable long-lived DW-induced GWs from other cosmological sources, with significant implications for future GW observatories.

This article examines the impact of solar flare electromagnetic radiation on the state and dynamics of the Earth's upper atmosphere and the applicability of experimental and theoretical methods for assessing changes in the upper ionosphere. One of the most important parameters of ionospheric disturbances is the ionization rate. The article presents data from calculating vertical profiles of the electron production rate for altitudes from 60 to 600 km for two X--class solar flares that occurred on 6 September 2017, using the FISM2 Flare solar irradiance model and the NRLMSISE--00 neutral atmosphere model. The results are verified using experimental measurements of variations in the ionospheric total electron content using a GNSS receiver located at the Mikhnevo mid--latitude geophysical observatory. Two types of estimates of the ionization rate were obtained: without and with the recombination process taken into account. It was demonstrated that the combination of the FISM2 Flare and the NRLMSISE--00 models qualitatively correctly predicts the temporal dynamics of the ionization rate. In general, the results obtained demonstrate the validity of the proposed approaches and open the possibility of further research in this area.

The 1.3 mm ground-based very long baseline interferometry (VLBI) array Event Horizon Telescope (EHT), is limited by Earth's diameter, restricting horizon-scale imaging to only M87* and Sgr A*. Extending baselines to the Moon would achieve ~0.7 μas angular resolution at 230 GHz, enabling shadow detection for many more supermassive black holes (SMBHs). The concept is motivated by space VLBI missions and lunar exploration, including the ongoing Lunar Orbit VLBI EXperiment (LOVEX) aboard QueQiao-2 (Chang'E-7) and the planned International Lunar Research Station (ILRS). We assess shadow detectability for 31 SMBHs with predicted large angular sizes, assuming optically thin emission at 230 GHz, exploring different telescope locations and antenna sizes. Assuming a telescope at the lunar antipode, we simulate the Moon-Earth (u, v) coverage and show that sources near the Moon's orbital plane yield projected baselines spanning a wide range, enabling sampling of the first visibility null - a key shadow signature. Using a geometric ring model, we identify six shadow-detectable candidates: M104, NGC 5077, and NGC 1052 are detectable with a 5 m lunar-based telescope; PGC 049940 with 10 m; NGC 524 with 20 m; and NGC 5252 with 40 m. If additional space telescopes fill the baseline coverage gaps between Moon and Earth, 14 candidates are detectable for the n = 1 photon-ring region with a lunar-based telescope up to 40 m. These results provide a clear scientific and technical motivation for lunar-based telescopes in future black hole shadow studies.

The nature of the mechanisms that drive mass transfer in symbiotic stars remains an area of active research in stellar astronomy. Constraining the role that both stellar winds and Roche-lobe overflow play in this process is crucial to improving our understanding of these binaries and connecting them to important transient events such as recurrent novae and Type Ia supernovae. The high-resolution capabilities of an optical interferometer can resolve the geometric structure of the red giant in symbiotic stars and help answer this question. This work presents the results of an optical interferometric study using the Center for High Angular Resolution Astronomy (CHARA) Array for the purpose of measuring the angular diameter of and imaging the cool giant in four symbiotic and related systems. Here we report \textit{H} band observations collected with MIRC-X. Model fitting and image reconstruction are used to test for Roche-lobe-filling geometries. Near-simultaneous infrared spectroscopy taken using the NASA InfraRed Telescope Facility (IRTF) is used to determine the fundamental stellar parameters of the cool giant in each system. The parametric fits reported here favor circularly symmetric disk models over elongated geometries, while imaging suggests the presence of surface features on three of these stars. We find that the three systems with constrained orbits have inferred time-averaged filling factors below unity.

Recent observations of V1298~Tau\,b, a warm sub-Neptune (R$=9.85 \pm 0.3\,R_\oplus$, M$=13.1 \pm 5.3, M_\oplus$, T$_\mathrm{eq} = 670\,$K) orbiting a young (10-30\,Myr) K star, show depleted methane and surprising abundances of CO$_2$ in its atmosphere. This makes the planet an interesting target to study the "missing methane problem", where HST, Spitzer, and JWST have revealed many sub-Jovian planets with effective temperatures cooler than 800\,K to be depleted in methane compared to equilibrium chemistry predictions. On V1298~Tau\,b, an intrinsic temperature (T$_\mathrm{int}$) of 500\,K is required to explain the methane depletion if strong mixing from a warm interior is the reason for the missing methane, but this T$_\mathrm{int}$ is too large for a planet of its age and size according to standard interior structure evolution theories. Here, we show that stellar flares can result in methane depletion in a warm planet's atmosphere with nominal T$_\mathrm{int} \sim 100$\,K. During a stellar flare, fast methane photolysis rates cannot be balanced by diffusion from below into the upper atmospheric layers probed by observations. Young active stars flare frequently, and we show that the timescale of diffusion for the methane to recover from a flare-induced depletion can be slow compared to the flare frequency. Over time, the atmosphere reaches a new steady state set by the average flare frequency and energy. This new steady state shows depleted methane in the 2\,mbar region, and abundant CO, CO${_2}$, and HCN, which results in synthetic transmission spectra that reproduce the main features of the recent JWST observations of V1298~Tau\,b.

Globally self-gravitating accretion disks in active galactic nuclei (AGN) have been frequently discussed in the literature, but never observed. Few dozen mega-masering accretion disks in AGN have been detected, which display a clear Keplerian rotation on scales of 0.1-1 pc, allowing to estimate their masses within the sphere of influence (SoI) of the central supermassive black holes (SMBHs) to be smaller by more than a factor of 10, compared with the parent SMBH masses. Furthermore, the stellar components, deep inside the SoI, are dwarfed by the SMBH masses of M_BH ~ few X 10^6 - few X 10^7 Mo. Theoretically, no limit exists on sizes and masses of gaseous disks in AGN, which in principle, can exceed masses of their central compact objects. We analyze instabilities which can operate in gaseous disks, i.e., fragmentation for a locally dominant self-gravity and spontaneous breaking of axial symmetry for the globally self-gravitating disks. We invoke the gas response to the latter instability which leads to gravitational collapse, leaving a negligible mass behind and dynamically stable remnants. Consequently, the characteristic timescale for globally self-gravitating disks to exist in AGN should not exceed few rotations, t_phi ~ 10^{3-4} yrs for M_BH ~ 10^{6-8} Mo. Disk rebuilding is expected to be > 10^7 yrs, meaning that probability of finding is < 10^{-3}, which explains their lack of detection. We conclude that observed sub-parsec disks in AGN, at least the Keplerian masering ones, can be remnants of globally self-gravitating accretion disks, and the instability timescale can be related to the duty cycle of AGN, t_duty ~ 10t_phi ~ 10^{4-5} yr.

In dense stellar environments such as globular clusters and active galactic nucleus (AGN) disks, stellar-mass black holes (sBHs) may frequently collide with massive stars. We investigate this process using semi-analytic models, three-dimensional hydrodynamical simulations, and one-dimensional stellar evolution calculations, focusing on collisions between sBHs and a $100\,M_\odot$ main-sequence star. We find that gas drag retains the BH within the stellar envelope unless the impact velocity exceeds $\sim2\sqrt{G(M_\star+M_\bullet)/R_\star}$. The post-collision outcome depends primarily on the BH-to-star mass ratio. For $M_\bullet\gtrsim30\,M_\odot$, the retained envelope is either quasi-spherical or disc-like, but remains dynamically unstable because of shock heating. In contrast, for $M_\bullet\lesssim10\,M_\odot$, the collision forms a ``black hole star'' (BH*): a quasi-hydrostatic, extended stellar envelope surrounding the embedded BH. These results agree with our analytic prediction that BH* formation necessarily requires $M_\bullet\lesssim0.2\,M_\star$. Follow-up \texttt{MESA} calculations further show that, for these low-mass BHs, the shock-heated remnant thermally relaxes without triggering runaway expansion. We discuss several astrophysical implications of BH*s, including their evolution, the possibility of gravitational-wave events from BH binaries assembled within a stellar envelope, and repeated star--sBH collisions as a pathway for rapid BH growth in dense stellar systems. This mechanism may contribute to the formation of massive BHs in high-redshift nuclear star clusters and may be relevant to the origin of the ``little red dots'' discovered by JWST.

Measurements of thermal X-ray flux emitted by neutron stars can constrain their radii and the equation of state of cold dense matter. Accurate flux modeling of rapidly rotating neutron stars requires an approximation for their oblate surface shape, usually given by a shape function. We examine the accuracy of five shape functions by comparing them against numerical relativistic stellar surfaces for seven representative equations of state over a broad range of compactness and spin. We characterize their errors in the surface radius and their derivative with respect to colatitude, test the extent of quasi-universality, and propagate these errors into the differential solid angle dΩ, a geometric factor underlying the observed flux, under the oblate Schwarzschild approximation. We find that the shape functions produce distinct error patterns associated with their forms and parameter ranges. These errors remain structured in compactness, spin, and colatitude. Simple polynomial corrections substantially reduce the radius errors of several shape functions, with most corrected errors within approximately 0.5%. We show that errors in dΩ may be understood as coming from an area contribution, which scales with twice the relative radius error, and a projection contribution controlled primarily by the error in the surface derivative. The projection contribution grows towards the limb, where small surface errors can produce much larger local errors in dΩ. We provide a set of guidelines for the construction of improved quasi-universal shape functions that can be used in future radius estimation efforts. Our recommendations include that both the shape and its derivative be modeled accurately, that more accurate predictions of the polar radius be developed, and that the shape function be calibrated over the same compactness-spin range that is to be tested.

We present JUG (JAX-based Unified pulsar timinG), a JAX-based, fully independent pulsar timing package emphasising speed and ease of use, designed to confidently handle the increasingly large and complex pulsar timing array datasets that are being created in the pulsar timing field. JUG implements the entire pulsar timing pipeline itself, from data handling and clock corrections through to the timing model and fitting, without relying on other timing software. It enables Pythonic programming at the speed of compiled code, is GPU-capable, and can be operated via a Python API or an interactive GUI. A user of JUG can interactively explore data, fit timing models with complex stochastic noise, model deterministic signals such as continuous gravitational waves, and obtain accurate point estimates of the parameters of the stochastic processes present, thereby bridging frequentist timing and Bayesian noise analysis. JUG is faster than PINT by more than fifty times and is comparably fast to Tempo2, can handle millions of arrival times, agrees with PINT at the picosecond level, and can reliably recover known timing model and noise parameter values. In this paper we describe its design, performance, and validation, and demonstrate its advantages for pulsar timing data analysis.

Light low-energy cosmic ray antinuclei constitute powerful probes for detecting dark matter or other sources of new physics in our Galaxy. This ASTRA Initiative Mission Concept reviews the theoretical motivation, highlighting the transformative potential and current experimental status. Motivated by exciting tentative results, it makes a clear case for the need for the next flagship mission to confirm or refute claims of cosmic antinuclei as signs of new physics.

We report a multi-wavelength study of two flaring episodes of the blazar BL Lacertae during MJD 60500-60800 (9 July 2024 - 5 May 2025). The source reached a daily-averaged $γ$-ray flux of $(1.03 \pm 0.05) \times 10^{-5} \, \mathrm{ph \, cm^{-2} \, s^{-1}}$ ($E > 100$ MeV) on MJD 60588 (5 October 2024). Using orbit-binned data from the Large Area Telescope (LAT) onboard the \textit{Fermi Gamma-ray Space Telescope}, we identify a minimum flux halving timescale of $τ= 1.33 \pm 0.29$ hr. This constrains the upper limit on the $γ$-ray emitting region size to $R \le 2.0 \times 10^{15}$ cm, as well as its distance from the central supermassive black hole to $R_\mathrm{H} \le 5.9 \times 10^{16}$ cm, assuming a Doppler factor of $δ= 14.8$ derived from the spectral energy distribution (SED) modeling. We find tentative evidence for sub-minute $γ$-ray variability with a minimum doubling time of $0.7 \pm 0.2$ min ($p$-value = 0.03). This may originate from an extremely compact region with a size of $R \le 1.8 \times 10^{13}$ cm, suggesting that the emission arises from magnetohydrodynamic substructures, such as plasmoids within a magnetic reconnection zone. Spectral analysis reveals a significant ``softer-when-brighter'' trend ($r = 0.96, p = 4.5 \times 10^{-4}$) during the minute-scale flare peaks, indicating a complex interplay between particle acceleration and radiative cooling. The SED is reproduced using a one-zone leptonic model, in which synchrotron self-Compton (SSC) and external Compton (EC) scattering effectively account for the high-energy emissions. The reduced magnetic field strengths and hard electron injection spectral indices observed during the flaring states suggest enhanced particle acceleration efficiency, possibly associated with relativistic magnetic reconnection.

Binary black holes (BBHs) in gaseous medium, such as active galactic nucleus (AGN) disks, are important gravitational-wave sources, yet the gas-driven torque that governs their orbital evolution remains to be fully understood. Most existing studies of BBHs in gas often approximate the net torque as the sum of independent dynamical friction (DF) forces exerted on each black hole by its own wake, neglecting the mutual gravitational coupling between the two wakes. We perform three-dimensional hydrodynamic simulations of circular BBHs in a uniform flow and find the torque is determined by the wake-wake interactions. The net torque is controlled by a single parameter $η\equiv v_g/v_o$, the ratio of the gas flow velocity to the binary orbital velocity. At small $η$, the wakes merge into a single overdense envelope and the time-averaged torque is negative; as $η$ increases, the wakes separate and the torque becomes positive. In AGN disks, capture-channel binaries in a disk model naturally produce $η$ in the positive-torque regime; the expansion timescale is comparable to or shorter than the disk lifetime, suggesting that gas-driven expansion can compete with gravitational-wave inspiral and suppress the capture-channel merger rate.

We investigate the origin of long-term spectroscopic and photometric variability in the blue supergiant rho Leo, with particular emphasis on distinguishing between intrinsic pulsations and variability induced by a possible companion. Our analysis is based on an 11.5-year spectroscopic time series obtained at Tartu Observatory, complemented by high-cadence, high-resolution spectroscopy from the Hertzsprung SONG telescope and space-based photometry from TESS. We studied line-profile variability using normalised moments of the HeI 6678, HeI 5875, and SiIII 4552 lines. Periodic signals were identified using the generalised Lomb-Scargle periodogram with iterative pre-whitening, and their temporal stability was examined with the weighted wavelet Z-transform. We detect a persistent periodic signal at P = 16.46 d in the first and third moments, present throughout the full observing interval, with a radial-velocity amplitude of 3.9 km/s. This signal is also present in the SONG data and is visible in multiple spectral lines, indicating a global origin. Photometric observations reveal a dominant variability timescale near 33 d, approximately twice the spectroscopic period. The stable 16.46-day period, present throughout the entire observing interval, most likely results from non-radial pulsations of the supergiant. A binary origin of the signal is not excluded, but distinguishing between these scenarios is complicated by the supergiant's complex variability pattern.

We present space-based follow-up observations of the superluminous Type I supernova (SLSN-I) SN 2025wny at redshift $z_{SN}=2.0151$, gravitationally lensed by two galaxies at redshifts $z_{G1}=0.3755$ and $z_{G2}=0.3766$ into five resolved images. SN 2025wny is the first strongly lensed SLSN discovered and the first galaxy-scale lensed supernova for which both photometric and spectroscopic time-delay measurements are feasible. As such, it opens a new observational window for precision cosmology and the study of stellar explosions near the epoch of peak cosmic star formation. Our follow-up observations comprise two epochs of Hubble Space Telescope (HST) imaging, together with near-infrared imaging and spectroscopy obtained with the James Webb Space Telescope (JWST). From these data, we measure precise astrometry and multi-band photometry for the five resolved supernova images, the host galaxy, and the two deflecting galaxies. HST provides accurate relative image positions and rest-frame ultraviolet photometry, while JWST delivers complementary near-infrared imaging and spectroscopy probing the rest-frame optical at high signal-to-noise ratio. Together they yield a detailed characterization of both the lensing configuration and the supernova spectral energy distribution over a broad wavelength range. The data presented here provide the observational foundation for the accompanying analyses of the supernova properties, lens modeling, and time-delay cosmography, including the astrometric, photometric, and spectroscopic information required to measure $H_0$.

In-ice radio detectors have been developed primarily for the detection of high-energy neutrinos via the Askaryan effect, but have recently been shown to also be sensitive to cosmic ray air showers impacting the ice sheet. Using CORSIKA 8 to simulate impacting air showers, we find that the lateral width of the in-ice cascade is sensitive to the atomic mass of the primary cosmic ray. The width of the shower core is accessible through the shape of the Askaryan radio spectrum, while the amplitude encodes the total in-ice charge excess. Using these two observables, we show that in-ice radio detectors can be used to measure cosmic ray mass composition in the region above $10^{17}$eV, if the in-ice receivers are placed to adequately sample the Askaryan emission pattern. We also show that the in-ice core width is highly, but not exactly, correlated with the depth of maximum particle count ($\mathrm{X}_{\mathrm{max}}$), the most commonly-used observable for reconstructing cosmic ray mass composition.

X-ray absorption variability in active galactic nuclei (AGN) provides key constraints on the structure and dynamics of the circumnuclear obscuring medium, the so-called torus. A fraction of nearby AGN, however, have been classified as nonvariable in line-of-sight (LoS) column density based on limited temporal coverage. We present the first systematic study of a sample of 11 local (z &lt;= 0.1) obscured (N<SUB>H</SUB> &gt;= 10<SUP>22</SUP> cm<SUP>-2</SUP>) AGN, initially classified as nonvariable. The sample is selected from the Swift Burst Alert Telescope (Swift-BAT) 100-month catalog and comprises 60 observations from Chandra, XMM-Newton, and NuSTAR, spanning timescales from days to nearly two decades. We simultaneously model all available spectra for each source adopting physically motivated torus models: X-skirtor, RXTorusD, and UXCLUMPY. This approach allows us to derive the global properties of the obscurer while tracking possible epoch-to-epoch variations in the LoS column density and intrinsic X-ray emission. We find that the original nonvariable classification (based on only two X-ray observations) is frequently not robust: Clear N<SUB>H,LoS</SUB> variability is detected in half of the sample, whereas 7 out of 10 AGN require intrinsic flux variability, with the rest showing flux--N<SUB>H,LoS</SUB> degeneracies. We also find that the probability of identifying absorption variability increases with the number of observations, and the largest column density changes preferentially occur on long timescales, consistent with absorption by extended, structured clouds on torus scales. These findings support a clumpy and dynamic obscuring medium as a common feature of nearby AGN and highlight the importance of long-term X-ray monitoring for accurately characterizing AGN obscuration.

Gravity waves in the upper mesosphere produce diverse spatial patterns in nighttime airglow, but their global morphology has been difficult to characterize because manual identification is impractical for the massive satellite image archive. We developed a machine learning framework to detect and classify gravity wave events in imagery from the Visible Infrared Imaging Radiometer Suite Day/Night Band (VIIRS DNB) on three satellites. A machine learning based object detector called YOLOv8 (You Only Look Once, version 8) was trained to identify four airglow morphological classes: concentric gravity waves, frontal waves, ripples, and other gravity wave events. On an independent test set, the model achieved a mean average precision of 0.832 at an intersection over union threshold of 0.3. At the confidence threshold adopted for catalog generation, the mean precision and recall were 0.828 and 0.778, respectively. The trained detector was applied to 12 years of moon--free VIIRS DNB observations from Suomi National Polar--orbiting Partnership, NOAA--20, and NOAA--21, resulting in an event catalog containing more than 100,000 detected wave event instances from more than 65,000 images with positive detections, which was archived in a public repository. The catalog captures physically plausible large--scale gravity wave occurrence patterns while also showing that detectability is reduced under elevated sensor noise and strong artificial light contamination. These results demonstrate that machine learning based object detection can systematically extract diverse mesospheric gravity wave events from the long--term VIIRS DNB nightglow record.

Doppler frequency shifts (DFSs) recorded by continuous wave--high frequency Doppler sounding systems and ionograms observed by five ionosondes in Taiwan and Japan are used to study three--dimensionally seismo-- and tsunami--traveling ionospheric disturbances (STIDs and TTIDs) triggered by the 29 July 2025 Mw8.8 Kamchatka earthquake. Prominent STIDs in DFSs travel horizontally with the supersonic speed of 3.7 km/s, the period of 20 s, and the wavelength of 74 km, and vertically upward with the speed of sound, the period of about 40 s, and the wavelength of about 16 km. TTIDs consist of infrasonic and/or acoustic--gravity waves, which make vertical phase speed and period difficult to estimate, whereas TTIDs travel horizontally close to the tsunami wave speed of about 200 m/s. Results show that the associated STIDs and TTIDs in DFSs are tens of thousands of times larger than the vertical fluctuations of seismic and tsunami waves on the ground.

We explore how perturbations of a Schwarzschild black hole can redistribute energy among scalar modes and seed turbulent-like cascades. We make use of the van der Pol-Krylov-Bogoliubov averaging method and derive coupled mode equations that describe near-resonant interactions between neighboring multipoles. We compare two routes to instability, namely the difference-frequency mixing between adjacent modes and the diagonal (Mathieu) self-modulation channel. We show that, at high multipole number (eikonal limit), the difference-frequency route dominates and drives a one-way cascade from higher to lower frequencies. We chart the corresponding instability regions (``tongues'') and quantify their detuning dependence. The framework provides a simple, quantitative mechanism for energy transfer in black hole ringdowns and clarifies when and how turbulent signatures can arise within linear probes on a weakly perturbed background.

We model and constrain the unique indirect detection signature produced by dark matter particles that annihilate through a U(1) gauge symmetry into dark photons that subsequently decay into three-photon final states. We focus on scenarios where the dark photon is long-lived, and show that γ-ray probes of celestial objects can set strong constraints on the dark matter/baryon scattering cross section that in many cases surpass the power of current direct detection constraints, and in some cases even peer into the neutrino fog.

We present a mechanism for gravitational wave (GW) production from isocurvature perturbations in spectator scalar fields during inflation. These energetically subdominant fields develop blue-tilted power spectra through inflationary dynamics, generating second-order scalar perturbations that source a stochastic GW background. The mechanism naturally satisfies CMB constraints at large scales while producing enhanced signals at smaller scales across a broad frequency range 10<SUP>-20</SUP>--1 Hz. We perform comprehensive numerical and analytical calculations of the complete isocurvature spectrum evolution, including gravitational particle production, reheating dynamics, and scalar-induced GW generation. For spectator fields with effective masses 0.5 ≲ m <SUB> χ,eff</SUB>/H<SUB>I</SUB> , the resulting GW energy density reaches Ω<SUB>GW</SUB> h <SUP>2</SUP> ~ 10<SUP>-19</SUP>--10<SUP>-14</SUP>, accessible to pulsar timing arrays, space-based interferometers, and next-generation CMB experiments. Our analysis reveals that GW-induced constraints exceed current isocurvature bounds. We examine both unstable (curvaton-like) and stable (dark matter) spectator fields, demonstrating strong sensitivity to reheating temperature, inflaton-spectator coupling, and decay dynamics. This framework establishes isocurvature-sourced GWs as a powerful probe of early universe physics, enabling simultaneous constraints on inflationary dynamics, dark matter production, and reheating through coordinated multi-frequency GW observations.

We solve analytically the long-term octupole evolution of librating Kozai-Lidov cycles - those with a negative Kozai constant, in which the argument of pericenter librates - in the double-averaged restricted hierarchical three-body problem. Librating cycles reach extreme eccentricities when the normal component of the orbital angular momentum vanishes, as rotating cycles do, but their slow dynamics was left unsolved: the azimuth of the eccentricity vector jumps by half a turn every cycle, so the leading-order octupole kick alternates in sign and cancels pairwise. We show that the surviving dynamics, at second order in the octupole strength, is a simple pendulum with explicit coefficients. The pendulum predicts slow oscillations of the normal angular momentum with amplitude linear in the octupole strength, evolving on a timescale of order the secular timescale divided by the octupole strength, together with an explicit criterion for orbital flips. At octupole strengths typical of hierarchical triples, these amplitudes are comparable to - and in part of the librating window can exceed - those of rotating cycles, provided one waits the longer timescale. The analytic model agrees with numerical integrations of the double-averaged equations across the librating window, for systems ranging from hot-Jupiter formation to gravitational-wave sources.

We present a comprehensive characterisation of the La Paz Southern Sky Survey, a collection of 915 photographic plates obtained in La Paz, Bolivia, between 1926 and 1929 by the German Bolivia astronomical expedition under the auspices of the Astrophysical Observatory Potsdam. The survey covers 91 Kapteyn Selected Areas south of declination −24° and records an estimated 50,000─60,000 individual stellar spectra in low-dispersion objective-prism mode, the large majority of which have never been individually examined or classified. We provide a detailed description of the historical and instrumental background of the survey, the characteristics of the three plate series, and the ongoing digitisation programme at Sonneberg Observatory, which to date has produced high-resolution TIFF scans of 168 Series 1 (single-prism) plates. The single-prism plates have a mean spectral dispersion of ∼18 nm mm<SUP>−1</SUP> and record spectra over the wavelength range (∼3400─6900 Å; 340─690 nm) with a mean photographic limiting magnitude of approximately 11.8 mag for spectral classification. Cross-matching of seven survey fields against the Wray emission-line catalogue and the Strasbourg─ESO Catalogue of Galactic Planetary Nebulae identifies 15 known emission-line objects and at least one planetary nebula within SA 156 (Ophiuchus/Scorpius), and 43 known emission-line objects and at least three planetary nebulae within SA 173 (Vela/Carina) fields for which digitised La Paz plates are available at Sonneberg Observatory. These cross-matches establish the presence of independently confirmed emission-line sources on the digitised plates and define the priority targets for forthcoming pipeline validation. As a first identification step, all 19 Wray objects brighter than approximately 12 mag in SA 173 have been individually located on a single digitised Series 1 plate (plate 60066), using the brighter field stars as positional references, and finder charts have been produced for each object. Visual inspection of the spectral crops reveals candidate emission features in four of the identified objects, the emission-line star CD−44 5201 (= Wray 15-338 = Hen 3-252) and the variable stars S Vel, RS Vel, and RW Vel, pending quantitative confirmation from the full-resolution scans. A computational pipeline for automated emission-line detection is under development; spectroscopic recovery of these known targets and full quantitative performance evaluation will be the subject of a forthcoming publication. The La Paz archive represents a unique temporal resource: its ∼1926─1929 observational epoch provides a ∼100 yr baseline relative to contemporary spectroscopy that is inaccessible to any ongoing survey. *Pipeline code and notebook publicly available at https://github.com/tauseef1417/La-Paz-Southern-Sky-Survey-Emission-Line-Object-Pipeline

We study gravitational lensing by <inline-formula><mml:math><mml:semantics><mml:mrow><mml:mi>k</mml:mi><mml:mo>-</mml:mo><mml:mi>n</mml:mi></mml:mrow></mml:semantics></mml:math></inline-formula> generalized black-bounce space-times both in regimes of weak and strong field approximations. These metrics interpolate between regular black holes and one-way or traversable wormholes. First, we investigate the light-like geodesic trajectories and derive an analytical expression for the deflection angle in terms of the bounce parameter in the weak-field gravitational regime. We then turn to the strong-field gravitational regime and display the behavior of the bending angle as a function of both the impact parameter and the bounce parameter. Next, using the lens equations, we analyze how the observables for Sagittarius A* behave concerning the bounce parameter. We obtain the shadow's radii for some black-bounce metrics and plot the graph of their sizes, comparing them with the Schwarzschild one.

We propose a new approach to axion-like particle (ALP) searches based on long, coiled optical fibers in an external magnetic field. We develop the theoretical framework required to describe photon-ALP conversion in this geometry by incorporating transverse boundary conditions and fiber bending. For solid silica fibers with refractive index considerably larger than unity, we show that the leading signal is a phase shift of the photon, with negligible loss due to ALP production. This setup has the potential to set new constraints in the regime of large ALP mass. We further identify parameter regions in which boundary effects become important, in particular for hollow-core fibers, where signals due to ALPs can be significantly enhanced.

Massive cryogenic calorimeters read out by transition-edge sensors (TES) can reach eV-scale baseline resolution, but the single-channel dc-SQUID readout conventionally used in rare-event searches, with one amplifier chain and several wires per detector, limits practical arrays to a few tens of channels. We propose to apply microwave SQUID multiplexing ($μ$MUX), developed for fast X-ray and neutrino-mass microcalorimeters, to massive BGO (Bi$_4$Ge$_3$O$_{12}$) calorimeters operated at $\simeq 20$~mK; sapphire and TeO$_2$ absorbers are covered by the same framework. Using the established thermal and noise model for massive TES calorimeters, we derive a noise model for the multiplexed readout, including the HEMT, two-level-system and SQUID contributions, and its scaling with the multiplexing factor $N_{\rm mux}$. Since the slow thermal signals require only about a kHz of sampling per channel, the limiting requirement is not bandwidth but an input-coil sensitivity of $( 0.1$ to $1)\,μ$A$/Φ_0$, a factor of $10$ to $30$ beyond current $μ$MUX devices, matched to the detector current noise of ($9$ to $10$)~pA$/\sqrt{\rm Hz}$, which is independent of the absorber mass. With a total flux noise of $\simeq$$1.2\,μΦ_0/\sqrt{\rm Hz}$, the readout degrades the baseline resolution by less than $2\%$ up to $N_{\rm mux}=1000$, negligible compared with the TES-limited resolution. These results are implemented in a single-tower design: 52 BGO crystals of 100~g each and one HEMT amplifier. The tower is the unit of a multi-tower array of several kilograms aimed at CE$ν$NS and dark matter searches.

We propose boundary theories, CFT$_{p}$ with $p\in β\mathbb{N}/\mathbb{N}$, which can be interpreted as an ensemble of theories in the context of AdS/CFT duality, when the boundary spacetime dimension is more than one. These theories are only emergent in the infinite $N$ limit of the boundary CFT and depend on $p$, which corresponds to the different ways one can take a generalized form of the infinite $N$ limit, in the presence of a chaotic or an oscillatory operator. This generalized infinite $N$ limit is called an \emph{ultralimit}, and $p$ is a \emph{free ultrafilter} on $\mathbb{N}$. We propose that the gravitational path integral computes an average of CFT$_{p}$ in each of its sectors; and in the appropriate cases, it produces baby universes and spacetime wormholes. We apply this proposal to the Antonini-Sasieta-Swingle (AS$^{2}$) like states.

Time-delay cosmography offers a one-step, distance-ladder-independent route to the Hubble-Lemaitre constant, H_0. We present new cosmography-grade lens models of three quadruply imaged quasars based on JWST-NIRCam/F115W imaging (WFI2033-4723, HE0435-1223, PG1115+080). We use the STARRED modeling technique, introduced in our previous analysis of WFI2033-4723, to reconstruct the complex JWST-NIRCam Point Spread Function at high fidelity. We combine NIRCam-based lens models with improved external convergence estimates, published time delays, and aperture-integrated stellar velocity dispersions from JWST NIRSpec to infer H_0. The analysis was carried out blindly for HE0435-1223 and PG1115+080, while it was not blind for WFI2033-4723, as we build upon the previous published model. For comparison with previous HST-based work, we limit our analysis to the case of no internal mass-sheet degeneracy ($λ_{\rm int}=1$). We quantify the impact of improved imaging, single-aperture kinematics, and environment measurements on central values and uncertainties. Within flat $Λ$CDM, assuming a uniform prior on $Ω_{\rm m}$, we find H_0 = 71.8$_{-7.0}^{+9.2}$ $λ_{\rm int}$ km s$^{-1}$ Mpc$^{-1}$ for PG1115+080, 74.2$_{-4.2}^{+4.2}$ $λ_{\rm int}$ km s$^{-1}$ Mpc$^{-1}$ for HE0435-1223, and 73.4$_{-4.4}^{+3.4}$ $λ_{\rm int}$ km s$^{-1}$ Mpc$^{-1}$ for WFI2033-4723. Combining the three lenses yields H_0 = 73.5$_{-2.8}^{+2.7}$ $λ_{\rm int}$ km s$^{-1}$ Mpc$^{-1}$, consistent with HST-based results (73.6$_{-2.6}^{+2.6}$ $λ_{\rm int}$ km s$^{-1}$ Mpc$^{-1}$), but with reduced scatter between the three systems. These models will be incorporated in the TDCOSMO-2026 milestone paper with free $λ_{\rm int}$ in a hierarchical fashion. We close by outlining how 16 forthcoming JWST NIRCam targets will further tighten uncertainties toward percent-level precision on H_0.

The direct measurement of masses and transverse motions of individual stars and compact objects in distant galaxies remains an outstanding challenge, leaving extragalactic stellar populations constrained only through model-dependent population fits. We show that time-resolved intensity interferometry of strongly lensed quasars, combined with flux-ratio photometry, can break the source-size, microlens-mass, and transverse-velocity degeneracies of conventional light-curve microlensing. Using the quadruply lensed quasar B1422+231 as a fiducial system and a next-generation interferometer ($\sim$800\,m$^2$ collecting area, spectral resolving power of 20,000, and few-picosecond timing), we forecast the precision on the quasar source size and on the mass, position, and transverse motion of an individual stellar-mass microlens in the lens galaxy. A single epoch determines the accretion disk size to $4\%$ in favorable geometries ($10\%$ for a typical detectable configuration) and the microlens mass to order unity for $m_l \gtrsim 0.1\,M_\odot$. An eight-year, 33-epoch campaign reaches $\lesssim1\%$ on the disk size, localizes the microlens' impact parameter to $\sim0.1$-$0.5,μ\mathrm{as}$, and resolves its proper motion. Such observations would enable direct measurements of individual extragalactic compact-object masses and transverse motions at moderate redshift. They also yield sub-$μ\mathrm{as}\,\mathrm{yr}^{-2}$ sensitivity to light-centroid acceleration, which can help separate stellar microlensing from dark matter substructure lensing, the subject of a companion paper.

We compute high frequency gravitational wave radiation in shockwave collisions of a light mass compact object with energy $μ_L$ off a heavy compact object (black hole) with energy $μ_H \gg μ_L$. A formal solution is obtained in terms of shockwave propagators that provide snapshots of $O(μ_Lμ_H^n)$ tidal response functions sensitive to classical and potentially semi-classical dynamics of black hole formation. In a perturbative expansion, the first nontrivial contribution of $O(μ_Lμ_H)$ is the emission of a graviton from the Lipatov vertex generated by the fusion of two reggeized gravitons. For graviton frequencies $ω\rightarrow 0$, the Lipatov amplitude reduces to the ultrarelativistic limit of the single-graviton exchange Weinberg amplitude. At $O(μ_Lμ_H^2)$, the Lipatov amplitude includes a piece accounting for the rescattering of the graviton off a reggeized graviton and another, corresponding to graviton emission from a vertex fusing three reggeized gravitons. These nontrivial contributions again simplify to the Weinberg radiative amplitude for two-graviton exchange in the soft limit. We highlight throughout double copy structures to gluon radiation in dilute-dense collisions of Yang-Mills shockwaves. We relate our shockwave results to the eikonal multiple scattering framework of Veneziano et al.

We consider that the very early Universe was well described by an Emergent Universe, whose geometry was that of a static and classically stable Einstein Universe, which is possible in certain Two Measures Theories (TMT). These solutions do not have a big bang, but rather they extend to arbitrarily early times. The TMT we consider are theories with spontaneously broken scale invariance and contain a dilaton field, crucial for the implementation of the scale invariance, that after the symmetry breaking acquires a nontrivial effective potential, which we study in the Einstein frame. Using the conserved quantity associated with the dilaton, we recast the cosmological evolution in terms of an effective potential $V(\dotφ)$, which exhibits a divergent barrier separating the static solution from the subsequent expanding evolution. Quantizing the corresponding minisuperspace Hamiltonian, we evaluate the tunneling probability in the WKB approximation. The tunneling action is well defined and finite once the branch of the square root is fixed by requiring a consistent semiclassical interpretation of the tunneling probability. We find that the barrier gives rise to a logarithmic contribution to the tunneling exponent, yielding a power-law rather than the usual exponential dependence of the tunneling probability, which for the parameter values considered is close to unity. The Universe thus emerges with a finite scale factor into a superinflationary phase that develops into slow-roll inflation. This quantum creation of an inflationary Universe does not represent a quantum creation of spacetime, which exists before the tunneling.

This study continues our ongoing research on contact binary systems by presenting a detailed analysis of 10 targets. Ground-based observations from six different observatories were conducted and used together with TESS data for the analysis process. Photometric data from our observations were reduced with the recently developed AutoWISP pipeline, yielding high-quality light curves with reliable precision for analysis. An investigation of orbital period variations identifies long-term trends in six of the ten analyzed binaries, including three that also display cyclic variations. Four targets show essentially constant orbital periods. The secular trends are attributed to mass transfer. The cyclic modulations in three systems are caused by either magnetic activity cycles or the Light-Travel Time Effect (LTTE) of a third body, while that in the remaining system is solely due to the LTTE. The BSN application was used to model the photometric light curves of the 10 target binaries. Iterative fitting and MCMC refinement provided robust estimates of the system parameters, while starspot modeling was applied for systems showing O'Connell-effect asymmetries. We refine the empirical orbital period-mass relationship for short-period contact binaries by analyzing a homogeneous dataset of systems and deriving an updated primary-mass calibration based on the spectroscopic subset. Using this calibrated relation, the fundamental parameters of the studied systems were subsequently estimated.

In an optically thin setting, gravitational lensing around a black hole creates multiple delayed images of any localized source, appearing at different positions on the observer's screen. Even if particular sources cannot be singled out, this effect may be revealed in a black-hole movie (time-dependent image) by examining the two-point spatiotemporal correlation function of intensity fluctuations in the movie. Recently, the correlation function derived from a movie obtained by ray tracing of a general-relativistic magnetohydrodynamic simulation demonstrated the plausibility of this idea, even when the movie was blurred to angular resolutions corresponding to next-generation terrestrial very-long-baseline interferometric arrays. In this work, we further develop this method and study how some possible corruptions of the movie, motivated by real observational limitations, affect the ability to identify the extreme-lensing signatures by correlations. The effects are compared for both the original and blurred movies. We discuss the implications of our analysis for upcoming observations of M87* and Sgr A*, the two main targets of the Event Horizon Telescope and its future extensions. Our case study suggests that the types of data corruption we have explored, in themselves, do not preclude an identification of extreme-lensing effects in correlation measurements. We use our results to roughly estimate that, most importantly, for a successful correlation measurement, M87* may need to be continuously monitored for $\gtrsim 2$ years, while Sgr A* may need to be measured at a cadence $\gtrsim 1$ frame per minute. Finally, we outline a new analysis method that reduces the data in the complete correlation function---a large dataset defined on a five-dimensional configuration space---to a two-dimensional histogram that could be useful for black-hole parameter inference.

We construct regular, spherically symmetric, compact energy-cutoff equilibria for gravitational Vlasov--Poisson systems sourced by positive and negative mass distributions in the context of stellar dynamics. Motivated by Bondi's notion of negative mass and its relation to the weak field limit of Einstein gravity with a signed mass--energy source, we show that the internal structure of the steady states depends qualitatively on the type of negative mass present. In the Bondi convention, the signs of inertial, passive gravitational, and active gravitational mass are reversed together, preserving the equivalence principle. The resulting equilibria consist of a central overlap core containing both mass species, surrounded by a finite positive mass shell and an exterior vacuum. Thus, although a pure Bondi negative mass gas cannot form a compact steady state, Bondi negative mass can be spatially confined by a suitable positive mass distribution. In the gravitational-charge convention, only the passive and active gravitational masses change sign, so that the two species obey opposite free-fall laws and unlike masses repel. The resulting equilibria are spatially segregated into a negative mass core, a vacuum gap, a positive mass shell, and an exterior vacuum. For cutoff exponent $n=-1/2$, the radial matching is explicit, while for the regular cutoff $n=1/2$ the matter regions satisfy Lane--Emden-type equations. These results provide a kinetic framework for investigating the distribution of negative mass in astrophysical and cosmological settings.

In this work, we investigate whether machine learning can be used to infer averaged cosmological quantities directly from the present day matter density distribution. Using an implementation of the simplified silent universe framework, we generate a dataset consisting of 92610 independent relativistic, simplified cosmological simulations spanning a range of initial conditions and average cosmological parameters. We train a convolutional neural network to take the present-time matter density field as input and predict the averaged matter, cosmological constant, curvature, and kinematical backreaction density parameters as well as the Hubble parameter, at both initial and present time. The network achieves coefficients of determination exceeding 0.9 for all predicted quantities, with error distributions showing that only a small fraction of predictions reach percent-level errors or above. Although our use of the simplified silent universe approximation precludes direct application of the trained model to observational data, the results provide a proof-of-principle that neural networks can successfully recover averaged cosmological properties, including backreaction, at different epochs, simply from the late-time matter distribution. More broadly, our findings demonstrate that information about the averaged cosmological history of a universe is encoded in its present-time density field and can be extracted using machine learning techniques. This opens the possibility of applying similar approaches to more realistic cosmological simulations and observational probes such as N-body simulations and weak-lensing maps, ultimately providing a new avenue for constraining the large-scale evolution of the Universe.

Ultralight scalar fields nonminimally coupled to curvature can endow rotating black holes with stationary hair and alter nearby orbits. Using recently constructed hairy black-hole spacetimes, we model the transition to plunge of an extreme-mass-ratio inspiral. For scalar masses $μM=0.01$ and $0.1$ and dimensionless curvature coupling $ζ=10^{-3},10^{-4}$, we find $\mathcal{O}(10)$ rad of gravitational-wave dephasing relative to general relativity over $\mathcal{O}(10^3)$ orbits. A multimode Fisher forecast at $μM=0.2$, where neighbouring hair solutions permit a numerical $μ$-derivative, suggests that $ζ$ and $μ$ could be measured to precisions of $\simeq0.2\%$ and $0.6$--$1.1\%$, respectively, for a source with signal-to-noise ratio of about 80 in LISA.

Contact binaries (CBs) are key systems for investigating the late evolutionary stages that may lead to stellar coalescence. Systems with an extremely low mass ratio and high fill-out factor are of particular interest as potential merger candidates and possible progenitors of luminous red novae. A combined photometric and spectroscopic study of the CB systems AL Lep, ASAS J082243+1927.0, and ZZ PsA is presented. The aim is to derive self-consistent orbital and physical parameters, assess their evolutionary state, and examine whether they have reached the terminal and unstable phase of their evolution. High-resolution VLT/UVES spectra were analysed to derive radial velocity values, spectroscopic mass ratio, and metallicity. The results were combined with multi-band light-curve modelling within a Monte Carlo framework to determine the system geometries and absolute parameters. Orbital period variations were investigated through O-C analysis, while the evolutionary status of the systems was assessed using the Darwin instability criterion, critical mass ratio estimates, fill-out factor, and orbital period variation. Mass ratio values of q = 0.1332, 0.1041, and 0.0789 were derived for AL Lep, ASAS J082243+1927.0, and ZZ PsA, respectively. The corresponding primary mass values are M1 = 1.656 +/- 0.081 Msun, 1.275 +/- 0.078 Msun, and 1.795 +/- 0.111 Msun. The locations of their components show significant deviations from single-star ZAMS and TAMS reference curves, indicating strong binary interaction and energy redistribution through the common envelope. The spin-to-orbital angular momentum ratio for AL Lep and ASAS J082243+1927.0 remains below the standard Darwin instability threshold, while ZZ PsA lies close to the instability regime and may be consistent with an unstable configuration within the derived uncertainties.

Recent space missions such as Kepler have provided large-scale observations of the γ-Doradus instability strips (IS), which can be used to constrain models and explore their limitations. One persistent limitation is the prediction of the blue edge of the γ- Doradus IS, where a significant number of γ-Doradus stars are observed. Despite these observational advances, no systematic study has been undertaken to explore the effects of different physical processes on the γ-Doradus. Our aim is to systematically explore the theoretical γ-Doradus IS with modern tools, accounting for the effects of rotation and metallicity, providing a large grid of models and their oscillation parameters for the scientific community. We investigated the non-adiabatic pulsation properties of stars in a grid of stellar models with masses between 1.35 M{_\odot} and 2.5 M{_\odot}, metallicities between Z= 0.01 and Z= 0.025, and solid-body rotation rates ranging from Ω = 0 to 0.5 {Ω_{crit}}, where {Ω_{crit}} denotes the critical rotation rate. We find that, across all computations, the theoretical γ-Doradus IS agrees well with the observed IS, except in the extended blue region. In terms of radial orders, our models consistently reproduce the excited modes in broad agreement with observations for l= 1, l= 2, and Rossby modes. We also show that the range of excited radial orders is strongly dependent on the effective temperature. The range of excited radial orders can be used to constrain the position of a star within the γ-Doradus IS and may provide insights into the physical mechanisms responsible for the discrepancies observed in the blue region. All computed grids are made available and include mode damping and growth rates for γ-Doradus stars, obtained with a time-dependent treatment of the convection-oscillation interaction.

The Canadian Galactic Emission Mapper (CGEM) radio telescope is mapping polarized Galactic foregrounds from 8-10 GHz to aid in the search for B-modes in the Cosmic Microwave Background (CMB). Here we describe the design and early on-sky characterization of the CGEM optics. CGEM employs an on-axis, hat feed optical design that is a body of revolution (BOR) and exhibits excellent intrinsic polarization purity. We describe how we have optimized the optics with a novel framework that can directly minimize simulated intensity to polarized intensity ($T\rightarrow P$) leakage in angular power spectrum space. The optimized optics exhibit simulated $T\rightarrow P$ leakage that is orders of magnitude below anticipated $C_\ell^{BB}$ for $r = 10^{-3}$ when scaled from 8-10 GHz to the CMB observing window near 95 GHz. We go on to describe the mechanical design of the optics, including a novel secondary mirror support made from Astroquartz composite that has low loss, low dielectric constant, and preserves the BOR symmetry of the optics. We then showcase the early on-sky performance of the optics with observations of the Sun and satellites, which probe the beam to 40 dB down from the peak. A beam model for the deployed CGEM optics based on electromagnetic simulations is in excellent agreement with the on-sky data.

We investigate black hole shadows and photon sphere properties for two families of covariant quantum-corrected black-hole metrics (hereafter called BH-I and BH-II) formulated within a general $μ$-scheme, parameterised by a power-law exponent $s$ and an amplitude $ξ$. The extension to general (including non-integer) $s$ is a phenomenological interpolation between the $μ_0$-scheme ($s=0$) and $\barμ$-scheme ($s=1$) and reveals a rich phenomenology masked when $s$ is usually fixed to 1 in previous literature. For BH-I, the photon sphere exists for all parameter values and exhibits an exact cancellation at $s=1$ where the coordinate location $r_{\rm ph}=3M$ is restored for any $ξ$. For BH-II, both the horizon and the photon sphere exhibit critical curves in the $(ξ,s)$ parameter plane; the photon sphere disappears when $ξ$ exceeds a closed-form critical value $ξ_c^{\rm PS}(s)$. We prove analytically that the photon sphere is always unstable ($λ_{\rm ph}>0$) throughout the physical parameter space of both metrics, and derive closed-form expressions for the Lyapunov exponent. Systematic parameter scans reveal that for fixed $ξ$ the shadow radius decreases monotonically with $s$ for BH-II and non-monotonically for BH-I. We derive small-parameter analytic expansions for the photon-sphere radius, shadow radius, and Lyapunov exponent, and demonstrate that a single shadow measurement suffers an observational degeneracy in the two-dimensional $(ξ,s)$ space; the degeneracy can be broken by a simultaneous measurement of the Lyapunov exponent. Using Event Horizon Telescope (EHT) measurements, we derive constraints on the $(ξ,s)$ parameter space and find that BH-II is constrained roughly $2$--$4$ times more tightly than BH-I.

A small fraction of A-type stars host strong fossil magnetic fields. Identifying them relies on indirect indicators such as chemical peculiarities, slow rotation, and rotational modulation, which are also shared by non-magnetic stars. Assessing their reliability is essential for future surveys. We magnetically characterise seven slowly rotating, chemically peculiar A-type stars selected through two complementary strategies. Three were selected from abundance analysis combined with potential intrinsically slow rotation, and four from a spectral depression at 5200 Angstrom combined with rotational modulation in TESS photometry. We obtained high-resolution spectropolarimetry, applied least squares deconvolution, and measured longitudinal field strengths for detections. For non-detections, we derived upper limits on polar field strength and evaluated the critical fields of Zahn and Spruit. We detect magnetic fields in all four stars selected via the spectral depression and photometric criterion, with longitudinal field strengths of approximately 145-2900 G, while none of the three stars selected via abundance and slow rotation shows a Zeeman signature. Combined upper limits for two non-detections lie below or near the magnetic desert boundary, but only one is also below the critical fields required for rigid rotation. The non-detections are most naturally interpreted as Am stars. Among the detections, HD 63843 stands out as a magnetic $δ$ Scuti pulsator, promising for magneto-asteroseismology. In conclusion, slow rotation combined with chemical peculiarity alone does not reliably trace large scale magnetic fields, whereas adding the 5200 Angstrom depression and stable rotational modulation in space photometry appears to select magnetic A-type stars with high efficiency, providing a practical guideline for future spectropolarimetric surveys.

In cosmology, the Hubble tension has become one of the most serious challenges in the last decade. Assuming that all the observational data are right, one of the ways out is to modify the standard $Λ$CDM cosmology. In the literature, the theoretical modifications are mainly made in the early and the late/local universes. But on both sides, some no-go arguments have been proposed recently. In particular, the general no-go arguments for the late-time modifications are mainly based on the PAge parameterization. In the present work, we note that there are some flaws in the (original) PAge parameterization, and then propose various generalized PAge (GPAge) parameterizations, which can be extended to $z>z_{\rm CMB}$ and hence the cosmic microwave background (CMB) can be taken into account, while they are also more accurate at low redshifts. With these GPAge parameterizations, we revisit the Hubble tension by using not only the late-time observations but also the observational data of CMB. We find that the Hubble tension could be alleviated (or even resolved) in GPAges significantly different from the standard $Λ$CDM cosmology, while they are overwhelmingly preferred over $Λ$CDM by the observational data in terms of all the information criteria. Surprisingly, we find that the new physics in the mid-time might be the key to resolve the Hubble tension.

Understanding the role of internal magnetic fields in stars remains a major challenge for the description of angular momentum transport and stellar evolution. It is therefore essential to probe these magnetic fields within the star, and asteroseismology provides a powerful means to do so. In this work, we present a new implementation of the 2D oscillation code ( ), which incorporates the effects of both stellar rotation and magnetic fields. Adaptive Code of Oscillations towards Realistic modeling The code has been rendered modular, making it possible to specify the set of equations to solve and the assumptions through a symbolic calculus approach. The full set of adiabatic, non-radial pulsation equations is solved using a spectral approach for the angular part of the modes and high-order finite differences for the radial part. As a first step, we focus on a magnetic field that is purely toroidal and axisymmetric about the star's rotation axis. The numerical results are compared against first-order perturbative predictions in the weak-field regime and with the traditional approximation of rotation and magnetism (TARM) in the case of stronger magnetic fields. We validate this new implementation of against perturbative and TARM approaches, showing good agreement and demonstrating the robustness of the code. The breakdown of these methods provides general validity limits. We show that internal magnetic fields leave signatures in the period spacing of g modes. These features provide a promising seismic diagnostic to probe deep stellar magnetism in γ Dor stars. Future work will aim to extend this framework to more realistic magnetic field topologies and a broader range of pulsating stars, including red giants.

Earth is surrounded by two highly dynamic concentric belts of particle radiation. The outer radiation belt exhibits coherent variability at solar-cycle, seasonal, and 27-day (Carrington) timescales. While the solar-cycle and Carrington variations have been attributed to the recurrence of coronal hole solar wind, the seasonal variation has long been explained by local geometric effects that modulate the solar wind-magnetosphere coupling. Here, we challenge this paradigm by showing that the periodic recurrence of coronal hole solar wind likewise drives the seasonal variation. We further demonstrate that the Alfvénic nature of this solar wind is responsible for the observed electron flux enhancement in the outer radiation belt. These findings provide a unifying framework linking solar magnetic topology, solar wind properties, and magnetospheric dynamics across multiple timescales at Earth and beyond.

Extragalactic foregrounds contaminate cosmic microwave background (CMB) temperature maps at small angular scales and limit their utility for precision cosmology. The internal linear combination (ILC) is a well-known technique for suppressing these contaminants, but residual foreground power remains a limiting factor. Kusiak et al. (2023) proposed adding galaxy number-density maps as additional ILC channels, exploiting their correlation with the large-scale structure sourcing these foregrounds to suppress contamination. Here we apply this framework to forecast the gains in CMB-based cosmological parameter constraints from near- and next-generation experiments. Using a halo-model foreground pipeline and a Fisher forecast from joint TT+TE+EE power spectra, we quantify the improvement from galaxy-tracer-assisted ILC cleaning across three configurations: enhanced Simons Observatory (SO) with unWISE or Rubin-like galaxy catalogs, and a futuristic CMB-HD configuration with a hypothetical deep galaxy survey. We find that adding galaxy tracers reduces the residual foreground power in the cleaned temperature map by $\sim4\%$, $\sim22\%$, and $\sim32\%$ at $\ell\sim10,000$ for the unWISE, Rubin-like, and futuristic samples, respectively. For the overall variance of the cleaned map at $\ell\sim10,000$, it provides $8\%$, $24\%$, and $17\%$ improvements for each combination. The resulting reduction in marginalized parameter error bars is modest for the base six-parameter $Λ$CDM model: sub-percent for SO+unWISE, rising to $\sim2\%$ for SO+Rubin-like tracer. Including the effective number of relativistic species $N_{\rm eff}$, we find at most $2.2\%$ improvements for both SO+Rubin-like and CMB-HD+Futuristic tracer. These results establish the expected gains from combining near-term CMB experiments with current and forthcoming large-scale-structure surveys.

We performed a deep study of the open cluster Trumpler 11, located in the southwestern region of the Carina Nebula, using Gemini South GMOS spectroscopy in multi-object mode. We determined the physical parameters and spectral type of 24 late B-type stars, characterized the reddening across the cluster field, and obtained accurate estimates of the cluster's distance and age. This spectroscopic analysis was complemented with {\sl GAIA DR3} photometry and {\sl TESS} light curves. By comparing the properties and evolutionary status of Trumpler 11 with those of nearby open clusters, we explored the large-scale structure and star- formation history of the Carina-Sagittarius arm.

The warm, swift Gulf Stream (GS) plays a key role in shaping weather and climate patterns across the North Atlantic. Using 31--year (1993--2023) of continuous satellite altimeter observations, we identify a pronounced intensification of the free--flowing GS after its separation from the coast beginning around 2014 and persisting thereafter, following a prolonged period (2005--2014) of weaker transport. This intensification coincides with a northward displacement and reduced meandering of the GS path, which appears to be linked to a spin--up of the North Atlantic subtropical gyre. This gyre acceleration is largely driven by an increase in the negative wind stress curl, partially modulated by the two leading modes of atmospheric variability in the region: the North Atlantic Oscillation and the East Atlantic Pattern. Our analysis also suggests that GS intensification may have a local air--sea feedback leading to anomalous wind stress curl.

Lidar observations above McMurdo, Antarctica from 2011 to 2024 are used to characterize gravity wave (GWs) potential energies (${E}_{p}$) in the mesosphere and lower thermosphere (MLT). Alongside characterizations in the middle atmosphere (30--70 km), the GW baselines show dissipation at all altitudes from 30 to 110 km. Stronger dissipation occurs for GWs with shorter ${\lambda }_{z}$ and in regions of lower ${N}_{B}^{2}$, likely driven by convective and shear instabilities, critical level filtering, and viscous damping. Energy baselines are then used to estimate the diffusion--like transport of constituents and heat induced by non--breaking GWs. The corresponding wave--induced constituent and thermal diffusivities ${K}_{\mathrm{W}\mathrm{a}\mathrm{v}\mathrm{e}}$ and ${K}_{H}$ are compared to estimates made at other locations, while this study represents the first such observations in the middle atmosphere. Estimated ${K}_{\mathrm{Wave}}$ and ${K}_{H}$ are up to 1,000 times typical eddy and molecular diffusion values in the middle atmosphere and 10 times typical values in the MLT.

Although half-wave plates (HWPs) are becoming a popular choice of polarization modulators for cosmic microwave background (CMB) experiments, their non-idealities can introduce systematic effects that should be carefully characterized and mitigated. One possible mitigation strategy is to incorporate information about the non-idealities at the map-making level, which helps to reduce the HWP-induced distortions of the reconstructed CMB. Nevertheless, the non-idealities can only be known with finite precision. In this paper we investigate the consequences of discrepancies between their true frequency profiles and those assumed by the map-maker. We present an end-to-end framework, including a blind component-separation step, and use it to translate these discrepancies into a bias on the tensor-to-scalar ratio, r, for the LiteBIRD satellite mission. We subsequently derive realistic and conservative measurement requirements for accurately characterizing the HWP non-idealities to ensure they do not compromise LiteBIRD's ambitious scientific goals. We find that the obtained results are robust against sky models with varying complexity.

On the basis of observations from Sanya incoherent scatter radar (SYISR), we investigated the vertical structures of multiple medium--scale traveling ionospheric disturbances (MSTIDs) over low latitudes on December 28, 2022. Nine MSTIDs were observed to occur continuously during the night (17:18--00:18 LT) at 150--250 km altitude. These MSTIDs are generated by gravity waves (GWs) propagating from the lower atmosphere. Among them, five GWs exhibit periods of 34--49 min and horizontal phase velocities of 148--324 m/s, while the remaining four displayed periods of 17--22 min and horizontal phase velocities of 134--276 m/s. 8 of 9 GWs propagated northwestward with azimuths of 289°--339°, whereas one 4th GW propagated northeastward at an azimuth of 59°. Three--dimensional reconstructions of the multiple MSTIDs reveal phase fronts that initially appeared at higher altitudes and subsequently at lower altitudes, which is consistent with the phase progression of upward--propagating GWs. All GWs exhibit downward vertical phase velocities of 91--265 m/s and amplitudes of ~3%--9%. The vertical and horizontal wavelengths of these GWs increased with altitude, whereas the periods and amplitudes initially increased with altitude, peaked near the bottom of the F layer, and then decreased. This altitudinal variation reflects the dissipative filtering of upward--propagating GWs through viscosity and thermal conduction. Ray--tracing results suggest that the nine MSTIDs likely originated from secondary waves, which were excited by primary waves generated by deep convection.

Thermal tides on Venus have been extensively studied near the cloud tops, where their three--dimensional structure and contribution to the atmospheric momentum budget have been characterized from temperature and wind fields. However, their downward propagation and influence within the deep atmosphere remain uncertain, and their behavior in the deep atmosphere, particularly near the surface, remains poorly constrained. Using the LMD Venus Planetary Climate Model, we investigate the near--surface thermal tides and their governing timescales. The simulations show that these tides are generated by heat transfer from the surface to the planetary boundary layer and produce a diurnal pressure response with a phase lag of about $30{}^{\circ}$ corresponding to a radiative adjustment timescale of about 10 Earth days. In addition, a 35--day oscillation appears within the stably stratified 10--20 km layer, consistent with a planetary--scale internal gravity wave. These results suggest that coherent oscillations beyond the diurnal tide can develop in the deep atmosphere, with the surface pressure variability dominated by a superposition of three modes: the diurnal and semidiurnal tides and the 35--day oscillation. Together, these components account for about 70$\%$ of the total surface pressure variance, with potential implications for gravity measurements by forthcoming missions such as VERITAS and EnVision.

We propose time-domain astrometric weak lensing of multiply imaged quasars as a probe of substellar dark matter (DM) halos. In $Λ$CDM, the photon path of each macro-image traverses numerous microhalos, which collectively produce a stochastic centroid motion with a calculable red power spectrum. Halos whose crossing times exceed the survey time impart a relative angular acceleration between image pairs. The response is strongest for subhalos with sizes of 0.01-1 pc (masses of $10^{-6}$-$1~M_\odot$ in $Λ$CDM), extending lensing sensitivity 12 to 14 orders of magnitude below the smallest DM structures detected to date. We forecast the sensitivity of ten-year campaigns with 300 epochs for two benchmark systems: the galaxy-lensed quadruple B1422+231 at a 0.1 $μ$as per-epoch precision forecast for extended-path intensity correlation (EPIC), and the wide-separation cluster-lensed triple SDSS J1029+2623 at 1 $μ$as. The angular-acceleration channel reaches the standard $Λ$CDM microhalo population with a variance signal-to-noise ratio of order ten for the galaxy lens and order unity for the cluster under the (optimistic) assumption that half of the projected mass density at the image positions resides in microhalos. A positive detection would: raise universal lower bounds on the DM particle mass to $\gtrsim400$ keV for fermions and $\gtrsim10^{-12}$ eV for bosons; constrain the DM kinetic decoupling temperature to $\gtrsim 10$ MeV; and be sensitive to the running of the spectral tilt at the 0.01 level over 15-20 e-folds of the primordial curvature power spectrum. A robust null result across well-characterized lenses would constrain microhalo survival and/or imply violations of the above inequalities. These signatures motivate differential astrometric observations with extreme 0.1-1 $μ$as light-centroiding precision on multiply imaged quasars. [Abridged]

Classical Ae stars (CAe) are main sequence, A-type stars with H$α$ emission but no signature of dust; they are thought to be the cool extension of the classical Be (CBe) stars to lower stellar masses. We investigate the use of H$α$ and the CaII IR triplet observed at low spectroscopic resolution ($R=1800$) as diagnostics for the circumstellar disks of the CAe stars. Using a sample of 159 CAe stars from the LAMOST survey (DR5), we find that circumstellar disk masses and star/disk viewing inclination angles can be reliably determined from low resolution H$α$ profiles. The CAe disk mass distribution agrees well with the previous range found for late-type CBe stars, although there is an apparent increase in disk mass for the latest CAe spectral sub-types (A3 and A4) which we attribute to selection effects. Over the spectral range A2 through B6, the average disk-to-star mass ratio for the CAe and CBe stars is consistent with $\log_{10}(M_{\rm disk}/M_*)=-9.1$. A minority of the CAe sample ($\sim$16%) also show emission in the CaII IR triplet. The observed emission is well within the range predicted by the disk models, and there is statistical evidence that the CaII emitters have systematically larger H$α$ disk masses.

Hot subdwarf stars of spectral types O and B (sdO/B) in binaries form as products of substantial mass loss near the tip of the red giant branch and offer powerful constraints on binary-star evolutionary models. However, details of some formation channels remain missing. We present a comprehensive analysis of the short-period binary population in the 500 pc volume-limited sample of hot subdwarfs, enabled by precise Gaia DR3 parallaxes. Besides 45 known binaries within 500 pc, this work identifies 50 new single-lined radial-velocity variable systems, 34 with orbital solutions with periods between 0.07 and 22 days. We derive an overall short-period binary fraction of 34.7 (+2.8/-2.9)% for the full sample of 301 hot subdwarfs within 500 pc, corrected for orbital inclination and detection efficiency. The newly solved binaries predominantly occupy the 1-20 day range, a parameter space previously under-represented in the literature. We identify five new reflection-effect systems, three ellipsoidal modulation systems, a newly solved HW Vir system, and a new triple candidate. The sdB and sdO binary fractions are similar, while the sdOB class shows a fraction roughly half that of sdB/sdO stars, with periods over one day, suggesting a different evolutionary pathway. Underluminous hot subdwarfs below the canonical extreme horizontal branch show a binary fraction comparable to other sdB/sdO stars but host only white dwarf companions, which are more massive and mainly found at periods under one day. We provide the first volume-complete birthrate estimates for sub-populations, determining a Galactic merger rate of 2.5+-1.5x10^-5 yr^-1 for sdO/B binaries, explaining no more than ~12% of the eHe-sdO population. We also derive birthrates for two SN Ia progenitor channels, finding hot subdwarf binaries could account for up to 2.5 (+0.7/-0.5)% of the observed Galactic SN Ia rate.

We investigate thermodynamic criticality in a spatially flat Friedmann-Lemaître-Robertson-Walker universe with a non-extensive Loop Quantum Gravity inspired entropy on its apparent horizon. Using the full Kodama-Hayward temperature and the unified first law, we derive the modified Friedmann dynamics and construct the corresponding horizon equation of state. We see that a finite physical critical point only appears in the non-extensive branch $q>1$, while in the Bekenstein-Hawking limit $q\to1$, the critical point is continuously pushed to $v_c\to\infty$ and $T_c\to0$. Along the same spinodal curve, both the constant-pressure heat capacity and the isothermal compressibility become unbounded, and the extremum of this curve is located at the critical point. Below the critical temperature, the Gibbs free energy develops several thermodynamic branches, and the phase coexistence for different horizon states is verified by the equality of temperature, pressure, and Gibbs free energy. The critical exponents are $(α_{cr},β_{cr},γ_{cr},δ_{cr}) =(0,1/2,1,3)$, indicating that the system belongs to the standard mean-field universality class despite the non-algebraic form of the equation of state. The normalized Ruppeiner curvature diverges precisely on the spinodal curve and shows critical scaling $R_N\sim-|v-v_c|^{-4}$ on the critical isotherm, and $R_N\sim-|t|^{-2}$ on the critical isochore. Finally, the critical expansion scale is given by $H_c^2=2(\sqrt{5}-2)|β|$, which implies that the thermodynamic critical point occurs when the entropy deformation is of order unity. These results establish a self-consistent critical structure for the effective thermodynamic state space of the cosmological apparent horizon and retain the mean-field critical universality.

Quantum Yang-Mills theory in Euclidean AdS$_4$ with Neumann boundary conditions is studied as a function of the complex couplings $\frac{1}{g_\pm^2} \equiv \frac{1}{g^2}\mp \frac{i θ}{8 π^2}$. We define a "self-dual limit" by $g_- \to 0$ with $g_+ ~{\rm fixed}$. We argue that the limiting theory is well-defined perturbatively and equivalent to the BF formulation of self-dual Yang-Mills theory with a particular boundary condition relating $B$ and $F$ at the boundary $\partial$AdS$_4$. $g_+$ is the loop-counting parameter of the self-dual theory. This is in stark contrast to flat space, where $θ$ has no effect on perturbative dynamics. In the self-dual limit, it is shown that all tree-level zero-plus and single-plus boundary correlators vanish. A closed form expression is given for any number of gluons for the double-plus tree correlators. Finally, we show that in the flat space limit of AdS$_4$, the total energy poles in the tree boundary correlators correctly reduce to the single-minus gluon amplitudes.

We improve upon previous efforts to optimally combine overlapping galaxy samples in the DESI baryon acoustic oscillation analysis. By weighting each galaxy by its linear bias, overlapping galaxies are combined into a single, unified catalog, naturally avoiding double counting of cosmic volume and including all auto- and cross- information at the catalog level. Improvements over the previous effort include the addition of QSO out to $z=1.6$ to account for all overlapping DR2 tracers and redshift-dependent bias treatment to improve reconstruction. We report distance measurements using this unified tracer, and find them to be highly consistent with the baseline DR2 BAO analysis. We also test for tracer-dependent systematics within the DESI data, and find no evidence of tracer-dependent systematics within $0.8<z<1.6$. Finally, we take advantage of the unified tracer to rebin the analysis in redshift in order to more finely resolve the redshift-to-distance relation. Dynamical dark energy results on this finer redshift binning indicate that there is no missed feature in the expansion history in the redshifts $0.8<z<1.6$, and reproduces DESI's preference for an evolving dark energy equation of state.

We present photometric and spectroscopic investigations of 11 totally eclipsing contact binaries with mass ratios below 0.15, classifying them as extremely low mass ratio contact binaries. The ground-based multiband light curves were modeled with PHysics Of Eclipsing BinariEs to derive the photometric parameters of these systems. The TESS light curves of J011323 and J002747 show pronounced asymmetries and continuous variations. Markov Chain Monte Carlo modeling suggests that these variations are related to longitudinal migration of spots on the primary components. Spectral subtraction of the LAMOST spectra reveals excess chromospheric emission in six systems, while no detectable excess emission is found in the other five. The O$-$C analysis indicates secular period increases in six systems and secular decreases in five systems. We estimated their orbital angular momenta and performed a dynamical analysis. {Within our adopted semi-analytical framework without energy transfer, the formation of these observed systems requires additional angular momentum loss beyond saturated magnetic braking and gravitational radiation, but this requirement could be modified by different assumptions on mass transfer or radius evolution.

We conduct an investigation of the global structure of Kerr-Newman-BR spacetime and its various subcases such as Schwarzschild-BR spacetime. In this work, we extend the result of our previous studies, where we found that $r\to \infty$ is not the proper conformal infinity. By using the reciprocal coordinate $y=1/r$, we show that the whole family of Kerr-Newman-BR spacetimes can be continuously extended through the surface $r\to \infty$. However, the conformal structure after passing $r\to\infty$ strongly depends on the type of spacetime one is considering (either rotation is present, or not) and on the polar direction one chooses to be fixed (namely, whether we consider generic polar angle $θ$, or we focus on the behaviour near the equatorial plane $θ=π/2$, or near the poles $θ=0,π$). Finally, we discuss the universality of such a continuous extension.

General relativity coupled to multiple scalar fields is a diffeomorphism-invariant constrained system. Consequently, a naive counting of the perturbative degrees of freedom unavoidably overestimates the true number of physical modes propagating in the theory, as gauge redundancies and constraint equations remove non-dynamical ones. While this problem has been solved for linear fluctuations, this work presents the first explicit calculation of all large-scale gauge-invariant phase-space variables in multifield inflation and at second order in perturbation theory, in a Hamiltonian language. Building upon the well-known Sasaki-Mukhanov variables, we show how to construct a finite-dimensional basis of quadratic corrections which are invariant under gauge transformations. Although our procedure is generic to any number of fields and at any scale, we restrict to super-Hubble scales for their explicit solution, which we deliver. Henceforth, we prove that it is possible to recover the usual flat-gauge and comoving-gauge fluctuations as large-scale gauge-invariant combinations, making for a robust consistency check of the gauge-fixed procedure to connect theoretical predictions above the horizon to observations. We derive the quadratic and cubic Hamiltonian of multifield inflation in a gauge independent manner, then we gauge fix our theory by going into the flat gauge, and we show perfect agreement with the literature on this topic, usually based on a Lagrangian approach. After these concrete steps, we propose a more formal proof of the existence of gauge-invariant variables at quadratic order, and we provide a sketch of the procedure that should allow to go to higher orders in perturbation theory.

Red clump (RC) stars are excellent standard candles for mapping the three-dimensional structure of the Milky Way. We construct an all-sky catalog of 6.5 million primary RC stars using spectroscopic estimates of asteroseismic parameters inferred from Gaia DR3 low-resolution XP spectra. We train a mixture density network (MDN) on a cross-matched sample. The network maps each 343-dimensional corrected XP spectrum to estimates of $ΔΠ_{1}$, the asymptotic period spacing of dipole gravity modes, and $Δν$, the large frequency separation. We select primary RC stars using these two estimates. We release two complementary catalogs defined by different parameter-space cuts and thresholds: a high-purity Tier 1 sample of 532,189 stars with 97% purity and a high-completeness Tier 2 sample of 6,534,931 stars with 86% completeness. Both catalogs cover the full celestial sphere. We provide distances and extinction values for all stars. We obtain a median photometric distance precision of 6% for Tier 1 RC stars. Using the resultant distances, we independently calibrate the Gaia DR3 parallax zero-point offset. The three-dimensional density distribution traced by the Tier 2 sample extends continuously to $R\approx25$ kpc. Both catalogs are publicly available. These catalogs provide a valuable resource for Galactic archaeology, delivering a homogeneous dataset to trace the chemo-dynamical evolution of the Milky Way and to calibrate models of stellar populations.