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We report a $γ$-ray excess toward the radio-quiet narrow-line Seyfert 1 galaxy 1H 1934-063 using data collected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope and taking into account the LAT 16-year Source List (FL16Y). During the flare interval, the excess is detected in the 1--500 GeV band at a significance of $\sim 5.2σ$ (TS = 27.12), with a photon flux of $(4.94\pm2.33)\times10^{-10}$ ph cm$^{-2}$ s$^{-1}$ and a hard photon index of $Γ=1.50\pm0.25$. The best-fit $γ$-ray position is consistent with the radio position of 1H 1934-063, while the nearby source FL16Y J1936.9-0552 is not significantly detected during the same interval. In the absence of contemporaneous multiwavelength data, the broadband interpretation cannot be tightly constrained. A compact nonthermal component can produce the hard GeV emission, but the present data do not allow a unique physical interpretation. The excess therefore provides an interesting case for probing high-energy activity in radio-quiet NLS1 galaxies, although the underlying physical mechanism remains uncertain.

We investigate gravitational lensing in Kerr spacetime in the presence of a modified photon propagation law arising from higher-curvature effective field theory corrections. Adopting a deformed dispersion relation, we analytically derive the deflection angle and the propagation time delay for null trajectories in a rotating background. We show that the modified propagation leads to explicit and calculable deviations from the standard Kerr predictions, affecting both the bending angle and the time delay. These corrections exhibit a nontrivial dependence on the black hole spin and are expected to become more relevant in the strong-field regime. In particular, near the photon region-where the spin-dependent geometry influences photon trajectories-such effects may play a role in shaping observable propagation features. Our results establish a concrete and systematic framework to quantify deviations from standard photon propagation in gravitational lensing. They further indicate that observables such as relativistic image separations and time delays provide a potential avenue to probe ultraviolet corrections to gravity in strong-field environments.

We describe a classical (non-quantum) radiation process: additional (to Hawking) emission by a black hole evaporating in an external magnetic field in vacuum. The electromagnetic radiation process is completely electric charge-free and bears some resemblance to the Gertsenshtein-Zel'dovich effect. The time evolution of the spacetime metric perturbs a static background magnetic field, inducing a radiative field that acts as an effective electromagnetic source even in the absence of physical charges or currents. To isolate the dynamic effects of the time-dependent spacetime on the external magnetic field, we approximate Hawking radiation as a spherically symmetric outflow of null fluid governed by the prescribed time-dependence of the central mass $M(t)$. We employ Laplace transform, which selects the retarded outgoing branch of the electromagnetic response, producing fields proportional to $Θ(t-r)$ and thereby fixing a causal radiative arrow of emission. The emitted spectral energy is red-dominated, scaling as $d\mathcal{E}_B/dω\propto B_0^2 m_0^2 τ_H^{-2/3} ω^{-8/3}$, where $τ_H$ is the Hawking evaporation timescale, and corresponds to a pure Transverse Electric (TE) mode. There is no final bright burst at the end of the evaporation. We offer classical analogues for this mechanism as transmission-line emission and, separately, as the displacement current emission from a medium with time-varying dielectric permittivity.

We present effective temperature (Teff) estimates of low-mass stars and T Tauri stars (TTS) candidate detections derived from automated spectroscopic measurements and low-complexity machine-learning models applied to the LAMOST DR10 V2 survey. Equivalent widths of key diagnostic spectral features, including the atomic lines Halpha, LiI 6708 AA and TiO/VO molecular bands, are automatically measured for all stars within 1 kpc observed by LAMOST. Using nine spectral features as inputs, we train a Gradient Boosting Machine tree-based regression model, calibrated with synthetic spectra from the PHOENIX library, to predict Teff over the range 2,500 - 5,100 K. We apply a logistic regression model to the principal components derived from the measured spectral features, enabling efficient identification of TTS candidates. Both models exhibit strong performance in validation tests. Finally, a Monte Carlo framework is employed to propagate input uncertainties and estimate Teff and its associated uncertainties for low-mass stars from 1,733,802 spectra and to identify 2,534 candidate TTS from 3,121 spectra.

A direct separation of the linearized Einstein equations in Kerr is presented. The trace of the perturbed metric is found to obey the spin-0 perturbation equation and so is irrelevant for the spin-2 perturbations. By combining the traceless condition, the Killing-Yano symmetry, a parity requirement, and the de Donder gauge condition, it has been found possible to reduce the linearized Einstein equations in Kerr to a manageable level, thereby enabling the direct separation of the equations and the derivation of a unique set of decoupled mode functions for the spin-2 perturbation of the Kerr black hole.

Three-body encounters are frequent events in stellar systems, intrinsically chaotic, and computationally costly to model with direct N-body integration. Predicting whether such encounters lead to binary formation is therefore challenging, particularly in large-scale simulations. We aim to develop an accurate and physically interpretable machine-learning model that predicts binary formation from the initial conditions of three-body encounters, to assess its reliability, and to identify the physical parameters that most strongly determine the outcome. We trained an XGBoost binary classifier on a balanced dataset of three-body scattering experiments computed with the REBOUND code and the IAS15 integrator. The input to the model consists of 30 physically motivated features describing the masses, energies, and kinematics of the initial configuration. The classifier achieves excellent performance on a balanced test set, with accuracy, precision, recall, and F1-score all above 0.94, and with ROC-AUC and PR-AUC values of 0.99. Feature-importance analysis shows that the outcome is governed primarily by the mass hierarchy and hardness ratio of the encounter, followed by velocity fraction and mass entropy. The predicted probabilities are well calibrated, with an expected calibration error (ECE) of 0.02. Inference is approximately 400 times faster than direct N-body integration. The model also generalizes well across encounter radii, although its performance decreases in the weak-interaction regime where binary formation becomes intrinsically rare. These results show that machine learning can provide fast, accurate, and physically interpretable predictions of binary formation in three-body encounters. Such models offer a practical complement to direct N-body simulations and may enable efficient probability estimates in large-scale simulations of stellar systems.

Observations reveal a pronounced deficit of white dwarfs (WDs) in open clusters (OCs) relative to theoretical expectations, suggesting that a significant fraction of WDs may have escaped from their parent clusters after formation. In this work, we perform a systematic search for escaped WD candidates from OCs by back-tracing the motions of WDs and star clusters from Gaia DR3 catalogs. We identify 476 candidate WDs with kinematics consistent with having escaped from one of 175 OCs. A control-field Monte Carlo (MC) test yields a contamination rate of 87.6% +/- 4.3%. Given this high contamination rate, we filter the candidates by ensuring each WD's total age is consistent with its host cluster age, thereby establishing a more reliable follow-up sample of 109 stars. The excluded candidates with anomalous ages are more likely field interlopers or products of accelerated binary evolution. Among these, the low-mass regime exhibits a clear excess over expected field binary merger rates, whereas the high-mass regime remains broadly consistent with binary population synthesis predictions. Finally, comparing escaped WDs with cluster properties, absolute escape counts appear limited by Gaia's distance-dependent incompleteness. The normalized escape fraction shows little dependence on cluster age, possibly favouring WD loss near formation over gradual evaporation, but is strongly anticorrelated with cluster mass, plausibly because deeper potential wells of massive clusters retain more of their WDs.

In Newtonian spacetime, the canonical description of a classical $N$-particle system requires $3N$ degrees of freedom. Not all of these are physical, however, since the conservation of the net momentum implies that only $3(N-1)$ accelerations are independent. Hence, three constraints can be used to eliminate the unphysical centre-of-mass variables, at the level of the Lagrangian, leaving only the subset of observable displacements and momenta, which are relational. Imposing the constraints does not change the dynamics of these variables, at the classical level, and is analogous to a gauge-fixing procedure, which removes redundancy in the description of the system. In classical physics, therefore, the number of physical degrees of freedom equals the number of independent relational degrees of freedom. Here, we show that this is not the case in quantum mechanics. While an operator-analogue of the classical net momentum exists, it cannot be used to impose constraints that restrict the degrees of freedom in the theory, without a loss of physical information. This means that all $3N$ canonical degrees of freedom are physical, even though only $3(N-1)$ of them are relational. We explore the physical consequences of the non-relational variables and show that they give rise to generalised uncertainty relations (GURs), for the relational quantities that define the quantum reference frame (QRF). Hence, it is shown that the non-relational degrees of freedom refer to the frame itself and that the non-Heisenberg terms in the GURs define its Galilean-invariant spreads, in both real space and momentum space. The implications of this result for recent work on relational models, including the ``perspective neutral'' framework for QRFs, are discussed. Its implications for the wider relational program, and, in particular, the relevance of the latter to quantum gravity research, are also critically assessed

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.

Fuzzy Dark Matter (FDM) predicts the existence of virialized halos with interference-driven granular structure generated by the wave nature of ultralight bosons. Since these fluctuations produce time-dependent gravitational fields, they can be proposed as a potential source of observable dynamical effects on baryonic matter. In this work we test whether such fluctuations generate measurable temporal correlations between FDM and a coupled gas component. We evolve coupled FDM-gas configurations with the Schrödinger-Poisson-Euler system in three dimensions. The FDM component is initialized through multimerger configurations that relax toward core-halo structures, while the baryonic component is modeled as an ideal gas. After virialization, we analyze the temporal fluctuations of both components through correlation functions and spectral diagnostics. The FDM density field shows fluctuations with significant high-frequency content, whereas the gas develops smoother and longer-lived coherent structures. Although the gas dynamically responds to the gravitational potential generated by the FDM halo, we find no strong temporal correlation between the interference-driven fluctuations of FDM and the gas dynamics. This behavior persists across the explored range of gas temperatures. Our results indicate that baryonic matter reacts to the global gravitational potential of the virialized halo rather than to the detailed phase-dependent granular structure of FDM. This weak temporal coupling may limit the possibility of directly detecting FDM granularity through local baryonic temporal fluctuations.

The polar magnetic field is the most reliable precursor for predicting the amplitude of the solar cycle, and the 2D surface flux transport (SFT) model is widely used to reconstruct its evolution. Traditional 2D SFT models can not capture the surface-interior coupling of the surface field, causing delays in polar field reversals. This deficiency is conventionally corrected by adding a decay term $-B_r/τ$ with a poorly constrained radial decay timescale $τ$. Here, we present a self-consistent estimate of $τ$ through a comparative study of radial flux transport in the 2D SFT model and the 3D kinematic dynamo model, STABLE. By keeping the same transport parameters for both models and assuming surface-interior coupling is diffusive, the poloidal field evolution equation reduces to an eigenvalue problem, which yields a spectrum of $τ$ that decrease with increasing angular modes $l$. To capture realistic surface-interior coupling, we further perform data-assimilated 2D SFT simulations with real magnetograms and compare those results with that of the data-assimilated 3D STABLE model to constrain $τ$ and effective decay modes. With our choice of transport parameters, a value of $τ=~2~\text{yr}$ keeps the surface dynamics of the two models consistent, and this timescale corresponds to the angular mode $l=8$ from our self-consistent estimate. We also perform 2D SFT simulations with only large-scale active regions, as the source. We find that $τ=7~\text{yr}$ accurately captures the radial decay of the dipole mode ($l=1$) and removes the secular drift in the polar fields.

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.

We investigate the geometric quantum discord of bipartite Werner states influenced by Hawking radiation in the quantum atmosphere of a Schwarzschild black hole. We find that the geometric quantum discord in the physically accessible region exhibits a nonmonotonic behavior: it first decreases and then increases as the normalized radial distance increases, while the discord in the physically inaccessible region shows the exact opposite trend. A pronounced extremum of geometric quantum discord occurs precisely at the position corresponding to the peak intensity of Hawking radiation. Furthermore, we find that the Hartle Hawking constant and the event horizon radius exert opposite effects on the strength of quantum correlation redistribution: a larger Hartle Hawking constant enhances the redistribution effect, whereas a larger event horizon radius suppresses it.

We present a uniform IRAM-30\,m survey analysis of four oxygen-bearing complex organic molecules (COMs), methanol (CH$_3$OH), acetaldehyde (CH$_3$CHO), methyl formate (CH$_3$OCHO), and dimethyl ether (CH$_3$OCH$_3$), toward 50 high-mass star-forming regions (HMSFRs) associated with 6.7\,GHz methanol masers. Column densities were derived through a homogeneous rotation-diagram approach, with CH$_3$CN used as a proxy excitation-temperature reference when needed. In CH$_3$OH-normalized abundance-ratio space, CH$_3$OCHO/CH$_3$OH and CH$_3$OCH$_3$/CH$_3$OH show the strongest pairwise correlation, whereas the correlations involving CH$_3$CHO are weaker. No clear monotonic trends are found with Galactocentric distance or beam-averaged H$_2$ column density. Comparison with previous observations places the CH$_3$OCHO--CH$_3$OCH$_3$ behavior within the range of earlier abundance-ratio measurements, while CH$_3$CHO shows larger inter-study variation. A representative warm-up chemical model is used only for qualitative comparison with the observed abundance ranges, which are most closely matched during the decline from the post-desorption abundance peaks in the model. These results provide homogeneous beam-averaged abundance-ratio constraints for common O-bearing COMs in high-mass star-forming regions and show that their source-to-source behavior is molecule-dependent rather than fully described by a single common abundance pattern.

Binary--single encounters occur frequently in stellar systems, constitute a non-integrable chaotic three-body problem, and are computationally expensive when treated with N-body codes. We aim to construct an accurate and physically interpretable surrogate model for binary--single scattering final states (ionization, flyby, exchange, or hierarchical), evaluate the reliability of its probabilistic predictions, and trace its predictive failures to the underlying chaotic nature of the scattering problem. We trained an XGBoost multiclass classifier on a class-balanced dataset of numerically integrated binary--single scattering experiments, using physically motivated features. The model achieves a test accuracy of 88.32 percent and a top-2 accuracy of 98.77 percent. Feature importance indicates binary hardness as the dominant predictor. Misclassifications concentrate near the chaotic boundary separating exchange and hierarchical outcomes. Basin-entropy analysis reveals that such misclassifications are due to intrinsically ambiguous regions of parameter space. Therefore, a fast machine-learning surrogate can predict binary--single scattering final states with high accuracy, and residual errors arise from chaotic regions rather than model inadequacy.

Estimating the iron abundance ([Fe/H]) of Classical Cepheids (CCs) is crucial both for validating the cosmic distance scale through the Period-Luminosity relation and for tracing the chemical evolution of young stellar populations. However, standard spectroscopic determinations are highly time-consuming, limiting their application to large or distant samples. This work delivers a practical, multi-band alternative by investigating whether light-curve Fourier parameters derived from Gaia mission photometry can serve as reliable proxies for [Fe/H]. Our reference sample comprises 398 fundamental-mode CCs from Gaia DR3 with high-resolution spectroscopic metallicities available in the literature, spanning a wide range of pulsation periods. Light curves in the G, G_BP, and G_RP bands were modeled with a truncated Fourier series to extract characteristic amplitudes, amplitude ratios, and phase differences. We implemented a replicated Random Forest algorithm as a feature selection tool to isolate the most predictive parameters based on their total increase in node purity. Using the selected features, we calibrated an empirical, multi-variable relation via linear regression, incorporating higher-order polynomial terms to capture complex morphological dependencies. The primary unweighted OLS model yields a residual rms of 0.213 dex and a Pearson correlation of 0.61. As an external validity check, we applied this calibration to large target samples of CCs in the Milky Way, LMC, and SMC. The resulting photometric metallicity distributions correctly reproduce the expected chemical enrichment history and peak values of the three galaxies, proving the reliability of this relation for population studies in the Gaia DR4 era.

Conical geometries provide the standard description of disclinations, but they concentrate the curvature at a singular apex. We introduce a Yukawa-type regularization that replaces this singularity by a smooth curvature distribution while preserving the asymptotic topology of the defect. Exact expressions are obtained for the conformal factor, curvature, and enclosed topological charge. The resulting geometry exhibits a scale-dependent topological charge and a corresponding radius-dependent holonomy, establishing a direct connection between distributed curvature and geometric phases. We further investigate the dynamics of massless Dirac quasiparticles in this background and show that the regularized core modifies the spin connection while preserving the asymptotic topological signature of the defect. These results provide a finite-core extension of the conventional conical description and offer a natural framework for studying geometric and topological effects in graphene-like systems.

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.