Papers

Context. Solar blowout jets are a distinct subclass of ubiquitous extreme-ultraviolet (EUV) and X-ray coronal jets. Aims. Most existing models of blowout jets prescribe an initial magnetic field configurations and apply ad-hoc changes in the photosphere to trigger the jets. In contrast, we aim for a self-consistent magneto-convective description of the jet initiation. Methods. We employ a 3D radiation magnetohydrodynamic (MHD) model of a solar coronal hole region using the MURaM code. The computational domain extends from the upper convection zone to the lower corona. We synthesize the emission in the extreme UV and X-rays for a direct comparison to observations and examine the evolution of the magnetic field structure of the event. Results. In the simulation a twisted flux tube forms self-consistently, emerges through the surface and interacts with the pre-existing open field. Initially the resulting jet is of the standard type with a narrow spire. The release of the twist into the open field causes a broadening of the jet spire turning the jet into a blowout type. At the same time this creates a fast heating front propagating at the local Alfvén speed. The properties of the modeled jet closely match observations of blowout jets: a slow (180 km/s) mass upflow and a fast (500 km/s) propagating front form, the latter being a signature of the heating front. Also the timing of the jet with respect to the flux emergence and subsequent cancellation matches observations. Conclusions. The near-surface magneto-convection self-consistently generates a twisted flux tube that emerges through the photosphere. The tube then interacts with the pre-existing magnetic field by means of interchange reconnection. This transfers the twist to the open field region and produces a blowout jet that matches the main characteristics of this type of jet found in observations.

Global ideal magnetohydrodynamic models of the heliosphere typically predict a greatly exaggerated magnetic field pile-up in the inner heliosheath (IHS), the region between the termination shock and heliopause. However, Voyager 1 and 2 observations show only a gradual increase throughout this region. This mismatch is largely attributed to the simplified assumption of a unipolar solar magnetic field in many global models, which neglects the complex, folded structure of the heliospheric current sheet (HCS). The IHS, especially at low heliolatitudes, contains these compressed sector boundaries, widely considered prime locations for magnetic dissipation via reconnection. To align global model simulations with observations without incurring the prohibitive computational cost of resolving the kinetic-scale current sheet, this work introduces a phenomenological term into the magnetic field induction equation. This term captures the macroscopic effect of magnetic energy dissipation due to unresolved HCS dynamics. It is designed to mitigate the artificial magnetic pile-up, preserve the topological integrity of the magnetic field lines, and avoid explicit magnetic diffusion. This study demonstrates that incorporating a phenomenological dissipation term into global heliospheric models helps to resolve the longstanding discrepancy between simulated and observed magnetic field profiles in the IHS. The proposed mechanism reduces exaggerated magnetic energy (converts it into thermal energy), aligns model output with Voyager measurements of both magnetic field and proton density, and produces the outward shift in termination shock position and a reduction of the IHS thickness. We found that the characteristic time for magnetic field dissipation of about 6 years provides improved agreement with Voyager data in the IHS.

Under ideal conditions, the theory of shock acceleration for cosmic rays predicts that different elements should exhibit strictly identical spectral indices when accelerated to the same rigidity (R). However, recent high-precision measurements of elemental energy spectra have definitively established the existence of variations in spectral indices across different elements. This study constrains the spectral indices of cosmic-ray elements using AMS-02 and DAMPE observations within the Spatially Dependent Propagation (SDP) model. For elements with A/Z = 2, spectral indices shows significant positive correlations with both atomic number Z and mass number A, likely due to A or Z-dependent fragmentation cross-sections. Predictions indicate that the observed spectra of Ni and Zn will align with the Fe spectrum, while their injection spectra will exhibit slightly softer spectral indices compared to Fe. Future observations from AMS-02, DAMPE and HERD are expected to verify these findings, while theoretical models are needed to systematically explain this phenomenon.

Interstellar hydrocarbon dust containing aromatic and aliphatic hydrocarbons, like polycyclic aromatic hydrocarbons (PAHs), is believed to be processed by various factors including UV radiation fields and mechanical shocks in the galactic environments. We systematically investigate the processing of hydrocarbon dust, especially the likely causes for the variations of the luminosity ratio of aliphatic to aromatic hydrocarbon emission features, using the near-infrared (IR) spectral features at wavelengths 3.3 um and 3.4-3.6 um observed with AKARI/IRC. We analyzed 243 near-IR spectra of 240 star-forming (U)LIRGs (the total IR luminosity, $L_\rm{IR}>10^{11}\ L_\odot$), 119 spectra of 105 star-forming IRGs ($10^{10}\ L_\odot<L_\rm{IR}<10^{11}\ L_\odot$), and 94 spectra of 65 sub-IRGs ($L_\rm{IR}<10^{10}\ L_\odot$), in addition to 232 spectra of 36 Galactic HII regions as a reference sample. We performed near-IR spectral model fitting to estimate the luminosities of the aromatic and aliphatic hydrocarbon features and the HI recombination line Br$\rm{\alpha}$. The result indicates that the luminosity ratios of the aliphatic to the aromatic hydrocarbons ($L_\rm{ali}/L_\rm{aro}$) in the sample galaxies show considerably large variations, compared to those in the Galactic HII regions, $L_\rm{ali}/L_\rm{aro}$ systematically decreasing with $L_\rm{IR}$ and $L_\rm{Br\alpha}$. We find that (sub-)IRGs with continuum colors bluer at 4 um tend to have higher $L_\rm{ali}/L_\rm{aro}$, which is likely to reflect the intrinsic nature of PAHs outside the HII region where the PAHs remain non-processed by strong UV radiation fields. We also find that some ULIRGs with continuum colors redder at 4 um show extremely low $L_\rm{ali}/L_\rm{aro}$, which is likely to be caused by blending aliphatic emission and absorption features due to the presence of an obscured galactic nucleus in merger systems.

The origin of late-time radio flares in tidal disruption events remains unclear. In particular, the peculiar radio flare observed in AT2018hyz has motivated two leading scenarios: a delayed outflow launched $\sim1000\,\rm days$ after discovery, or an off-axis relativistic jet directed far from our line of sight. Very long baseline interferometry (VLBI) imaging provides the most direct way to distinguish between these scenarios. In this paper, we calculate synthetic radio images for both models and examine their observational signatures. The motion of the emission centroid is the most powerful diagnostic for breaking the degeneracy. In the delayed-outflow scenario, the centroid motion is confined within a non-relativistic distance, whereas in the off-axis jet scenario it exhibits apparent superluminal motion. Detecting such superluminal motion would therefore provide a smoking-gun signature of the off-axis jet interpretation. We also find that the jet image exhibits characteristic features, including a non-monotonic evolution of the image aspect ratio. These results are expected to be generic and applicable to other jetted explosions, such as microquasars and gamma-ray bursts.

The Moon has been regarded as a natural Weber bar capable of amplifying gravitational waves (GWs) for detecting events across a wide range of frequencies. However, accurately determining the amplification effects remains challenging due to the absence of 3D numerical simulation methods. In this study, we develop a high-order 3D finite element method (spectral-element method, SEM) to numerically simulate the lunar response to GWs below 20 mHz. We verify the accuracy of our method by comparing the resonant peaks of our results with those from semi-analytical solutions and find that the frequency deviation is less than 3% for the first peak at about 1 mHz and less than 0.8% for the subsequent peaks up to 10 mHz. Using this method, we evaluate the amplification of GW signals due to 3D topographic effects of the Moon, and we find enhancements at a series of specific frequency components. These results highlight the non-negligible effect of surface topography on the lunar response to GWs, as a fundamental factor that holds significant implications across both global and regional analyses. Our work paves the way for a comprehensive evaluation of the Moon's resonant response to GWs, helpful for the strategic planning of lunar GW detections.

Reheating is essential for transforming the cold, vacuum dominated Universe at the end of inflation into the hot thermal bath required by the Standard Model. In many well motivated inflationary models, however, the inflaton has no direct couplings to other fields, raising the question of how the Universe becomes repopulated with particles. We address this question within the framework of geometric reheating, where energy transfer occurs purely through gravitational effects. Focusing on a Higgs inflationary scenario with a non-minimal curvature coupling $\xi \phi^2 R$, we derive the post-inflationary dynamics and compute particle production using the Bogoliubov formalism. We show that the rapid, oscillatory evolution of the curvature scalar after inflaton acts as a time dependent gravitational pump, creating scalar spectator particles even in the absence of explicit interactions. This curvature driven production mechanism provides a natural and efficient route to reheating, demonstrating that gravity alone can initiate the standard thermal history and bridge inflation with radiation domination in minimal, coupling free models of the early Universe.

Recent JWST observations claim the existence of a significant fraction of bars in the kinematically hotter and thicker disk at high redshift Universe. These observations challenge the current understanding of disk stability in galaxies similar to the Milky Way. The analytical work and N-body simulations suggest that the kinematically hot (dispersion-dominated) and thick disk are stable against bar formation. In this work, we perform the controlled N-body simulations of a kinematically hot and thick disk, which is residing in a non-rotating and spinning dark matter halo. We report that the disk, which is classically stable against bar instability in the live and non-rotating halo, leads to bar formation in a spinning halo environment. The spinning halo model is 8 times more efficient in transporting angular momentum from the disk to the halo compared to the non-spinning halo. We claim that Ostriker-Peebles and ELN bar formation criteria do not predict bar formation for both the non-roating and spinning halo. The recent criteria from Jang-Kim successfully predict the bar stability for the non-rotating halo model, but not for the spinning halo model. These results provide an important insight into the bar formation processes for thick and hot disks at high redshift.

Reliable predictions of (anti)neutrino spectra and luminosities are essential for assessing the feasibility of detecting pre-supernova neutrinos. Using the stellar evolution code MESA, we calculate the (anti)neutrino spectra and luminosities under realistic conditions of temperature, density, and electron fraction. Our study includes (anti)neutrinos produced by both thermal processes and nuclear weak-interaction reactions. By comparing the results of the thermal quasiparticle random-phase approximation with the standard technique based on the effective $Q$-value method, we investigate how thermal effects influence the spectra and luminosities of emitted (anti)neutrinos. Our findings show that a thermodynamically consistent treatment of Gamow–Teller transitions in hot nuclei enhances both the energy luminosity and the average energies of the emitted (anti)neutrinos.

We investigate inflation models governed by the Siegel modular group $Sp(4,\mathbb{Z})$. The $Sp(4,\mathbb{Z})$ group extends the $SL(2,\mathbb{Z})$ framework from one modulus to three moduli while preserving the hyperbolic geometry of the Kähler potential, allowing for the construction of cosmological $\alpha$-attractor models. In this context, we use genus $g=2$ absolute invariants to construct inflationary potentials within specific subspaces of the Siegel moduli space. These models are driven by the imaginary components of the moduli $\tau$ and naturally yield plateau-like potentials consistent with Planck 2018 observations in large field limit. We employ two-dimensional complex subspaces to realize E-model and T-model like two-field inflation scenarios. We explore the subspace of complex dimension one to construct a modified polynomial $\alpha$-attractor model, which can accommodate the larger spectral index $n_s$ favored by recent ACT and SPT data, particularly in the larger $N$ regime.

The recent discovery of M31 UCXB-1, the first extragalactic ultracompact X-ray binary (UCXB) with an orbital period of $T_{\rm orb} \sim 465$ s, presents a unique laboratory for studying close binary evolution and an unprecedented target for continuous gravitational wave (GW) searches. Its identification as a strong candidate black hole-white dwarf (BH-WD) system, combined with its exceptionally short period and high X-ray luminosity, suggests it may be one of the most vital low-frequency GW sources in M31. In this Letter, we investigate the detectability of its GW signal for future space-borne detectors in multiband GW detection. We find that while its signal-to-noise ratio (S/N) for low-frequency detectors remains marginal for high-confidence detection, middle-frequency detectors such as DECIGO and BBO are far more promising, potentially achieving S/N $\varrho>8$ within reasonable observational duration. With a primary mass of only $m_1 > 5.4M_\odot$ (or $6.6M_\odot$), the network of all low and middle frequency detector (or BBO alone) is capable of detecting GW from this system with a $\varrho > 8$, during 10-year observation. Furthermore, orbital eccentricity can enhance the GW strain at higher harmonics, further improving its detectability, especially for middle-frequency detectors. This study establishes M31 UCXB-1 as a key prototype of short-period UCXBs, cementing its role as a cornerstone for multiband, multi-messenger astrophysics and a vital bridge between X-ray astronomy and the future GW era.

Tidal Disruption Events (TDEs) have recently been proposed as potential probes for Population III stars. However, the properties of the accretion flow and the wind from the Pop III star TDE system are not clear. By performing radiative hydrodynamic simulations, we study the 'circularized' accretion flow of the Pop III star TDE system. The masses of the black hole (BH) and the disrupted star are $10^6$ and $300$ solar masses, respectively. We focus on the properties of the wind. We find that the black hole accretion rate is highly super-Eddington. A strong wind is driven by radiation pressure. Due to the presence of a strong wind, only $25\%$–$35\%$ of the fallback debris is accreted by the BH. The remaining part is taken away by the wind. The kinetic power of the wind can be as high as $10^{46} {\rm \ erg \ s^{-1}}$. The properties of the wind obtained in this paper may be useful for understanding the radiation properties of Pop III star TDEs in the context of the wind 'reprocessing' model.

Catastrophic disruptions of planetesimals occur in high-velocity collisions. Radioisotope dating of planetesimal disruption events recorded in meteorites confirms frequent catastrophic collisions in the first 10 Myr of the Solar System, reflecting a violent environment of the time. However, the nebula gas can damp the eccentricity of planetesimals and suppress the frequency of planetesimal collisions. Strong dynamical mechanisms that excited the protoplanetary disk are required. Here we show that the sweeping secular resonances of Jupiter and Saturn induced by the nebular gas dissipation, together with the mean motion resonances of Jupiter, can trigger a large number of catastrophic collisions, which occur episodically when the secular resonances are at 2-3 astronomical units and continue thereafter. After the gas dissipation completes, catastrophic collisions decrease in frequency, with scattering by planetary embryos becoming the major driving force of the collisions. Our results suggest that the violent environment excited by secular and mean motion resonances can be ubiquitous in protoplanetary disks during nebula dissipation.

Ground-based high-resolution spectroscopy has identified various chemical species in the atmospheres of ultra-hot Jupiters, including neutral and ionized metals, providing key insights into planet formation through refractory element abundances. We observed the dayside thermal emission spectrum of the UHJ HAT-P-70b using the high-resolution spectrographs CARMENES and PEPSI. Through cross-correlation analysis, we detect emission signals of Al i, AlH, Ca ii, Cr i, Fe i, Fe ii, Mg i, Mn i, and Ti i, marking the first detection of Al i and AlH in an exoplanetary atmosphere. Tentative signals of C i, Ca i, Na i, NaH, and Ni i are also identified. These detections enable atmospheric retrievals to constrain the thermal profile and elemental abundances of the planet's dayside hemisphere. The retrieved temperature-pressure profile reveals a strong thermal inversion. The chemical free retrieval yields a metallicity of [Fe/H] = 0.38(+0.74/-1.11), while the chemical equilibrium retrieval gives [Fe/H] = 0.23(+1.08/-0.98), both consistent with solar metallicity. We also tentatively find an enhanced abundance of Ni, possibly due to the accretion of Ni-rich planetesimals during formation. On the other hand, elements with condensation temperatures above 1400 K (e.g., Ca, Ti, and V) appear slightly depleted, which may be caused by nightside cold trapping. However, Al, with the highest condensation temperature at 1653K, displays a solar like abundance, which might reflect the formation-related enrichment of Al. Our retrieval indicates extremely high volume mixing ratios of metal ions (Fe ii and Ca ii), which are significantly inconsistent with predictions from chemical equilibrium models. This disequilibrium suggests that the atmosphere is likely undergoing significant hydrodynamic escaping, which enhances the atmospheric density at high altitudes where the ionic lines are formed.

As part of the ALMA Large Program "Early Planet Formation in Embedded Disks" (eDisk), 12CO (2 - 1) was observed towards 19 nearby low-mass protostars. Of these objects, 15 sources are found to show molecular outflow emission. Based on their morphological and kinematical structures, the CO outflows are classified into three types: a wind-driven shell, where ambient material is swept up by a wide-angle wind from the star, a bow shock, and a slow disk wind, which is a conical or parabolic flow with onion-like velocity structure. We categorize 11 outflows as a slow disk wind, 7 as a wind-driven shell, and 1 as a bow shock. Four of these outflows were found to show signs of both slow disk wind and wind-driven shell characteristics. Five objects show misalignment between the red- and blue-shifted outflows. Seven objects show significant misalignment between the outflow axis (either or both of the red- and blue-shifted outflows) and the minor axis of the dust continuum emission around the protostar. For the objects showing wind-driven shell emission, we compare simple parametrized models with the observations to derive physical properties of the observed shells, such as their dynamical ages. This shows evidence of a time variability in the outflows, such as changes in their direction. In some objects, large differences are seen between the properties of the red- and blue-shifted outflows, possibly indicating differences in the properties of the ambient medium with which the outflow interacts.

We compare low-redshift ($z<0.1$) BPT-selected pure optical AGN hosts in SDSS DR7 to colour-selected "green-valley" analogue central galaxies in IllustrisTNG100 and EAGLE Ref-L0100N1504. To reduce cross-dataset systematics, we define the green valley internally using $(g-r)$ percentiles: for galaxies with $\log_{10}(M_\star/M_\odot)>10$, we select the 75th-95th percentiles (SDSS observed-frame fibre colours; simulations rest-frame synthetic colours within 30 kpc). SDSS hosts are linked to the MPA-JHU catalogue for stellar masses and aperture-corrected total SFRs. TNG green-valley centrals are almost entirely quenched, with a sharp pile-up at the imposed SFR floor and median $\log_{10}\mathrm{sSFR}\simeq-14.85$ ($\sim$3.5 dex below SDSS). EAGLE instead produces a broad, continuous distribution with median $\log_{10}\mathrm{sSFR}\simeq-11.71$ and substantial overlap with SDSS, robust to varying the lower percentile between 60 and 90. At fixed mass, TNG yields higher green-valley occupancy fractions (reaching $\gtrsim60$ per cent near $M_\star\sim10^{11}M_\odot$) than EAGLE (20-40 per cent). A simple forward model of nebular line ratios places EAGLE analogues across the star-forming and composite loci in the BPT plane, while TNG analogues concentrate in a LINER-like, low-sSFR regime. We infer that TNG's kinetic mode drives an efficient, near-binary shutdown of star formation, whereas EAGLE's stochastic thermal feedback supports a slower decline more consistent with local AGN hosts. All catalogues and analysis scripts are publicly released.

Astrophysical black holes are invariably embedded in matter environments whose gravitational influence can alter key strong-field features of the spacetime. In this work, we investigate the impact of spherically symmetric dark-matter distributions on black hole geometry, geodesic structure, and ringdown phenomenology. Modeling the surrounding matter through Einstein clusters, we construct self-consistent spacetimes for three widely used density profiles - the Hernquist, Navarro-Frenk-White (NFW), and Jaffe models - and examine how their near-horizon behavior modifies the location and stability of circular timelike and null geodesics, including the innermost stable circular orbit (ISCO) and light rings. In the low-compactness regime, we derive analytical expressions showing that environmental effects generically shift the ISCO inward and the principal light ring outward, leading to parametric deviations in their associated orbital frequencies and Lyapunov exponents. At higher compactness, we explore the emergence of additional light rings, marginally stable orbits, and secondary horizons, identifying the regions of parameter space in which these ultracompact configurations arise. Using time-domain evolutions of scalar perturbations, we demonstrate how such structures can imprint characteristic signatures on the ringdown signal, including long-lived trapped modes and echo-like modulations associated with multiple potential barriers. Our results provide a unified framework for assessing environmental effects around black holes and highlight the importance of matter-induced corrections for interpreting upcoming electromagnetic and gravitational-wave observations.

Constraining inflationary models with high precision bispectra across broad parameter ranges is a challenging task, requiring intensive computations at all stages, first, predicting the primordial inflation bispectrum from quantum field theory, secondly, projecting this forward with transfer functions to the late universe and, finally, comparing with the bispectrum extracted from the observational data and matching mock catalogues. Here, the longstanding separable Modal pipeline for constraining primordial bispectrum templates using WMAP and Planck CMB data has been supplemented by the more recently developed Primodal code to accurately calculate bispectra numerically from inflation models, showing great potential for enhanced computational efficiency; Primodal exploits the in-in separability of the tree-level in-in formalism, together with a separable mode-expansion technique to bypass the need for point-by-point bispectrum calculations. Building upon this progress, we propose a bispectrum pipeline that systematically explores the parameter space of inflationary Lagrangians, numerically computing the tree-level bispectrum (and power spectrum) for each scenario and comparing with the Modal bispectrum decompositions obtained from the Planck 2018 data. Our pipeline identifies and excludes disfavored scenarios through this analysis, providing direct constraints on the parameter space, the sound speed and other quantities from the surviving observationally viable scenarios. This is preparatory work for a planned analysis using much higher-resolution CMB data from the Simons Observatory. To validate our pipeline, we perform a proof-of-concept analysis of the IR DBI inflation model, obtaining constraints of $c_s \geq 0.073$ for the sound speed and $\beta \leq 0.39$ for the parameter space, demonstrating the pipeline's accuracy and effectiveness.

We discuss the impact of the recent EPOS.LHC-R hadronic interaction model on the scenario in which most of the cosmic rays with energies above 5 EeV originate in the nearby Centaurus A radiogalaxy. The heavier composition inferred from this hadronic model has important implications for the interpretation of the spectral features and for the anisotropies. In particular, the amount of H and He present above the ankle is now very suppressed. The elements of the CNO group from the source play a predominant role in the instep region just above the ankle, while the elements of the Si and Fe groups contribute significantly in the suppression region of the energy spectrum above 50 EeV. The lack of He from the source above the ankle also leads to a smaller expected anisotropy around the Cen A direction at energies of 10 to 20 EeV. The expected dipolar anisotropy in different energy bins above 4 EeV is well consistent with the measurements for appropriate values of the extragalactic turbulent magnetic field and source lifetime. The overall fit to the different observables improves considerably with the new hadronic model. A new method is introduced to extract the information on the cosmic ray masses from that of the depth of the maximum development of the air showers, which significantly improves the existing method.

Cosmic ray shower detection using large radio arrays has gained significant traction in recent years. With massive improvements in signal modelling and microscopic simulations, the analysis of incoming events is still severely limited by the simulation cost of radio emission to interpret the data. In this work, we show that a neural network can be used for simulating such radio pulses. This work serves as a proof of concept that simple neural networks can be used for emergent deterministic macroscopic phenomena of microscopic simulations. We also demonstrate how such a neural network can be used for the physics use case of $X_\mathrm{max}$ reconstruction, while retaining comparable resolution to using full Monte-Carlo simulations for radio emission. Code available at https://anonymous.4open.science/r/radio_nn-21BF/.

Recent analyses on the central compact object in the HESS J1731-347 supernova remnant reported not only surprising structural properties (mass $M$ and radius $R$), but also an interesting thermal evolution. More precisely, it has been estimated that $M=0.77^{+0.20}_{-0.17}M_\odot$ and $R=10.4^{+0.86}_{-0.78}$ km (at the $1\sigma$ level), while a redshited surface temperature of $153^{+4}_ {-2}$ keV at an age of 2-6 kyrs has been reported. In the present work, we conduct an in-depth investigation on the possible nature (hadronic, hybrid, quark) of this compact object by attempting to not only explain its mass and radius but also the corresponding estimations for its temperature and age. In the case of hybrid stars we also examine possible effects of the symmetry energy on the activation of different neutrino emitting process, and hence on the resulting cooling curves. We found that the reported temperature and age may be compatible to hadronic stellar configurations regardless of whether pairing effects are included. In the scenario of hybrid stars, we found that the strange quark matter core has to be in a superconducting state in order to reach an agreement with the observational constraints. In addition, the hadronic phase must be soft enough so that the direct Urca process is not activated. Furthermore, we have shown that the considered cooling constraints can be reconciled within the framework of strange stars. However, quark matter has to be in a superconducting state and the quark direct Urca process needs to be blocked.

We explore the sensitivity of weak lensing surveys to gravitational waves (GWs) emitted by inspiraling supermassive black hole binaries (SMBHBs) in the nanohertz to microhertz frequency band, bridging the gap between pulsar timing arrays and space-based interferometers. Building on the formalism for GW-induced shear distortions, we develop a signal-to-noise framework that incorporates survey characteristics such as cadence, angular resolution, and depth. We model the effective galaxy population to evaluate the noise power spectral density and derive characteristic strain sensitivity curves. Applying this framework to both LSST-like and idealized survey configurations, we show that current surveys are limited by angular resolution and measurement noise, while an idealized, cosmic-variance-limited survey could in principle probe this frequency range. We emphasize that such sensitivity requires observational capabilities far beyond those of existing or planned facilities, and our results should be interpreted as an ultimate limit on the information accessible through weak lensing measurements.

We introduce GraviBERT, a novel deep learning framework for gravitational wave inference, built on a multi-scale feature extractor with a transformer encoder and a suitable regression head. A key novelty of GraviBERT is its staged training: a BERT-style self-supervised pretraining phase to learn transferable representations, followed by supervised fine-tuning on labeled data. GraviBERT demonstrates consistent transfer learning across detector configurations and waveform models. On in-domain data, pretraining reduces the MAE by up to $31\%$ and accelerates convergence by $\sim 6.6 \times$, with mean relative precision for point estimates reaching the few-percent level and MAE in effective spin of $\sim 10^{-3}$ at SNR = 10. For domain adaptation to new detector noise profiles, the pretrained model converges up to $15\times$ faster on small target datasets and reduces estimation errors by up to $\sim 47\%$, demonstrating detector-agnostic learning. Cross-waveform approximant transfer achieves up to $44\%$ MAE reductions and up to $15\times$ training speedups, with $R^2$ scores consistently exceeding $0.9$ for mass parameters at SNR = 10 compared to $0.74$ - $0.87$ when training from scratch. GraviBERT works directly with noisy waveforms, and in its current form quantifies predictive uncertainty through MC dropouts. After pretraining, the regression head could be adapted to multiple downstream inference tasks in gravitational-wave astronomy.

Observed rotation curves of disk galaxies remain a sharp empirical probe of the relationship between baryons and dynamics. We study a minimal, explicitly phenomenological alternative to standard halo parameterizations: an additional inward radial acceleration proportional to the local tangential speed, $a_{\vca}(r)=\gamma(r)\,v(r)$, with a saturating coupling $\gamma(r)=\vinf/(r+\rzero)$. Combining this ansatz with the circular-motion condition yields a quadratic equation for $v(r)$ with a closed-form physical branch.We fit this “velocity-coupled acceleration” (\vca) model to $N_\mathrm{gal}=171$ rotation curves from the SPARC sample using the published baryonic decompositions (gas, disk, bulge), and we compare to two commonly used two-parameter halo models (NFW and Burkert) using an identical optimization pipeline and error model.For a fiducial systematic error floor $\sigma_0=5~\mathrm{km\,s^{-1}}$, the \vca model is typically competitive with an NFW halo and performs comparably (though not uniformly better) than a Burkert halo in information-criterion comparisons.We further perform MCMC inference for \vca parameters, quantify posterior predictive coverage, and show that parameter posteriors exhibit a strong $\vinf$–$\rzero$ degeneracy for many galaxies; only $47/171$ galaxies yield well-identified posteriors under simple width-based criteria. We also perform a simple radial holdout cross-validation (outer 30% of radii) and find predictive RMSE comparable to NFW and Burkert under this protocol.Finally..

The space-based gravitational wave (GW) detectors are expected to observe lensed GW events, offering new opportunities for cosmology and fundamental physics.Across the millihertz band, lensing effects transition from the wave-optics regime at lower frequencies to the geometric-optics approximation at higher frequencies.Although traditional GW identification methods, such as matched filtering, are well established and effective, the intense computational resources required motivate the search for more efficient alternatives to accelerate candidate event screening. To address this bottleneck, we introduce a Dual-Channel Lensing feature extraction eXtended Long Short-Term Memory Network (DCL-xLSTM). Unlike conventional recurrent architectures, DCL-xLSTM uses a matrix-valued memory structure and a memory-mixing mechanism to effectively capture amplitude patterns that span the entire millihertz frequency band. Trained on data generated by Point Mass (PM) and Singular Isothermal Sphere (SIS) models accounting for the transition from wave-optics to geometric-optics, the proposed method achieves an area under the curve (AUC) exceeding 0.99, maintaining a true positive rate (TPR) above $98\%$ at a false positive rate (FPR) below $1\%$.The network is robust against variations in signal-to-noise ratio, lens type, and lens mass, establishing its viability as a high-efficiency tool for future space-based GW detection.

Gravitational waves provide a unique window into gravity, cosmology, and high-energy physics, enabling the exploration of fundamental phenomena across a wide range of scales. This review presents a coherent and pedagogical framework that bridges foundational theory with observational frontiers. We begin by developing the theory of gravitational radiation within linearized general relativity, deriving gravitational waves as solutions to the linearized Einstein equations and clarifying their physical interpretation, polarization states, and key properties. We then deepen the discussion through a geometric perspective, tracing the connection between gravitational radiation and the algebraic structure of the Weyl tensor and its role in defining energy and angular momentum in asymptotically flat spacetimes. Extending beyond flat backgrounds, we examine gravitational waves in an expanding universe, following their evolution across cosmological epochs and their generation during inflation. Within this setting, we discuss adiabatic modes and consistency relations that reveal universal properties of long-wavelength perturbations, and derive the inflationary spectrum of vacuum gravitational waves together with their contribution to the integrated Sachs-Wolfe effect. We also survey the main observational strategies for detecting gravitational waves across a broad frequency range, including cosmic microwave background polarization, pulsar timing arrays, ground- and space-based laser interferometers, and resonant cavity detectors. We then discuss the astrophysical and cosmological mechanisms responsible for generating gravitational radiation. We conclude by summarizing the current status of the field and outlining promising directions for future theoretical and observational developments.

We explore how the physical properties of disc galaxies relate to the presence of bars using data from the SDSS-IV MaNGA survey. By combining internal kinematical properties and environmental diagnostics, we find that barred galaxies are more frequently associated with centrally concentrated stellar mass distributions (within 1 and 2 effective radii) and exhibit lower values of the stellar angular momentum $\lambda_{Re}$. At fixed total stellar mass, barred galaxies exhibit: (i) higher stellar mass, and (ii) lower angular momentum, both in their inner regions than their unbarred counterparts. We find a bimodal dependence of the bar fraction on tidal interactions produced by the nearest neighbour. Specifically, the bar fraction peaks in the most isolated galaxies, where bars form unequivocally through internal secular processes, decreases at intermediate interaction strengths, and rises again in the strong interaction regime, likely reflecting the role of dense environments in sustaining or triggering bars. Our results suggest that internal gravitational instabilities are the primary driver of bar formation. External tidal perturbations play a secondary role, capable of triggering or enhancing bar formation in galaxies that are already internally predisposed. Our findings provide robust observational validation of theoretical bar formation and evolution models in galaxies.

The AAVSO-based historical light curve of the oxygen-rich Mira variable R Leonis is used to determine and analyse the properties of the star's maxima and minima. The pulsation period is found to have shortened by about 3 days over the past two centuries. Superimposed on the mean period are clear modulations on timescales of approximately 35 and 98 years. The depths of extrema show non-random behaviour: minima in particular display strong similarity in depth over extended intervals, with a mean depth difference of 0.26 magnitude for adjacent minima compared to a 0.38 magnitude difference for random pairs. Depth coherence persists for up to about 43 years. Examination of extrema depths over the full observational history of the star reveals gradual long-term changes, consistent with evolution of the circumstellar dust environment.

The Office of Astronomy for Development (OAD) believes that in order for astronomy-for-development activities to be effective, a scientific approach is required. Evaluation is an essential component in identifying which projects work best, for whom and under what conditions. Evidence-informed project design and selection ensures that projects build on past lessons, thereby reducing the risk of negative unintended consequences and increasing the probabilities of positive cost-effective impact. The OAD has developed an Impact Cycle that aims to enhance project design, selection and delivery systems to support such continual improvement and potential expansion. By determining what works - and, importantly, what doesn't work - the OAD can build a library of evidence on best practice and ensure a positive feedback loop for future projects.

We present a chemical abundance study of giant stars in the Galactic open cluster NGC 5822, which hosts two barium stars (#002 and #201) and three lithium-enriched giants (#006, #102, and #240). Using high-resolution optical and near-infrared ($H$ and $K$ band) spectra from FEROS and IGRINS, we determine atmospheric parameters and abundances for 23 elements (Li, C, N, O, F, Na, Mg, Al, Si, P, S, K, Ca, Sc, Ti, Cr, Fe, Ni, Y, Ce, Nd, Yb, and Pb). This includes species not yet studied in this cluster, such as F, P, K, Yb, and Pb, as well as oxygen isotopic ratios $^{16}$O/$^{17}$O and $^{16}$O/$^{18}$O. Membership was assessed using astrometry and chemical abundances, providing insight into the evolutionary stages of Li-enriched giants and cluster parameters (age, distance, extinction). However, the identification of Ba-stars remains challenging due to their binary nature and less reliable astrometric solutions. The cluster's abundances are broadly consistent with expectations for the Galactic thin disk. The mean fluorine abundance agrees with chemical evolution models predicting that young clusters (<2 Gyr) exhibit elevated [F/Fe], with production from SN II, SN Ia, AGB, and Wolf-Rayet stars. No distinct chemical or rotational features were found to explain the lithium enrichment, likely occurring either during the red clump phase or near the RGB tip. For the Ba-stars, nucleosynthesis models combined with the cluster's turn-off mass suggest polluting companion masses of 3.00 and 3.75 $M_{\odot}$ for stars #002 and #201. These results highlight the importance of open clusters as laboratories for chemically peculiar stars.