Papers

Gravitational waves at kilohertz and higher frequencies offer a unique probe of the early Universe at temperatures well beyond the reach of the cosmic microwave background, corresponding to energy scales $\gtrsim 10^9$GeV. Existing detector concepts fall many orders of magnitude short of the big-bang nucleosynthesis (BBN) bound on the stochastic background in this regime. We propose a new interferometric architecture based on closed optical loops, in which the gravitational-wave-induced phase shift accumulates coherently over many traversals. This produces sharp, narrowband resonances whose predictable comb structure provides a distinct experimental signature. For a folded loop with parameters compatible with the Einstein Telescope infrastructure, and finesse values of order 500, we project sensitivity that approaches and even surpasses the BBN bound up to tens of kilohertz after one year of integration. Such loop interferometers thus open a realistic and distinctive path toward exploring high-frequency stochastic gravitational-wave backgrounds.

We revisit and invalidate all dark photon dark matter constraints from resonant conversion of dark photons into photons (plasmons) in the early universe. These constraints rely on the resonant transfer of a substantial portion of the dark photon energy density into the SM plasma, heating the plasma in the process. We demonstrate that this resonant transfer saturates because of plasma nonlinearities. Dark photon dark matter resonantly converts into $k \simeq 0$ Langmuir waves in the early universe electron-ion plasma. Once the Langmuir-wave energy approaches the thermal energy of the plasma, nonlinear effects driven by the ponderomotive force become significant. In particular, we show using dedicated Particle-in-Cell simulations that large-amplitude $k = 0$ Langmuir waves excite higher-k Langmuir and ion acoustic waves, producing strong spatial variations in density and plasma frequency. These inhomogeneities suppress further resonant conversion, limiting the deposited energy to about the thermal energy of the electrons at the time of conversion, orders of magnitude below observable cosmological thresholds. Consequently, the dark photon dark matter constraints are weaker by factors of $3000$ to $10^7$ across ten orders of magnitude in dark photon mass.

We present a global three-dimensional radiation magnetohydrodynamic (RMHD) simulation of a circumbinary disk (CBD) around a massive black hole binary (MBHB) with a total mass $2 \times 10^7\,M_{\odot}$ and mass ratio $0.1$, separated by $100\, GM_{\rm tot}/c^2$. The inclusion of radiation makes the disk thinner, denser, less eccentric at the inner edge, and more filamentary when compared to an otherwise identical locally isothermal MHD disk. The RMHD disk has accretion rate $\sim 0.23\,\dot{M}_{\mathrm{Edd}}$ and produces thermal emission peaking in the near-UV/optical with a luminosity of $\sim 1\, \% L_{\rm {Edd }}$. Compared with an equal-mass binary with the same total mass, the thermal emission of the CBD around the unequal-mass binary is several orders of magnitude brighter and much more variable at far-UV/soft X-rays frequencies. Similarly, we find that the light curve associated with the $0.1$ mass ratio binary exhibits dominant periodicity corresponding to 2 binary orbits, compared to the equal-mass binary that shows periodicity at 2.5-5 binary orbits. Our results highlight the importance of radiation for the structure and observational properties of MBHB circumbinary disks and have implications for detecting electromagnetic counterparts to LISA gravitational wave precursors and for the heavier binaries targeted by the Pulsar Timing Arrays.

We present a fully Bayesian, data-driven framework for identifying quasinormal modes in high-accuracy Cauchy-Characteristic Evolution (CCE) gravitational waveforms. Applying this to a public catalog, we identify QNM overtones, retrograde modes, and nonlinear modes up to cubic order in the ringdown. Multiple high-order overtones are found near the merger, confirming their physical significance for modeling the ringdown. The ringdown mode content is tabulated across a wide range of start times for all available simulations, providing a systematic reference for theoretical and observational studies. We also search for late-time power-law tails, which are, as expected, absent from the CCE waveforms.

Extragalactic nebular emission has long been a workhorse probe of the processes driving galaxy evolution, but the richness of JWST spectroscopy has shifted the bottleneck from data acquisition to physical interpretation and modelling. In this context, we present a major update to the Monte Carlo radiative transfer code COLT to facilitate self-consistent modelling of nebular line and continuum emission from simulated galaxies. We introduce a new thermal equilibrium solver that iteratively couples to the existing ionization solver and radiation field to compute effective gas temperatures by accurately balancing photoionization heating, radiative and dielectronic recombination, collisional ionization, charge exchange, metal and primordial line cooling, free-free emission, and Compton scattering. To prevent over-cooling where non-equilibrium hydrodynamics dominate, we introduce a Courant-limited cooling prescription tied to each cell's sound-crossing time, preserving temperatures in the diffuse halo while allowing physically motivated cooling in the interstellar medium (ISM). Applied to an isolated local galaxy simulation, the equilibrium solver reshapes the ISM phase space by reducing spuriously excessive lukewarm ($T=10^3-10^4$K) gas and better resolving warm ionized and cold neutral phases, while leaving the CGM largely intact. We further implement a level population solver based on modern atomic data, enabling accurate cooling and emissivities for a large library of UV to infrared metal lines, together with newly implemented primordial nebular continuum emission from free-free, free-bound, and two-photon processes. Finally, by applying COLT to the high-redshift THESAN-ZOOM simulations, we reproduce observed emission-line ratios, establishing COLT as a robust framework for forward modelling nebular emission across cosmic time.

We present a radiation-hydrodynamics (RHD) scheme that enables 3D simulations resolving both protostellar interiors and their surrounding accretion flows within a single framework, to clarify how a protostar evolves while interacting with the accretion flow. The method builds on an explicit two-moment M1 closure scheme with a reduced speed of light approximation (RSLA) for massively parallel computation. Our scheme introduces a complementary non-RSLA radiation component that dominates in optically thick regions. This hybrid treatment restores physical energy conservation inside protostars, which would otherwise be violated under the RSLA, while retaining the advantage of large time steps. To overcome the limitation of the conventional M1 closure in solving radiative transfer in extremely optically thick regions inside protostars and across steep optical-depth gradients near their surfaces, we incorporate the optical-depth information of neighboring cells into the radiative transfer calculation. We further evolve photon-number densities in addition to radiation energy densities to reconstruct an effective local spectrum on the fly without resorting to costly multi-frequency transport. We implement this scheme in the adaptive mesh refinement code SFUMATO and verify its validity through a series of test calculations. As an application, we follow the early evolution of a massive protostar formed at high redshift, within a full cosmological context. The results reveal a continuous structure connecting the swollen protostar and its surrounding disk, which cannot be captured in conventional 1D models. This RHD scheme opens a path to studies of protostellar evolution and its interaction with the accretion flow in realistic 3D environments.

We propose using current and future large-volume neutrino telescopes as “Large Neutrino Colliders" (L$\nu$Cs) to explore TeV-scale physics beyond the Standard Model. Cosmic neutrinos with energies above 100 PeV colliding with nucleons in the detector reach center-of-mass energies beyond the 14 TeV limit of the Large Hadron Collider (LHC). Using recently predicted and measured high-energy and ultra-high-energy neutrino fluxes from IceCube and KM3NeT, we estimate mass-scale sensitivities for representative new physics scenarios at 1–30 km$^3$ L$\nu$Cs. Our results demonstrate that L$\nu$Cs provide a novel avenue to probe multi-TeV particles with sensitivities comparable to, or even surpassing, those of the LHC.

We investigate magnetic-field amplification driven by the nonresonant hybrid (NRH or Bell) instability and its impact on cosmic-ray (CR) acceleration at reverse shocks of ultrafast outflows (UFOs) from active galactic nuclei (AGN). Previous kinetic studies by particle-in-cell simulations have demonstrated that when maximum CR energy is near the injection scale, NRH instability efficiently amplifies magnetic field up to the saturation level. However, the efficiency of NRH instability goes down as maximum energy increase since CR current is carried by escaping CRs near the maximum energy. We employ a one-dimensional MHD–CR framework solving telegraph-type diffusion–convection equations to trace the coupled evolution of CRs, magnetic fields, and shock dynamics under realistic parameters. We find a distinct transition with magnetic field strength: for weak background fields ($B_{0}\!\lesssim\!10^{-4}\,\mathrm{G}$), NRH instability efficiently amplifies upstream turbulence, driving a self-regulated state where $E_{\max}$ becomes independent of initial strength of magnetic turbulence. In contrast, for stronger background fields ($B_{0}\!\gtrsim\!10^{-3}\,\mathrm{G}$), the escaping CR current is too weak to drive NRH instability, and magnetic turbulence further decays through parametric instabilities, potentially reducing the acceleration efficiency. We give the physical interpretation for the transition and discuss conditions for PeV–EeV acceleration at UFO reverse shocks.

Ultralight dark matter may couple quadratically to Standard Model particles. Such quadratic interactions give rise to both coherent and stochastic signals in pulsar timing array (PTA) observations. In this work, we characterize these signals, including the effects of dark matter propagation in a finite-density medium, and assess the sensitivity of current and upcoming PTA observations to their detection. For coherent signals, we find that the sensitivity of current PTA observations competes with and sometimes exceeds that of other probes, such as equivalence principle tests and atomic clocks. For stochastic signals, we find that PTA sensitivities underperform equivalence principle constraints for both existing and upcoming PTA data sets.

We present $\texttt{SBi3PCF}$, a simulation-based inference (SBI) framework for analysing a higher-order weak lensing statistic, the integrated 3-point correlation function (i3PCF). Our approach forward-models the cosmic shear field using the $\texttt{CosmoGridV1}$ suite of N-body simulations, including a comprehensive set of systematic effects such as intrinsic alignment, baryonic feedback, photometric redshift uncertainty, shear calibration bias, and shape noise. Using this, we have produced a set of DES Y3-like synthetic measurements for 2-point shear correlation functions $\xi_{\pm}$ (2PCFs) and i3PCFs $\zeta_{\pm}$ across 6 cosmological and 11 systematic parameters. Having validated these measurements against theoretical predictions and thoroughly examined for potential systematic biases, we have found that the impact of source galaxy clustering and reduced shear on the i3PCF is negligible for Stage-III surveys. Furthermore, we have tested the Gaussianity assumption for the likelihood of our data vector and found that while the sampling distribution of the 2PCF can be well approximated by a Gaussian function, the likelihood of the combined 2PCF + i3PCF data vector including filter sizes of $90'$ and larger can deviate from this assumption. Our SBI pipeline employs masked autoregressive flows to perform neural likelihood estimation and is validated to give statistically accurate posterior estimates. On mock data, we find that including the i3PCF yields a substantial $63.8\%$ median improvement in the figure of merit for $\Omega_m - \sigma_8 - w_0$. These findings are consistent with previous works on the i3PCF and demonstrate that our SBI framework can achieve the accuracy and realism needed to analyse the i3PCF in wide-area weak lensing surveys.

Consistency relations of large-scale structure offer a unique and powerful test of the weak equivalence principle (EP) on cosmological scales. If the EP is violated, different tracers will undergo different accelerations in response to a uniform gravitational field, and this loss of universality manifests as a dipole with a characteristic $1/K$ scale dependence in the squeezed limit of the bispectrum. In this work we show that such a violation can be identified with a particular anti-symmetric modulation in the local cross-power spectrum of distinct tracers. Based on this observation, we propose to test the EP using quadratic estimators as a more practical alternative to the conventional approach of directly estimating the bispectrum. We apply our quadratic estimator to a DESI-like survey and forecast constraints on the overall amplitude of EP violation. Including mildly nonlinear scales in our reconstruction ($k_\mathrm{max}\simeq0.15\, h\,\mathrm{Mpc}^{-1}$), we find that our estimator is competitive with the more exhaustive direct bispectrum approach. This shows that surveys like DESI can already benefit from the quadratic estimator approach.

Double-bump showers are a rare class of extensive air showers (EAS) predicted by Monte Carlo simulations. They occur when a high-energy secondary particle, the leading particle, travels significantly farther than the rest, creating a distinct double-peaked longitudinal profile. So far, no experiment has been able to directly detect these showers. The unique radio footprint of double-bump showers, characterized by multiple Cherenkov rings, provides a way to reconstruct longitudinal profiles from radio observations. With its dense antenna array and broad frequency range, the Square Kilometer Array Observatory (SKAO) will be the first experiment capable of detecting these features, offering a new opportunity to probe hadronic interactions and constrain particle cross sections at high energies. In our analysis, we simulate the EAS using CORSIKA with the CoREAS plugin for radio. We developed a new method based on the Akaike information criterion to identify double bump showers in simulations by analyzing their longitudinal profiles. Then we investigate the prevalence of these double bump showers across different cosmic ray primary particles and various hadronic interaction models. We create a skeleton of the EAS which consists of all the particles with at least $1\%$ of the primary energy, allowing us to confirm the leading particle hypothesis and track shower development following these particles. This will enable us to relate the attributes of the leading particle to measurable parameters. Depending on the exact shower properties, the radio footprint of a double bump shower can create a complex interference pattern, consisting of multiple rings. From this information, the longitudinal profiles can be extracted. SKA due to its dense antenna array and frequency range will be the first experiment able to observe these double bump showers in detail.

The polarization of X-ray synchrotron emission in blazars directly probes the magnetic field geometry and particle acceleration processes in relativistic jets. We use particle-in-cell simulations of magnetic reconnection and magnetized turbulence, coupled to polarization-sensitive radiative transfer code, to interpret IXPE observations of Mrk 421 during a high flux state recorded in December of 2023. To evaluate the fitness of the two theoretical scenarios, we rely on a quantitative comparison of the statistical properties of simulated and observed X-ray flux and polarization light curves using five evaluation metrics, rather than attempting to fit individual data points. We propose a turbulence-driven multi-zone model where jet emission is represented as the sum of the radiative output of N independent cells, each described by a particle-in-cell simulation. Comparison of ensembles of simulated Stokes-parameter light curves with IXPE data shows that magnetic reconnection dominated models provide the best match to the observed X-ray flux and polarization dynamics. The optimal configuration corresponds to N = 15 emitting cells, which reproduces the observed amplitudes and timescales of the X-ray flux and polarization variations. Magnetized turbulence models underpredict both the flux and polarization variability. Our results indicate that a multi-zone, reconnection-powered emission scenario can describe the X-ray polarization behavior of Mrk 421 and establish a quantitative framework for testing theoretical models against IXPE observations of other high-synchrotron-peaked blazars.

Photometric classification of Type Ia supernovae (SNe Ia) is critical for cosmological studies but remains difficult due to class imbalance and observational noise. While deep learning models have been explored, they are often resource-intensive and lack interpretability. We present a computationally efficient and interpretable classification framework that maintains high performance on imbalanced datasets. We emphasize the use of PR-AUC and F1-score as more informative metrics than ROC-AUC in severely imbalanced settings. Using an XGBoost ensemble optimized via Bayesian hyperparameter tuning, we classified light curves from the Supernova Photometric Classification Challenge (SPCC), comprising 21,318 events with a 3.19 imbalance ratio (non-Ia to Ia). Our model achieved a PR-AUC of $0.993^{+0.03}_{-0.02}$, an F1-score of $0.923 \pm 0.008$, and a ROC-AUC of $0.976 \pm 0.004$, matching or exceeding deep learning performance on precision-recall trade-offs while using fewer resources. Despite slightly lower overall accuracy, our method balances false positives and false negatives, improving the efficiency of spectroscopic follow-up. We show that optimized ensemble models offer a reproducible and lightweight alternative to complex architectures, particularly for large-scale surveys such as the Legacy Survey of Space and Time (LSST) where transparency and efficiency are essential.

The redshifted cosmic 21 cm line signal of neutral hydrogen provides the possibility to constrain the matter power spectrum. Cross correlating temperature maps at different frequencies (corresponding to different redshifts along the line of sight) allows to determine multifrequency angular power spectra. Primordial magnetic fields raise the amplitude of the linear matter power spectrum on small scales dominating over the contribution of the adiabatic primordial curvature mode. Multifrequency angular power spectra could provide a new possibility to probe primordial magnetic fields including its evolution present before decoupling. Here first multifrequency angular power spectra of the 21 cm line signal are obtained for cosmological models including the adiabatic, primordial curvature mode as well as the compensated magnetic mode for different values of the magnetic field parameters. For this temperature maps are simulated with the modified linear matter power spectra for magnetic fields with magnetic field strength $B_0=4$ nG and spectral indices $n_B=-2.9$ and $n_B=-2.5$, respectively, which have been chosen as examples. Moreover foregrounds have not been taken into account. As examples these multifrequency angular power spectra have been calculated for frequency ranges set around central frequencies of uGMRT Band 3 data as well as MeerKAT L band data. For these using only system noise signal-over-noise ratios are obtained as well as for SKA1-MID which is part of the currently under construction SKAO. Within this simple model results of this first study seem to be promising for constraining magnetic field parameters especially for SKA1-MID.

Primordial magnetic fields (PMFs) are magnetic fields generated during the early universe. These fields are thought to be the seeds of extragalactic magnetic fields. The origin of PMFs is not well known. Further, if they are indeed sources of extragalactic fields, then there is a possibility that observations of extragalactic magnetic fields could provide insights into the primordial physics. With this motivation, we study the generation of the primordial magnetic field in the context of loop quantum cosmology (LQC). In LQC, inflation is preceded by a quantum bounce. In this work, we consider an electromagnetic field coupled to the background as a test field and study its evolution through the bounce and through the subsequent inflationary phase. We investigate the power spectra generated in LQC and show that it is scale-dependent. We study the power spectra with different initial conditions, discuss equivalent forms of coupling functions, investigate backreaction, and compute the amount of primordial magnetic field which can be measured today. We conclude the article with a summary and discussion of the results.

A long-lived central engine embedded in expanding supernova ejecta can alter the dynamics and observational signatures of the event, producing an unusually luminous, energetic, and/or rapidly-evolving transient. We use two-dimensional hydrodynamics simulations to study the effect of a central energy source, varying the amount, rate, and isotropy of the energy deposition. We post-process the results with a time-dependent Monte Carlo radiation transport code to extract observational signatures. The engine excavates a bubble at the centre of the ejecta, which becomes Rayleigh-Taylor unstable. Sufficiently powerful engines are able to break through the edge of the bubble and accelerate, shred, and compositionally mix the entire ejecta. The breakout of the engine-driven wind occurs at distinct rupture points, and the outflowing high-velocity gas may eventually give rise to radio emission. The dynamical impact of the engine leads to faster rising optical light curves, with photon escape facilitated by the faster expansion of the ejecta and the opening of low-density channels. For models with strong engines, the spectra are initially hot and featureless, but later evolve to resemble those of broad-line Ic supernovae. Under certain conditions, line emission from ionized, low-velocity material near the centre of the ejecta may be able to escape and produce narrow emission similar to that seen in interacting supernovae. We discuss how variability in the engine energy reservoir and injection rate could give rise to a heterogeneous set of events spanning multiple observational classes, including the fast blue optical transients, broad-line Ic supernovae, and superluminous supernovae.

We present the first XRISM/Resolve observation of the persistently accreting neutron star (NS) low-mass X-ray binary Serpens X-1. The source was observed on October 17th, 2024, for approximately 350 ks of elapsed time, resulting in 171 ks of exposure. The source exhibited 22% variability with respect to the average count rate of 73.1 count/s during the observation, but remained in a spectrally soft state throughout. The time averaged spectrum was analyzed in conjunction with spectra extracted from periods of different count rate to check for variations in spectral components. The unprecedented energy resolution of 4.5 eV at 6 keV of XRISM/Resolve provides a detailed look at the shape and structure of the Fe emission line within the data, which shows a dual-peaked structure with an extended red-wing, and steep decline in the blue-wing of the line profile. Fits with the reflection model relxillNS are able to describe the structure in the Fe line region, and confirms previous results that the disk is close to the NS ($R_{\rm in}$ = $1.02_{-0.01}^{+0.21}\ R_{\rm ISCO}$). These models also measure a low systemic inclination ($i=5^{\circ}\pm1^{\circ}$), confirming prior X-ray and optical studies. Alternative models were explored to describe the structure of the Fe line profile, however, relativistic reflection provides the simplest and statistically best explanation of the data.

Galactic cosmic rays (CRs) play a crucial role in galaxy formation and evolution by altering gas dynamics and chemistry across multiple scales. Typical numerical simulations of CR transport assume a constant diffusion coefficient for the entire galaxy, despite both numerical and theoretical studies showing that it can change by orders of magnitude depending on the phase of the interstellar medium. Only a few simulations exist that self-consistently calculate CR transport with diffusion, streaming, and advection by the background gas. In this study we explore three subgrid models for CR diffusion, based on popular theories of CR transport. We post-process an isolated, star-forming MHD galactic disk simulated using the RAMSES code. The resulting diffusion coefficients depend solely on the subgrid turbulent kinetic energy and the MHD state variables of the plasma. We use these models to calculate coefficients for vertical transport. We find that they depend critically on the local magnetic field tilt angle. Across models, our resulting diffusion coefficients range from $10^{26}~\rm cm^2s^{-1}$ to $10^{31}~\rm cm^2s^{-1}$, and yield CR energy densities at the midplane from $1$ to $100 ~\rm eV cm^{-3}$, suggesting varied degrees of backreaction on their environment. Using simple approximations, we show that the gamma ray luminosity of the galaxy depends primarily on the gas surface density and the turbulent confinement of CRs by the galactic corona.

A significant fraction of stars experience close interactions, including collisions resulting from gravitational encounters and mergers within close binary systems. These processes can produce more massive stars that may give rise to relatively rare objects such as blue stragglers. Distinguishing the outcomes of collisions and mergers is challenging yet essential for interpreting observations. This study utilizes the magnetohydrodynamics code AREPO to simulate collisions and mergers of $5$ to $10 \,\mathrm{M}_{\odot}$ main-sequence stars, systematically comparing the properties of the resulting products. Both collisions and mergers yield more massive, strongly magnetized, rapidly and differentially rotating stars with cores enriched in hydrogen, but notable quantitative differences emerge. Merger products exhibit core hydrogen fractions up to $10\%$ higher than those of collision products. In both scenarios, turbulent mixing amplifies magnetic field energies by $9$ to $12$ orders of magnitude. However, magnetic fields in small-impact-parameter collision products display small-scale reversals that may dissipate over time, whereas merger products and large-impact-parameter collision products develop large-scale ordered, potentially long-lived magnetic fields. Additionally, only merger products display magnetically driven, bipolar outflows with radial velocities exceeding $300$ to $400 \,\mathrm{km}\,\mathrm{s}^{-1}$. These distinctions may result in different long-term evolutionary outcomes, which warrant further investigation in future studies.

Radial velocity searches may lead to detection of exoplanets at large orbital separations only if long-enough time-series of data are available. Therefore publication of precise measurements collected in the past is very valuable even if not successfully completed with a definitive detection. Here we present 309 precise ($\sigma$RV$\approx$5-7 m s$^{-1}$) multi-epoch radial velocities for 28 stars observed with the Hobby-Eberly Telescope and its High Resolution Spectrograph between 2004 and 2013. Based on the observations gathered we present a low mass companion ($m_{p}\sin{i}$ = 10.6 $M_{J}$ in 1887.76 $\pm$ 0.01 d, 4.65 au orbit with $e$ = 0.59 $\pm$ 0.01) to a K giant BD+37 3172 ($M$=3.75$\pm$ 0.86 M$_{\odot}$), and a planetary mass companion (m$_{p}\sin{i}$=0.55 M$_{J}$ in 123.05$\pm$0.04 day, 0.55 au orbit with e=0.73$\pm$0.03) to a K giant BD+42 2315 ($M$=1.38$\pm$ 0.30 M$_{\odot}$). We also present two preliminary detections of new spectroscopic binaries: BD+56 2957 (K5) and HD 236555 (G5).

We propose a simple and unified framework that simultaneously explains the origins of light Dirac neutrino masses, asymmetric dark matter (ADM), and the baryon asymmetry of the Universe. The model is based on an extended $U(1)_X$ Froggatt-Nielsen–like mechanism, which naturally generates suppressed Yukawa couplings and realizes a Dirac seesaw for neutrino masses. An additional $\mathbb{Z}_4$ symmetry stabilizes the dark sector, where chiral fermions charged under $\mathbb{Z}_4$ serve as ADM candidates. Leptogenesis occurs through the out-of-equilibrium decays of heavy Dirac neutrinos, where the generated asymmetry is shared between the visible and dark sectors due to exact lepton-number conservation. The same suppression mechanism that explains the smallness of neutrino masses also determines the GeV-scale ADM mass. Numerical studies demonstrate that a fully asymmetric DM scenario is realized, consistent with relic abundance, Big Bang nucleosynthesis, and direct detection constraints. This framework provides an experimentally testable connection between neutrino physics, dark matter, and baryogenesis within an anomaly-free setup.

We investigate the stellar shape and size-mass relationship of X-ray selected Active Galactic Nuclei (AGN) host galaxies using the high-angular resolution and deep sensitivity in the near-infrared of the COSMOS-Web JWST survey field. We present the rest-frame 1-$\mu m$ size, stellar mass, Sersic index, axis-ratio, Gini-$M_{20}$ parameters of 690 moderate luminosity AGNs between redshift 0-3 and with stellar mass $\log M_s\sim 10.75$. We find that AGN host galaxies have an effective radius of 1-5 kpc, which is between star-forming (SFG) and quiescent galaxies (QGs) of the same stellar mass. AGN hosts have similar size-mass trends as SFG and QGs, being smaller at higher redshift for the same stellar mass. The slope of the size-mass relationship of AGN host galaxies is steeper than that of star-forming galaxies. Their rest-frame 1$\mu m$ stellar morphology indicates a significant spheroidal component. We observed a low merger fraction (6%) in our sample as well as substructures similar to disks, bars, and spiral arms in the residual images, which are in tension with evolutionary pathways that require major mergers. However, it may also be due to the different timescales between mergers and AGN activity.

Physics-Informed Neural Networks (PINNs) embed the partial differential equations (PDEs) governing the system under study directly into the training of Neural Networks, ensuring solutions that respect physical laws. While effective for single-system problems, standard PINNs scale poorly to datasets containing many realizations of the same underlying physics with varying parameters. To address this limitation, we present a complementary approach by including auxiliary physically-redundant information in loss (APRIL), i.e. augment the standard supervised output-target loss with auxiliary terms which exploit exact physical redundancy relations among outputs. We mathematically demonstrate that these terms preserve the true physical minimum while reshaping the loss landscape, improving convergence toward physically consistent solutions. As a proof-of-concept, we benchmark APRIL on a fully-connected neural network for gravitational wave (GW) parameter estimation (PE). We use simulated, noise-free compact binary coalescence (CBC) signals, focusing on inspiral-frequency waveforms to recover the chirp mass $\mathcal{M}$, the total mass $M_\mathrm{tot}$, and symmetric mass ratio $\eta$ of the binary. In this controlled setting, we show that APRIL achieves up to an order-of-magnitude improvement in test accuracy, especially for parameters that are otherwise difficult to learn. This method provides physically consistent learning for large multi-system datasets and is well suited for future GW analyses involving realistic noise and broader parameter ranges.

Supernova 1987A was the closest supernova event to be observed in nearly 400 years. The outflowing ejecta from the explosion continues to interact with extended circumstellar material and with the equatorial ring (ER) in the triple ring system, while observations of the system have continued across the whole electromagnetic spectrum. This review mainly focuses on works published over the past ten years on Supernova 1987A and its remnant. These include (a) submillimetre, infrared and X-ray studies of molecules, ions and dust in the ejecta, and (b) infrared, optical and X-ray studies of dust and ionized gas in the ER and in the surrounding circumstellar medium, including their time evolution as the ER is shocked and eroded by the impact of high velocity ejecta. Since 2022, the James Webb Space Telescope has become available for high angular resolution infrared observations of Supernova 1987A and has made significant contributions to both (a) and (b) above. Its discovery of redshifted narrow-line emission from multiple ion species located at the centre of the ejecta strongly requires the presence there of either a cooling hot neutron star, or a pulsar wind nebula, to power the emission.

The sustained gamma ray emission (SGRE) from the Sun is one of the fascinating high energy phenomena closely related to the acceleration of protons to energies >300 MeV. Here we report on the solar cycle variation of SGRE events based on observations from Fermi's Large Area Telescope (LAT). This report covers solar cycles (SCs) 24 and 25 during which Fermi has been operating. Since SGRE events are closely related to solar energetic particle (SEP) events and interplanetary type II radio bursts caused by fast and wide coronal mass ejections (CMEs), we consider these phenomena as well. Many studies have shown that SC 25 is similar or slightly stronger than SC 24. The number of SEP events, GLE events, IP type II bursts, and fast and wide CMEs confirm this conclusion. However, the number of SGRE events observed by Fermi LAT has diminished significantly in SC 25 relative to SC 24. One of the issues has been the reduced coverage of the Sun since 2018 due to a mechanical problem with a solar array of the Fermi mission. By identifying the Fermi LAT gaps and the number of energetic events (fast and wide CMEs, interplanetary type II bursts) we conclude that about three times more SGRE events must have occurred than the 15 events observed by Fermi.

In extreme/intermediate-mass-ratio inspirals (E/IMRIs) embedded in dark-matter (DM) spikes, the secondary black hole can accrete collisionless particles from the surrounding halo. We study how the companion's spin controls this process, and the ensuing back-reaction on the magnitude and direction of the companion's spin vector. We find that higher spin suppresses the mass accretion rate but enhances the accretion-induced torques, driving spin-down and secular alignment of the companion's spin with the orbital plane. Collisionless DM accretion generically imprints a near-universal mass-spin correlation characterized by a spin-evolution parameter $s \simeq 2.8$, much larger than is the case for typical astrophysical environments, and largely independent of the local DM density and the spike slope. The associated spin-down proceeds on astrophysically relevant timescales, thus observations of rapidly spinning IMRI companions would disfavor the presence of dense DM environments, providing constraints complementary to those arising from dynamical friction.

Recently, in the VSX database, G. Murawski reported the discovery of an oscillation with a period of about 40 min in the probable cataclysmic variable 1RXS J014549.6+514314. To confirm the existence of this oscillation and precisely measure its period, I conducted extensive photometric observations of the object over 25 nights between 2022 and 2024. The total duration of these observations was 139 hr. The observations revealed the oscillation on each observation night. This oscillation was coherent throughout all the observations covering 18 months. Due to the large coverage of observations, I was able to determine the oscillation period with high precision. It was found to be 41.485867+\-0.000026 min. The semi-amplitude of the oscillation was large, averaging 0.154(2) mag. The pulse profile of the oscillation did not change during the observations and followed a perfect sinusoidal pattern. With the high precision of the period, I created an ephemeris for the oscillation with a validity time of 30 years. This ephemeris can be used in future studies of changes in the oscillation period. Although short-period X-ray oscillations have not yet been detected in 1RXS J014549.6+514314, the high coherence of its 41-minute oscillation suggests that this object is most likely to be an intermediate polar.

The structural evolution of rotating protoneutron stars encodes essential information about their observable signatures, while microscopic properties provide complementary knowledge to advance observational investigations. Using a relativistic mean-field model with density-dependent couplings that account for temperature and particle composition, we investigate rotation, neutrino-emission-driven changes in angular momentum, particle distributions, temperature profiles, and sound speed to probe the internal dynamics of protoneutron star matter. Additionally, we track the evolution of macroscopic quantities such as energy distribution and gravitational mass and establish direct links between microphysics and global evolution. Extending the framework of Phys. Rev. D 112, 023007 (2025), which focuses on the global properties of rotating protoneutron star evolution, our results reveal that protoneutron star deformation and thermal evolution are governed by angular momentum, mass, and composition. Exotic matter (hyperons and $\Delta$-resonances) and rapid rotation enhance deformation leading to a reduction in core temperature, whereas slowly rotating stars like PSR J0740$+$6620 remain nearly spherical. Our predicted equatorial radii for PSR J0740$+$6620, $13.0\ \mathrm{km} < R_e < 13.5\ \mathrm{km}$, are consistent with NICER measurements. These findings constrain the EoS, requiring a self-consistent treatment of rotation, mass-dependent compression, and composition-driven modeling to accurately model protoneutron star evolution in the context of multi-messenger astrophysics.

We study the orbital structure and precession dynamics of neutral test particles in the magnetized Kerr black hole (MKBH) spacetime-an exact electrovacuum solution of the Einstein-Maxwell equations that self-consistently incorporates the curvature effects of an external magnetic field. This geometry allows a unified treatment of gravitational and magnetic influences across weak to ultra-strong regimes. The analysis reveals a critical magnetic field strength above which no circular geodesics, timelike or null, can exist, establishing an upper magnetic bound for orbital motion. For subcritical fields, the photon circular orbit admits two real roots, the outer of which defines an outermost stable circular orbit (OSCO), complementing the conventional innermost stable circular orbit (ISCO) and confining stable motion within a finite radial domain. Exact expressions for the orbital, radial, and vertical epicyclic frequencies, and their associated precession rates, show substantial deviations from Kerr behavior, including a magnetically induced reversal of periastron precession within a finite radial range. For astrophysically relevant magnetic field strengths, the retrograde precession could be observable at large radii around astrophysical BHs, offering a potential diagnostic of large-scale magnetization. These findings highlight the geometric influence of magnetic curvature on strong-field dynamics, providing a self-consistent framework to interpret quasi-periodic oscillation phenomenology and potential magnetic imprints in precision timing observations of compact objects.