Papers for Friday, Jan 09 2026

Astronomy, often perceived as a distant or luxury science, holds immense potential as a driver for sustainable local socio-economic development. This paper explores how astronomy can create tangible benefits for communities through education, tourism, technology transfer, and capacity building. Using case studies from South Africa, Chile, Indonesia, and India, we demonstrate how astronomical facilities and initiatives have stimulated local economies, generated employment, supported small enterprises, and enhanced STEM participation, while simultaneously inspiring a sense of shared global heritage. The analysis identifies both successes and challenges, including unequal benefit distribution, limited local ownership, and sustainability gaps once external funding ends. Building on these lessons, we propose a practical framework/guidelines for designing, implementing, and evaluating astronomy-based community initiatives, rooted in participatory engagement and aligned with the UN Sustainable Development Goals (SDGs). This paper positions astronomy as a catalyst for inclusive growth, demonstrating that investment in the cosmos can translate into grounded, measurable benefits for people and places on Earth.

In-space manufacturing is essential for achieving long-term planetary colonization, particularly on Mars, where material transport from Earth is both costly and logistically restrictive. Traditional subtractive manufacturing methods are highly equipment-, energy-, and material-intensive, making additive manufacturing (AM) a more practical and sustainable alternative for extraterrestrial production. Among various AM technologies, selective laser melting (SLM) stands out due to its exceptional versatility, precision, and capability to produce dense metallic parts with complex geometries. However, conventional SLM processes rely heavily on inert argon environments to prevent oxidation and ensure high-quality part formation, conditions that are difficult to reproduce on Mars. This study investigates the feasibility of using carbon dioxide (CO2), which makes up over 95% of the Martian atmosphere, as a potential substitute for argon in SLM. Single-track and two-dimensional 316L stainless steel specimens were fabricated under argon, CO2, and ambient air environments with a wide range of laser parameters to evaluate the influence of atmospheric composition on surface morphology, microstructural cohesion, and oxidation behavior. The results reveal that no single parameter controls the overall part quality; rather, a balance of parameters is essential to maintain thermal equilibrium during fabrication. Although parts produced in CO2 exhibited slightly inferior surface finish, cohesion, and oxidation resistance compared to argon, they performed significantly better than those fabricated in ambient air. These findings suggest that CO2-assisted SLM could enable sustainable in situ manufacturing on Mars and may also serve as a cost-effective alternative shielding gas for terrestrial applications.

We investigate the effect of charge migration and residual non-linearity on the JWST/NIRSpec G395H NRS1 and NRS2 detectors using Bright Object Time Series (BOTS) observations of the ultra-hot Jupiter WASP-121b. These full-orbit phase curve observations were taken over 37.8 hours (1.57 days), and provide an excellent testbed of the non-linearity behavior of NRS1 and NRS2 over long timescales. For both detectors, our analysis demonstrates charge losses at the center of the spectral trace and charge excesses at the trace edges. We find that the NRS1 detector displays ~3x larger deviations from linearity compared to NRS2. Given the large transit (~1.5%) and eclipse (~0.5%) signals for WASP-121b, we also investigate variations in the distribution of charge throughout the time-series observation. Our results show that charge distribution varies at different planetary orbital phases for NRS1, which manifests as a change in the morphology and shape of the spectral trace over the course of the time-series. The effect of charge distribution on the trace shape is not evident for NRS2.

Binary black holes (BBHs) exhibiting spin-induced orbital precession offer unique insight into compact-binary formation channels, cosmology, and tests of general relativity. We conduct a dedicated search for precessing BBHs in Advanced LIGO's third observing run (O3) using the harmonic decomposition method of precessing waveforms. We introduce a novel scheme to reduce the number of filters in a harmonic search. With our new approach, our template bank requires $5\times$ fewer filters compared to another proposed precessing search in the same region. We do not find any new significant events. Our new search method achieves up to $\sim 28\%$ improvement in sensitivity and up to $5\times$ lower computational costs compared to existing precessing search pipelines. Our method enables scalable, sensitive searches for precessing BBHs in future gravitational-wave observing runs.

We propose a new Bayesian framework to infer the neutron star equation of state (EOS) from mass and radius observations and neutron matter theory by defining priors that directly parameterize mass-radius space instead of pressure-energy density space. We use direct and accurate inversion approximations to map mass-radius relations to the underlying EOS. We systematically compare its EOS inferences with those inferred from traditional EOS parameterizations, taking care to quantify the systematic prior uncertainties of both. Our results show that prior uncertainties should be included in all Bayesian approaches. The more natural alternative framework provides broader coverage of the physically allowed mass-radius space, especially small radius configurations, and yields enhanced computational efficiency and substantially reduced dependence on prior choices. Our results demonstrate that direct parameterization in observed space offers a robust and efficient alternative to traditional methods.

Context. We study a series of response models to investigate the formation of specific morphological features in the central 1 kpc region of the gas component in barred spiral galaxies. Aims. We aim to understand how structures, such as nuclear rings and spirals, form by varying the parameters of a general gravitational potential and gas properties. Our goal is to determine how much the shape of these structures is driven by the orbital dynamics of the models compared to the influence of the hydrodynamics of the gas. In particular, we examine the effects of the bar strength, bar shape, pattern speed, and central density, as well as their mutual interdependence. Methods. We modeled the gas flow using hydrodynamical simulations run with the Eulerian RAMSES code. The underlying gravitational potential was a two-dimensional Ferrers bar and the gas was considered to be isothermal. Alongside analyzing the gas response to the imposed gravitational potentials, we carried out orbital studies for all models. This involved assessing the shapes and stability of periodic orbits and analyzing the distribution of regular versus chaotic regions within the systems. Results. The parameters of the gravitational potential alone are insufficient to accurately predict the gas dynamics in a system. The morphology of the gaseous response varies substantially with changes in sound speed, emphasizing the fundamental role of hydrodynamic processes in determining the structure of the gas within the central region. We identify the factors that affect the morphology of nuclear rings and trailing and leading nuclear spirals. The best alignment between our models and structures observed in local barred galaxies is achieved by assuming a sound speed of $c_s=20\,\rm{km\,s^{-1}}$.

We present a five-year X-ray spectral and timing analysis of the optically selected Tidal Disruption Event (TDE) AT2019teq, which displays extreme variability, including order-of-magnitude changes in flux on minute-to-day timescales, and a rare late-time emergence of hard X-ray emission leading to the longest-lived corona in a known TDE. In one epoch, we detect sub-mHz quasi-periodic oscillations with significance tested via MCMC-based red-noise simulations (p $\leq 0.03$). AT2019teq exhibits a clear spectral evolution from a soft (blackbody-dominated) state to a hard (power-law-dominated) state, with a late-time radio brightening that may be associated with the state transition. We identify similarities between AT2019teq's evolution and X-ray binary soft-to-hard state transitions, albeit at higher luminosity and much faster timescales. We use the presence of both a disk-dominated and a corona-dominated state to apply multiple mass estimators from X-ray spectral and variability properties. These techniques are mutually consistent within $2\sigma$ and systematically yield a lower black hole mass ($\log(M_{BH}/M_{\odot}) = 5.67 \pm 0.09$) than inferred from host galaxy scaling ($\log(M_{BH}/M_{\odot})=6.14 \pm 0.19$).

A new tension is emerging between the tight cosmological upper bounds on the total neutrino mass ($\sum m_\nu \lesssim 0.06 \, \rm{eV}$) and the lower limits from oscillation experiments, with potentially far-reaching implications for cosmology and particle physics. Neutrinos decaying into massless BSM particles with lifetimes $\tau_\nu \sim 0.01-1\, \rm{Gyr}$ represent a theoretically well-motivated mechanism to reconcile such measurements. Using DESI DR2 and CMB datasets, we show that such decays relax the bound on the total neutrino mass up to $\sum m_\nu < 0.23 \, \rm{eV}$ (95%), restoring full agreement with oscillation data. We also present the first late-time cosmological analysis of neutrino decays into lighter neutrinos in a manner consistent with the measured mass splittings. In contrast to the decays into massless BSM particles, we find that this scenario only marginally alleviates - or even tightens - the cosmological neutrino mass bounds, depending on the mass ordering.

The Atacama Large Millimeter/submillimeter Array and the James Webb Space Telescope are transforming our understanding of galaxy formation and evolution in the early Universe. By combining their capabilities, these observatories provide unprecedented insights into the gas, dust, and stars of high-redshift galaxies at spatially resolved scales, unveiling the complexities of their interstellar medium, kinematics, morphology, active galactic nuclei, and star formation activity. This review summarizes recent breakthroughs in the study of galaxies during the first billion years of cosmic history, highlighting key discoveries, open questions, and current limitations. We discuss how observations, theoretical models, and simulations are shaping our understanding of early galaxy evolution and identify promising directions for future research. While significant progress can be achieved through optimized use of existing facilities and collaborative efforts, further advances will require enhanced angular resolution and sensitivity, motivating upgrades to current instruments and the development of next-generation observatories.

At high eccentricities, tidal forcing excites vibrational modes within orbiting bodies known as dynamical tides. In this paper, we implement the coupled evolution of these modes with the body's orbit in the \texttt{REBOUNDx} framework, an extension to the popular $N$-body integrator \texttt{REBOUND}. We provide a variety of test cases relevant to exoplanet dynamics and demonstrate overall agreement with prior studies of dynamical tides in the secular regime. Our implementation is readily applied to various high-eccentricity scenarios and allows for fast and accurate $N$-body investigations of astrophysical systems for which dynamical tides are relevant.

The Fermi and eROSITA bubbles in the Milky Way represent an archetypal case of galactic nucleus feedback, yet their origin remains highly debated. Here we use hydrodynamic simulations to investigate the formation of the "Fermi bubbles" in the nearby Circinus galaxy, a pair of kpc-scaled elliptical bubbles seen in both radio and X-ray observations. We find that a pair of active galactic nucleus (AGN) jets drive forward shocks in the circumgalactic medium, and after evolving for ~0.95 Myr, the shock-delineated bubble pair roughly matches the observed Circinus bubbles in size and morphology. Our mock X-ray image and spectrum reproduce the observed edge-brightened X-ray surface brightness distribution and spectrum quite well, and suggest that non-thermal emissions from the jet ejecta also contribute substantially to radio and X-ray emissions from the inner "hotspot" region. We further show that AGN winds tend to produce more spherical bubbles with a wider base near the galactic plane, inconsistent with observations. The hotspot emissions and the misalignment between the galaxy rotational axis and the bubble's axis argue against a starburst wind origin. Our study thus corroborates the AGN jet-shock model for the origin of both the Circinus bubbles and the Fermi bubbles, and suggests that AGN jet feedback may be a common origin of extended gaseous bubbles in regular disk galaxies, potentially playing an important role in their evolution.

We study the flow of gas in a barred-galaxy model, in which a considerable part of the underlying stable periodic orbits have loops where, close to the ends of the bar, several orbital families coexist and chaos dominates. Such conditions are typically encountered in a zone between the 4:1 resonance and corotation. The purpose of our study is to understand the gaseous flow in the aforementioned environment and trace the morphology of the shocks that form. We use two conceptually different hydrodynamic schemes for our calculations, namely, the mesh-free Lagrangian SPH method and the adaptive mesh refinement code RAMSES. This allows us to compare responses by means of the two algorithms. We find that the big loops of the orbits, mainly belonging to the x1 stable periodic orbits, do not help the shock loci to approach corotation. They deviate away from the regions occupied by the loops, bypass them and form extensions at an angle with the straight-line shocks. Roughly at the distance from the center at which we start to observe the big loops, we find characteristic "tails" of dense gas streaming towards the straight-line shocks. The two codes give complementary information for understanding the hydrodynamics of the models.

We investigate the ionized gas kinematics of HII regions in the disk of NGC 7331 using integral field unit data collected with the Circumgalactic H$\alpha$ Spectrograph (CH$\alpha$S). NGC 7331 is a well-studied nearby galaxy with HII regions resolved by seeing-limited observations, making it ideally suited for this work. The galaxy disk features vigorous star formation, especially in the central ring of starburst activity. We present a catalog of 136 HII regions detected in the SIRTF Nearby Galaxies Survey (SINGS) H$\alpha$ image. Using this refined catalog, we perform aperture photometry on the SINGS narrowband H$\alpha$ images of NGC 7331, extracting the H$\alpha$ luminosity L(H$\alpha$) of these regions. We present corresponding measurements of the average line-of-sight ionized gas velocity dispersion $\sigma$ in these HII regions with CH$\alpha$S. High-resolution velocity and dispersion maps of the galactic disk are produced from the CH$\alpha$S spectral imaging, selecting spaxels with high signal to noise in order to measure velocity dispersions as low as 12 km s$^{-1}$. Our measurements of the L(H$\alpha$), $\rm \Sigma_{SFR}$ and $\sigma$ in NGC 7331 are consistent with spatially resolved observations of HII regions in large surveys of nearby galaxies. We explore the L(H$\alpha$)$- \sigma$ relationship, identifying turbulent HII regions with nonthermal dispersions likely driven by stellar feedback. The dispersion is correlated with the star formation rate surface density, and using the relation $\rm \sigma \propto \epsilon \Sigma_{SFR}^{\alpha}$, HII regions in NGC 7331 are best fit by $\epsilon = 80$ , $\alpha =0.285$.

We present the longest-term optical analysis of the AM CVn system KL Dra using $\sim11$ years of monitoring from TESS and wide-field ground-based surveys. The continuous TESS coverage allows us to characterise its frequent outbursts with unprecedented detail, providing the first comprehensive study of an AM CVn during outbursts and enabling detailed modelling of these systems. The superoutbursts in KL Dra generally include a precursor, and are followed by a series of rebrightenings after which a sequence of 3-4 large amplitude normal outbursts is observed. We fit parametric profiles to each superoutburst component (precursor, rise to plateau, plateau, decay), to rebrightenings, and to normal outbursts, which let us quantify every high state feature and investigate correlations with the system's long term supercyle evolution. Our continuous coverage reveals an average value for the supercycles, superoutbursts and normal outbursts of $60.4 \pm 0.1$ d, $5.67\pm0.03$ d and $1.17 \pm0.01$ d, respectively. The supercycle duration may be correlated with the rebrightenings duration and superoutburst amplitude, and anticorrelated with the plateau length. Within a supercycle, normal outbursts grow in amplitude and duration, and the first normal outburst is usually highly asymmetric, while subsequent normal outbursts are more symmetric. We detected superhumps in TESS superoutbursts but not in the rebrightenings or normal outbursts. We interpret the results within the disk instability model, considering additional effects, such as changes in the donor mass transfer rate.

Decayless kink oscillations are frequently observed in solar coronal loops and are considered potential contributors to coronal heating. Despite the ubiquity of this wave phenomenon, its driving mechanism remains unclear. Studies to derive the polarization state of these oscillations, which would be a key to identifying the drivers, have been limited due to observational constraints. We analyze a 3D MHD simulation of coronal loops using the MURaM code. Synthetic extreme ultraviolet (EUV) emission maps, combined with velocity diagnostics, are used to identify and characterize transverse wave motions in the simulated loop structures. This is the first demonstration of decayless kink waves emerging self-consistently in a 3D MHD loop-in-a-box model. The simulation produces persistent, low-amplitude, decayless kink oscillations that closely match observed properties. These oscillations arise spontaneously, without any imposed periodic driver, and exhibit clear linear polarization with oscillation planes not aligned to the principal axes. The observed coherency of linear polarization with oscillation cycles favors a self-sustained or quasi-steady type wave driver over a stochastic or broadband source.

The recent detection of a nanohertz stochastic gravitational wave background (SGWB) challenges conventional astrophysics by observed signal amplitude exceeds predictions from standard SMBHB populations without implausible accretion histories. To resolve this amplitude tension, we introduce the Radiative SIDM Dilution this http URL explain the observed spectrum emerges as a hybrid signal by an astrophysical floor, dynamically suppressed by the cored halos of Self-Interacting Dark Matter (SIDM),and a dominant cosmological peak generated during a supercooled phase transition in the dark sector. By performing a free spectral reconstruction and Bayesian model comparison, we demonstrate that a transition defined by a nucleation temperature $T_* \approx 1.24$ MeV and inverse duration $\beta/H_* \approx 150$ not only fills the spectral gap left by stalled binaries but yields statistical evidence($\Delta \text{BIC} \approx 15$) over purely standard astrophysical interpretations. The thermodynamics required to reproduce this SGWB signature also resolves the thermal overproduction of resonant SIDM. The entropy injected by the transition naturally provides the specific dilution factor $D \approx 100$ needed to reset the dark matter relic density to observation. This mechanism also has broader cosmological this http URL residual dark radiation alleviates the Hubble tension $\Delta N_{\rm eff} \sim 0.3$ while bubble collisions generate magnetohydrodynamic turbulence sufficient to seed primordial magnetic fields $B_0 \sim 10^{-13}$ G. These convergences suggest that the NANOGrav excess is not an anomaly, but the acoustic signature of the entropy injection event that rendered the dark sector cosmologically viable.

Spectroscopic observations by the James Webb Space Telescope (JWST) have revealed young, compact, high-redshift ($z$) galaxies with high nitrogen-to-oxygen (N/O) ratios. GN-z11 at z=10.6 is one of these galaxies. One possible scenario for such a high N/O ratio is pollution from supermassive stars (SMSs), from which stellar winds are expected to be nitrogen-rich. The abundance pattern is determined by both galaxy evolution and SMS pollution, but so far, simple one-zone models have been used. Using a galaxy formation simulation, we tested the SMS scenario. We used a cosmological zoom-in simulation that includes chemical evolution driven by rotating massive stars (Wolf-Rayet stars), supernovae, and asymptotic giant branch stars. As a post-process, we assumed the formation of an SMS with a mass between $10^3$ and $10^5$ $M_\odot$ and investigated the contribution of its ejecta to the abundance pattern. The N/O ratio was enhanced by the SMS ejecta, and the abundance pattern of GN-z11, including carbon-to-oxygen and oxygen-to-hydrogen ratios, was reproduced by our SMS pollution model if the pollution mass fraction ranges within 10-30 per cent. Such a pollution fraction can be realized when the gas ionized by the SMS is polluted, and the gas density is $10^4$-$10^5$ cm$^{-3}$ assuming a Strömgren sphere. We also compared the abundance pattern with those of other N/O-enhanced high-$z$ galaxies. Some of these galaxies can also be explained by SMS pollution.

The field of time-domain astronomy has experienced unprecedented growth due to the increasing deployment of robotic telescopes capable of autonomous, round-the-clock sky monitoring. These instruments have revolutionized the detection and characterization of transient phenomena such as supernovae, gamma-ray bursts, variable stars, and gravitational wave counterparts. This paper explores the transformative role of robotic telescopes such as ZTF, ATLAS, and LCOGT in enabling rapid-response observations and building large time-series datasets. We review the design principles and scheduling algorithms behind robotic observatories and assess their scientific contributions across different wavelength regimes. Particular attention is given to the synergy between robotic systems and machine learning pipelines that enable real-time classification of transient events. We also discuss challenges such as data deluge, follow-up prioritization, and observational biases, as well as future directions in global telescope networks

We present a systematic study of the evolution of low- and intermediate-mass X-ray binaries (L/IMXBs) consisting of a $1.4\,M_{\odot}$ neutron star (NS) and a donor star of mass $1-8\,M_{\odot}$. Using grids of detailed MESA simulations, we show that for donor masses of $2-8\,M_{\odot}$, mass transfer may be dynamically unstable, leading to a common envelope (CE) phase. By adopting CE ejection efficiencies in the range $\alpha_{\rm CE} = 0.3-3.0$, we find that post-CE binaries frequently experience a CE decoupling phase (CEDP), which plays a critical role in determining their final orbital and compositional properties. Systems with initial donor masses $\gtrsim 3.5\,M_{\odot}$ predominantly evolve into NS binaries with carbon-oxygen or oxygen-neon white dwarfs (WDs) with masses between $0.5\,M_{\odot}$ and $1.4\,M_{\odot}$. Comparison with the observed population of binary pulsars with a WD companion shows better agreement with higher CE ejection efficiencies ($\alpha_{\rm CE} = 3.0$). Furthermore, we demonstrate that NSs can accrete a sufficient amount of matter ($\gtrsim 0.01\,M_{\odot}$) during the CEDP and subsequent Case BA/BB/BC mass transfer phases to be effectively recycled into millisecond pulsars. We identify two distinct evolutionary channels capable of reproducing the observed characteristics of the millisecond pulsar PSR J1928+1815 with a helium-star companion. Our results highlight the importance of the CEDP in the formation of recycled pulsars and provide constraints on the CE ejection efficiency during binary evolution.

Tidal disruption event (TDE) light curves are increasingly used to infer the masses of quiescent supermassive black holes ($M_{\rm{BH}}$), offering a powerful probe of low-mass black hole demographics independent of host-galaxy scaling relations. However, the reliability of most semi-analytic TDE models assume full stellar disruption, despite theoretical expectations that partial disruptions dominate the TDE population. In this work we test the robustness of current TDE models using three repeating partial TDEs (rpTDEs), in which the multiple flares produced by the same surviving stellar core must yield consistent black hole masses. We present spectroscopic observations establishing AT 2023adr as a rpTDE, making it the third such spectroscopically confirmed event. We independently model the flares of the three rpTDEs; 2020vdq, 2022dbl, and 2023adr, applying fallback-accretion fits, stream-stream collision scaling relations, luminosity-based empirical relations, and cooling-envelope fits. After accounting for statistical and model-specific systematics, we find that all TDE models generally return self-consistent $M_{\rm{BH}}$ values between flares, and are broadly consistent with host-galaxy $M_{\rm{BH}}$ proxies, recovering $M_{\rm{BH}}$ to within 0.3-0.5 dex. However, the convergence of fallback models towards unphysical stellar masses and impact parameters reveals limitations in the existing fallback model grids. We also show that light curve coverage, particularly in the near-UV, is critical for constraining model parameters. This has direct implications for interpreting the thousands of TDE light curves expected from upcoming surveys such as the Rubin Observatory's Legacy Survey of Space and Time, where from simulations, we find that $M_{\rm{BH}}$ may be underestimated on average by 0.5 dex without additional follow-up.

Active galactic nuclei (AGNs) are the compact, energetic central regions of galaxies, powered by supermassive black holes that accrete surrounding gas and dust. Their optical spectra can be identified by strong emission-line signatures (broad and/or narrow lines). Those showing only narrow lines are classified as 'Type 2' AGN. Extensive surveys like SDSS cover AGN in the Northern Sky, but the equivalent coverage in the Southern Sky remains limited. We address this by presenting a new catalogue of Type 2 AGN from the 6dF Galaxy Survey (6dFGS), which has 136,304 spectra covering roughly 17{,}000~\mathrm{deg}^2, mainly of low-redshift galaxies. We use a median absolute deviation cut on the continuum-fitted spectrum to select emission line galaxies. AGN were identified by fitting the 6dFGS spectra with a modified Python QSO fitting tool (PyQSOFit). All selected spectra were visually inspected and corrected for fitting errors where necessary. 10,492 narrow emission line galaxies were identified in 6dFGS, including 5000 Type 2 AGN classified from Baldwin--Phillips--Terlevich (BPT) diagram. They have a median redshift of z$ \sim 0.032$ and a median $[\mathrm{O\,III}]$ luminosity of $\Log(L_{[\mathrm{O\,III}]}/ergs s^{-1}) \sim 40.04$.

Nuclear yields are powerful probes of supernova explosions, their engines and their progenitors. In addition, as we improve our understanding of these explosions, we can use nuclear yields to probe dense matter and neutrino physics, both of which play a critical role in the central supernova engine. Especially with upcoming gamma-ray detectors that can directly detect radioactive isotopes out to increasing distances from gamma-rays emitted during their decay, nuclear yields have the potential to provide some of the most direct probes of supernova engines and stellar burning. To utilize these probes, we must understand and limit the uncertainties in their production. Uncertainties in the nuclear physics can be minimized by combining both laboratory experiments and nuclear theory. Similarly, astrophysical uncertainties caused by simplified explosion trajectories can be minimized by higher-fidelity stellar-evolution and supernova-engine models. This paper reviews the physics and astrophysics uncertainties in modeling nucleosynthetic yields, identifying the key areas of study needed to maximize the potential of supernova yields as probes of astrophysical transients and dense-matter physics.

The jet compositions of gamma-ray bursts (GRBs) are very important to understand the energy dissipation and radiation mechanisms, but it remains an open question in GRB physics. In this paper, we present a systematic analysis to search for 88 bright GRBs that include a total of 129 pulses observed by Fermi/GBM with redshift measured, and extract the spectra of each pulse with Band function (Band), cutoff power-law (CPL), blackbody (BB), non-dissipative photospheric (NDP), Band+BB, as well as CPL+BB. We find that 80 pulses, 35 pulses, and 14 pulses present purely non-thermal, hybrid, and thermal spectra, respectively. By focusing on those 80 pulses with purely non-thermal spectra, one can estimate the lower limits of magnetization factor ($\sigma$) via suppressing the pseudo-thermal component. It is found that 30 pulses in 21 GRBs are the lower limit of $\sigma>5$ at the photosphere by adopting $R_{0}=10^{10}$ cm. It suggests that at least the outflow of those GRB jets with high $\sigma$ is dominated by Poynting-flux. On the other hand, we also perform the light curve fitting with a fast-rise-exponential-decay (FRED) model for 15 bright GRBs with a high magnetization factor in our sample, and find that a correlation between pulse width ($w$) and energy of 13 GRBs really exists in their energy-resolved light curves. It is also a piece of independent evidence for those GRBs with a high value $\sigma$ to support the origin of the Poynting flux outflow.

We present a detailed transit photometric analysis of the ultra-hot Jupiter WASP-12 b using data from the Transiting Exoplanet Survey Satellite (TESS). The study is based on publicly available calibrated light curves and target pixel files accessed through the Mikulski Archive for Space Telescopes (MAST) cloud infrastructure. After extracting and normalizing the photometric time series, the light curve was phase-folded using an initial ephemeris and modeled with a physical transit model to determine the system's geometric parameters. From the transit modeling, we measure the planet-to-star radius ratio, orbital inclination, impact parameter, and transit duration. Adopting stellar parameters from the literature, we derive the planetary radius and transit depth, confirming the highly inflated nature of WASP-12 b. Individual mid-transit times were measured and used to refine the orbital ephemeris through a weighted linear fit. The resulting refined orbital period and reference epoch improve the predictive accuracy of future transit times over the TESS observational baseline. An observed-minus-calculated (O-C) analysis reveals no statistically significant transit timing variations, indicating that the timing data are consistent with a linear ephemeris within the measurement uncertainties. This work demonstrates the capability of TESS photometry to provide precise transit characterization and ephemeris refinement for well-studied exoplanet systems, and provides updated parameters that are relevant for future atmospheric and dynamical investigations of WASP-12 b.

We present the UV/X-ray joint spectral analyses of four Seyfert~1 galaxies (PG 0804+761, NGC 7469, SWIFT J1921.1-5842, and SWIFT J1835.0+3240) using the data acquired with the Ultraviolet Imaging Telescope and Soft X-ray Telescope onboard AstroSat. We model the intrinsic UV/X-ray continuum with the accretion disk, warm and hot Comptonization using the OPTXAGNF and FAGNSED models, where the disk seed photons are Comptonized in the warm and hot corona. The Eddington ratio of the four Seyferts ranges from 0.01 to 1. In the case of SWIFT J1835.0$+$3240, we infer a compact warm corona ($ R_{warm} - R_{hot} \lesssim 18 r_{g}$) while, PG 0804+761, NGC 7469, and SWIFT J1921.1-5842 may exhibit a larger warm Comptonizing region ($\gtrsim 32r_{g}$). We could constrain the spin parameter in PG 0804+761, $a^{\star} = 0.76_{-0.20}^{+0.08}$ (1$\sigma$ error), with the FAGNSED model. In SWIFT J1835.0+3240 and SWIFT J1921.1-5842, the UV/X-ray spectral variability may be driven by the thermal Comptonization of the disk seed photons in the hot corona. Furthermore, the observed spectral hardening with the decrease in disk temperature and accretion rate compared to earlier observations may indicate a state transition in SWIFT J1835.0+3240 from a high/soft to a low/hard state.

In this pilot study, we investigate the PN population in M~33, a nearby spiral galaxy ($\simeq 840$~kpc), using data from the DR3 of the Javalambre-Photometric Local Universe Survey (J-PLUS), a 12-band photometric dataset extensively used to identify H$\alpha$ line emitters. From the 143 known PNe of M~33, the photometry of only 13 are present in the J-PLUS catalog, as available on the J-PLUS portal. With the aim of recovering a larger fraction of the M~33 PN population, the software SExtractor is adopted to extract the sources in the J-PLUS images and obtain the photometric data for the PNe known in the literature, performing PSF photometry when possible. With this procedure the photometry of 98 PNe was obtained using H$\alpha$ image as detection image, including the 13 already present in the J-PLUS catalog. Using diagnostic color-color diagrams (DCCDs) based on criteria developed for Milky Way halo PNe, we identified 16 sources with PN-like colors. Cross-match with existing catalogs revealed that most of these candidates are H II regions, though one source remains unidentified. Additionally, analyzing their full width at half maximum, most of them would not be PN candidates. This highlights the method's ability to select emission-line objects but also underscores the challenge of distinguishing PNe from contaminants using photometry alone. The J-PLUS colors of 98 known PNe were analyzed, together with literature information on their radial velocities, resulting in the identification of one possible halo PN. This is the first paper which aims at detecting extragalactic PNe in multi-band surveys such as J-PLUS, the Southern Local Universe Survey (S-PLUS) and the Javalambre-Physics of the Accelerating Universe Astrophysical Survey (J-PAS), paving the way for similar studies in these surveys for other nearby galaxies, which lack catalogs of known PNe.

Multiple-frequency periodograms -- based on time series models consisting of two or more independent sinusoids -- have long been discussed. What is new here is the presentation of a practical, simple-to-use computational framework implementing this concept. Our algorithms have super resolution that evades the Rayleigh criterion, as well as provision for statistical weighting and tapering. They can be used for essentially any time series (e.g. time-tagged events or point measurements) with arbitrary sampling -- even or uneven. Examples of super resolution of synthetic data, sunspot numbers, and the rich pulsations of white dwarf J0135+5722, demonstrate practical applications. Appendices derive generalized periodograms using an arbitrary number of arbitrary basis functions (following Bretthorst, 1988)and define several examples of non-sinusoidal bases for these ``omnigrams.'' Application beyond the frequency domain is demonstrated with an autoregressive model exhibiting super resolution in the time domain. A GitHub repository containing omnigram code, and symbolic algebra scripts for generating it, will soon be available.

Far-ultraviolet (FUV) radiation is a driving source of photochemistry in planetary atmospheres. Proper interpretation of atmospheric observations requires a full understanding of the radiation environment that a planet is exposed to. Using the Suborbital Imaging Spectrograph for Transition-region Irradiance from Nearby Exoplanet host stars (SISTINE) rocket-borne spectrograph, we observed the Sun-like binary system $\alpha$ Centauri AB and captured the FUV spectrum of both stars simultaneously. Our spectra cover 980--1570 Å, providing the broadest FUV wavelength coverage taken in a single exposure and spanning several key stellar emission features which are important photochemical drivers. Combining the SISTINE spectrum with archival observations, model spectra, and a novel stellar activity model, we have created spectral energy distributions (SEDs) spanning 5 Å--1 mm for both $\alpha$ Centauri A and B. We use the SEDs to estimate the total high-energy flux (X-ray--UV) incident on a hypothetical exoplanet orbiting $\alpha$ Centauri A. Because the incident flux varies over time due to the orbit of the stellar companion and the activity level of each star, we use the VULCAN photochemical kinetics code to estimate atmospheric chemical abundances in the case of minimum and maximum flux exposure. Our results indicate that enhanced atmospheric mass loss due to stellar binarity will likely not be an issue for future exoplanet-hunting missions such as the Habitable Worlds Observatory when searching for Earth-like planets around Sun-like stars.

Research on dual active galactic nuclei (AGNs) is crucial for understanding the coevolution of galaxies and supermassive black holes. However, the current number of dual AGNs remains scarce. In this work, we selected 173 new dual AGNs, 4 AGN triplets, and 1 AGN quadruplet from the Million Quasars Catalog, all with low redshift ($z < 0.5$), a projected distance ($r_p$) of no more than 100 kpc, and a line-of-sight velocity difference ($|\Delta v|$) of less than 600 km s$^{-1}$, thus supplementing existing low-redshift dual AGNs demographics. Visual inspection of the optical images from the Dark Energy Spectroscopic Instrument Legacy Survey was performed for each pair, revealing that $\sim$16\% of pairs exhibit tidal features. Statistical analyses show an increasing number of dual AGNs with decreasing redshift, with velocity difference primarily at $|\Delta v| < $ 300 km s$^{-1}$, which is likely an artifact of our selection strategy. The tidal sample peaks as having 13 pairs at 5-20$h^{-1}_{70}$ kpc, but drops to 1 pair $> 55\,h^{-1}_{70}$ kpc. Our study also explores thewide separation ($r_p>10$ kpc) dual AGNs, finding 165 such systems, with 25 displaying clear tidal features. Furthermore, some extra galaxies, AGNs, and/or their candidates were found in the same regions of the pairs or multiplets forming interacting systems with these pairs or multiplets.

Extensive astronomical surveys, like those conducted with the {\em Chandra} X-ray Observatory, detect hundreds of thousands of unidentified cosmic sources. Machine learning (ML) methods offer an efficient, probabilistic approach to classify them, which can be useful for making discoveries and conducting deeper studies. In earlier work, we applied the LightGBM (ML model) to classify 277,069 {\em Chandra} point sources into eight categories: active galactic nuclei (AGN), X-ray emitting stars, young stellar objects (YSO), high-mass X-ray binaries, low-mass X-ray binaries, ultraluminous X-ray sources, cataclysmic variables, and pulsars. In this work, we present the classification table of 54,770 robustly classified sources (over $3\sigma$ confidence), including 14,066 sources at $>4\sigma$ significance. To ensure classification reliability and gain a deeper insight, we investigate the multiwavelength feature relationships learned by the LightGBM model, focusing on AGNs, Stars, and YSOs. We employ Explainable Artificial Intelligence (XAI) techniques, specifically, SHapley Additive exPlanations (SHAP), to quantify the contribution of individual features and their interactions to the predicted classification probabilities. Among other things, we find infrared-optical and X-ray decision boundaries for separating AGN/Stars, and infrared-X-ray boundaries for YSOs. These results are crucial for estimating object classes even with limited multiwavelength data. This study represents one of the earliest applications of XAI to large-scale astronomical datasets, demonstrating ML models' potential for uncovering physically meaningful patterns in data in addition to classification. Finally, our publicly available, extensive, and interactive catalogue will be helpful to explore the contributions of features and their combinations in greater detail in the future.

Our prior research found that a $90^{\circ}$ configuration of two planetary groups were temporally associated with significant changes in global electromagnetic standing waves (Schumann resonances) during and after the three $90^{\circ}$ configuration events occurring in late 2017 and early 2018. Specifically noted were reductions in variability moving into an event and level changes immediately after a event. Because global standing-wave data have a short history and no $90^{\circ}$ events have occurred since that period, we examine here whether these geometric configuration events correspond to similar signatures in the long sunspot count record. Using daily sunspot data from January 1935 through December 2024, we conducted empirical studies assessing variance changes, post-event level shifts, and potential intrinsic oscillatory structure. In Study A, a variance-ratio test showed that sunspot variability was systematically lower during the events than in the preceding period, with 21 of 26 events since 1935 exhibiting reduced variance (binomial $p=0.0025$). In Study B, solar activity level declined roughly 21 days after events ended, with 21 of 26 events showing negative changes (binomial $p=0.0025$). In Study C, wavelet and filtering analyses revealed no internal solar oscillations at comparable timescales. These findings provide empirical evidence that the configuration events are associated with shifts in solar activity. The next three configuration events in mid- and late-2026 offer an opportunity to assess these patterns in real time.

We observed high-resolution optical spectra of 11 RV Tauri stars without IR excess, with the primary goal of searching for chemical depletion patterns. Using equivalent widths of absorption lines, we calculated photospheric parameters and chemical element abundances for five stars in the sample: HD 172810, V399 Cyg, AA Ari, V457 Cyg, and V894 Per. Only the abundance pattern of V457 Cyg suggests depletion. In the spectrum of this star, TiO lines are also observed in emission in addition to metal emissions. V457 Cyg is likely a binary system that was once surrounded by a circumbinary disc. In the spectrum of V894 Per, we find a set of spectral lines that appear to belong to another star, corroborating that it is an eclipsing variable rather than an RV Tauri star. The high overabundance of sodium may result from mass transfer within the binary system.

Self-interacting dark matter (SIDM) is a well-motivated extension of cold dark matter that can modify halo structure on galactic and group scales while remaining consistent with large-scale structure. However, practical SIDM work often requires bridging several layers, including microphysical scattering models, velocity-dependent effective cross sections, phenomenological astrophysical constraints, and (separately) data-driven halo fits, such as rotation curves. In this paper, we describe \texttt{sidmkit}, a transparent and reproducible Python package designed to support SIDM ``micro$\rightarrow$macro'' calculations and to provide a robust batch pipeline for fitting rotation curves in the SPARC data. On the SIDM side, \texttt{sidmkit} implements velocity-dependent momentum-transfer cross sections for a Yukawa interaction using standard analytic approximations (Born, classical, and Hulthén-based) with a numerical partial-wave option for spot checks. It also provides consistent velocity-moment averaging for Maxwellian relative speeds, scattering-rate utilities, and curated literature \emph{summary} constraints for regression tests and exploratory scans. On the rotation-curve side, we implement bounded non-linear least squares fits of NFW and Burkert halo models to SPARC baryonic decompositions, with optional mass-to-light priors and information-criterion summaries (AIC/BIC). For the demonstration dataset, we process 191 \texttt{rotmod} galaxies (LTG+ETG bundles) and fit both NFW and Burkert models (382 total fits). We find that Burkert is preferred by $\Delta \mathrm{BIC} > 0$ for $65.4\%$ of galaxies, with ``strong'' preference ($\Delta \mathrm{BIC}>6$) in $32.5\%$ of galaxies;

We present a rigorous and comprehensive investigation of a generalized inflationary perturbation theory designed to address persistent large-scale anomalies in the Cosmic Microwave Background (CMB). Motivated by the Trans-Planckian problem and potential non-canonical dynamics in the early Universe, we introduce a generalized Sasaki-Mukhanov equation characterized by a time-dependent correction term, parameterized by a coupling constant f. Unlike the standard slow-roll approximation, we derive the exact analytical solutions for the mode functions in terms of Whittaker functions, ensuring a precise treatment of the mode evolution across the horizon. We compute the resulting primordial scalar power spectrum, which exhibits scale-dependent oscillatory modulations and a distinct suppression of power at low multipoles. We numerically implement this modified framework within the Cobaya Bayesian inference engine. Utilizing the latest Planck 2018 temperature and polarization likelihoods combined with high-resolution data from the Atacama Cosmology Telescope (ACT) DR6, we perform a robust Monte Carlo Markov Chain (MCMC) analysis. Our results place stringent constraints on the modification parameter, |f| <= 10^-4, at a 95% confidence level. However, we find intriguing hints that the generalized model provides a better fit to the low-l CMB spectrum compared to the standard LambdaCDM model, effectively alleviating the low-quadrupole anomaly without compromising the fit at smaller scales. We discuss the implications of these findings for the energy scale of inflation and the validity of the effective field theory description during the inflationary epoch.

The absolute calibration of period-luminosity (PL) relations of Cepheids in the Milky Way (MW) and its nearby galaxies has been a cornerstone in determining extragalactic distances and the current local expansion rate of the Universe. However, the universality of PL relations is still debated; particularly, the metallicity effect on the Cepheid PL relation. Due to the HIF-stellar photosphere interactions in Cepheids, different period-color (PC) relations at different phases can influence the corresponding PL relations at those this http URL have considered the PL relations at multiple pulsation phases as they capture the ensemble radiation hydrodynamic properties at those phases. We investigate the effect of metallicity on PL relations based on multiphase analysis of classical Cepheid light curves in the MW, Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC). Multiphase metallicity coefficients $(\gamma)$ are derived in five different photometric bands ($V$, $I$, $G$, $G_{\rm BP}$, $G_{\rm RP}$) and two Wesenheit indices ($W_{VI}$, $W_{G}$). We show that the coefficients of multiphase period-luminosity-metallicity (PLZ) relations vary dynamically as functions of Cepheid pulsation phases over a complete pulsation cycle. We find significant differences in the $\gamma_{\lambda}$ values between the short- $(0.4 \leq \log{P} < 1)$ and long-period $(1 \leq \log{P} < 2)$ Cepheids at multiple phases, in two bands, $G_{\rm RP}$ and $W_{G}$. The weighted averages of the multiphase $\gamma_{\lambda}$ values are found to be in good agreement with the latest results published in the literature. Our methods and results provide new insights into the metallicity effect on the Leavitt law, which can be useful in constraining pulsation models. Additionally, this study shows that the metallicity effect on mean-light PL relations can be recovered from its phase-dependent nature found in this study.

Modern radio telescope surveys, capable of detecting billions of galaxies in wide-field surveys, have made manual morphological classification impracticable. This applies in particular when the Square Kilometre Array Observatory (SKAO) becomes operable in 2027, which is expected to close an important gap in our understanding of the Epoch of Reionization (EoR) and other areas of astrophysics. To this end, foreground objects, contaminants of the 21-cm signal, need to be identified and subtracted. Source finding and identification is thus an important albeit challenging task. We investigate the ability of AI and deep learning (DL) methods that have been previously trained on other data domains to localize and classify radio galaxies with minimal changes to their architectures. Various well-known pretrained neural network architectures for image classification and object detection are trained and fine-tuned and their performance is evaluated on a public radio galaxy dataset derived from the Radio Galaxy Zoo. A comparison between convolutional neural network (CNN)- and transformer-based algorithms is performed. The best performing architecture is systematically optimized and an uncertainty estimation is performed by means of an ensemble analysis. Radio source classification performance nearly comparable to the current leading customized models can be obtained using existing standard pretrained DL architectures, without modification and increase in complexity of the model architectures but rather adaptation of the data, by combining various transformations on replicated image channels. Using an ensemble of models can also further improve performance to over 90% accuracy, on par with top-performing models in the literature. The results can be transferred to other survey data, e.g. from the Murchison Wide-field Array (MWA), and in the future be used to study the EoR with the SKAO.

We present a new measurement of the Hubble constant ($H_0$) resulting from the first joint analysis of standard sirens with weak gravitational lensing and galaxy clustering observables comprising three two-point correlation functions (3$\times$2pt). For the 3$\times$2pt component of the analysis, we use data from the Dark Energy Survey (DES) Year 3 release. For the standard sirens component, we use data from the Gravitational-Wave Transient Catalog 4.0 released by the LIGO-Virgo-KAGRA (LVK) Collaboration. For GW170817, the only standard siren for which extensive electromagnetic follow-up observations exist, we also use measurements of the host galaxy redshift and inclination angle estimates derived from observations of a superluminal jet from its remnant. Our joint analysis yields $H_0 = 67.9^{+4.4}_{-4.3}$~km~s$^{-1}$~Mpc$^{-1}$, a $6.4\%$ measurement, while improving the DES constraint on the total abundance of matter $\Omega_m$ by $22\%$. Removing the jet information degrades the $H_0$ precision to $9.9\%$. The measurement of $H_0$ remains a central problem in cosmology with a multitude of approaches being vigorously pursued in the community aiming to reconcile significantly discrepant measurements at the percent-level. In light of the impending new data releases from DES and LVK, and anticipating much more constraining power from 3$\times$2pt observables using newly commissioned survey instruments, we demonstrate that incorporating standard sirens into the cosmology framework of large cosmic surveys is a viable route towards that goal.

On 26 September 2022, the NASA Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, the secondary component of the binary asteroid (65803)~Didymos. This experiment tested the Kinetic Impactor technology for diverting dangerous asteroids. Due to the impact, the binary system's angular momentum has changed, resulting in a significant change in the orbital period of Dimorphos. Precise values of the pre- and post-impact orbital periods were derived from a large set of photometric light curves measured for the Didymos-Dimorphos system during six apparitions from 2003 to 2023. We used these data to detect a possible change in the rotation period of the primary as a consequence of the impact. We analyzed the binary system's light curves using the binary asteroid light curve decomposition method. We selected parts of the light curves covering orbital phases outside mutual events, which represent the primary rotational light curves. We applied the light curve inversion method to construct a convex shape model of Didymos and determine its rotation period before and after the impact. These two periods were treated as independent free parameters of the modeling. We found a value of 2.2603891 +/- 0.0000002 h for the pre-impact period and 2.260440 +/- 0.000008 h for the post-impact period. Their difference 0.18 +/- 0.03 s is small yet significant, indicating that the rotation of Didymos became slower after the DART impact. The most plausible physical explanation is Didymos's post-impact reshaping, making its shape more oblate.

We investigated the long-term evolution of the cyclotron line energy, as well as the relationship between cyclotron line energy and luminosity in the high-mass X-ray binary Vela X-1, based on archival Swift/BAT monitoring from 2005 to 2024 and pulse-to-pulse analysis of nine NuSTAR observations from 2012 to 2024. Our results provide the first confirmation that the long-term decay of the harmonic line energy ($E_{\rm cyc,H}$) in Vela X-1 has ended. We further report the first detection of a transient increase in $E_{\rm cyc,H}$ between 2020 and 2023, which suggests a sudden and significant change in the magnetic field configuration or accretion geometry. In addition, $E_{\rm cyc,H}$ shows slightly lower values at low luminosities and tends to flatten at higher luminosities, in the range of $(0.13\text{--}1.21) \times10^{37} $erg $\rm{s}^{-1}$. The fundamental line energy ($E_{\rm cyc,F}$) exhibits no significant variation with time or luminosity, remaining stable at approximately 25 keV.

When a stellar binary encounters a spinning black hole, interesting phenomena might result due to the mutual interaction between the binary spin, orbital angular momentum and the black hole spin. Here we consider such encounters between an intermediate mass spinning black hole and a close identical white dwarf binary system whose center of mass follows a parabolic trajectory. After studying a corresponding three-body problem in the point particle approximation, we perform a suite of smoothed particle hydrodynamics based numerical simulations of such scenarios. For this, we integrate the geodesic equations for the spinning black hole, while considering the hydrodynamics and the self and mutual gravitational interactions of the stars in a Newtonian approximation, an approach justified by the choice of parameters in the theory. We consider various initial configurations of the binary center of mass leading to equatorial and off-equatorial orbits, as also various initial inclinations between the binary's initial spin angular momentum and its initial orbital angular momentum. We find that the effects of black hole spin manifest clearly in the tidal dynamics of the binary components, while the observables of tidal encounters such as mass fallback rates are strongly dependent on the initial inclination angle. We show that the influence of the black hole spin emerges in distinct ways for different initial configurations of the binary's spin alignment. We establish that within the ambits of the Hills mechanism, in certain cases, the fallback rate may show a three-hump structure, due to interactions between tidal debris of the individual stars.

While the temporal variations of the spectro-polarimetric nature of pulsars remains unexplored, this investigation offers significant potential for uncovering key insights into pulsar emission mechanisms, magnetic field geometry, and propagation effects within the magnetosphere. We developed a package for investigating time-varying spectral behavior for full Stokes parameters and demonstrate it on a millisecond pulsar (MSP) J2144-5237 in a binary system (orbital period ~10 days) using the Parkes UWL receiver. In this study we report rotation measure (RM) variation with orbital phase. We find that the temporal variations in the spectra of Stokes I, Q, and V are generally correlated throughout the orbit, while Stokes U exhibits intervals of both correlation and anticorrelation with Stokes I, depending on the orbital phase. We also provide a Poincare sphere representation of the polarization properties of J2144-5237, demonstrating a systematic temporal change of Poincare sphere location for the main component with orbital phase. To our knowledge, this is the first investigation of time-varying properties of the spectro-polarimetric nature of any pulsars or MSPs. Extending this study to probe the spectro-temporal nature of full Stokes data on a larger sample of MSPs or pulsars has the potential to provide vital information on emission mechanisms inside the magnetosphere, interstellar propagation effects, and binary interactions.

Context. Turbulent convection models in nonlinear radial stellar pulsation models rely on an extra equation for turbulent kinetic energy and fail to adequately explain mode-selection problems. Since multidimensional calculations are computationally expensive, it is reasonable to search for generalizations of physically grounded 1D models that approximate multidimensional results with sufficient accuracy, at least in a given parameter range. A natural way of progressing from one-equation models is to use additional nonlocal equations. While these types of models also exist in the literature, they have not been adopted for this type of object. Aims. We aim to adapt the three-equation turbulent convection model from Kuhfuss to radial stellar pulsation modeling. Methods. We use a Reynolds-stress one-point closure approach to derive our extensions alongside the model, while using additional models from the literature to close the anisotropy and dissipation terms. Results. We provide five extensions to the original model. These include an enhanced dissipation correction to the mixing length, a local anisotropy model replacing eddy viscosity, a second-order correction for turbulent ion transport in the atmosphere (alongside opacity effects), and turbulent damping of entropy fluctuations and convective flux.

The search for the sources of ultra-high-energy cosmic rays (UHECRs) using high-energy neutrinos represents a frontier in high-energy astrophysics. However, a critical bottleneck remains: the ability to rapidly survey the sizable sky areas defined by the localization uncertainties of neutrino detectors and to provide rapid spectroscopic classification of the multitude of optical transients found within them. By deploying a large field-of-view with high-multiplex Multi-Object Spectroscopy (MOS) on a large aperture telescope, one can instantaneously cover neutrino error circles, thus providing crucial spectroscopic classifications of potential counterparts discovered, for example, by the Vera C. Rubin Observatory (LSST) with unprecedented efficiency. Furthermore, simultaneous operation of a giant panoramic central Integral Field Spectrograph (IFS) would allow for detailed kinematic and environmental characterization of primary candidates. This facility would unlock deep synergies between next-generation neutrino telescopes (IceCube-Gen2, KM3NeT) and gamma-ray observatories (CTAO), transforming unique multi-messenger alerts into a comprehensive physical understanding.

I suggest that some of the mysterious temporal properties of Fast Radio Bursts (FRB) may be explained if they are produced by dynamically triaxial magnetars. If the bursts are narrowly collimated along open field lines, then observed repeating FRB may be those in which the moment of inertia tensor is only slightly triaxial and the rotation axis, open field lines and radiation point nearly to the observer. Apparently non-repeating FRB may be triaxial with the direction of open field lines and radiation wandering across the sky, reducing their duty factors by several orders of magnitude. A slightly triaxial moment tensor in repeaters moves the line of sight into or out of the radiation pattern or within it, explaining periods of greater or lesser (or absent) activity, and making the probability of detecting a burst vary aperiodically. The dynamics of triaxial bodies may also thwart the coherent integration of gravitational signals from fast-rotating accreting neutron stars.

The origin of supermassive black holes (SMBHs) remains a long-standing problem in astrophysics. Recent JWST observations reveal an unexpectedly abundant population of overmassive black holes at z>4-6, where the BH masses lie far above local scaling relations and not reproduced by current cosmological models. How such overmassive black holes form and rapidly grow within young galaxies has remained unclear. Here we present fully cosmological radiation-hydrodynamic simulations that, for the first time, self-consistently follow the birth, early growth, and emergent observable signatures of SMBHs in proto-cluster environments. We find that heavy seeds of order $10^6 M_\text{sun}$ naturally form, exceeding typical theoretical expectations by an order of magnitude. These seeds rapidly develop dense, optically thick disks whose strong electron scattering produces broad H$\alpha$ emission comparable to that seen in little red dots (LRDs). Sustained super-Eddington accretion then drives fast growth to $\sim 3 \times 10^7 ~M_\text{sun}$ by $z \sim 8$. These results provide a unified physical scenario in which LRDs correspond to a short-lived, enshrouded phase of heavy-seed formation, naturally evolving into the overmassive quasars detected by JWST and ultimately the progenitors of today's SMBHs.

To investigate the formation and evolution of vertical structures in disk galaxies, we measure global $\operatorname{sech}^2$ scale heights, averaging thin and thick components when present, for 2631 edge-on disk galaxies with $M_*>10^{10} M_\odot$ at $0< z < 3.5$ from the JWST COSMOS-Web survey. We show that dust extinction systematically overestimates scale heights at shorter rest-frame wavelengths, and therefore adopt a fixed rest-frame wavelength of 1 $\mu$m. After further correcting for projection-induced bias using a new accurate method, we find that the median disk scale height increases from $0.56\pm0.03$ kpc at $z=3.25$ to $0.84\pm0.04$ kpc at $z=1.25$, and subsequently decreases to $0.67\pm0.06$ kpc at $z=0.25$. The disk length-to-height ratio remains constant at $2.7\pm0.2$ for $z>1.5$, but rises to $4.0\pm0.4$ at $z=0.25$. These results imply that the high-redshift progenitors of present-day thick disks were of intermediate thickness, neither thin nor thick, yet dynamically hot and dense. The observed radial variation of scale height is consistent with the artificial flaring expected from observational effects, disfavoring minor mergers as the primary mechanism of disk thickening. Instead, we suggest that the high-redshift intermediate-thickness disks were single-component systems that increased their vertical scale height through decreasing surface mass density and/or violent gravitational instabilities, eventually producing thick disks. Thin-disk growth begins at $z\approx2$ and dominates at $z\lesssim1$, yielding a vertically more compact system with decreasing scale heights from $z\approx1$ to $0$. The inferred thin-disk mass fraction increases from $0.1\pm0.03$ at $z=1$ to $0.6\pm0.1$ at $z=0$. Together, these findings reveal a continuous evolutionary link between high-redshift single-component disks and present-day thick thin disk systems.

The nature of the remnant of a binary neutron star (BNS) merger is uncertain. Though certainly a black hole (BH) in the cases of the most massive BNSs, X-ray lightcurves from gamma-ray burst (GRB) afterglows suggest a neutron star (NS) as a viable candidate for both the merger remnant as well as the central engine of these transients. When jointly observed with gravitational waves (GWs), X-ray lightcurves from BNS merger events could provide critical constraints on the remnant's nature. We aim to assess the current and future capabilities to detect a NS remnant through X-ray observations following GW detections. To this end, we simulate GW signals from BNS mergers and the subsequent X-ray emission from newborn millisecond magnetars. The GW detectability is modeled for both current and next-generation interferometers, while the X-ray emission is reproduced using a dedicated numerical code that models magnetar spin-down and ejecta dynamics informed by numerical-relativity simulations. In our simulations, 2% - 16% of BNS mergers form millisecond magnetars. Among these, up to 70% could be detectable, amounting to up to 1 millisecond magnetar detection per year with SVOM/MXT-like instruments during the LIGO Virgo KAGRA LIGO India (LVKI) O5 run, with optimal detectability occurring about 2 hours post-merger. For next-generation GW interferometers, this rate could increase by up to three orders of magnitude, with peak detectability 3 to 4 hours post-merger. We also explore how the magnetar's magnetic field strength and observer viewing angle affect detectability and discuss optimized observational strategies. Although more likely with upcoming GW interferometers, detecting the spin-down emission of a millisecond magnetar may already be within reach, warranting sustained theoretical and observational efforts given the profound implications for mergers, GRBs, and NS physics of a single detection.

A sample of 278 triple systems with outer separations under 300 au and resolved inner pairs is studied, focusing on the mutual alignment between inner and outer orbits. The degree of alignment increases with (i) decreasing outer separation, (ii) decreasing ratio of outer and inner separations, (iii) decreasing mass of the inner primary component, and (iv) increasing inner mass ratio. There is no dependence on the outer mass ratio. The average mutual inclination is ~40deg for the full sample and ~10deg for 38 triples with primary components less massive than 1 solar and outer separations below 50 au. Inner eccentricities in aligned triples are smaller compared to misaligned ones. In another sample of 371 hierarchies with known outer orbits and inner eclipsing subsystems, only 22% show mutual alignment within 20deg, while the rest are aligned randomly. These findings match qualitatively current understanding of the formation of hierarchical systems, where the N-body dynamics dominates at large scales, while the accretion and migration shape systems closer than $\sim$100 au. Fragmentation of isolated cores apparently produces approximately aligned low-mass hierarchies.

The launch of relativistic jets of plasma on astrophysical to cosmological scales are observed in a variety of astrophysical sources, from active galactic nuclei to X-rays binaries. While these jets can be reproduced by the general relativistic magneto-hydrodynamic (GRMHD) and particle-in-cells (GRPIC) simulations of the dynamical Kerr magnetosphere, the development of analytic models to describe the physics of the jets has remained limited. A key challenge is to analytically describe the individual trajectories of accelerated charged particles which ultimately build up the jet and emit radiation. In this work, we provide a first simple but fully analytical model of jet launching from the Kerr magnetosphere based on the motion of charged particles. To that end, we use the integrability of electrogeodesic motion in the Kerr monopole magnetosphere to study the ejection of charged particles near the poles. This enables us to derive (i) a criterion for the rotation axis to constitute a stable latitunal equilibrium position, thereby representing an idealized jet, (ii) the expression for the magnetic frame-dragging effect, and (iii) the condition for an asymptotic observer to measure blueshifted particles emanating from the black hole surroundings. Our study reveals that particles can be accelerated only in a specific region whose maximal radius depends on the spin and magnetization of the black hole. Alongside these results, we provide a detailed review of the construction of test magnetospheres from (explicit and hidden) symmetries of the Kerr geometry and the condition for the separability of the electrogeodesic motion in a test magnetosphere, which serves as a basis for the model we study in this work.

Ionisation controls the chemistry, thermal balance, and magnetic coupling in protoplanetary discs. However, standard ionisation vectors such as stellar UV, X-rays, Galactic Cosmic Rays (GCRs) might not be efficient enough, as UV/X-rays are attenuated rapidly with depth, while GCRs are modulated. Turbulence-induced magnetic reconnection in disc atmospheric layers offers a physically motivated, in-situ source of energetic particles (EPs) that has never been considered. We quantify the ionisation and heating produced by EPs accelerated by turbulent reconnection, identify where they dominate over X-rays and GCRs, and determine energetic thresholds for their relevance. We provide scalable diagnostics tied to the local energy budget. We adopt a Fermi-like acceleration model with parameters linked to a turbulent reconnection geometry trigger by the magneto-rotational instability, yielding a steady-state energy distribution of the EP forming a power-law of index $p=2.5$. We propagate electrons and protons through the disc and compute primary and secondary ionisation and associated heating on a fiducial T Tauri disc model background. The non-thermal normalisation is set by the fraction of local viscous accretion energy dissipation channelled to EPs, parametrised by $\kappa$. For $\kappa\gtrsim 0.4\%$, EPs ionisation overpass standard sources like X-rays and GCRs in the disc atmosphere and intermediate/deep layers out to radii of a few tens of AU. Even at $\kappa\sim 0.025\%$, EPs contribute at the few-percent level, thus are chemically and dynamically relevant. EP-induced heating complements UV/X-ray heating in the atmosphere and persists deeper. These results identify EPs accelerated by turbulence-induced magnetic reconnection as a rather robust, disc-internal ionisation channel that should be included in thermo-chemical and dynamical models of protoplanetary discs.

Overdense regions can collapse into primordial black holes (PBHs) in the early universe, which are a compelling candidate for dark matter. Current constraints leave the asteroid-mass window the only possible one for PBH to account for all the dark matter, which can only be probed indirectly by the scalar-induced gravitational waves (GWs) sourced by the curvature perturbation which forms PBH. In this work, we explore the capabilities of future space-based gravitational wave detectors, including LISA, Taiji, and TianQin, to constrain such induced GWs as well as the PBH abundance. We systematically account for the width of the primordial curvature power spectrum, and find that the asteroid-mass window can be fully probed by all three space-based interferometers. If PBHs constitute the majority of dark matter, the induced GW leaves a strong signal in the mHz band with a signal-to-noise ratio of $10^3\sim10^4$.

The origin of carbon monoxide (CO) in Saturn's stratosphere remains uncertain, with proposed sources including internal thermochemical production, cometary impacts, and exogenic material from the rings and icy moons (i.e. Enceladus). We aim to constrain the vertical and meridional distribution of stratospheric CO and assess the relative contributions of these potential sources. Here, we analysed high-spectral-resolution ALMA observations of the CO (J=3-2) line obtained on 25 May 2018, sampling Saturn's limb from 20°S to 69°N. CO vertical profiles were retrieved using a line-by-line radiative transfer model combined with spectral inversion techniques, testing multiple prior scenarios representative of different source hypotheses. CO is confined to a narrow layer between 0.1 and 1 mbar, with a robust negative vertical gradient and mean abundances of (3.7+/- 0.8) x 10$^{-8}$ at 0.1 mbar and (7.2 +/- 0.9) x 10$^{-8}$ at 1 mbar. The meridional distribution is statistically homogeneous, with a marginal enhancement near 60° N plausibly related to Enceladus. No significant equatorial enhancement is detected. The absence of a strong equatorial enhancement rules out a long-lived steady source associated with ring infall. The observations are most consistent with a relatively recent ($\approx$200-year-old or younger) cometary impact whose material has since been horizontally mixed, while any Cassini Grand Finale ring influx was either too recent or inefficient to affect CO abundances at the probed pressure levels.

Radiation-hydrodynamics (RHD) determines the bulk evolution and observable emission in a wide variety of high-energy astrophysical phenomena. Due to their complexity, RHD problems must usually be studied through numerical simulation. We have extended the publicly available RICH code, which previously solved the equations of RHD in the limit of grey flux-limited diffusion (FLD), to operate with a multigroup FLD solver. RICH is a semi-Lagrangian code that solves the equations of RHD on an unstructured moving mesh, and is the first multigroup RHD moving mesh code, making it uniquely applicable to problems with extreme dynamic range and dynamically important radiation forces. We validate our multigroup module against multiple analytic benchmarks, including a novel test of the RHD Doppler term. The computational efficiency of the code is aided by a novel scheme to accelerate convergence in optically thick cells. Finally, we apply multigroup RICH in a pilot study of a stellar tidal disruption event (TDE), using a $10^4 M_\odot$ intermediate-mass black hole. Our simulations self-consistently produce a bright early-time X-ray flash prior to peak optical/UV light, in qualitative agreement with post-processing of (grey) RICH simulations of supermassive black hole TDEs, as well as X-ray observations of the TDE AT 2022dsb.

Active galactic nuclei are known to exhibit flux variations across the entire electromagnetic spectrum. Among these, correlations between UV/optical and X-ray flux variations serve as a key diagnostics for understanding the physical connection between the accretion disk and the corona. In this work, we present the results of analysis of ultraviolet (UV) and X-ray flux variations in the narrow line Seyfert 1 galaxy Mrk 1044. Simultaneous observations in the far-UV band (FUV: 1300$-$1800 Å) and the X-ray band (0.5$-$7 keV) obtained during 31 August $-$ 8 September 2018 with the Ultraviolet Imaging Telescope and the Soft X-ray Telescope onboard \textit{AstroSat} were used for this study. Significant flux variability was detected in both FUV and X-ray bands. The fractional root mean square variability amplitude ($F_{\rm var}$) was found to be 0.036 $\pm$ 0.001 in the FUV band and 0.384 $\pm$ 0.004 in the X-ray band. To explore potential time lag between the two bands, cross-correlation analysis was performed using both the interpolated cross-correlation function (ICCF) and just another vehicle for estimating lags in nuclei (JAVELIN) methods. Results from both approaches are consistent within 2$\sigma$ uncertainty, indicating that X-ray variations lead the FUV variations, with measured lags of 2.25$\pm$0.05 days (ICCF) and $2.35_{-0.01}^{+0.02}$ days (JAVELIN). This is the first detection of a time delay between UV and X-ray variations in Mrk 1044. The observed UV lag supports the disk reprocessing scenario, wherein X-ray emission from the corona irradiates the accretion disk, driving the observed UV variability.

We establish a general, void-based consistency test for Galileon scalar-tensor theories. We show that the previously reported unphysical breakdown of the predicted Newtonian force in certain Galileon models is controlled by a single condition linking non-linear void dynamics to the cosmic expansion history. This connection yields a redshift-dependent upper bound on the allowed depth of voids and promotes this requirement to a new viability condition, complementary to standard stability criteria. As an example, we apply this void-based criterion to a linear parameterization in the scale factor constrained by theoretical and observational bounds; we find that $\sim 60\%$ of the parameter space is excluded, with most problematic models failing by $z\lesssim 10$. These results position cosmic voids as sharp, broadly applicable, theory-informed filters for viable modified gravity, enabling more informed priors and parameter-space choices in future cosmological inference.

The structure of dark matter haloes is often described by radial density profiles motivated by cosmological simulations. These are typically assumed to have a fixed functional form (e.g. NFW), with some free parameters that can be constrained with observations. However, relying on simulations has the disadvantage that the resulting profiles depend on the dark matter model and the baryonic physics implementation, which are highly uncertain. Instead, we present a method to constrain halo density profiles directly from observations. This is done using a symbolic regression algorithm called Exhaustive Symbolic Regression (ESR). ESR searches for the optimal analytic expression to fit data, combining both accuracy and simplicity. We apply ESR to a sample of 149 galaxy clusters from the HSC-XXL survey to identify which functional forms perform best across the entire sample of clusters. We identify density profiles that statistically outperform NFW under a minimum-description-length criterion. Within the radial range probed by the weak-lensing data ($R \sim 0.3 - 3$ h$^{-1}$ Mpc), the highest-ranked ESR profiles exhibit shallow inner behaviour and a maximum in the density profile. As a practical application, we show how the best-fitting ESR models can be used to obtain enclosed mass estimates. We find masses that are, on average, higher than those derived using NFW, highlighting a source of potential bias when assuming the wrong density profile. These results have important knock-on effects for analyses that utilise clusters, for example cosmological constraints on $\sigma_8$ and $\Omega_m$ from cluster abundance and clustering. Beyond the HSC dataset, the method is readily applicable to any data constraining the dark matter distribution in galaxies and galaxy clusters, such as other weak lensing surveys, galactic rotation curves, or complementary probes.

A demonstrated failure mode for operational solar flare forecasting is the inability to forecast flares that occur near, or just beyond, the solar limb. To address this shortcoming, we develop a "4pi" full-heliosphere event forecasting framework and evaluate its statistical classification ability against this specific challenge. A magnetic surface flux transport model is used to generate full-sun maps of the photospheric radial magnetic field from which active regions (ARs) are identified and tracked using a new labeling scheme that is observer-location agnostic and allows for post-facto modifications. Flare-relevant magnetic parameters couple to a "visibility" index that specifies AR location relative to the visible solar limb and expected flare detection. Flare labels are assigned according to peak Soft X-ray flux, and a statistical classification is performed using nonparametric discriminant analysis. A version where new or emerging ARs on the far ("invisible" side of the Sun are incorporated into the model by way of far-side helioseismology, is also tested. We evaluate the new framework by its performance specifically including the limb areas using Brier Skill Score and ROC Skill Score, finding improvement at the 2-sigma level or less. However, we do find that the number of False Negatives, or "missed" forecasts decreases, and find strong evidence that the additional information provided by the far-side helioseismology can help predict near- and just-beyond-limb flares, particularly for East-limb events. While individual components of this framework could be improved, we demonstrate that a known failure mode for solar flare forecasting can be mitigated with available resources.

The 21cm signal of neutral hydrogen contains a wealth of information about the poorly constrained era of cosmological history, the Epoch of Reionization (EoR). Recently, AI models trained on EoR simulations have gained significant attention as a powerful and flexible option for inferring parameters from 21cm observations. However, previous works show that AI models trained on data from one simulator fail to generalize to data from another, raising doubts about AI models' ability to accurately infer parameters from observation. We develop a new strategy for training AI models on cosmological simulations based on the principle that increasing the diversity of the training dataset improves model robustness by averaging out spurious and contradictory information. We train AI models on data from different combinations of four simulators, then compare the models' performance when predicting on data from held-out simulators acting as proxies for the real universe. We find that models trained on data from multiple simulators perform better on data from a held-out simulator than models trained on data from a single simulator, indicating that increasing the diversity of the training dataset improves a model's ability to generalize. This result suggests that future EoR parameter inference methods can mitigate simulator-specific bias by incorporating multiple simulation approaches into their analyses.

The Nancy Grace Roman Space Telescope will carry out a wide-field imaging and slitless spectroscopic survey of Type Ia Supernovae to improve our understanding of dark energy. Crucial to this endeavor is obtaining supernova spectra uncontaminated by light from their host galaxies. However, obtaining such spectra is made more difficult by the inherent problem in wide-field slitless spectroscopic surveys: the blending of spectra of close objects. The spectrum of a supernova will blend with the host galaxy, even from regions distant from the supernova on the sky. If not properly removed, this contamination will introduce systematic bias when the supernova spectra are later used to determine intrinsic supernova parameters and to infer the parameters of dark energy. To address this problem we developed an algorithm that makes use of the spectroscopic observations of the host galaxy at all available observatory roll angles to reconstruct a three-dimensional (3d; 2d spatial, 1d spectral) representation of the underlying host galaxy that accurately matches the 2d slitless spectrum of the host galaxy when projected to an arbitrary rotation angle. We call this ``scene reconstruction''. The projection of the reconstructed scene can be subtracted from an observation of a supernova to remove the contamination from the underlying host. Using simulated Roman data, we show that our method has extremely small systematic errors and significantly less random noise than if we subtracted a single perfectly aligned spectrum of the host obtained before or after the supernova was visible.

We present a general method to reproduce a given cosmological background through energy exchange between dark energy (DE) and dark matter (DM). This can be simply realized with a standard quintessence scalar field that controls the DM mass. In particular a background with phantom crossing can be effectively realized without introducing ghosts or other pathologies. For example one can reproduce exactly the background that gives the best fit to the recent DESI+CMB+DESY5 data, within the Chevallier-Polarski-Linder (CPL) parametrization of DE. Although the background evolution is identical, the perturbations differ, leading to modified growth of structures. If the DM mass varies at late times, early-time observables are not modified and can reproduce the main predictions of the target model, but late-time observables are affected. We discuss in particular the effects on the matter power spectrum, CMB lensing and ISW effect. When reproducing the best fit CPL background model, this scenario generically predicts $\mathcal{O}(10\%)$ deviations in such observables. However, for suitable choices of parameters, effects on the matter power spectrum can be smaller, motivating a detailed study. In general, energy exchange between DE and DM generates a mismatch between the matter power spectrum and the gravitational potential amplitudes compared to the decoupled case, that can lead to deviations observable in future experiments.

The central molecular zone (CMZ), surrounding the Galactic centre, is the largest reservoir of dense molecular gas in the Galaxy. Despite its relative proximity, the 3D structure of the CMZ remains poorly constrained, primarily due to projection effects. We aim to constrain the line-of-sight location of two molecular clouds in the CMZ -the 50 and 20 km/s clouds- and to investigate their possible physical connection using stellar kinematics and photometry. This study serves as a pilot for future applications across the full CMZ. We estimated the line-of-sight position of the clouds by analysing stellar kinematics, stellar densities, and stellar populations towards the cloud regions and a control field. We find an absence of westward moving stars in the cloud regions, which indicates that they lie on the near side of the CMZ. This interpretation is supported by the stellar density distributions. The similar behaviour observed in the two clouds, as well as in the region between them (the ridge), suggests that they are located at comparable distances and are physically linked. We also identified an intermediate-age stellar population (2-7 Gyr) in both regions, consistent with that observed on the near side of the CMZ. We estimated the line-of-sight distances at which the clouds and the ridge become kinematically detectable (i.e. where the proper motion component parallel to the Galactic plane differs from that of the control field at the 3 sigma level) by converting their measured proper motions parallel to the Galactic plane using a theoretical model of the stellar distribution. We find that the 50 and 20 km/s clouds are located at $43\pm8$ pc and $56\pm11$ pc from Sgr A*, respectively, and that the ridge lies at $56\pm11$ pc; this supports the idea that the clouds are physically connected through the ridge.

Quarks and antiquarks carry color and electric charges and belong to the color-triplet $3$ group and the color-antitriplet $\bar 3$ group respectively. The product groups of $3$ and $\bar 3$ consist of the color-singlet $1$ and the color-octet $8$ subgroups. Therefore, quarks and antiquarks combine to form color-singlet $[q \bar q]^1$ quark matter and color-octet $[q \bar q]^8$ quark matter. The color-octet quark matter corresponds to the $q\bar q$ quark matter as envisaged in the realm of present knowledge but the color-singlet quark matter is as yet unexplored and now submitted for exploration. The color-singlet quark matter with two flavors can be separated into charged and neutral color-singlet quark matters. In the neutral color-singlet quark matter, the quark and the antiquark interacting only in the QED interaction may form stable and confined colorless QED mesons non-perturbatively at about 17 MeV and 38 MeV (PRC81,064903(2010) and JHEP(2020(8),165). It is proposed that the possible existence of the QED mesons may be a signature of the neutral color-singlet quark matter at $T=0$. The observations of the anomalous soft photons at CERN, and the anomalous bosons with mass about 17 MeV at ATOMKI, DUBNA, and HUS, and mass about 38 MeV at DUBNA hold promising experimental evidence for the existence of such QED mesons, pending further confirmations.

We present a minimal relativistic completion of MOND in which (i) General Relativity is recovered exactly in the high-acceleration regime, while (ii) the Bekenstein--Milgrom (AQUAL) equation emerges in the low-acceleration regime, without introducing additional propagating fields beyond those already present in a right-handed gauge sector. The construction is motivated by an $E_6\times E_6$ framework in which $SU(3)_R\rightarrow SU(2)_R\times U(1)_{Y'}\rightarrow U(1)_{\rm dem}$, leaving a healthy repulsive $U(1)_{\rm dem}$ interaction whose charge is the square-root mass label. Gravity itself arises from the $SU(2)_R$ connection via a Plebanski/MacDowell--Mansouri mechanism, yielding an emergent tetrad and the Einstein--Hilbert action. MOND is implemented by an infrared (IR) metric deformation $\Delta S_{\rm IR}[g]$ that is UV-vanishing (so GR is recovered) while its deep-MOND/static limit is fixed by a symmetry principle: in three spatial dimensions, the deep-MOND action is conformally invariant with a 10-parameter group isomorphic to $SO(4,1)$ (the de Sitter group). The single MOND acceleration scale is set by a de Sitter radius selected dynamically in the IR, $a_0=c^2/(\xi\,\ell_{\rm dS})$ with $\xi={ O}(1)$ fixed by matching to the static limit. MOND resides in perturbations and quasistatic systems; the homogeneous FRW background is controlled by the IR vacuum kinematics rather than an ad hoc cosmological constant.

We propose a general framework in which a phase transition is triggered during cosmic inflation by the slow-roll dynamics of a spectator field. The topological defects formed at the transition are inflated outside the horizon, reenter it after inflation, and can subsequently generate characteristic gravitational-wave (GW) signals. Quantum fluctuations of the spectator field modulate the timing of the transition, imprinting large-scale anisotropies in the resulting GW background. As an explicit realization, the spectator field may be identified with the Higgs field in a supersymmetric Standard Model. More generally, our framework applies to a wide class of spectator-modulated phenomena, providing a generic mechanism for producing anisotropic GW signals.

We show that metastable cosmic strings break at early times, either via finite-temperature effects or by attaching to pre-existing monopoles during network percolation. The resulting segments can be initially super-horizon in size and thus persist for a significant amount of time. If the strings do not re-percolate, the network's eventual destruction is typically due to this early-time breaking rather than late-time quantum tunnelling. Survival of strings to epochs probed by NANOGrav requires $m_M^2/\mu\gtrsim 10^3$, where $m_M$ and $\mu$ are the monopole mass and the string tension respectively, over an order of magnitude larger than previous estimates. We also revisit quantum-tunnelling induced breaking. Results from numerical simulations suggest that this occurs mainly at rare high-tension points on the strings, yielding a rate much larger than is usually assumed. We briefly discuss the related scenario of flux tubes in a dark QCD-like hidden sector with dark-quark masses above the confinement scale.

In this paper, we investigate the occurrence of late-time cosmological singularities, namely, the rip scenarios within the framework of interacting Fractional Holographic Dark Energy (FHDE). We start our investigation with the Granda-Oliveros (GO) cutoff, i.e., $L=(\gamma H^{2}+\delta\dot{H})^{-\frac{1}{2}}$, and highlight the range of allowed $\alpha$ (Lévy's index) values for which big, little and pseudo rip can occur. In particular, we highlight the occurrence of a big rip for fractional values of the Lévy's index in the allowed range $1<\alpha\leq2$. Moreover, we conclude that the occurrence of a pseudo-rip requires Lévy's index to be $\alpha>2$. Therefore, we reject the possibility of pseudo-rip within the GO cutoff. Furthermore, we demonstrate that the occurrence of the little rip in FHDE equipped with a GO cutoff is rather contrived and requires a specific functional form of the IR cutoff $L\sim(\gamma H^{2}+g(H))^{-\frac{1}{2}}$, which belongs to a larger class of Nojiri-Odintsov (NO) cutoffs. To extend our perspective beyond the GO cutoff, we investigate the interacting FHDE framework equipped with the Hubble cutoff, i.e., $L=H^{-1}$, in developing an ansatz-based approach to the little and pseudo-rip singularities as they fail to appear in the GO cutoff. Within this approach, we invoke the expression of the Hubble parameter, $H(t)$, which corresponds to the little and pseudo-rip, into the cosmological parameters such as the Equation of State (EoS) and Squared Sound Speed (SSS) as a function of cosmic time $t$. We produce numerical plots of these parameters in both linear and non-linear $Q$ regimes, which supplement our theoretical findings. In summary, our results highlight the occurrence of little and pseudo-rip singularities within a Hubble cutoff for a non-linear $Q$ term within the FHDE framework.

We demonstrate that primordial magnetic fields (PMF) play a decisive role in the braneworld baryogenesis scenario of [Phys. Rev. D $\textbf{110}$, 023520 (2024)], where C/CP violation arises from the coupling of visible and hidden matter-antimatter sectors through a pseudo-scalar field. Although this mechanism generates baryon number efficiently only after the quark-hadron transition, by incorporating a realistic stochastic PMF within a semi-analytical framework, we find that matching the observed baryon-antibaryon asymmetry robustly requires PMF strengths of order $10^{10}$ T right after the transition, in agreement with causal QCD-era magnetogenesis. We further reveal that magnetic fluctuations drive the baryon-density spectrum to white noise on large scales, yielding an isocurvature component compatible with Cosmic Microwave Background (CMB) bounds. This establishes a predictive link between the braneworld baryogenesis model and realistic early-Universe magnetic fields.

Radiation hydrodynamics describes the interaction between high-temperature hypersonic plasmas and the radiation they emit or absorb, a coupling that plays a central role in many astrophysical phenomena related to accretion and ejection processes. The HADES code was developed to model such systems by coupling hydrodynamics with M1-gray or M1-multigroup radiative transfer models, which are well suited to optically intermediate media. Despite its accuracy, radiation hydrodynamics simulations remain extremely demanding in terms of computational cost. Two main limitations are responsible for this. First, the M1-multigroup model relies on a closure relation with no analytic expression, requiring expensive numerical evaluations. Second, the Courant-Friedrichs-Lewy condition strongly restricts the time step of the explicit schemes used in HADES. To overcome these difficulties, two complementary Artificial Intelligence based strategies were developed in this thesis. The first approach consists in training a Multi-Layer Perceptron to approximate the M1-multigroup closure relation. This method achieves excellent accuracy while reducing the computational cost by a factor of 3000, making it the most efficient approach currently available for this task. This performance gain enables high-fidelity simulations of radiative shocks, in which radiation directly influences the shock structure. In particular, increasing spectral resolution slows down the shock and enlarges the radiative precursor. The second approach explores the use of Physics-Informed Neural Networks to directly solve the radiation hydrodynamics equations and extrapolate simulations beyond their initial time range. Tests on purely hydrodynamic shocks show accurate handling of discontinuities, but application to radiative shocks remains challenging and requires further investigation.

We investigate the quantum geometry of the Seiberg-Witten curve for $\mathcal{N}=2$, $\mathrm{SU(2)}^n$ linear quiver gauge theories. By applying the Weyl quantization prescription to the algebraic curve, we derive the corresponding second-order differential equation and demonstrate that it is isomorphic to the Extended Heun Equation with $n+3$ regular singular points. The physical parameters of the gauge theory are linked to the canonical coefficients of the Heun equation via a polynomial representation of the Seiberg-Witten curve. This framework provides the necessary mathematical foundation to apply non-perturbative gauge-theoretic techniques, such as instanton counting, to spectral problems in gravitational physics, most notably for higher-dimensional black holes.

Inflation is a necessary cosmic mechanism to cure basic inconsistencies of the standard model of cosmology. These problems are usually `fixed' by postulating the existence of a scalar field (called the ``inflaton''). However, other less ad hoc options are possible. In the running vacuum model (RVM) framework, the vacuum energy density (VED) is a function of the Hubble rate $H$ and its time derivatives: $\rho_{\rm vac}=\rho_{\rm vac}(H, \dot{H},\ddot{H},\dots)$. In this context, the VED is dynamical (there is no rigid cosmological constant $\Lambda$). In the FLRW epoch, $\rho_{\rm vac}$ evolves very slowly with expansion, as befits the observed $\Lambda\simeq$const. behavior. In contrast, in the very early universe the vacuum fluctuations induce higher powers $H^N$ capable of unleashing fast inflation in a short period in which $H\simeq$ const. We call this mechanism `RVM-inflation'. It does not require an inflaton field since inflation is brought about by pure quantum field theory (QFT) effects on the dynamical background. It is different from Starobinsky's inflation, in which $H$ is never constant. In this work, we study a closely related scenario: the decay of the exact de Sitter vacuum into FLRW spacetime in its radiation epoch and the subsequent impact on the current universe, and compare with the RVM. We find that in both cases inflation is driven by $H^4$ powers together with subleading contributions of order $H^2$ that ease a graceful-exit transition into the radiation-dominated epoch, where the FLRW regime starts and ultimately develops a mildly evolving VED in the late universe: $\delta\rho_{\rm vac}\sim {\cal O}(m_{\rm Pl} ^2 H^2)$. The outcome is an unified QFT approach to inflation and dark energy (conceived as dynamical vacuum energy) with potentially measurable phenomenological consequences in the present universe which can help to cure the cosmological tensions.