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The maximal gravitational mass of nonrotating neutron stars (<inline-formula><mml:math><mml:msub><mml:mi>M</mml:mi><mml:mrow><mml:mi>TOV</mml:mi></mml:mrow></mml:msub></mml:math></inline-formula>) is one of the key parameters of compact objects and only loose bounds can be set based on the first principle. With reliable measurements of the masses and/or radii of the neutron stars, <inline-formula><mml:math><mml:msub><mml:mi>M</mml:mi><mml:mrow><mml:mi>TOV</mml:mi></mml:mrow></mml:msub></mml:math></inline-formula> can be robustly inferred from either the mass distribution of these objects or the reconstruction of the equation of state of the very dense matter. For the first time we take the advantages of both two approaches to have a precise inference of <inline-formula><mml:math><mml:mrow><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mi>TOV</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>2.2</mml:mn><mml:msubsup><mml:mrow><mml:mn>5</mml:mn></mml:mrow><mml:mrow><mml:mo>-</mml:mo><mml:mn>0.07</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>0.08</mml:mn></mml:mrow></mml:msubsup><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mo>⊙</mml:mo></mml:mrow></mml:msub></mml:mrow></mml:math></inline-formula> (68.3% credibility), with the updated neutron star mass measurement sample, the mass-tidal deformability data of GW170817, the mass-radius data of PSR <inline-formula><mml:math><mml:mrow><mml:mi>J</mml:mi><mml:mn>0030</mml:mn><mml:mo>+</mml:mo><mml:mn>0451</mml:mn></mml:mrow></mml:math></inline-formula> and PSR <inline-formula><mml:math><mml:mrow><mml:mi>J</mml:mi><mml:mn>0740</mml:mn><mml:mo>+</mml:mo><mml:mn>6620</mml:mn></mml:mrow></mml:math></inline-formula>, as well as the theoretical information from the chiral effective theory and perturbative quantum chromodynamics (pQCD) at low- and very high-energy densities, respectively. This narrow credible range is benefited from the suppression of the high <inline-formula><mml:math><mml:msub><mml:mi>M</mml:mi><mml:mrow><mml:mi>TOV</mml:mi></mml:mrow></mml:msub></mml:math></inline-formula> by the pQCD constraint and the exclusion of the low <inline-formula><mml:math><mml:msub><mml:mi>M</mml:mi><mml:mrow><mml:mi>TOV</mml:mi></mml:mrow></mml:msub></mml:math></inline-formula> by the mass function. Three different EoS reconstruction methods are adopted separately, and the resulting <inline-formula><mml:math><mml:msub><mml:mi>M</mml:mi><mml:mrow><mml:mi>TOV</mml:mi></mml:mrow></mml:msub></mml:math></inline-formula> and <inline-formula><mml:math><mml:msub><mml:mi>R</mml:mi><mml:mrow><mml:mi>TOV</mml:mi></mml:mrow></mml:msub></mml:math></inline-formula> are found to be almost identical, where <inline-formula><mml:math><mml:msub><mml:mi>R</mml:mi><mml:mrow><mml:mi>TOV</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>11.9</mml:mn><mml:msubsup><mml:mn>0</mml:mn><mml:mrow><mml:mo>-</mml:mo><mml:mn>0.60</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>0.63</mml:mn></mml:mrow></mml:msubsup><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mi>km</mml:mi></mml:math></inline-formula> is the radius of the most massive nonrotating neutron star. This precisely evaluated <inline-formula><mml:math><mml:msub><mml:mi>M</mml:mi><mml:mrow><mml:mi>TOV</mml:mi></mml:mrow></mml:msub></mml:math></inline-formula> suggests that the EoS of neutron star matter is just moderately stiff and the <inline-formula><mml:math><mml:mrow><mml:mo>∼</mml:mo><mml:mn>2.5</mml:mn><mml:mi>─</mml:mi><mml:mn>3</mml:mn><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mo>⊙</mml:mo></mml:mrow></mml:msub></mml:mrow></mml:math></inline-formula> compact objects detected by the second-generation gravitational wave detectors are most likely the lightest black holes.

We present spectroscopic follow-up observations of binary systems from the Gaia Data Release 3 (DR3) binary catalog that were selected to have large enough mass functions for their companions to be black holes or neutron stars. The selection includes 20 stars that are astrometric and/or spectroscopic binaries, as well as 11 stars with large accelerations both in the plane of the sky and along the line of sight but no DR3 orbital solution. We provide classifications for this entire sample, including radial velocity orbital solutions for 12 binaries. Apart from the previously published binaries Gaia BH1, Gaia BH , and Gaia NS1, we show that the Gaia orbits are incorrect for all of the stars with candidate dark companions above 2 M<SUB>⊙</SUB>. We suggest more conservative cuts on the significance and goodness-of-fit parameters that may be useful for identifying reliable orbital solutions in the tail of the binary star distribution. Although we find no new confirmed black hole or neutron star companions, one accelerating system has a minimum companion mass of 1.16 ± 0.01 M<SUB>⊙</SUB> that is likely to be a neutron star or an ultramassive white dwarf. The acceleration catalogs may therefore provide a largely unexplored source of additional wide binaries containing compact objects. *This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile.

The recent detection of TeV neutrinos from nearby Seyfert galaxies (e.g., NGC 1068) by IceCube suggests that active galactic nuclei (AGNs) could make a significant contribution to diffuse astrophysical neutrinos. The absence of TeV gamma-rays from NGC 1068 indicates neutrino production in a compact opaque region of gamma-rays. The vicinity of the supermassive black hole, such as the disk corona, is an ideal region, where the high radiation density leads to efficient neutrino production and gamma-ray attenuation. Disk-corona models predict that the neutrino emission from AGNs correlates with X-ray emission, which traces the coronal activity. In this paper, we assess whether diffuse TeV neutrinos can originate from X-ray-emitting AGNs with Monte Carlo simulations, considering the predicted performance of future neutrino telescopes. We test this hypothesis by searching for spatial correlations between the X-ray AGN population and high-energy neutrinos, assuming that the neutrino flux scales with the AGN X-ray flux. After accounting for the fraction of the AGN X-ray flux resolved by eFEDS and the remaining unresolved AGN component, we find that an AGN origin of diffuse neutrinos can be tested at a significance of about 3σ with 10 years of IceCube-Gen2 observations. With improved angular resolution and sensitivity, a 30 km<SUP>3</SUP> scale underwater neutrino telescope such as HUNT is expected to reach a significance of about 6σ with one year of exposure. The detection significance decreases if AGNs contribute partially to the total astrophysical neutrino flux. Our results highlight the critical role of angular resolution in diagnosing the AGN origin of diffuse TeV neutrinos.

We studied the magnetic Penrose process (MPP) in the Kerr-Bertotti-Robinson (KBR) spacetime, an exact rotating electrovacuum solution describing a black hole (BH) immersed in an intrinsic, uniform electromagnetic field. We analyze the behavior of charged particles in this geometry and find that the spacetime structure itself responds non-monotonically to the background magnetic field B. Specifically, both the event horizon and the static limit surface first expand as B increases, reach a maximum size at an intermediate field strength, and then contract toward the extremal limit. Although the ergoregion itself shrinks monotonically with B, this structural feature gives rise to a pronounced non-monotonic dependence of the energy extraction efficiency on the magnetic field B, i.e., the efficiency initially rises, attains a maximum value, and subsequently falls as the extremal condition is approached. This contrasts sharply with the monotonic trends usually associated with magnetic enhancements in the Kerr geometry. We further explore an astrophysical application of the MPP by estimating the maximum energy of electrons escaping from the ergoregion of the KBR BH. Modeling neutron beta decay occurring near the event horizon, we derive an analytical expression for the energy gained by electrons accelerated by the magnetic field. Applying our results to the supermassive BH at the Galactic center, SgrA^*, we find that electrons can be accelerated up to energies of ∼ 10<SUP>15</SUP> eV for realistic values of the spin and magnetic field. Although these energies exceed the observed upper range of cosmic-ray electrons, radiative losses such as synchrotron emission and inverse-Compton scattering can efficiently reduce them to the observed TeV scale. The KBR BH thus provides a clear example of how intrinsically electromagnetic fields can qualitatively affect the BH energetics, introducing an optimal magnetic field strength for rotational energy extraction, a feature with potential implications for high-energy astrophysical environments where magnetic fields are present. Our results show that in electrovacuum spacetimes where the magnetic field is intrinsic to the geometry, the MPP can be significantly modified, revealing a new regime of BH energy extraction.

Solar eruptions are sudden ejections of coronal mass and magnetic fields accompanied by intense energy release. The eruptive structure does not always erupt successfully: it sometimes fails to escape the Sun after initiation. The failure of an eruption, however, provides an invaluable opportunity for improving our understanding of the intricate mechanism of eruptions. Here we present a comprehensive set of observations of a failed prominence eruption on the Sun that takes advantage of multi-viewpoint and multi-messenger imaging. Simultaneous off-limb and on-disk observations provides evidence of magnetic reconnection processes occurring at different sites during the flare. In addition to the standard flare reconnection behind the eruption, strong external reconnection occurs on the erupting flux rope, as evidenced by a wealth of signatures via multi-wavelength imaging and spectroscopy. The two reconnection processes may play contrasting roles in the acceleration of the flux rope and compete in altering the magnetic flux in the rope. As the high rate of external reconnection proceeds, the flux rope and embedded prominence decelerate noticeably and fail to erupt into the heliosphere, under strong magnetic confinement of overlying fields. Our results illustrate a well-defined physical picture for solar eruptive activities and provide insight into the lack of coronal mass ejections seen in other solar-type stars.

There continues to be growing interest in using standard language constructs for parallel and accelerated HPC computing, avoiding the need for (sometimes vendor-specific) external APIs. For Fortran applications, language features such as 'do concurrent' loops open the door for compilers to implement multi-threaded, GPU-accelerated, and even distributed multi-node code with only the standard language. Here, we explore the current status of using 'do concurrent' for GPU-accelerated Fortran applications across three major GPU vendors (NVIDIA, AMD, and Intel). Using a production application, we test their current capabilities, showing where the standard language alone can be used, and where augmenting the code with a directive-based API (e.g., OpenMP) is still desirable or required. Multi-GPU tests are performed with GPU-aware MPI libraries. We find that the three GPU vendors can now GPU-accelerate pure Fortran (zero directives), but that manual data movement directives can help with performance and compatibility. The results show that there is rapid advancement towards making GPU-accelerated scientific HPC code performance portable using the Fortran standard language.

We investigate neutron star matter with hyperons within a density-dependent relativistic mean-field framework using Bayesian inference, considering three composition scenarios: purely nucleonic matter, hyperonic matter under SU(6) flavor symmetry, and hyperonic matter under SU(3) symmetry with free vector-sector parameters. The analysis incorporates constraints from empirical nuclear matter properties, theoretical inputs at low densities, and multimessenger observations of neutron stars. We find that the SU(6) scheme, grounded in the quark model and isospin counting rule, leads to a significantly softer equation of state. In contrast, the additional flexibility of the SU(3) framework enhances vector repulsion and yields a comparatively stiffer equation of state consistent with observational bounds across the explored parameter space; in particular, the posterior distributions favor values of the vector coupling ratio $α_v$ lower than the SU(6) limit $α_v = 1$. These differences are reflected in neutron star observables, including mass--radius relations, tidal deformabilities, direct Urca thresholds, and oscillation properties, all of which remain compatible with current constraints within the SU(3) scenario. We further examine structural signatures through the curvature of the mass--radius relation and find that, although hyperon-rich configurations can induce noticeable variations, such features depend sensitively on the stiffness of the equation of state and are therefore not universally robust indicators. Bayesian model comparison further shows that present constraints do not meaningfully discriminate between the purely nucleonic and SU(3) hyperonic scenarios, while providing positive, but not decisive, evidence against the more restrictive SU(6) framework.

Accretion-induced collapse (AIC) of a rotating oxygen-neon-magnesium white dwarf (WD) is an alternative channel of neutron-star formation, in which a mass-accreting star near the Chandrasekhar mass collapses instead of being disrupted thermonuclearly. If the progenitor WD is sufficiently magnetised, it can drive magnetorotational outflows analogous to those of magnetorotational supernovae and may serve as a site for rapid neutron-capture ($r$-process) nucleosynthesis. We post-process tracer particles from five three-dimensional general-relativistic neutrino-(magneto)hydrodynamic AIC simulations, spanning four initial rotation rates, with the WinNet nuclear reaction network. Ejecta mass, the fraction of matter reaching nuclear statistical equilibrium, and the mass ejected beyond the iron group all increase monotonically with rotation rate, with magnetic fields amplifying these trends. The slowest-rotating model synthesises essentially only iron-group material, while the most rapidly rotating and magnetised model reaches the second $r$-process abundance peak at mass number $A \approx 130$, with a trace, non-robust signal up to $A \approx 244$. The corresponding $^{56}$Ni mass rises from $0.007$ to $0.014 M_\odot$, lower than representative yields for core-collapse supernovae and hypernovae by factors of five to more than forty, implying a correspondingly faint radioactively powered component. Contrary to the picture established for magnetorotationally driven supernovae, the heaviest ejecta do not track the polar outflow: they instead reside in equatorial-to-mid-latitude, moderate-entropy lobes, while the polar column is itself a local minimum in some heavy elements. We conclude that rapidly rotating, magnetised AIC events could contribute to the Galactic yields of trans-iron and weak $r$-process nuclei, although none of our models produces a robust third $r$-process peak.

The quantum memory burden effect can suppress the late-time Hawking evaporation of primordial black holes (PBHs), allowing PBHs below the standard evaporation threshold of approximately $10^{15}\,\mathrm{g}$ to survive until the present epoch and potentially contribute to the dark matter abundance. We investigate primary and secondary neutrino emission from memory burdened Bardeen and Kerr PBHs, including Galactic and extragalactic fluxes and the effects of memory suppression, Bardeen regularization, and Kerr rotation. We constrain their abundance using observations from IceCube, Super-Kamiokande, and ANTARES, together with the projected sensitivities of IceCube-Gen2, GRAND200k, and Hyper-Kamiokande. We find that Bardeen regularization and Kerr rotation produce qualitatively different effects. Increasing the Bardeen parameter suppresses the Hawking temperature and neutrino flux, thereby weakening the abundance constraints. In contrast, rapidly rotating Kerr PBHs that retain a significant residual spin at the onset of the memory burdened phase can exhibit enhanced neutrino emission and substantially stronger constraints. Increasing the memory burden suppression index $k$ reduces the flux normalization but also allows lighter and hotter PBHs to survive, shifting the relevant signal toward higher energies. Consequently, HESE provides the leading sensitivity for weak suppression, whereas IceCube-Gen2 and GRAND200k become particularly important for stronger suppression. These results demonstrate the complementarity of current and future neutrino observations in probing memory burdened PBHs and the effects of regular geometry and rotation on their evaporation.

The degree of black-hole spin─orbit misalignment ("tilts") in the astrophysical population could be a powerful diagnostic to distinguish between binary formation in isolation, in dynamical environments, or in hierarchical triples. However, robust population-level spin tilt measurements are complicated by model mis-specification as well as numerical and Poisson variance, ultimately owing to poor single-event constraints on tilts. Motivated by reports of a possible peak in the spin tilt distribution, we analyze the fourth LIGO─Virgo─KAGRA gravitational-wave transient catalog with two population models designed to test for preferred spin orientations at different black hole masses. We find that a peak in spin tilts is neither statistically significant nor model independent. Since the data cannot be used to reliably identify subpopulations based on their spin tilt properties, we also consider a complementary approach: measuring the spin magnitude and tilt distributions at fixed mass scales. We find no confident correlation between mass and spin tilt, but we do confirm a confident correlation between spin magnitude and mass, corroborating recent analyses.

We construct a unified framework for anisotropic strange quark stars combining de Rham-Gabadadze-Tolley (dRGT)-like massive gravity with dark matter (DM) introduced via extended gravitational decoupling (EGD), in which both metric potentials are deformed by independent functions ξ(r) and h(r). Two DM density profiles are embedded in the decoupled θ-sector: the Einasto spike and the Bose--Einstein condensate (BEC). The baryonic sector is governed by the MIT bag model (quark-matter radial pressure <mml:math><mml:mrow><mml:msubsup><mml:mi>p</mml:mi><mml:mi>q</mml:mi><mml:mi>r</mml:mi></mml:msubsup><mml:mo>=</mml:mo><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mrow><mml:mi>∊</mml:mi></mml:mrow><mml:mi>q</mml:mi></mml:msub><mml:mo>-</mml:mo><mml:mn>4</mml:mn><mml:mi>B</mml:mi><mml:mo>)</mml:mo></mml:mrow><mml:mo>/</mml:mo><mml:mn>3</mml:mn></mml:mrow></mml:math>), while the pressure anisotropy is parametrized by the Horvat-Ilijic-Marunovic (HIM) prescription applied to the total effective radial pressure <mml:math><mml:msubsup><mml:mi>p</mml:mi><mml:mrow><mml:mrow><mml:mi>e</mml:mi></mml:mrow><mml:mi>f</mml:mi><mml:mi>f</mml:mi></mml:mrow><mml:mi>r</mml:mi></mml:msubsup></mml:math>. We show that the cooperative action of the graviton-mass coupling (m<SUP>2</SUP>c<SUB>1</SUB> &lt; 0) and the DM-induced modification of the effective pressure balance (ρ<SUB>E0</SUB> or <mml:math><mml:mrow><mml:msub><mml:mi>ρ</mml:mi><mml:mi>s</mml:mi></mml:msub><mml:mo>≳</mml:mo><mml:mn>50</mml:mn><mml:mspace></mml:mspace><mml:mrow><mml:mi>MeV</mml:mi><mml:mspace></mml:mspace><mml:msup><mml:mtext>fm</mml:mtext><mml:mrow><mml:mo>-</mml:mo><mml:mn>3</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:mrow></mml:math>), together with positive anisotropy (β<SUB>anis</SUB> &gt; 0), drives the maximum mass into the mass-gap window 2.5--5 M<SUB>⊙</SUB>. The predicted GW190814 companion radii (12.3--12.8 km) and the PSR J0740+6620 radii (11.6--12.5 km) are consistent with NICER measurements. We verify the Harrison--Zel'dovich--Novikov stability criterion, the Chandrasekhar condition Γ &gt; 4/3, the Herrera cracking condition <mml:math><mml:mrow><mml:mrow><mml:mo>|</mml:mo></mml:mrow><mml:msubsup><mml:mi>v</mml:mi><mml:mi>t</mml:mi><mml:mn>2</mml:mn></mml:msubsup><mml:mo>-</mml:mo><mml:msubsup><mml:mi>v</mml:mi><mml:mi>r</mml:mi><mml:mn>2</mml:mn></mml:msubsup><mml:mrow><mml:mo>|</mml:mo><mml:mo>&lt;=</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:mrow></mml:math>, causality (<mml:math><mml:mrow><mml:msubsup><mml:mi>v</mml:mi><mml:mi>r</mml:mi><mml:mn>2</mml:mn></mml:msubsup><mml:mo>,</mml:mo><mml:msubsup><mml:mi>v</mml:mi><mml:mi>t</mml:mi><mml:mn>2</mml:mn></mml:msubsup><mml:mo>&lt;=</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:math>) and all dominant energy conditions. We observe that the Buchdahl compactness bound 2M/R &lt; 8/9 employed here is the standard GR result. In the present dRGT-like massive gravity framework, the bound receives corrections that we estimate but do not derive in full generality, confirming physical self-consistency throughout the parameter space.

We investigate the kination-amplified inflationary gravitational-wave background (GWB) interpretation of the signal recently reported by various pulsar timing array (PTA) experiments. Kination is a post-inflationary phase in the expansion history dominated by the kinetic energy of some scalar field, characterized by a stiff equation of state w = 1. Within the inflationary GWB model, we identify two modes that can fit the current data sets (NANOGrav and EPTA) with equal likelihood: the kination-amplification (KA) mode and the ordinary, no-kination-amplification (no-KA) mode. The multimodality of the likelihood motivates a Bayesian analysis with nested sampling. We analyze the free spectra of current PTA data and mock free spectra constructed with higher signal-to-noise ratios using nested sampling. The analysis of the mock spectrum designed to be consistent with the best fit to the NANOGrav 15 yr (NG15) data successfully reveals the expected bimodal posterior for the first time while excluding the reheating mode that appears in the fit to the current NG15 data, making a case for our correct and comprehensive treatment of potential multimodal posteriors arising from future PTA data sets. The resultant Bayes factor is <inline-formula> <mml:math><mml:mi>B</mml:mi><mml:mo>≡</mml:mo><mml:msub><mml:mrow><mml:mi>Z</mml:mi></mml:mrow><mml:mrow><mml:mi>no</mml:mi><mml:mo>-</mml:mo><mml:mi>KA</mml:mi></mml:mrow></mml:msub><mml:mo>/</mml:mo><mml:msub><mml:mrow><mml:mi>Z</mml:mi></mml:mrow><mml:mrow><mml:mi>KA</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>2.9</mml:mn><mml:mo>±</mml:mo><mml:mn>1.9</mml:mn></mml:math> </inline-formula>, indicating comparable statistical significance between the two modes. Given the theoretical model-building challenges of producing highly blue-tilted primordial tensor spectra, the KA mode has the advantage of requiring less blue primordial spectra, compared with the no-KA mode. The synergy between future cosmic microwave background polarization, pulsar timing, and laser interferometer measurements of gravitational waves will help resolve the ambiguity implied by the multimodal posterior in PTA-only searches.

The plasma frequency, the transverse permittivity, the spectrum, and the energy density of the thermal electromagnetic radiation of stellar matter were determined. For the non-degenerate matter, the calculations were performed using Vlasov's equations. The degree of ionization was determined by the Saha's equations. The chemical composition of the matter was chosen to be close to that of the Sun. The unperturbed particle energy distribution function was obtained by expanding the Fermi distribution function. This allows calculations to be made for density and temperature values close to degeneracy. The decrease in the thermal radiation density due to the spectrum distortion in stellar matter was determined. For hot (&gt;) neutrino-opaque quark matter the calculations were performed in the hydrodynamic approximation. For the ratio of the electrons leptonic and baryonic charge densities was set 0.4. It was shown that the contribution of u quarks and electrons to the numerical value of the plasma frequency is several times greater than the contributions of other charged particles. For certain temperatures the temperature dependence of the plasma frequency of quark matter is weak. At lower temperatures the thermal radiation density in such matter is only 46% of the possible vacuum value.

Early JWST observations of TRAPPIST-1 have revealed an unexpected puzzle: energetic white-light flares (E &gt; 10<SUP>30</SUP> erg) reach temperatures of only ~3500--4000 K, nearly 3 times cooler than typical solar flares, which peak around 9000--10,000 K. Here we explain this difference by identifying the physical mechanism that regulates flare temperatures on late M dwarfs. The key factor is that in the cool, dense atmosphere of TRAPPIST-1, magnetic heating is strongly moderated by the dissociation of molecular hydrogen (H<SUB>2</SUB>) into atomic hydrogen. This ``H<SUB>2</SUB> dissociation thermostat'' acts as an efficient energy sink, preventing flare regions from heating above ~4000 K. Our chemical equilibrium and heat capacity calculations show that this effect depends sensitively on stellar atmospheric pressure and the local abundance of H<SUB>2</SUB>. In hotter stars, from early M dwarfs to solar-type stars, the scarcity of molecular hydrogen renders this mechanism ineffective; instead, atomic hydrogen ionization limits flare temperatures near ~9000 K.

We propose a novel approach for the timing of pulsars orbiting a supermassive black hole, which implements the fully relativistic calculations of the photon travel time into a robust timing model. We generate realistic mock catalogs of pulsar times of arrival for several putative pulsars on tight orbits around the Galactic Center supermassive black hole, Sagittarius A* (Sgr A*). Then, we perform a proof-of-concept sensitivity analysis to forecast the accuracy that future observational facilities, like the Square Kilometre Array, will achieve in the characterization of the parameters of our timing model. Our analysis shows how the observation of pulsars at the Galactic Center will open an incredibly promising avenue for the characterization of the physical properties of Sgr A*, which can improve by at least 3 orders of magnitude the current constraints on the black hole's mass achieved with S-stars and event-horizon scale observations.

Modern cosmology and galaxy formation rely on an understanding of how cosmic baryons are distributed, a significant portion of which exists in the diffuse gas confined to halos. Fast radio bursts (FRBs) are a promising probe of the Universe's ionized gas. At low redshift, the contribution to the dispersion measure (DM) from the intergalactic medium (IGM) and intervening halos is subdominant, allowing us to study the circumgalactic medium (CGM) of the host galaxies, if the host interstellar medium (ISM) can be sufficiently suppressed. We select a sample of five local Universe FRBs with host halos spanning a wide range in mass (~10<SUP>11-13</SUP> M<SUB>⊙</SUB>), and with indicators that host ISM DM is negligible. We use these FRBs to constrain the CGM in each halo by comparing to simulations and measuring the CGM mass assuming a range of spherical gas profiles. We find that one of our sources, the only massive elliptical host galaxy, strongly disfavors low feedback scenarios in simulations, and has been evacuated of its baryons (~ 10% of the cosmological average <inline-formula> <mml:math><mml:mfrac><mml:mrow><mml:msub><mml:mrow><mml:mi>Ω</mml:mi></mml:mrow><mml:mrow><mml:mi>b</mml:mi></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>Ω</mml:mi></mml:mrow><mml:mrow><mml:mi>m</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:mfrac></mml:math> </inline-formula> within R<SUB>vir</SUB>). This galaxy shows evidence of a past episode of active galactic nucleus (AGN) activity, consistent with the picture of strong AGN feedback in galaxy group-scale halos. The gas mass measurements for the other sources tentatively support more baryon retention in L<SUB>*</SUB> galaxies compared to group-scale halos. Finally, we demonstrate that a large sample of local Universe FRBs will enable precision measurements of halo gas.

Space-based gravitational-wave detection missions typically deploy three spacecraft in a widely spaced triangular formation in deep-space heliocentric or high Earth orbits. Maintaining high-precision coherence across this distributed, large-scale, and multi-degree-of-freedom system is critical to long-term, stable, and precise detector operations. High-accuracy orbit determination is foundational to mission success. Although a variety of tracking and measurement techniques exist, achievable orbit-determination accuracy is constrained by tracking coverage, systematic measurement errors, formation geometry, orbit-control capability, and the geometry of ground-based tracking networks. This paper presents a systematic overview of orbit-determination requirements for different mission architectures, analyses the performance and technical characteristics of ground-based and space-based tracking methods applicable to spacecraft in heliocentric and geocentric orbits, and discusses current challenges and future directions in high-precision orbit determination technologies to enable reliable, precise operation of space-based gravitational-wave detectors.

The predominant fusion chain in stellar nucleosynthesis produces positron and neutrino byproducts in equal amounts. An extremely high neutrino flux can be directly measured, but the unobservable, yet equally high flux of positrons is traditionally considered to be short-lived antimatter that annihilates upon contact with electrons. The electrons are traditionally assumed to be populated in such excess that their annihilation with positrons could be sustained indefinitely. This paper posits that, considering the extremely high positron and neutrino flux within a stellar core, there is an opportunity for localized positron populations and accumulation. As there are no existing methods to directly observe a positron accumulation within the solar core, evidence must rely largely on observations of the surface and above. The difficulties of direct observation into internal stellar processes introduces a chance to overlook critical components such as a theoretical positron accumulation, thus exacerbating unresolved stellar questions surrounding observed coronal signatures and high-energy emission channels. This investigation examines the potential for stellar positron accumulation, its consequences for core dynamics, and observational signatures that could support the existence of long-lived positrons. The framework is applied to problems in stellar and galactic physics, solar weather forecasting, and high-energy-density plasma systems.

Primordial black holes (PBHs), produced in the early Universe, can source a stochastic background of induced gravitational waves (GWs) and provide a non-thermal origin for dark matter (DM). We investigate DM production in a PBH-dominated cosmological framework, including contributions from PBH evaporation, gravitational production, and thermal freeze-in and freeze-out mechanisms, and determine the regions consistent with the observed DM relic abundance. We find that thermal freeze-in can compensate for the underabundance of PBH-sourced DM, while indirect detection remains largely insensitive due to the feeble interaction strength, making future GW observatories such as LISA and the Einstein Telescope (ET) unique probes of this scenario. For freeze-out DM, indirect detection experiments constrain regions with relatively large annihilation cross-sections, whereas GW observations probe complementary regions with heavier DM masses and smaller interaction strengths. Consequently, the same DM parameter space cannot be simultaneously probed by both indirect detection searches and GW missions. These results establish GW observations as a powerful and independent probe of DM production in PBH-dominated cosmologies, opening a new observational window into DM properties and the thermal history of the pre-BBN Universe.

We study a cosmological scenario featuring an early phase of null energy condition (NEC) violation. Within this framework, we show that perturbative unitarity bounds place strong constraints on both the amplitude and the spectral tilt of primordial gravitational waves. Our analysis is largely insensitive to the detailed realization of the transition between the NEC-violating phase and subsequent cosmological phases, allowing our results to be extended to a broader class of models. Finally, the perturbative unitarity approach employed here is applicable to a wide range of cosmological scenarios.

We revisit the upper bound on the annihilation cross-section, &lt;σv&gt; of a stable dark matter (DM) of mass 500-10<SUP>14</SUP> GeV by considering five different channels: W <SUP>+</SUP> W <SUP>-</SUP>, bb̅, μ <SUP>+</SUP> μ <SUP>-</SUP>, τ <SUP>+</SUP> -, and e <SUP>+</SUP> e <SUP>-</SUP>. We use the observed electron and positron fluxes from CALET, DAMPE, HESS, positron flux from AMS-02, and gamma-ray flux from HAWC, GRAPES-3, CASA-MIA to constrain the annihilation cross-section. We also consider unstable DM of mass 10<SUP>3</SUP>-10<SUP>16</SUP> GeV decaying to W <SUP>+</SUP> W <SUP>-</SUP>, bb̅, μ <SUP>+</SUP> μ <SUP>-</SUP>, τ <SUP>+</SUP> τ <SUP>-</SUP>, and e <SUP>+</SUP> e <SUP>-</SUP> and derive the corresponding lower bound on the DM lifetime, τ <SUB>DM</SUB>. We find that the latest AMS-02 data provide the most stringent constraints on &lt;σv&gt; for DM masses below 2 TeV, while HESS yields the strongest limits for M <SUB>DM</SUB> ≳ 2 TeV. The HESS gives a much more stringent limit on the DM lifetime, excluding τ <SUB>DM</SUB> --&gt; μ <SUP>+</SUP> μ <SUP>-</SUP> ≲ 𝒪(10<SUP>30</SUP>) s for a 10 TeV mass of DM. The limits on &lt;σv&gt; derived from the e <SUP>+</SUP> e <SUP>-</SUP> flux are competitive with those from γ-ray and neutrino observations for DM masses in the range 10<SUP>5</SUP>--10<SUP>11</SUP> GeV, and become the most stringent beyond this range. For decaying DM, the e <SUP>+</SUP> e <SUP>-</SUP> flux provides the strongest constraints on the DM lifetime over the mass range 10<SUP>3</SUP>--10<SUP>9</SUP> GeV.

Active galactic nuclei (AGNs) are among the most powerful sources in the Universe, with their X-ray and radio emissions revealing the physics of black hole accretion and jet processes. We investigate the radio properties of Seyfert galaxies selected from the Swift-BAT 70-month hard X-ray survey, using radio observations from VLASS and RACS. From a parent sample of 752 unbeamed AGNs, we compile 604 Seyfert galaxies with measurements of radio luminosity, X-ray luminosity, and black hole mass. The sample spans X-ray Eddington ratios L<SUB>X</SUB>/L<SUB>Edd</SUB> from 10<SUP>-7.5</SUP> to 1, with most sources ≳ 10<SUP>-4</SUP>. We first characterise the distribution of the X-ray-radio loudness, finding a broad, continuous range spanning about 4 orders of magnitude, with no clear evidence for a bimodal separation between radio-quiet and radio-loud populations. We also revisit the fundamental plane (FP) in an Eddington-scaled form and quantify its dependence on optical type and radio morphology. Subsamples by Seyfert type show consistent FP relations within uncertainties once a luminosity cut is applied, implying that optical classification does not significantly impact the radio-X-ray correlation. Radio morphology introduces secondary but systematic shifts, i.e., compact sources align with the FP for RIAF-dominated systems with compact jets, while extended and jet-like morphologies display excess radio luminosity at fixed L<SUB>X</SUB>/L<SUB>Edd</SUB>. This possibly reflects additional contributions from jets and/or star formation. We further discuss the implications for AGN unification, noting that orientation does not play a key role in shaping the FP.

We present a systematic reassessment of cosmological constraints beyond ΛCDM by progressively relaxing the assumptions underlying Dark Energy (DE), Curvature, Neutrinos, and Inflation. Using the latest CMB data together with DESI BAO and different SN catalogues, we show that the preference for dynamical DE persists across all the extended cosmologies considered. Ω<SUB>k</SUB> remains compatible with flatness, despite a mild 2.2σ preference for Ω<SUB>k</SUB> &gt; 0 that is substantially degraded in dynamical DE extensions. Constraints on N<SUB>eff</SUB> are broadly consistent with <mml:math><mml:mrow><mml:msub><mml:mi>N</mml:mi><mml:mrow><mml:mrow><mml:mi>e</mml:mi></mml:mrow><mml:mi>f</mml:mi><mml:mi>f</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>3.04</mml:mn></mml:mrow></mml:math>, while cosmological upper limits on the total neutrino mass vary substantially across the cosmologies explored, ranging from ∑m<SUB>ν</SUB> ≲ 0.06 eV to ≲ 0.2 eV. We quantify both the preference for the mass ordering and the apparent tension between cosmology and oscillation experiments, showing that they are strongly framework dependent. We find no evidence for inflationary tensor modes, with r ≲ 0.035. Constraints on the spectral index n<SUB>s</SUB> show significant model dependence. Allowing for the scalar runnings produces a mild shift toward α<SUB>s</SUB> &gt; 0 and β<SUB>s</SUB> &gt; 0 that can reabsorb the preference for larger n<SUB>s</SUB> found in small-scale CMB data, although both α<SUB>s</SUB> and β<SUB>s</SUB> remain consistent with zero at ~ 1.5σ. We highlight the implications for slow-roll inflation and benchmark models. None of the extensions considered here can resolve the H<SUB>0</SUB> tension. We discuss the implications for Ω<SUB>m</SUB> and S<SUB>8</SUB>. Overall, dynamical DE is the only significant deviation from ΛCDM and has the strongest impact on the inferred conclusions in the other sectors of the model.

Calcium is a highly depleted element in the interstellar medium (ISM), however its composition in the solid phase remains elusive. The detection of Ca-bearing dust has been limited due to its lack of distinct spectral features in the cold phase of the diffuse ISM. X-rays provide a direct method for exploring the absorption and scattering properties of interstellar dust. In this study, we utilize high-resolution X-ray absorption spectroscopy to characterize Ca-bearing dust analogs at the Ca K-edge using X-ray Absorption Fine Structure. We present new X-ray absorption spectra of seven calcium-bearing interstellar dust analogs measured at the National Synchrotron Radiation Research Center in Taiwan. The extinction cross sections, calculated from the laboratory measurements are incorporated in the dust absorption model AMOL of the X-ray spectral fitting tool SPEX. We select three Low Mass X-ray Binaries (LMXBs) with high column densities, GX 340+00, GX 5─1, and GX 13+1, as background sources to study the intervening ISM along their sightlines. The best-fit models are compared with Chandra archive data using SPEX. Additionally, we employ simulations with the XRISM and NewAthena telescopes to achieve enhanced resolution and more effective coverage at the energy range near the Ca K-edge. These simulations set the boundary conditions for the future X-ray observation of calcium in the interstellar medium.

We study gravitational wave production from strongly supercooled first-order phase transitions while consistently tracking the evolution of the cosmological background. Our analysis includes the reheating process that ends the period of thermal inflation and restores radiation domination. We find that this background evolution leaves the spectral shape largely intact, except for a causality-driven tail on super-horizon scales. However, for sufficiently slow transitions, the peak amplitude and frequency exhibit a weaker dependence on the transition rate β than the usual scaling of <mml:math><mml:mrow><mml:mo>∝</mml:mo><mml:msup><mml:mi>β</mml:mi><mml:mrow><mml:mo>-</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math> and ∝β, respectively.

Numerical studies of critical phenomena in gravitational collapse have provided key insights into the nonlinear dynamics of Einstein's field equations in the strong-field regime. However, most prior investigations have been restricted to highly symmetric models, limiting our understanding of the universality of critical behavior. Extending these studies to more general systems poses substantial computational challenges, as resolving the fine-scale structure near the black hole threshold requires extremely high spatial and temporal resolution. In this work, we present the first direct comparison between the discontinuous Galerkin (DG) and finite-difference methods applied to critical phenomena. For the case study, we used the classical example of spherically symmetric gravitational collapse of massless scalar fields. The DG method, which combines the high-order accuracy of spectral techniques with the flexibility and locality of finite-difference schemes, demonstrates significant computational advantages: Near criticality, it achieves comparable accuracy with fewer degrees of freedom, approximately half the number of computational steps, and a third of the run-time required by finite-difference methods. These improvements mitigate the run-time and resolution limitations characteristic of finite-difference simulations in higher dimensions and complex field systems. A detailed extension of the DG framework to the collapse of nonlinear, axisymmetric gravitational waves will be reported in future work.

We report the first measurement of the Hubble constant <inline-formula><mml:math><mml:msub><mml:mi>H</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:math></inline-formula> using the stochastic gravitational-wave background arising from binary black hole mergers. This astrophysical background is sensitive to the expansion history of the Universe and, thus, can be used for cosmological parameter inference independently of not only electromagnetic methods, but also gravitational-wave standard siren approaches. We describe the background's cosmological dependence and show how it can be used as a "stochastic siren" to measure <inline-formula><mml:math><mml:msub><mml:mi>H</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:math></inline-formula>. By analyzing existing resolved binary black hole mergers and the current nondetection of the background, we find that <inline-formula><mml:math><mml:msub><mml:mi>H</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:math></inline-formula> can be measured more accurately relative to using resolved mergers alone. We also note that the stochastic siren may serve a unique role in the Hubble tension in that the lower bound of the <inline-formula><mml:math><mml:msub><mml:mi>H</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:math></inline-formula> measurement would progressively increase with continued nondetection of the background.

Solar radio bursts are signatures of dynamic processes in the solar corona, including particle acceleration and shock propagation associated with solar flares and coronal mass ejections. The e-CALLISTO archive, the largest near-real-time solar radio network with 150+ stations, produces large FITS volumes affected by interference, noise, and irregular frequency setups. Each 15-min CALLISTO frame can split a burst across files, complicating event-level analysis. This work presents the e-CALLISTO FITS Analyzer, a unified, interactive, cross-platform application for processing e-CALLISTO dynamic spectra on Windows, macOS, and Linux. The application merges fragmented observations across time and frequency, applies an RFI-mitigation/background-subtraction pipeline with user-controlled clipping, and isolates bursts using an interactive polygon mask. It extracts a maximum-intensity backbone, supports outlier removal, and fits a power-law model to estimate drift rates, with uncertainties from the fit and backbone scatter. Shock height and speed are calculated using the Newkirk coronal density model, with optional n-fold density scaling. If the harmonic emission lane is used instead of the fundamental lane, its frequency drift is fitted separately. Analytical checks and empirical comparisons show that converting the harmonic lane to fundamental frequency changes estimated shock height and speed by only a few percent. For a Type II burst at Arecibo Observatory on 2022 March 2, the analyzer yielded an average drift rate of <inline-formula><tex-math>$-0.0400 \pm 0.0003$</tex-math></inline-formula> MHz s<inline-formula><tex-math>$^{-1}$</tex-math></inline-formula> and an average shock speed of <inline-formula><tex-math>$449 \pm 1$</tex-math></inline-formula> km s<inline-formula><tex-math>$^{-1}$</tex-math></inline-formula> at a height of <inline-formula><tex-math>$1.715 \pm 0.002\rm ~R_{\odot }$</tex-math></inline-formula>. It supports reproducible, event-focused SRB analysis and improves access to physically meaningful, uncertainty-quantified measurements.

We present a new class of exact charged isotropic compact star solutions in the framework of f(Q, T) gravity, where the nonmetricity scalar Q is linearly coupled with the trace of the energy--momentum tensor T. The Einstein--Maxwell field equations are solved for a static, spherically symmetric interior by adopting physically motivated metric potentials, and the interior spacetime is smoothly matched to the exterior Reissner--Nordström geometry at the stellar boundary. The resulting solutions describe three families of configurations determined by the charge parameter N corresponding to 0 &lt;= N &lt; 1, <mml:math><mml:mrow><mml:mi>N</mml:mi><mml:mo>=</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:math>, and N &gt; 1. Closed analytical expressions for the energy density, pressure, and electric charge are obtained and shown to satisfy all fundamental physical requirements for realistic compact stars, including regularity at the center, positive and monotonically decreasing thermodynamic quantities, causal sound speeds, and dynamical stability through the adiabatic index. The modified Tolman--Oppenheimer--Volkoff equation further confirms that equilibrium is maintained through the combined action of gravitational, hydrostatic, electric, and matter--geometry coupling forces. The coupling parameters σ<SUB>1</SUB> and σ<SUB>2</SUB> significantly influence the internal stiffness and compactness of the stellar configuration. The predicted mass--radius relations are consistent with observational constraints from massive neutron stars and gravitational-wave sources such as PSR J0437-4715, PSR J1012+5307, PSR J0740+6620, PSR J0952-0607, and the mass-gap event GW190814. In particular, the model allows Pulsars-like objects with radii in the range [11.3 km, 17.5 km] and GW190814-like objects with radii in the range [13.5 km, 17.2 km]. Among the three configurations, the case N &lt; 1 tends to produce higher masses and smaller radii with increasing σ<SUB>1</SUB>, while the case <mml:math><mml:mrow><mml:mi>N</mml:mi><mml:mo>=</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:math> permits comparatively larger radii as σ<SUB>2</SUB> increases, and the case N &gt; 1 provides an intermediate behaviour between these two limits. Overall, the results indicate that f(Q, T) gravity offers a flexible and physically consistent framework for modelling ultra-dense compact stars compatible with current astrophysical observations.

This work investigates whether the trace anomaly can diagnose the stellar response to a topological scalar field in tensor multi-scalar gravity. Eleven cold tabulated equations of state (EoSs) were examined, with six retained after general relativistic (GR) thermodynamic and causality checks. Their fiducial topological configurations were compared with the corresponding GR models under complementary matching prescriptions. After controlling for stellar mass and EoS dependence, the GR trace source strength $S_T$ remained strongly correlated with the topological mass response, with a partial Spearman coefficient $ρ=0.975$. Near $1.4\,M_\odot$, the topological configurations were systematically more compact, with Jordan frame radius reductions of $6.7$--$8.7\%$ at fixed baryonic mass and $0.87$--$1.29\,\mathrm{km}$ at fixed gravitational mass. These shifts are comparable to current uncertainties from the Neutron Star Interior Composition Explorer (NICER) and produce source dependent observational effects. Despite the global deformation, the interior effective source remained matter dominated, with a median topological contribution of about $0.8\%$. The GR matter trace therefore emerges as a useful diagnostic of the fiducial topological stellar response.

We present results from a multiwavelength study of the binary AGN candidate SDSS J095036.75+512838.1, which was identified as a candidate binary SMBH system due to its significant and variable broad H$β$ line shifts. We use available infrared-to-X-ray data to investigate the system's accretion properties. Analyzing recent Chandra observations, we characterize the X-ray emission and test the binary SMBH hypothesis. We find that the X-ray spectrum is well-modeled as a single AGN, with a 2--10 keV luminosity of $1.3 \times10^{43}$ erg s$^{-1}$. By assembling a comprehensive multiwavelength spectral energy distribution, we further examine the possibility of circumbinary accretion. The infrared-optical emission matches that expected from a single AGN, though we observe an excess in emission between $\sim 9500-19000 Å$ and a deficit near $\sim 2600 Å$. Archival optical spectra also suggest a deficit near $\sim 8500 Å$. We investigate whether these SED anomalies can be explained by long-term variability or interstellar reddening. We find no evidence of dimming, while reddening can account for the deficit in UV emission. However, the origin of the near-infrared excess remains unclear. Ultimately, the SED of SDSS J095036 is well described by emission from a single, reddened AGN. Future high-resolution infrared and X-ray spectral observations will be crucial for disentangling the origin of the infrared excess and testing the binary SMBH scenario in SDSS J095036.

In this work, we investigate the worldline deviation of spinning test particles in a weak gravitational wave (GW) spacetime. Within the pole-dipole approximation and the Tulczyjew spin supplementary condition, we consider the modified deviation equation, which contains the standard geodesic deviation term and an additional contribution generated by the Mathisson-Papapetrou-Dixon (MPD) force. We demonstrate how the deviation equation can be solved under viable approximations to yield a new expression for the change in the deviation vector in terms of the perturbation $h_{ij}$, its time derivative, the spin vector components and the longitudinal and transverse components of the deviation. The spin-curvature coupling is shown to play a crucial role in controlling the change in deviation. We then use this result to investigate the changes in the form and expressions of the net GW signal as well as our understanding of GW memory, in the presence of spin. We conclude with our attempts on the measurability of this spin-induced effect \emph{vis-a-vis} present GW observations.

This paper presents a comprehensive statistical analysis of minifilament eruptions (MFEs) using high-cadence full-disk H$α$ blue-wing observations from Big Bear Solar Observatory. Despite the recognized importance of MFEs for coronal dynamics and solar wind structuring, previous efforts were often limited by small sample sizes or restricted fields of view, leaving open questions about their global occurrence and characteristic properties. We developed an algorithm incorporating intensity thresholding and temporal tracking to detect sudden enhancements in H$α$ blue-wing images. A total of 1986 such events were identified during a 4 hr period on 2020 June 9. These detections were cross-validated using H$α$ line-center observations to confirm the presence of associated filament structures. The analysis yields an occurrence rate of $\sim$6.6$\times 10^4$ per day, an average length of $\sim$17 Mm, and a typical lifetime of $\sim$21 minutes. A power-law distribution in eruption lengths (with slope $\sim$-4.8) and a sublinear scaling between duration and length suggest that larger eruptions tend to last longer. The length distribution of MFEs was further analyzed relative to active region proximity, revealing that eruptions occurring nearby a sunspot region were, on average, larger than the global mean eruption length. Additionally, an eruption density map was used to analyze the spatial distribution of MFEs relative to coronal hole boundaries. The results indicate a mild suppression of activity inside coronal holes and intermediate eruption frequency in the boundary regions. We briefly discuss their potential role in structuring the small-scale solar wind features such as magnetic switchbacks and small-scale magnetic flux ropes.

The detection of a stochastic gravitational-wave background (SGWB) is a primary science objective for the Laser Interferometer Space Antenna (LISA). However, extracting these signals is difficult because both the signal and the instrumental noise are stochastic and overlapping in the millihertz band. In this work, we present a Bayesian framework for the joint estimation of LISA noise and SGWB signals. Our approach models the LISA instrumental noise using flexible log-penalized splines, employing a roughness penalty to prevent overfitting while maintaining computational efficiency. For the SGWB, we compare a power-law model with a spline-based model and study how the choice of signal model and noise prior affects signal recovery and detection. Using simulated LISA data, we find that the power-law model gives tighter estimates when the signal follows the assumed shape. However, it fails to recover a localized spectral feature that is not described by a power law, causing the signal to be absorbed by the instrumental-noise spline. The fully spline-based model is less restrictive and successfully recovers such features. We also find that stronger prior information about the test-mass noise helps reduce the degeneracy between the noise and SGWB models at low frequencies, improving signal detection. These results reflect a single trade-off: added model flexibility reduces sensitivity when the assumed signal shape is correct, and prevents bias when it is not.

We present a combined photometric and orbital period analysis of the contact binary systems OV Leo and V339 Leo using ground-based observations together with TESS photometry. The light curves were modeled with the BSN software through a Markov Chain Monte Carlo approach, providing physical estimates of the system parameters and their uncertainties. OV Leo is analyzed photometrically for the first time, while V339 Leo is reexamined using new observations and an updated modeling methodology. The light curve analysis show that both targets are W-subtype contact binaries in shallow-contact configurations. The O'Connell effect detected in V339 Leo is reproduced with a cool starspot model, whereas no spot is required for OV Leo. Three-dimensional geometric models further indicate that OV Leo undergoes total eclipses, while V339 Leo exhibits partial eclipses. Orbital period analysis based on eclipse timing extractions reveals opposite long-term period variations in the two systems, suggesting ongoing mass transfer under the assumption of conservative mass transfer. The absolute parameters were derived using the Gaia parallaxes, the photometric light curve solution, and standard astrophysical equations.

The recent evidence for a stochastic gravitational wave (GW) background at nano-Hz frequencies from pulsar timing arrays (PTAs) provides a strong science case for exploring cosmological histories and phase transitions at the Square Kilometer Array Observatory (SKAO). The latter cosmological events are of primary interest for physics of the early Universe associated with out-of-equilibrium and relaxation phenomena in the vicinity the quantum chromodynamics (QCD) epoch as well as those originating from dark sectors or other phenomena beyond the Standard Model of particle physics. Such a novel GW portal provides a complimentary access to particle physics phenomena that have so far escaped detection at particle colliders, and also probes fundamental aspects of out-of-equilibrium dynamics beyond the perturbation theory and their cosmological implications. This chapter aims at elucidating most interesting physics cases, theoretical models and approaches, as well as cosmological scenarios that are of particular relevance for future GW measurements at SKAO. We elaborate on how such measurements can deepen our understanding of particle interactions and violent processes in the early Universe, and discuss possible competitive advantages and complementarity of SKAO in this research compared to other experiments.

Coronal mass ejections (CMEs) are among the primary drivers of space weather disturbances at Earth, yet their early propagation in the low corona remains poorly constrained owing to occultation and projection effects inherent to coronagraph observations. Coronal dimmings offer an alternative diagnostic to infer CME propagation direction directly from the low corona. We present the DIRECD CME Direction Catalog, a unified dataset of three-dimensional CME propagation directions derived via the DIRECD (Dimming Inferred Estimation of CME Direction) method, which reconstructs CME cone geometry from SDO/AIA 211 Å coronal dimming observations. The catalog comprises 64 events spanning 2010-2026, combining 31 Solar Cycle 25 (2021-2026) events with 33 events from prior studies. For each event we report the 3D propagation direction, 2D inclination angles, angular width, and cone height. Statistical analysis reveals a systematic asymmetry in low-coronal CME propagation: meridional inclinations exhibit a systematic tendency toward latitude-dependent deflection, with poleward deflections more pronounced at higher source latitudes, while equatorial inclinations show no significant dependence on source longitude. This is consistent with low-coronal CME trajectories being governed primarily by local active-region magnetic topology, with the large-scale coronal field and heliospheric current sheet assuming a progressively dominant role at greater heliocentric distances. Incorporating DIRECD-derived propagation directions into CME arrival forecasts improves predictions of geomagnetic storm intensity, raising the correlation with observed storm strength from r = 0.58 to r = 0.70 when combined with CME speed. The DIRECD software, catalog, and all associated data products are publicly available to support space weather research.

The appearance of hyperons in the core of neutron stars generally softens the equation of state (EOS), posing a longstanding challenge to the existence of observed two-solar-mass compact stars. We investigate whether repulsive interactions mediated by a dark-sector vector portal can provide an additional source of high-density pressure and thereby modify the structure of hyperonic compact stars. The baryonic sector is described within the modified quark-meson coupling (MQMC) model, in which the octet baryons are treated as confined relativistic constituent-quark systems interacting self-consistently through the $σ$, $ω$, and $ρ$ fields within a mean field approximation. The dark sector consists of a fermionic dark matter coupled to baryonic matter through a neutral vector mediator $Z^\prime$, generating an additional repulsive contribution to the dense-matter EOS. We investigate the resulting equation of state, mass--radius relation, tidal deformability, and moment of inertia. The resulting mass--radius relations satisfy the observational bounds from massive pulsars, including PSR J0740 + 6620, with maximum neutron star masses reaching approximately $2 M_{\odot}$. The resulting changes in tidal and rotational observables provide additional avenues for testing the dark-sector interaction through multimessenger observations.

Westerlund 1 (Wd 1) is the closest supermassive star cluster to the Sun, with over 100,000 stars of all spectral types down to brown dwarfs. This population strongly heats the surrounding interstellar medium (ISM), making Wd 1 a key site to study stellar feedback on intracluster gas. We present the most detailed X-ray study to date of its diffuse emission, aiming to separate and quantify the point-source contribution to the true diffuse emission. We analysed 36 Chandra ACIS-I observations within an 8x8 arcmin window. After removing 4922 point sources with ACIS Extract using energy-dependent PSF models and adaptive 99% enclosed-energy masks, we subtracted PSF-wing contamination and corrected for background, then applied adaptive smoothing in soft, medium, and hard bands. Spectral fitting suggests a shocked thermal plasma, with diffuse X-rays correlating spatially with massive stars. The core (Region #2) fits an APEC+PSHOCK model, with temperatures of 1.81+/-0.24 and 4.11+/-1.98 keV and a 6.7 keV Fe K-alpha line. The outer Region #1 shows charge-exchange emission, fitting a CXE+NEI model with softer temperatures of 0.27+/-0.04 and 1.09+/-0.05 keV. Column densities range from 1.84-2.24x10^22 cm^-2, and the total (0.5-8.0 keV) diffuse luminosity is ~9.6(+/-0.3)x10^33 erg/s. Near the core, hard emission likely arises from thermalised Wolf-Rayet winds and wind-wind collisions, softened by adiabatic expansion and turbulent mixing with cooler ISM. The soft component extends farther out, possibly from CXE in lower-extinction regions. No non-thermal contribution is found. A cluster-wind model predicts a luminosity ~2.2 above that observed, consistent with a low-density, partially evacuated intracluster medium. The resulting wind-to-X-ray efficiency, eta ~4.3x10^-6, is about two orders of magnitude below Cygnus OB2, yielding comparatively subluminous diffuse X-ray emission.

Ultralight scalar dark matter can make space-based gravitational-wave detectors respond through both the scalar charge of freely falling test masses and scalar-induced changes of local solid length scales. Existing space-detector forecasts usually model the former as a center-of-mass force, while ground-based interferometer studies show that scalar fields can also act through material and optical-path transduction. We ask which part of a local material response survives after one-way Doppler measurements are assembled into delayed time-delay-interferometry observables. To this end, we formulate center-of-mass motion and endpoint-size breathing in a common link-response notation for LISA-, Taiji-, and TianQin-like detectors. The main result is a projection rule: in the equal-arm, identical-endpoint, common-field limit, endpoint breathing enters Michelson-$X$ as a common-mode link perturbation and is removed from the retained channel. Its leading leakage is controlled by finite scalar wave vector, unequal or time-dependent arms, nonidentical endpoint response, or auxiliary readouts, and carries extra geometric and delay suppressions beyond the local size response. We then give reproducible noise, sensitivity, and network-combination formulas, and quote multi-mission improvements only under explicit independent-stream and scalar-coherence assumptions. The result provides a controlled baseline for deciding when test-mass breathing can be neglected and when instrument-specific material response must be modeled.

Astrophysical binaries formed by a stellar-mass compact object and a massive black hole are among the most promising sources for future space-based gravitational-wave detectors. These extreme mass-ratio inspiral (EMRI) systems are tracked coherently over more than $10^{5}$ orbits, encoding detailed information about strong-field gravity. Translating a detection into physical parameters requires models of comparable precision. One outstanding difficulty is the treatment of transient orbital resonances. In this work we address the problem at the level of the Koopman operator, where the waveform is promoted to an observable and the evolution over one radial cycle is a linear operator. Removing the fast timescale without a singularity at a crossing is then a matter of choosing a function of that operator. We demonstrate the approach on a Kerr geodesic driven through the 3:2 crossing by a modelled forcing term. There the coefficient of the standard near-identity transformation diverges, while the finite-window generator attains its analytic bound to better than one part in $10^{6}$. Averaging over twice the crossing duration recovers the resonant jump with its predicted magnitude and phase dependence.

We constrain the large-scale isotropic random component of the Galactic magnetic field using the Planck reconstruction of the 408 MHz synchrotron sky. Our analysis simultaneously fits the random-field structure, the synchrotron contributions of the coherent field and local foregrounds, and isotropic and dipolar offsets. A new element of the analysis is the use of excess polarized emission at 30 GHz to model local foregrounds, allowing us to retain 97% of the sky without absorbing these structures into Galaxy-wide features of the magnetic field. Across variations in the coherent-field model, cosmic-ray electron distribution, sky mask, and field profile, we consistently find that the dominant random-field component is a vertically compact disk with a local rms strength of about 4 $μ$G and a 1/e scale height of approximately 1 kpc, substantially thinner than in most previous models. An annular enhancement in the inner Galaxy improves the fit to the data, whereas we find no evidence for either a large-scale spiral pattern or a thick random-field disk. The fits also yield an intensity monopole of 4-7 K, whose possible origin we discuss. We quantify the implications of the inferred random field for the angular smearing of ultrahigh-energy cosmic rays. Compared with previous models, the sky-median smearing angle is smaller by up to a factor of 1.7, and by up to 2.4 in individual directions.

Accurate modeling of the inflationary gravitational waves (GWs) requires time-consuming, iterative numerical integrations of differential equations to take into account their backreaction on the expansion history. To improve computational efficiency while preserving accuracy, we present the Stiff-amplified Gravitational-wave Emulator Network (SageNet), a deep learning framework designed to replace conventional numerical solvers (code available at https://github.com/YifangLuo/SageNet). SageNet employs a long short-term memory architecture to emulate the present-day energy density spectrum of the inflationary GWs with possible stiff amplification, Ω<SUB>GW</SUB>(f). Trained on a data set of 25,689 numerically generated solutions, SageNet allows accurate reconstructions of Ω<SUB>GW</SUB>(f) and generalizes well to a wide range of cosmological parameters; 90.9% of the test emulations with randomly distributed parameters exhibit errors of under 4%. In addition, SageNet demonstrates its ability to learn and reproduce the artificial, adaptive sampling patterns in numerical calculations, which implement denser sampling of frequencies around changes in spectral indices in Ω<SUB>GW</SUB>(f). The dual capability of learning both physical and artificial features of the numerical GW spectra establishes SageNet as a robust alternative to exact numerical methods. Finally, our benchmark tests show that SageNet reduces the computation time from tens of seconds to milliseconds, achieving a speedup of ~10<SUP>4</SUP> times over standard CPU-based numerical solvers with the potential for further acceleration on GPU hardware. These capabilities make SageNet a powerful tool for accelerating Bayesian inference procedures for extended cosmological models. In a broad sense, the SageNet framework offers a fast, accurate, and generalizable solution to modeling cosmological observables whose theoretical predictions demand costly differential equation solvers.

The growing demand for small satellites in precision science missions, ranging from swarm mega-constellations requiring controlled end-of-life disposal to monolithic drag-free space-based gravitational wave observatories demanding ultra-precise drag-free control, has created a need for propulsion technologies that deliver micro-Newton-level thrust, lower power consumption, and mission-specific robustness. Field emission thrusters meets these precision requirements (micronewton to millinewton), but their practical application is constrained by near-exclusive reliance on indium propellant. Its high melting temperatures (157 degrees Celsius), thermal control challenges, increases a risk of optical payload contamination, and limits total impulse density. Despite prior studies on indium-based FEEP performance, there is little to no systematic framework for evaluating alternative propellants under coupled propellant characteristics and smallsat operation constraints. This study introduces a unified design-to-mission performance framework of a field emission thruster with alternative propellants for smallsat applications. A physics-based analytical model, coupled with propellant properties, evaluates thruster performance and maps it to orbital mission capability under CubeSat power constraints (less than 60 W). The parametric exploration over emitter voltages (2--12 kV) and emission currents (sub-<mml:math><mml:mrow><mml:mi>μ</mml:mi></mml:mrow></mml:math>A to mA) establishes comprehensive performance maps, capturing the operational trade space. The normalized ionization power penalty metric quantifies efficiency losses caused by propellant energetics. The framework has been applied to representative 3U and 6U CubeSats mission archetypes, exhibiting improved capabilities. In addition, a mission-specific Figure of Merit (FoM) that includes safety, performance, and system density has been established to allow for quantitative propellant selection. Across all orbital mission scenarios, gallium consistently outperforms indium, with a roughly twofold higher figure of merit under power constraints. The framework provides a quantitative decision-support tool that establishes propellant selection as a key mission design variable for next-generation FEEP-based smallsat systems.

We present deep Hubble Space Telescope (HST) imaging of one of the nearest ultra-diffuse galaxies (UDGs) outside of the Local Group: F8D1, a satellite of M81 known to be tidally disrupting. UDGs are an enigmatic and diverse population, with evolutionary pathways ranging from tidal processing to bursty feedback and high initial angular momentum. To determine F8D1's evolutionary drivers, we resolve stars in F8D1's central ~1 kpc and in a parallel field ~6 kpc along its major axis to deep photometric limits, reaching below the red clump. We also image eight shallower fields along F8D1's major and minor axes. We calculate the star formation history (SFH) in the two deep fields, finding that while currently quiescent, both regions experienced a substantial burst ~2 Gyr ago and a smaller burst ~500 Myr ago, which likely formed F8D1's nuclear star cluster. In the shallow fields, using the ratio of evolved asymptotic giant branch and red giant branch stars out to ~13 kpc along F8D1's known stellar stream, we confirm that F8D1 was globally star-forming until at least ~2 Gyr ago. We estimate a total progenitor stellar mass, including the stream, of ~1.3 × 10<SUP>8</SUP> M<SUB>⊙</SUB>, with an average [M/H] ~ -0.8. We compare F8D1's properties to those of Local Group galaxies with similar initial stellar mass. We find that F8D1 is consistent with a progenitor star-forming galaxy similar to NGC 6822 that is in the midst of a transition to a Sagittarius-like system. Notably, this evolutionary sequence can be accomplished through tidal processing alone in galaxies that have experienced sufficiently bursty feedback to have created cored profiles.

Swift heavy ion irradiation of pure CH<SUB>3</SUB>CN ice was investigated to evaluate the influence of the initial ice morphology on its radiolytic evolution under astrophysically relevant conditions. Two deposition protocols were compared: (i) CH<SUB>3</SUB>CN ice deposited and irradiated at 50 K, and (ii) CH<SUB>3</SUB>CN ice deposited at 130 K, subsequently cooled to 10 K prior to irradiation, thereby preserving the structural organization established during deposition. In situ FTIR spectroscopy revealed efficient destruction of CH<SUB>3</SUB>CN and the formation of HCN, HC<SUB>3</SUB>N, CH<SUB>3</SUB>NC, NH<SUB>3</SUB>, and imine-like compounds. The thermally organized ice exhibited a distinct infrared spectral evolution, enhanced destruction, and differences in the stabilization of daughter species compared with the amorphous ice. Destruction cross sections of <mml:math><mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:mn>2.85</mml:mn><mml:mo>±</mml:mo><mml:mn>0.52</mml:mn><mml:mo>)</mml:mo></mml:mrow><mml:mo>×</mml:mo><mml:mn>1</mml:mn><mml:msup><mml:mrow><mml:mn>0</mml:mn></mml:mrow><mml:mrow><mml:mo>-</mml:mo><mml:mn>12</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math> and <mml:math><mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:mn>4.65</mml:mn><mml:mo>±</mml:mo><mml:mn>0.43</mml:mn><mml:mo>)</mml:mo></mml:mrow><mml:mo>×</mml:mo><mml:mn>1</mml:mn><mml:msup><mml:mrow><mml:mn>0</mml:mn></mml:mrow><mml:mrow><mml:mo>-</mml:mo><mml:mn>12</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math> cm<SUP>2</SUP> were determined for the amorphous and thermally organized ices, respectively. These results demonstrate that the thermal history of CH<SUB>3</SUB>CN ice, through its influence on the initial ice morphology, strongly affects radical diffusion, recombination, and product formation during irradiation. The present measurements provide benchmark radiochemical data for acetonitrile and establish a basis for future investigations of more realistic nitrile-bearing astrophysical ice analogues relevant to Titan and other outer Solar System environments.

We show that resonant processes during multi-field inflation can generate a large curvature perturbation on small scales. This perturbation naturally leads to the formation of primordial black holes that may constitute dark matter, as well as to the production of stochastic induced gravitational waves in the deci-Hz band. Such waves are within reach of future space-based interferometers such as LISA, DECIGO and BBO. In addition, primordial black hole binaries formed at late times produce merger gravitational waves that can be probed by the resonant cavity experiments in addition to DECIGO and BBO.

Neutrino self-interactions delay the onset of free-streaming in the early universe, leaving distinct, scale-dependent signatures on the matter power spectrum. We investigate these signatures in post-reionization 21-cm intensity mapping and the Lyman-α (Lyα) forest at redshifts z ∼ 2─3.5, and forecast the constraints achievable with upcoming surveys using Fisher matrix analysis. Modeling neutrino self-interactions through an effective four-fermion parameterization with coupling G <SUB>eff</SUB>, we compute modifications to the Lyα and 21-cm auto- and cross-power spectra for both strongly interacting (SI<SUB> ν </SUB>, log<SUB>10</SUB> G <SUB>eff</SUB> = -1.77) and moderately interacting (MI<SUB> ν </SUB>, log<SUB>10</SUB> G <SUB>eff</SUB> = -5) scenarios. We then combine these with forecasts for a representative next-generation cosmic microwave background (CMB) mission to evaluate the capabilities of SKA1-Mid and PUMA. We find that the Lyα─21-cm cross-correlation provides a systematics-resilient probe of the interaction signal, and decisively breaks the degeneracy between the primordial scalar power spectrum amplitude (A<SUB>s</SUB> ) and G <SUB>eff</SUB> that limits CMB only analysis, particularly for the SI<SUB> ν </SUB> mode. Furthermore, the CMB+PUMA combination emerges as the optimal survey configuration for both regimes, reaching 1σ constraints of 𝒪(10<SUP>-3</SUP>) on σ(log<SUB>10</SUB> G <SUB>eff</SUB>) for the SI<SUB> ν </SUB> mode and 𝒪(10<SUP>-2</SUP>) for the MI<SUB> ν </SUB> mode. Compared to the CMB-only baseline, this represents an improvement of approximately one order of magnitude for the SI<SUB> ν </SUB> mode, and nearly two orders of magnitude for the MI<SUB> ν </SUB> mode. We show that this conclusion holds uniformly over the full range of coupling strengths from log<SUB>10</SUB> G <SUB>eff</SUB> = -6 to -1.77.

Extreme mass-ratio inspirals (EMRIs) are among the most powerful probes of strong-field gravity and of the environments surrounding supermassive compact objects. Motivated by the expected presence of dark matter near galactic centers, we investigate the emergence and gravitational-wave imprints of chaotic dynamics in EMRIs evolving in non-vacuum spacetimes. Within a unified dynamical framework, we analyze test-particle motion in a broad class ofdark-matter-embedded geometries, including singular black holes, regular black holes, naked singularities, and Einstein-cluster configurations. We show that environmental perturbations generically break integrability in the strong-field regime, giving rise to chaotic motion whose onset, duration, and termination depend sensitively on horizon structure, core regularization, and matter distribution. Using the numerical Kludge approach, we demonstrate that chaotic trajectories produce systematic qualitative modifications of the emitted gravitational radiation, such as irregular amplitude modulation and loss of phase coherence, in contrast to the smooth, quasi-periodic waveforms generated by regular motion. Our results establish the robustness of chaos in environmentally perturbed EMRIs and provide a clear conceptual link between nonlinear orbital dynamics, spacetime structure, and observable gravitational-wave signatures.

In order to shed light on the quantum-to-classical transition of the primordial perturbations in single field inflation, we investigate the decoherence of large-scale (superhorizon) scalar curvature perturbations. The latter are considered as an open quantum system which undergoes quantum decoherence induced by a time-dependent environment of deep subhorizon tensorial modes through the trilinear interactions predicted by General Relativity. A complete calculation is a complex one and still to be fully performed. We advance in that direction, and we elaborate on various aspects that have been overlooked in the literature. We first prove that, in full generality, a time dependent subhorizon environment can be relevant for decoherence during inflation, by considering derivativeless interactions, which, in our case, give the most important results. For the first time, the time dependence of the environment is properly taken into account by modifying the quantum master equation. Important non-Markovian effects pop up, instead, when dealing with derivative interactions. We adopt a possible way to treat them which has been recently proposed and seems well suited for our case. Our results show that when considering the interplay between derivativeless and derivative interactions, decoherence is slowed down. This underlines the importance of accounting for all the interactions in open quantum-system calculations in an inflationary setting. We finally compute the quantum corrections to cosmological correlation functions, by solving the transport equations induced by the quantum master equation. We also compare the results to the solutions obtained by an alternative method previously used in the literature. We observe a resummation of the quantum corrections to the power-spectrum of the Sasaki Mukhanov variable v, which is a general property of quantum master equations. We extend these results to the bispectrum of v.

In this work, we investigate the structure of black hole shadows in the bumblebee gravity model formulated within the metric-affine framework, which incorporates spontaneous Lorentz symmetry breaking (LSB) through a vector field B<SUB>μ</SUB> with a non-zero vacuum expectation value. We analyze the influence of the dimensionless rotation parameter a = J/M and the Lorentz-violating (LV) coefficient X = ξb <SUP>2</SUP> on the photon sphere radius, the critical impact parameter, and the shadow morphology. Using ray-tracing simulations with the GYOTO code and accretion disks, we observe that increasing values of X induce progressive vertical flattening, asymmetric ``teardrop''-shaped deformations, and local collapse of the lower silhouette region, interacting with the rotational Doppler effect. These anisotropic signatures distinguish the bumblebee model from the standard Kerr metric and provide observational tests for LSB effects in strong gravity regimes, potentially detectable by the Event Horizon Telescope in sources such as M87* and Sgr A*.

We investigate fermionic phenomena in a noncommutative Kiselev black hole (NCKBH) spacetime surrounded by quintessence. Using the semiclassical tunneling framework, we derive the Hawking radiation (HR) temperature for Dirac particle emission and examine its dependence on the noncommutative (NC) parameter Θ and quintessence intensity p. Both NC corrections and quintessence suppress the HR temperature relative to the Schwarzschild value, with NC effects becoming significant for small horizon radii. Quantum gravity corrections are incorporated through the generalized uncertainty principle (GUP), yielding a modified temperature that further reduces fermionic emission, particularly for small black holes. The dynamical response of the NCKBH is studied through massless Dirac perturbations using the WKB approximation. The computed quasinormal mode frequencies indicate negative imaginary parts for all parameter combinations, confirming linear stability against fermionic perturbations. Quintessence suppresses both oscillation frequencies and damping rates, while NC effects enhance the real part of the spectrum and increase the quality factor of fundamental modes. Quality factor analysis reveals that higher multipole numbers yield longer-lived oscillations, and increasing Θ from 0.01 to 0.05 enhances the quality factor by approximately 70% for the <mml:math><mml:mrow><mml:mi>κ</mml:mi><mml:mo>=</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:math> fundamental mode. NC corrections also raise the real part of the fundamental Dirac frequency as Θ increases. Both homogeneous and inhomogeneous plasma distributions shift the photon sphere inward, with the quintessence parameters controlling the overall scale. Throughout, the Dirac modes are treated as test-field perturbations on a fixed background rather than as the metric perturbations observed in gravitational-wave ringdown, so they serve as a theoretical probe of such modified geometries.

We present a comprehensive analysis of the sensitivity of atomic transitions to light dark matter pair absorption. Unlike scattering, where only a fraction of the dark matter energy is deposited, pair absorption processes absorb the full mass and are therefore capable of constraining far lighter dark matter. Spin-flip and fine-structure transitions are able to constrain electroweak scale axial-vector couplings for bosonic dark matter with <inline-formula><mml:math><mml:mi>μ</mml:mi><mml:mi>eV</mml:mi></mml:math></inline-formula> to eV masses, while principal quantum number transitions are able to set similar constraints on bosonic dark matter with scalar couplings. Unfortunately, pair absorption is largely insensitive to light fermionic dark matter due to its necessarily tiny density at low masses. We also demonstrate the sensitivity of pair absorption to the cosmic neutrino background and find that spin-flip transitions can set constraints on the overdensity parameter of <inline-formula><mml:math><mml:msub><mml:mi>η</mml:mi><mml:mi>ν</mml:mi></mml:msub><mml:mo>≲</mml:mo><mml:msup><mml:mn>10</mml:mn><mml:mn>9</mml:mn></mml:msup></mml:math></inline-formula> for neutrino masses <inline-formula><mml:math><mml:msub><mml:mi>m</mml:mi><mml:mi>ν</mml:mi></mml:msub><mml:mo>≲</mml:mo><mml:mn>1</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mi>meV</mml:mi></mml:math></inline-formula>, around 100 times stronger than existing constraints.

This paper presents an experimental investigation of magnetic reconnection between two laser-produced expanding plasmas, focusing on the quantitative evaluation of the reconnection rate and energy conversion under varying initial conditions. By changing the separation distance between the drive laser focal spots (1 mm and 2 mm), we systematically controlled the inflow parameters. The reconnection region was probed using a two-directional laser Thomson scattering (LTS) system, which simultaneously measured the local plasma parameters parallel to the outflows and along the current sheet. Based on our established method incorporating macroscopic energy and mass conservation laws to derive the upstream magnetic field directly from LTS spectra, we characterized the temporal evolution of the current sheet and the reconnection rate. The larger spot separation allows the plasma bubbles to expand for a substantially longer time before the formation of a reconnection current sheet, resulting in different upstream conditions. Nevertheless, both configurations yielded comparable upstream magnetic fields and reconnection rates. These results suggest that the reconnection rate is relatively insensitive to the global inflow conditions and is primarily controlled by the local physics of the reconnection layer once a current sheet is formed.

Stellar activity complicates exoplanet transmission spectra, particularly for smaller planets around M dwarfs with JWST. The transit light source (TLS) effect, the imprinting of spectral differences between the average stellar disk and the occulted transit chord onto the transmission spectrum, makes it challenging to directly use the out-of-transit spectrum to correct for stellar contamination. Theory and observations suggest that spots may concentrate towards higher latitudes when the Coriolis force is substantial relative to buoyancy, leaving the equatorial region relatively quiet. Here, we evaluate how the latitudinal distribution of active regions shapes the strength of the TLS effect for planets spanning a range of impact parameters ($b$), using TRAPPIST-1 as a testbed. We first construct a fiducial model to illustrate two distribution regimes. With our model, the moderate-$b$ outer TRAPPIST-1 planets (f, g, h) occult a more typical region of the stellar disk than the inner planets and are thereby less affected by the TLS effect, though their bias may vary more from visit-to-visit as these active regions evolve with time. More generally, our results imply an impact parameter "sweet spot" for atmospheric characterization, independent of the sign of the active region temperature contrast, whose location depends on the distribution of active regions. The distribution may be revealed by transit residuals as multiple planets probe different latitudes, while longitudes are sampled in time, such that the variance and frequency of the correlated scatter could constrain active-region filling factors, sizes, and separations.

We study semiclassical tunneling in scalar field theories with slowly evolving homogeneous backgrounds. We formulate the problem by combining tadpole subtraction with an adiabatic expansion: the former maps the rolling system to an instantaneous multi-field tunneling problem, while the latter systematically tracks the slow evolution of the background. This formulation is particularly useful for tunneling during slow-roll inflation, where the tunneling direction may be transverse to the rolling inflaton direction. For a time-reflection-symmetric bounce on a fixed on-shell geometry, we show that the real tunneling exponent receives no direct correction linear in the rolling velocity. The tunneling rate nevertheless drifts along the rolling trajectory because the frozen tadpole-subtracted potential evolves. We also find that the exponent approaches a finite but nonanalytic limit as the tangential curvature vanishes, suggesting that a weakly tachyonic tangential direction can yield an exponent of the same order.

Higher-curvature terms modify the action but do not necessarily generate new vacuum geometries on the branch perturbatively connected to GR. We develop a first-order framework for static, spherical vacuum black holes in 4D metric theories with $\mathcal L_{\mathrm{grav}}=R/2+λΨ(R,X,Y)$, $X=R_{μν}R^{μν}$, and $Y=R_{μνρσ}R^{μνρσ}$. On the coupling-analytic branch, purely Ricci-based terms $Ψ(R,X)$, analytic in curvature with $Ψ(0,0)=0$, do not deform a Ricci-flat background under adopted regularity and boundary assumptions. Riemann-dependent terms can, since Kretschmann scalar is nonzero. In areal-radius gauge, we derive model-independent first-order expressions for the horizon shift, ISCO, epicyclic frequencies, periapsis advance, photon sphere, critical shadow impact parameter, Wald entropy, and Hawking temperature. For $Ψ_η=\ell_λ^{-2+4η}\mathcal G^η$, treating noninteger powers as phenomenological parametrizations of nonlinear curvature, we obtain a closed first-order Schwarzschild-connected solution. Perturbations decay for $η>1/2$, while fixed-ADM interpretation requires $η>2/3$; at $η=2/3$, sourced $1/r$ term mixes with asymptotic mass mode. For positive effective coupling, the horizon, ISCO, photon sphere, and critical shadow impact parameter increase for $2/3<η<1$ and decrease for $η>1$. On the fixed-ADM branch, mass, Wald entropy, and Hawking temperature satisfy $dM=T_H,dS_{\rm W}$ to first order at fixed couplings. At $η=1$, the linear 4D Gauss--Bonnet term leaves local geometry and geodesic observables unchanged but adds a constant topological entropy shift. Finally, an Event Horizon Telescope-inspired shadow-size criterion gives a conservative first-order sensitivity estimate for the effective dimensionless coupling, a geometric consistency test rather than a complete observational constraint.

Short tensor modes can generate a white noise contribution to the local scalar $K=8πGρ/3-θ^2/9$, but this does not induce an infrared-enhanced adiabatic curvature spectrum. For a conserved causal source, analyticity of the longitudinal velocity correlator requires $P_V=\mathcal O(k^2)$, hence $P_{\mathcal R}=\mathcal O(k^0)$ and $Δ_{\mathcal R}^2=\mathcal O(k^3)$, excluding the $Δ_{\mathcal R}^2\propto k^{-1}$ relic. We also construct a conserved conversion of radiation into gravitational waves: the white field resides in a compensated entropy mode, and the fluid response cancels the slowly decaying $a^{-2}$ relic. Adiabatic bounds on such sources are therefore source- and matching-dependent.

An introductory review is provided for those who are interested in exploring applications of qubits and other quantum excitations to the detection of dark matter (and any other physics beyond the Standard Model). Topics covered include the fundamental properties of qubits, the excitation mechanism of qubits due to the electric field induced by dark matter (with attention to the effects of the coherence of dark matter), the dynamics of coupled qubit-cavity systems modeled by the Jaynes-Cummings framework, and the influence of noise and decoherence (especially Markovian noise described by the Lindblad equation). In addition, the article introduces essential concepts in quantum sensing, including the operator-sum representation and positive operator-valued measures, the Cramér-Rao bound, the standard quantum limit and the Heisenberg limit, and the potential enhancement of sensitivity to dark matter achievable with entangled states. Throughout, these topics are discussed with particular emphasis on their application to the detection of wave-like dark matter.

We report the non-detection of stellar light associated with the dark galaxy candidate Cloud-9. Ultra-deep imaging obtained with HiPERCAM at the Gran Telescopio Canarias (GTC) reaches surface-brightness limits of 31.4 and 31.0 mag/arcsec$^2$ in g and r, respectively, approximately ten times deeper than previous deep imaging of the region. No stellar emission is detected within the central 1'$\times$1' ($\sim$1.3$\times$1.3 kpc) region of Cloud-9. Assuming an old, metal-poor stellar population, these limits imply a stellar surface mass density of no more than $\sim$0.01 M$_\odot$/pc$^2$ and an upper limit on the total stellar mass of 1.6$\times$10$^4$ M$_\odot$. This independent constraint from integrated light complements previous limits based on resolved-star counts and strengthens the case for Cloud-9 as a candidate starless galaxy.

We investigate how tidal locking affects the planetary dynamo and the magnetospheres of Earth-like planets orbiting the habitable zones of M dwarfs. We couple an empirical stellar wind model with two distinct planetary dynamo paradigms, direct rotational scaling and energy-flux scaling, using a Constant Time Lag (CTL) model to simulate continuous tidal spin-down until synchronization. We model two hypothetical planets based on a highly dissipative Modern Earth and a less dissipative, rapidly rotating Early Earth representative of the Paleoarchean. Our results show that tidal locking acts as a severe negative feedback on planetary magnetism across both paradigms, where the dipolar field frequently collapses before full tidal synchronization is reached. Essentially, a shielded atmospheric environment around M dwarfs requires a host massive enough ($\geq 0.32 M_\odot$) to place the HZ at wider orbital distances, sparing the planet from the sub-Alfvénic environment, and the internal tidal dissipation of the planet must be sufficiently low to prevent rapid rotational decay. For mid-to-late M dwarfs, the inevitable tidal locking and the extreme stellar wind pressures result in a total collapse of the magnetic shield, reducing the likelihood of atmospheric protection to essentially zero across the habitable zone.

We formulate a global optical-area method for shadows of static, spherically symmetric black holes. For the metric \(ds^{2}=-A(r)dt^{2}+B(r)dr^{2}+C(r)dΩ^{2}\), spherical sections of the optical geometry have area \(\mathcal{A}_{\rm opt}=4πC/A\). A null ray with impact parameter \(b\) can cross a spherical section only if \(b^{2}\leq C/A\). The capture threshold is fixed by the infimum of \(C/A\) on the connected interval between the observer and the black hole horizon. When attained at an interior point, the infimum gives \(b_{\rm sh}^{2}=\min(C/A)\), while a static observer outside the controlling minimum, on the inward-sky branch, measures \(\sin^{2}α_{\rm sh}=\mathcal{A}_{*}/ \mathcal{A}_{\rm opt}(r_{\rm o})\). The usual photon-sphere equation follows when the minimum occurs at a smooth interior point. Exponential instability additionally requires the minimum to be nondegenerate. The local optical-radius and photon-sphere formulas are established results. Our contribution is to organize them into an observer-to-horizon global selection rule that compares all stationary candidates and relevant endpoint limits. The radial function \(B(r)\) does not affect the shadow angle, although it enters the coordinate-time instability rate, whose numerical value also depends on the normalization of the static time coordinate. We derive compact first- and second-order formulas for deformed metrics, demonstrate candidate comparison with a synthetic two-minimum profile, and apply the construction to Reissner--Nordström, Bardeen, charged dilaton, and Kottler black holes. An explicit transformation of the charged-dilaton example from a nonareal to an areal radial coordinate verifies radial-coordinate invariance, while the Kottler example probes a nonasymptotically flat static region.

Africa has deep and diverse traditions of astronomical knowledge, ranging from archaeological astronomy, pharaonic stellar timekeeping, and manuscript astronomy in Timbuktu and the Sahel, to ecological seasonal astronomy in southern Africa and calendrical computation in the Ethiopian tradition. These multiple epistemic traditions form part of a long intellectual history that precedes and intersects with contemporary astronomy on the continent. In the context of this long-standing intellectual heritage, an important question arises regarding the contemporary circulation of African astronomical knowledge within the global scientific system. This study therefore examines where African astronomical knowledge is produced, validated, and circulated in modern scholarly communication. Using bibliometric data from the Web of Science Core Collection, our analysis investigates publication and citation patterns in the research area Astronomy and Astrophysics between 2000 and 2025, with particular attention to the publication venues of African scholars. The findings highlight a critical paradox: while African researchers are active contributors to global astronomical discovery, the intellectual capital generated through this work is largely stored, validated, and circulated through publication systems located outside the continent. This pattern reflects broader asymmetries within global scholarly communication, where dominant publishing infrastructures shape visibility, citation impact, and authority. By applying a decolonial lens to metrics such as citation impact and ownership, the paper calls for a critical reassessment of the academic practices that sustain epistemic coloniality. It concludes that achieving scientific equity requires a strategic shift in publication choices to build and fortify a sovereign African knowledge archive.

Previously, it was shown that static black hole event horizons cannot exist in time-dependent backgrounds without becoming naked singularities. In light of this, we are left with the question ``how does a black hole horizon evolve in an expanding universe, then?'' Here we offer a solution to this puzzle by showing in full generality that black hole apparent horizons tend to become comoving, thus confirming the necessity of a cosmological coupling and raising intriguing possibilities for the early growth of black holes.

A broad class of dark matter (DM) models predicts the existence of sub-structures residing in DM haloes on sub-resolvable angular scales. Techniques to extract such a generic feature from diffraction-limited observations are lacking. In this work, we propose a model-independent 'super-resolving' method applicable to strong gravitational lens systems that is fully data-driven, without reference to any lens models. This method relies on a specific way of applying the optical Liouville theorem across multiple scales in the imaging data, a technique we refer to as geometrical-duality. We test this method using realistic simulations and apply it to a 'constellation' consists of 11 compact star clusters seen in two giant arcs in the lensing cluster SMACS0723 imaged by JWST as a proof-of-concept. We find reasonable self-consistency with the expectation of non-detection given the statistical sensitivity, except for one pair of star clusters. Such an outlier can be explained in the context of CDM as sub-haloes lensing in the mass range $M_{\rm sub} = 10^8 - 10^9\,M_\odot$, for which the corresponding Einstein radius is smaller than the diffraction limit of JWST.

Every traversable wormhole reported so far in static (2+1) gravity coupled to nonlinear electrodynamics has come from a power-Maxwell Lagrangian L propto |F|^k restricted to k=1/2, always forcing the cosmological constant to a fixed sign or zero. We show these restrictions are artefacts of that single choice, not physical requirements, and give a complete classification of static traversable wormholes in this theory. Of the three mutually exclusive electromagnetic configurations compatible with the symmetry, the radial electric branch admits no throat for any Lagrangian or Lambda. In each remaining branch, azimuthal electric and magnetic, the field equations admit exactly two regimes: either the redshift function is fixed, leaving the shape function b(r) completely free with Lambda absorbed without constraint; or the redshift is generic, in which case b(r) becomes fixed instead. We solve both regimes in closed form in both branches, and show that fixing the Lagrangian to any single power k forces Lambda nonzero and determines b(r) up to finitely many constants: this freedom requires the Lagrangian to be genuinely unrestricted. One azimuthal-electric family reproduces the static BTZ mass function, turning the vacuum black hole into a wormhole once sourced by the nonlinear field. Applied to the unique conformal power-Maxwell theory, k=3/4, previously known only as a radial-branch charged black hole, the same Lagrangian yields genuine wormholes in the azimuthal and magnetic branches, showing the electromagnetic configuration, not the Lagrangian, decides between a horizon and a throat; Born-Infeld electrodynamics admits no throat in any branch.

The swift urbanization and administrative amalgamation among regions in Vietnam have intensified the demands on the construction area, requiring advanced vulnerability assessment tools that can capture inter-regional interactions and ecological integration. This research employed 10 m Sentinel-2 multispectral imagery alongside 317 field survey points to effectively classify land use land cover (LULC) through the application of Convolutional Neural Networks (CNN). The resultant LULC data was subsequently integrated with 16 terrain, natural, and anthropogenic variables within an Adaptive Neuro Fuzzy Inference System enhanced by an Artificial Bee Colony (ABC-ANFIS) framework, where the ABC algorithm optimized fuzzy membership functions and rule parameters to improve nonlinear predictions of vulnerability in urban development zones. The CNN model achieved remarkable classification performance, with Overall Accuracy (OA) exceeding 86% and a Kappa coefficient greater than 0.83, demonstrating its proficiency in distinguishing various cover types, especially constructed land, water features, and green areas. This investigation integrated both natural and anthropogenic terrain variables to create a vulnerability map of the construction area, attaining commendable results (R<SUP>2</SUP><SUB>adj</SUB> = 0.83; RMSE = 5.8; and MAE = 3.72). The findings indicated that Ho Chi Minh City, the Thu Duc -- Di An -- Thuan An urban corridor, and Ba Ria city emerged as resilience hotspots, with values surpassing 0.8, indicative of a high concentration of infrastructure coupled with a limited capacity for ecological buffering. Conversely, peri-urban ecological areas such as Can Gio, Phu Giao, and Xuyen Moc exhibited low vulnerability levels due to their extensive forest cover, water bodies, and agricultural landscapes which collectively contribute to environmental regulation. While the 10 m spatial resolution of Sentinel-2 satellite imagery is adequate for regional-scale analyses, it may constrain the detection of micro-scale infrastructure vulnerabilities in densely constructed urban environments. Overall, this research proposed a cohesive framework that integrates remote sensing and machine learning methodologies, aimed at enhancing resilience assessments in regions that have undergone administrative consolidation, thereby providing scientific guidance for spatial planning focused on sustainability and urban resilience.

This study uses convection-permitting simulations to examine the vertical extent, propagation, and nighttime preference of diurnal pulses (DPs) in tropical cyclones (TCs). DPs are outward-moving rings of cooler brightness temperatures near the storm center and may indicate TC intensification. Their initiation and propagation are poorly understood due to limited high-resolution observations. Here we leverage ensemble case study simulations of Typhoon Haiyan (2013) and Hurricane Maria (2017) to analyze DP events and quantify their structure and propagation characteristics. Results show that DPs are deep, column-spanning features visible in multiple atmospheric variables, including precipitation, temperature, vertical velocity, and radial wind. Interpreted through gravity-wave theory, their speeds and vertical structure largely match theoretical expectations, with deviations that are consistent with convectively coupled gravity waves. DPs are more frequent at night, likely due to constructive interference with the TC's diurnal circulation. These insights into DPs help clarify their initiation and propagation mechanisms.

Internal feedback from massive stars and active galactic nuclei play a key role in galaxy evolution, but external environmental effects can also strongly influence galaxies. We investigate the impact of environment and its dependence on baryonic physics implementation using Cosmology and Astrophysics with MachinE Learning Simulations (CAMELS) spanning a wide range of feedback implementations in the SIMBA, IllustrisTNG, ASTRID, and Swift-EAGLE models. We show that satellite galaxies are significantly affected by environment in all models, with gas fraction and star formation rate (SFR) suppressed in overdense regions compared to similar mass satellites in underdense environments at z = 0. Central galaxies are less sensitive to environment but tend to show lower gas fraction and SFR in overdense regions at low stellar mass, transitioning to higher gas fraction and SFR for massive galaxies in higher-density environments. Halo baryon fraction (f<SUB>B</SUB>) and circumgalactic medium mass fraction (f<SUB>CGM</SUB>) at z = 0 show clear environmental effects. In SIMBA, low-mass haloes in overdense regions have systematically lower f<SUB>B</SUB> and f<SUB>CGM</SUB> at fixed halo mass, while Swift-EAGLE haloes in overdense regions have higher f<SUB>B</SUB> and f<SUB>CGM</SUB> across the full halo mass range, and IllustrisTNG and ASTRID show opposite trends at the low and high mass ends. Environmental effects can flip at higher redshift, with SFR and f<SUB>B</SUB> increasing with local density in low-mass haloes before quenching at an increasing overdensity threshold. Our results demonstrate that the impact of environment depends significantly on galaxy formation model, and higher-density environments can either suppress or enhance star formation depending on galaxy mass and cosmic epoch.

We study leptogenesis via out-of-equilibrium decays of right-handed neutrinos in a parity symmetric extension of the Standard Model with gauge group $SU(3)_c \times SU(2)_L \times SU(2)_R \times U(1)_X$, spontaneously broken to the Standard Model gauge group at a scale $v_R$. We focus on the minimal Higgs realization, in which the strong CP problem is resolved without invoking additional symmetries. In this framework, lepton number is violated through Yukawa interactions, while neutrino masses arise only at higher loop order, a feature that permits the CP-violating quantum corrections to right-handed neutrino decays to be parametrically large. For thermal production of right-handed neutrinos, we find that successful leptogenesis requires $v_R \gtrsim 6\times 10^{12}$ GeV. Non-thermal production, however, relaxes this bound dramatically, requiring only $v_R \gtrsim 10$ TeV, a scale accessible to collider searches for new particles and searches for rare processes.

Galaxy-galaxy strong gravitational lensing is an established method to detect and characterise low-mass haloes, which are otherwise too faint to be directly observed. Recent analyses have shown empirically that there exists a characteristic radius within which the projected enclosed mass of these haloes can be robustly measured. Here we provide a physically and mathematically motivated definition of this robust radius based on the Fisher information matrix. We show that for any spherically symmetric smooth profile with at least two free parameters, there exists a pivot radius at which estimates of the projected mass become decorrelated from the local logarithmic slope and have minimum relative uncertainty. As a result, the projected mass within this radius can be recovered consistently by any profile that fits the data well enough. This robust radius coincides, to leading order, with the weighted geometric mean of the arc pixel distances from the halo, where the weights depend on the perturber deflection angle, the macro-model magnification, and the source surface brightness gradient. Beyond leading order, corrections are of order the weighted log-width of the arc. The data constraining power on the local properties of the halo profile beyond amplitude is shown to depend on the radial leverage of the arc around the perturber, and on the imprint of the perturber deflection angle on high signal-to-noise-ratio pixels. Our definition generalises to both subhaloes and line-of-sight haloes and naturally captures the important physical aspects of the problem and the effect of the data resolution and signal-to-noise ratio.

We study the one-point probability distribution function (PDF) for matter densities averaged with an arbitrary spherically symmetric window function. The PDF is analytically modeled within the path integral framework, enabling a non-perturbative description of large-scale structure. It contains a leading order contribution controlled by the spherically symmetric gravitational collapse dynamics, as well as an order-one factor arising from aspherical fluctuations. We develop a numerical pipeline to compute the leading spherical-collapse part of the PDF and apply it to a family of window functions interpolating between the TopHat and Gaussian filters in coordinate space, as well as to a window function with non-monotonic radial dependence. We find that the PDF weakly depends on the choice of the filter, provided the width of the filter is normalized to yield a fixed linear averaged density variance. For each filter and each value of the averaged density, our pipeline gives the most probable density profile. We find that these profiles vastly differ for different filters in the case of overdensities, but closely follow a universal curve at underdensities. We obtain a perturbative expression for the aspherical part of the PDF valid at small density contrasts. We find from it that all PDFs are equally sensitive to the effective field theory (EFT) corrections accounting for short-scale clustering, regardless of how smooth the filter's boundary is. We test our PDF model against the results of high-resolution N-body simulations. The agreement is excellent for filters with widths larger than 10 Mpc/h. Small discrepancies at a few percent level arise for narrower filters and are interpreted as higher-order perturbative corrections.

We investigate the relativistic dynamics of network nonlocality in general $n$-local networks with chain and star topologies using the Unruh-DeWitt detector model. We show that the relativistic degradation of network nonlocality is strongly governed by the underlying topology. While chain networks suffer an irreversible sudden death of non-$n$-locality under relativistic motion, star networks exhibit remarkable resilience against relativistic decoherence. Most strikingly, a minimal star network with three peripheral nodes exhibits a remarkable sudden death-sudden birth transition of network nonlocality as the acceleration increases. This reentrant behavior reveals a dual role of the Unruh effect: it can both suppress and protect network nonlocality, offering a new perspective on the relativistic effects of acceleration on quantum networks. For larger star networks ($n>3$), non-$n$-local correlations persist over the entire acceleration regime. These insights provide valuable conceptual guidance for the structural optimization and design of acceleration-resilient architectures for future relativistic quantum communication and sensing protocols.

We examine analytically the restricted 3-body problem in general relativity for a set of extremally charged black holes. We apply the method of Ferrell and Eardley, which consists in perturbing the Majumdar-Papapetrou solution that describes a static set of such black holes. We extend the method from a pair of black holes to a triplet. We compare the motion of a test particle and a small black hole in the field of a rotating black-hole binary and discover a repulsive self-force acting upon the third black hole.

We determine the complete solution set of the conformally flat isotropic pure Lovelock field equations for every order $N\ge2$ and every admissible dimension $d\ge2N+1$. Conformal flatness and pressure isotropy combine into a single identity that factorises exactly, splitting the solutions into two branches. The first is the constant-density Schwarzschild interior, which persists at every order with both metric potentials keeping their Einstein form. The second has no Einstein counterpart and is governed by the single dimension--order parameter $k=(d-2N)/[4(1-N)]$; we obtain its physically admissible orbit in explicit closed parametric form, both potentials included. A phase-space analysis on the projective line shows that no solution of this branch has a pressure-free boundary at finite radius, so only the Schwarzschild branch can describe a bounded star. The second instead loses all memory of its central data and relaxes onto a pure Lovelock isothermal sphere with $ρ\propto r^{-2N}$, a higher-curvature analogue of the singular isothermal halo, which we show to be the attractor of the whole family, approached at the closed-form rate $λ_*=-(d-2)/(d-2N)$ and with limiting equation of state fixed by $(d,N)$ alone. We prove that $p/ρ$ increases monotonically outward there, and that of the two regular-centre orientations only one is admissible. Since $k$ is rational the spatial potential is algebraic of degree $u+v$, where $2k=-u/v$; radical inversion is guaranteed for degree at most four, while four representative cases have full symmetric Galois group.

We analysed broadband emission spectra of a dense molecular clump in RCW 120, obtained with the APEX telescope in the 200--260 GHz range, in order to investigate molecular formation pathways in regions of massive star formation at an early evolutionary stage. We examined the correlations between the molecular column densities derived under the LTE assumption. An excess of methanol was found in the southern part of the dense clump relative to its northern part, while the abundances of other molecules, such as CH$_3$CN and CH$_3$CCH, remain comparable. The methanol abundance is also elevated relative to that of other oxygen-bearing molecules, such as OCS and SO. To identify possible causes of the enhanced methanol abundance in the southern part of the clump, we carried out simulations with the astrochemical model Presta in a two-phase approximation, accounting for chemical processes both in the gas phase and in the mantles of dust grains. The modelling shows that the enhanced gas-phase methanol abundance may be due to photodesorption from icy mantles. At Av values between $4^{m}$ and $6^{m}$, methanol desorbs efficiently from the ice mantles of dust grains upon interaction with photons, but is not yet destroyed by UV radiation in the gas phase. A strong linear correlation between molecular column densities indicates that the molecules form in the same phase --- either in the gas phase or on dust. Their integrated intensity maps may nevertheless differ, as is the case for CCH and CH$_3$CN. If two molecules form in different phases --- one in the gas phase and the other in dust mantles --- no correlation is observed, as for CCH and CH$_3$OH. The weak correlation between methanol and the oxygen-bearing molecules that form on dust suggests that only the upper part of the dust mantles, rich in CO ice, is destroyed in the southern part of the clump.

In this work, we investigate the cosmological reconstruction of $f(Q, T)$ gravity, where $Q$ is the non-metricity scalar and $T$ is the trace of the energy-momentum tensor. We consider the functional form $f(Q,T)=f(Q)+λT$ and reconstruct explicit forms of $f(Q)$ corresponding to the $Λ$CDM expansion history in Friedmann-Lemaître-Robertson-Walker (FLRW) universe. By employing the matter conservation equation and expressing the cosmological quantities in terms of $Q$, the reconstruction problem is formulated as a first-order linear differential equation for $f(Q)$. Analytical solutions for $f(Q)$ are obtained for various matter configurations, including dust-like matter, a perfect fluid with equation-of-state parameter $ω=-1/3$, and a nonisentropic perfect fluid with a time-dependent barotropic index. Additionally, an e-folding formulation of the reconstruction is considered to examine the cosmological evolution in terms of the e-folding parameter. The resulting forms of $f(Q)$ confirm that the $Λ$CDM expansion history can be successfully realized within the $f(Q,T)$ framework across diverse matter sectors.

Static black holes in conformal Weyl gravity differ from their Einstein counterparts in a simple but important way: the Mannheim--Kazanas geometry is encoded in a Bach-flat lapse function whose radial dependence is richer than that of Schwarzschild--de Sitter. We study the de Sitter branch of this solution in the Schwarzschild gauge, keeping the characteristic linear term together with the quadratic de Sitter term. In the branch continuously connected to the positive-mass Schwarzschild--de Sitter spacetime, a regular static region between a black-hole horizon and a cosmological horizon exists precisely when \[ -\frac{1}{3}<βγ<\frac{2}{3}, \qquad 0<κ<\frac{1+3βγ}{27β^{2}}. \] In this window the singularity at the origin is hidden, the two positive horizons obey $0<r_b<3β<r_c$, and the limiting endpoint is the Nariai geometry. The thermodynamic interpretation is subtler than the root structure: the two horizons generally have different temperatures, and the static patch has no asymptotic region that would select a unique normalization of time. We therefore compare the Killing, Bousso--Hawking normalized, Tolman local, and effective two-horizon temperature conventions, and we compute the corresponding Wald entropy for the pure Weyl-squared action. The result is a local horizon thermodynamic description that keeps the geometric facts separate from the ensemble-dependent choices needed for any global first law.

In a recent paper \cite{Chu:2026dhx}, the quantum stability of the fuzzy sphere was established at large but finite $N$. In addition, a tadpole was identified for the scaling fluctuation mode of the matrix geometry. In this paper, we show that the tadpole generates a positive surface tension and tends to contract the sphere if the horizon is left isolated. However, when the horizon is coupled to gravity, the tadpole requires the bulk geometry to adjust according to the junction condition of general relativity. Assuming a static, spherically symmetric and non-singular vacuum interior, pure de Sitter space is selected. The matching also fixes an intriguing large-$N$ soldering relation between the de Sitter time inside and the Schwarzschild time outside. Potential cosmological implications are discussed.

Vertical gradient of mean turbulent electromotive force (expressed by the dynamo coefficient, alpha, caused by the penetrating convection into the tachoclines of Sun-like stars leads to the non-propagating alpha-mode patterns, which result in the periodic variations of magnetic field horizontal components. The aim of the paper is to study the influence of the latitudinal variation of the dynamo coefficient on the linear dynamics of large-scale waves in the overshoot layers of the tachoclines in Sun-like stars. We use the linear magnetohydrodynamic (MHD) equations with the dynamo coefficient in a simple rectangular geometry. It is shown that the vertical gradient of the alpha coefficient has the same appearance in the induction equation as the Coriolis force in the momentum equation. Therefore, the latitudinal variation of alpha parameter excites new large-scale waves similar to the Rossby waves on a rotating sphere. The dispersion properties of the waves depend only on vertical and latitudinal gradients of the alpha parameter, therefore the modes are basically different from the ordinary dynamo waves. The alpha_theta waves may have either prograde or retrograde propagation depending on the signs of the gradients. The time scales of the waves may vary from hundreds of days to tens of years in various parameters of the solar tachocline. These waves are coupled with the Rossby waves on a rotating sphere in the existence of the large scale magnetic field, which may lead to the mutual transformation of convective and rotation energies.

We study a minimal effective field theory description of the three-dimensional Lyman-$α$ forest using the Sherwood and Sherwood--Relics hydrodynamical simulations. We model the Lyman-$α$ flux auto-power spectrum and its cross-correlation power spectrum with the dark matter density field using a tree-level bias model supplemented by the leading counterterms and stochastic contributions. We find that the model describes the simulated auto- and cross-power spectra well up to $k_{\mathrm{max}}=3\,h\,{\rm Mpc}^{-1}$ and $k_{\mathrm{max}}=2\,h\,{\rm Mpc}^{-1}$, respectively. We analyse simulations spanning multiple redshifts, reionisation histories, box sizes and resolutions to assess the robustness of the model. Even within this minimal model, we find strong parameter degeneracies, highlighting the need for independent constraints on nuisance parameters in applications to real data analyses. The redshift evolution of the linear bias parameters is consistent with previous simulation-based studies and is driven primarily by the evolution of the effective optical depth, $τ_{\mathrm{eff}}$. We also find that the inferred parameters are affected by the resolution of the simulation and, to a lesser extent, by the simulation box size. We also explore the impact of reionisation history, finding that variations mainly affect the linear bias parameters over the range of scales considered. Moreover, we find empirical correlations between model parameters and the Lyman-$α$ forest density bias that show some scatter, indicating that one single parameter is not enough to determine the model parameters. Finally, we compare our results with theoretical predictions from analytical models of the Lyman-$α$ forest.

Previously, it was shown that the interplay between the gravitational memory effect and the thermodynamics of an ensemble of spinning objects gives rise to a hysteresis effect, which can be termed Gravo-Thermo memory. This effect can be studied either through a statistical approach or via kinetic theory. Here, we present a general kinetic theory model for the general case of a fluid composed of spinning extended objects in the presence of gravity.

We develop a phase-space description of classical scattering in which the matter sector of the Dyson S-matrix is partially Weyl transformed while the radiation sector remains operator valued. The resulting S-matrix symbol provides a common origin for several classical observables: we show that the inclusive waveform, the classical displacement in phase-space (i.e. the impulse and position shift), and the angular momentum arise as different projections of the same object. We show that the partially Weyl-transformed $S$-matrix admits an exponential organisation in terms of an elastic phase and connected radiation kernels, while its inclusive one-point projection admits a coherent representative with waveshape $α_I$ describing classical radiation, extending our recent proposal. Furthermore, we show explicitly how nonlinear gravitational memory can be derived from an inclusive coherent waveshape. The dependence of the waveshape on the hard scattering data naturally leads to a quantum geometry, including an induced Berry connection on the space of waveforms, whose contribution to the phase-space displacement captures both radiation-reaction and static-field effects. We illustrate this structure by deriving static contributions to the position shift and field angular momentum in both scalar QED and gravity.

The observed diversity of galaxy centers motivates the possibility that the local dark matter composition may vary among galaxies. In conventional multicomponent dark matter scenarios, however, large stochastic variations in the relative abundances are not generically expected, with the cold component typically remaining dominant. We perform $N$-body simulations with a subdominant ultralight dark matter component carrying significant large-amplitude small-scale isocurvature perturbations. We find that although nonlinear evolution largely homogenizes its fraction on galactic scales,ultralight dark matter can still be enhanced and even dominate the centers of small halos because large initial ultralight dark matter fluctuations seed early potential wells that later form halo centers. The ultralight-dominated region can extend beyond $0.01R_{\rm vir}$ and account for more than half of the central dark matter density, even for a cosmological ultralight dark matter fraction below $O(10\%)$. This central segregation provides a possible route to stochastic cusp--core diversity, potentially explaining the observed diversity of galaxy centers.