Papers for Wednesday, Jun 03 2026

We test whether compact objects in the so called mass gap ($2.5 < M_{\rm max}/M_\odot < 5.0$) can be hybrid stars. Using a generic hybrid equation of state with a first-order deconfinement transition, we map the allowed parameter space in a Seidov-type diagram and confront it with modern mass--radius constraints. We find that mass-gap hybrid stars require an extremely early onset of deconfinement and very stiff quark matter. The Bayesian analysis, however, favors equations of state with deconfinement at typical neutron-star masses around $1.4\,M_\odot$ with mass-twin stars that, if confirmed, would rule out hybrid stars as candidates for observed mass-gap compact objects.

Wideband radio interferometers increasingly rely on analog quadrature hybrids to synthesize circular polarization from linear feeds. These systems are typically calibrated under the assumption that instrumental polarization leakage can be represented as a static complex offset, independent of parallactic angle. In this work, we demonstrate that this assumption breaks down in the presence of realistic hybrid imperfections. We show that amplitude and phase errors in the hybrid $\mathbf{H}(\nu)$ introduce a non-commutative interaction with parallactic rotation $\mathbf{R}(\chi)$, such that [$\mathbf{H}(\nu)\mathbf{R}(\chi) \neq \mathbf{R}(\chi)\mathbf{H}(\nu)$] leading to a time-dependent effective leakage term that rotates in the Stokes $(Q,U)$ plane. This effect causes systematic distortions in polarization angle and introduces frequency-dependent biases that can mimic or corrupt Faraday rotation measurements. We derive a first-order analytic model for this leakage and demonstrate that it manifests as a deterministic, geometrically modulated error proportional to total intensity. To mitigate this effect, we introduce a Static Offset Pre-correction (SOP) method that operates in the antenna frame, inverting the hybrid response prior to parallactic de-rotation. Unlike conventional calibration approaches, SOP removes the non-commutative error in the Jones domain, preventing its projection into the sky frame. Our results show that hybrid-induced leakage is not merely a calibration artifact but a fundamental systematic error that must be addressed to achieve high-fidelity wideband polarimetry.

Asteroids preserve the solar system's earliest history and pose real threats to Earth. Strengthening the UK's capabilities to detect, track, and characterise Near-Earth Objects (NEOs) is vital for national security, world-leading planetary science, and future space resource opportunities. The UK has been an influential contributor to planetary defence, from establishing the UK NEO Task Force in 2000 to active roles in the International Asteroid Warning Network (IAWN), the Space Mission Planning Advisory Group (SMPAG), and the development of the National Space Operations Centre (NSpOC). UK scientists contribute to major international asteroid missions including NASA's OSIRIS-REx, DART, Lucy, and Psyche; ESA's Hera and RAMSES; and JAXA's Hayabusa2 and MMX. However, the UK currently lacks dedicated funding streams to deliver asteroid missions. Ground-based observations of asteroids cannot definitively determine the physical characteristics of these objects, which are crucial for impact-risk assessment, deflection strategy, and resource evaluation. This white paper proposes UK leadership in autonomous, low-cost asteroid-rendezvous missions, leveraging technologies developed through the UKRI-funded REMORA programme. We outline four priorities: (1) strengthen NEO detection capabilities; (2) reinforce UK participation in international planetary defence missions; (3) develop autonomous rendezvous and in-situ characterisation technologies; and (4) enable the future space resource economy through targeted asteroid exploration. Together, these actions position the UK to lead rapid, affordable deep-space missions and secure a long-term strategic advantage.

The rapid accumulation of massive dust reservoirs in the early Universe remains a major challenge in astrophysics. While core-collapse supernovae can inject large dust grains ($a \gtrsim 0.1\,\mu{\rm m}$) on short timescales, explaining the total dust budgets in the early Universe likely requires efficient grain growth in the interstellar medium (ISM). Such growth depends critically on an abundant population of small grains, which maximize the surface area available for accretion and may be generated by rapid dust-processing or dust-formation channels. Here, we report the discovery of a QSO UDS-27023 at $z=4.556\pm0.003$, identified using JWST/NIRSpec spectroscopy. By quantitatively comparing the spectra to QSO composite templates, we find that UDS-27023 displays an exceptionally steep far-UV extinction curve ($A_{1500}/A_V \approx 8$) but notably lacks the 2175 Angstrom bump, indicating a dominance of small silicate dust grains. We interpret this phenomenology as evidence for active small-grain production and processing in the QSO environment. Mechanical shattering of pre-existing large grains by QSO-driven shocks and outflows provides one natural pathway, while in-situ condensation of silicate grains inside dense QSO-driven winds may offer an additional route. Such a population of steep-extinction QSOs (SEQs) may therefore reveal a short-lived phase in which luminous AGN generate, process, and redistribute small grains, potentially facilitating rapid ISM grain growth and enriching the circumgalactic medium.

We present a deep, high-resolution CO(4-3) IRAM-NOEMA observation of a main sequence, barred, spiral galaxy at $z\approx1.12$, with an on-source integration time of $\approx37$ hours and a beam FWHM of $\approx0.\!\!^{\prime\prime}3$. We use the molecular gas data in conjunction with the available deep multi-band JWST and HST imaging, covering restframe UV to near-IR wavelengths, to quantitatively study the gas flows in the disk plane of this cosmic noon barred spiral. We find that this target is a massive ($\log(M_{\rm{baryons}}/M_\odot)\approx10.96$), baryon-dominated ($f_{\rm{dm}}(<R_e)=u^2_{\rm{circ,dm}}(R_e)/u^2_{\rm{circ}}(R_e)\sim4\%$), gas-rich ($f_{\rm{gas}}=M_{\rm{gas}}/(M_{\rm{\star}}+M_{\rm{gas}})\approx40\%$) disk, hosting a long ($a_{\rm{bar}}\approx4.2$ kpc), strong ($Q_{\rm{b}}\approx0.37$), and fast ($\mathcal{R}=R_{\rm{CR}}/a_{\rm{bar}}\approx1.05$) bar, which rotates at an angular speed of $\Omega_{\rm{pattern}}\approx$ 50 km/s/kpc. This bar is driving molecular gas inflows with a net inflow rate of $\dot{M}\sim30$ $M_\odot$/yr, based on three estimates, which is of the same order as the galaxy-integrated star formation rate ($\rm{SFR}\approx36$ $M_\odot$/yr). We additionally identify evidence of a well-defined dust lane shock at the northwestern side of the bar, with gas motions parallel to this feature, in agreement with expectations for an established bar-driven flow. Our study highlights the possible role of bars as key drivers of galaxy evolution for a significant fraction of cosmic noon galaxies, offering a detailed picture of well-defined, bar-driven inflows in a high-$z$ barred spiral.

Gamma-ray burst (GRB) afterglows are thought to arise when relativistic ejecta launched by a compact central engine drive a blast wave into the surrounding circumburst medium, producing broadband synchrotron emission. We present a rigorous assessment, based on high-resolution special relativistic hydrodynamics simulations, of a widely adopted `two-zone model' for approximating the dynamics of the early afterglow phase. Before the onset of the Blandford-McKee (BMK) self-similar solution, the outflow generally produces two emission components, associated with the forward-shocked circumburst medium and the reverse-shocked ejecta. The subsequent evolution depends on whether the reverse shock significantly decelerates the ejecta as it crosses the shell, separating the so-called relativistic and Newtonian reverse shock regimes. We show that when the reverse shock is Newtonian, it crosses the ejecta shell long before BMK self-similarity is established, leaving a prolonged interval that can span $\sim$ hours in observer time in which the true hydrodynamic evolution is not captured by standard semi-analytic prescriptions. We demonstrate that this mismatch can substantially overpredict the reverse-shock emission from radio through ultraviolet frequencies, or overpredict the forward-shock emission at X-ray frequencies, depending on how the transition away from the two-zone model is prescribed.

The repeated tidal stripping of a star by a supermassive black hole, known as a repeating partial tidal disruption event (rpTDE), can give rise to a transient that rebrightens months to years after the first outburst. Among the rpTDE candidates so far observed, some exhibit dimmer peak luminosities during each successive outburst, which is a trend that has not been reproduced from theoretical models when the star survives more than one encounter with the black hole. Here we suggest that this trend can be recovered if the partially disrupted star is initially (i.e., prior to its first mass-stripping event) rapidly rotating, which is expected if the star was placed on its orbit through the Hills breakup of a tidally locked and tight binary. We test this hypothesis with hydrodynamical simulations of high-mass ($\geqslant 1 M_{\odot}$) main sequence stars repeatedly partially disrupted by a $10^6 M_{\odot}$ black hole, and demonstrate that successively dimmer outbursts are indeed recovered for high (tens of percent breakup) and prograde (i.e., aligned with the orbital angular momentum) stellar spins. Our results provide strong indirect evidence for the operation of the Hills mechanism in seeding the stars in rpTDEs.

ESA's Ariel Space Mission will characterise the atmospheres of approximately 1000 exoplanets to quantify population-level trends. We present HERMES (HiERarchical Modelling for Exoplanet Science), a multidimensional Bayesian framework that probes population-level correlations across multiple axes of diversity. The specific use case we present is the multidimensional relation between stellar metallicity, planetary mass, and atmospheric metallicity. Starting from the Ariel Mission Candidate Sample (Edwards & Tinetti 2022), we select confirmed planets with available masses and stellar metallicity, inject plausible multidimensional trends and demonstrate successful parameter recovery. Simulated surveys are generated with a variety of leverage and sample size, in the presence of intrinsic astrophysical scatter and measurement noise. By fitting independent Bayesian models to each survey, we confirm that survey leverage remains a reliable predictor of trend precision even in multiple dimensions and in the presence of intrinsic astrophysical scatter. For an Ariel Tier 2 transit survey of at least 400 planets, HERMES robustly recovers the correlation between stellar and planetary metallicity despite intrinsic scatter in planetary abundances as large as 1.2 dex. These results establish HERMES as a practical tool for survey design and science yield forecasting in preparation for Ariel and other surveys probing population-level trends.

Using the first spectroscopic data release from the Dark Energy Spectroscopic Instrument (DESI DR1), we search for AGN signatures in 1,678,787 low-redshift ($0.001 \le z \le 0.45$) line-emitting galaxies. Based on the [NII]-BPT emission-line ratio diagnostic, we identify AGN in 314,245/1,211,573 (25.9%) high-mass ($\log (M_{\star}/M_{\odot}) > 9.5$) and 9648/467,214 (2.1%) dwarf ($\log (M_{\star}/M_{\odot}) \le 9.5$) galaxies. Among these AGN, 17,949 are broad-line candidates (BL-AGN) with broad H$\alpha$ emission, enabling black hole (BH) mass estimates using single-epoch virial methods. We find that the AGN fraction in line-emitting galaxies increases monotonically with stellar mass, rising from $\sim$1.4% at the low-mass end to $\sim$93.3% at the high-mass end. Using the large BL-AGN sample, we extend the $M_{\rm BH} - M_{\star}$ scaling relation down to $\log (M_{\star}/M_{\odot}) \approx 7.8$ and $\log (M_{\rm BH}/M_{\odot}) \approx 4.4$. In the context of high-redshift overmassive BHs, our results suggest that galaxies and their central BHs may follow two distinct evolutionary pathways across cosmic time. With this paper, we release the EmFit value-added catalog, containing emission-line flux and width measurements for $\sim$7.4 million galaxies, the largest catalog with emission-line decomposition into narrow, broad, and outflow components to date. This work significantly expands upon the early DESI results and provides a statistical sample for probing the galaxy$-$BH connection in the low-mass galaxy regime.

We present a 'multiple-pass' data-reduction tool designed for Euclid, based on software developed for the Hubble Space Telescope (HST), which improves the astrometric and photometric precision for faint sources and in crowded fields. In this work, we apply it to Euclid Early Release Observations of the Galactic globular cluster NGC 6397. By combining our new catalogue with archival HST data, separated by a time span of approximately 20 years, we were able to measure high-precision proper motions and investigate the radial variations in the energy equipartition and velocity anisotropy of the cluster. The combination of deep and wide-field observations also allowed us to derive the present-day local mass function of NGC 6397 and to study the radial dependence of mass segregation and binary fraction. Finally, we report the discovery of a subtle under-density of stars in the colour-magnitude diagram of NGC 6397 around a stellar mass of 0.35 M$_\odot$ with a more than 5$\sigma$ confidence level. This feature is consistent with the Gaia M-dwarf gap discovered in Galactic field stars, but it has never previously been observed in a globular cluster. The gap is caused by the onset of full convection in stellar interiors. We demonstrate that the properties of the gap provide tight constraints on the distance to NGC 6397 and its intrinsic metallicity dispersion, offering a new benchmark for stellar evolution models.

The dynamical role of Lyman-$\alpha$ (Ly$\alpha$) radiation pressure feedback has been debated for nearly a century, with recent analytical and 1D numerical studies highlighting its potential dominance over other stellar feedback processes at Cosmic Dawn. Despite this, no multi-dimensional Ly$\alpha$ radiation hydrodynamics (RHD) simulations have been performed to date. In this paper, we present the first 2D Ly$\alpha$ RHD simulations using Lydion, an RHD code with a novel M1 moment method for Ly$\alpha$ transfer, and self-consistent dust dynamics. Lydion yields a $\sim \mathcal{O}(100) \,\times$ speed-up compared to Monte Carlo radiative transfer in simple benchmarks, making 2D Ly$\alpha$ RHD feasible. We perform simulations of star clusters and isolated stars embedded in dense, metal-poor ($Z/Z_\odot \leq 0.01$) clouds, and find that Ly$\alpha$ feedback dramatically boosts outflows and dominates over feedback from direct and infrared radiation pressure. Ly$\alpha$ leakage through lower-column density channels, Doppler shifts, and Ly$\alpha$ photon destruction, while important, cannot prevent the build-up of strong Ly$\alpha$ radiation pressure in H II regions, leading to radiative forces $\sim (2 - 16) \times L_{\rm bol}/c$, and Ly$\alpha$ force multipliers $M_{\rm F} \sim 10-60$. Ly$\alpha$ feedback may not preclude efficient star formation, but raises the threshold gas surface density for this to occur. We conclude that nearly all galaxy and star formation simulations are currently missing the strongest source of radiation pressure feedback in dense and metal-poor environments.

We constrain the difference in gravitational potential between our location and sources at $z \gtrsim 0.3$ using datasets at those redshifts. Our motivation is that the Hubble tension might be caused by a local void, as suggested by galaxy number counts. This would increase the redshift through outflow and gravitational redshift (GR). Only the latter is important at high redshift, where a void contributes a fixed additional GR contribution of $z_0$ due to our location on a potential hill. This $z_0$ model has various subtle effects that were not previously considered, including a hotter CMB and reduced BAO $r_{\rm d}$. We test whether $z_0$ can have the previously expected value of 0.84\%, which was based on fitting void parameters to galaxy number counts and local $H_0$ measurements. Combining BBN, CMB, BAO, and CC datasets at $z > 0.5$, we find that $z_0$ = $-0.4 \pm 0.9\%$, which rises to $0.0^{+0.6}_{-0.7}\%$ when extending our analysis down to $z > 0.29$. Although the results prefer the standard value of $z_0 = 0$, the best-fitting model with $z_0 = 0.84\%$ fits the data almost as well as $\Lambda$CDM, with $\Delta \chi^2 < 2$. We find that $\Lambda$CDM faces a $2.81\sigma$ BAO anomaly in the standard $(H_0 r_{\rm d}, \Omega_{\rm m})$ parameter space, where different regions are preferred by BAO and non-BAO datasets from $z > 0.29$. Fixing $z_0 = 0.84\%$ reduces this to $2.39\sigma$. This suggests that a local void large enough to solve the Hubble tension cannot be ruled out by higher-redshift datasets despite its novel impact on them.

Increasingly deep, confusion-limited radio surveys have pushed direct radio source-count measurements down to tens of $\mu$Jy at 1.4 GHz. Confusion-noise $P(D)$ analyses extend the statistical counts down below $1\,\mathrm{\mu Jy}$. Radio source counts have allowed for constraints on the radio--derived star formation rate density (SFRD) history through models of the backwards evolution of the local radio luminosity function, using the radio--FIR correlation, $q \propto \log(L_{\mathrm{FIR}}/L_{1.4})$, to convert radio luminosities to FIR luminosities and hence star-formation rates. Recent deep radio source counts from MeerKAT suggest a potential tension in the SFRD history between radio and UV/FIR measurements at $1\lesssim z\lesssim 2$. This corresponds to a ${>}3\sigma$ discrepancy between the predicted and measured source counts near $10\,\mathrm{\mu Jy}$. We introduce a purely radio-luminosity based parameterization of the redshift evolution of the radio--FIR correlation based on changing cosmic ray losses. We find evidence (${\gtrsim}2\sigma$) that an evolution in the radio--FIR correlation consistent with a mild decrease in $q$ out to $z{\sim}2$ arising from strengthening magnetic fields can mitigate the source count tension. We additionally show that intrinsic scatter in the radio--FIR correlation is likely bounded $\sigma_q\lesssim 0.3\,\mathrm{dex}$ at these redshifts if $q$ decreases. Although we find no evidence that current radio source counts imply a breakdown in the radio--FIR correlation, future deep radio surveys from the Deep Synoptic Array (DSA) will be able to push radio source counts down to several nJy, providing stronger constraints on the allowed evolution.

Scaling relations hold among observed quantities that describe the thermodynamic properties of the gas in galaxy clusters and groups. However, observed data show systematic departures from the self-similar model's baseline predictions, particularly in lower-mass systems. I show that the observed departures from self-similar predictions can be efficiently described by two physical quantities modeled with power laws: the gas mass fraction ($f_g \sim T^{f_1} E_z^{f_z}$) and the temperature variation ($f_T \sim T^{t_1} E_z^{t_z}$). Using a large variety of published X-ray scaling relations, this study proceeds with an MCMC-based meta-analysis to constrain the temperature- and redshift-dependence of the meta-parameters $f_g$ and $f_T$ to calibrate the model. These calibrations indicate that, while the gas mass fraction ($f_g$) does not show significant evolution with cosmic time ($f_z = -0.11 \pm 0.03$), it decreases significantly with decreasing halo mass ($f_1 = 0.50 \pm 0.01$). On the other hand, the temperature variation shows a mild positive increase with both mass and redshift. Overall, modeling the departures from the self-similar model with $\{f_g, f_T\}$ drastically improves predictive accuracy, reducing the number of scaling relations in $>3\sigma$ ($>5 \sigma$) tension from 49 (36) percent under the self-similar scenario to just 11 (3) percent (four and one out of 39, respectively) that might be identified for their peculiarity. Moreover, the modelization through the generalized form allows me to present an extended discussion of the expected slopes and redshift evolution for several X-ray scaling laws, including the new quantity $Y_{LGT0} = L^{-1} M_g^2 T^{1/2}$, a proxy for the cluster's volume which does not depend on $f_g$ and $f_T$ by construction, and is predicted to relate directly to the mass without any redshift evolution: $M \sim Y_{LGT0} f_g^0 f_T^0 E_z^0$.

The Cosmic Archipelago is an ensemble of galaxies, strongly lensed by the cluster MACSJ0416, showing extreme physical properties at $z\sim6.14$. We combine JWST/NIRCam with deep VLT/X-Shooter and JWST/NIRSpec IFU to perform a joint spectrophotometric analysis from the far ultraviolet to red optical rest-frame. We focus on CA4, a UV-faint ($M_{UV}=-17.7$), compact ($r_e=81\pm11$ pc) galaxy at $z=6.1446$, magnified by a factor $\mu=3.73$. CA4 is a young, low-mass ($M_\star =4.3\times10^6$ M$\odot$), star-forming (${\rm SFR}=0.46$ M$\odot$/yr), and metal-poor ($Z\sim0.02$ Z$\odot$) galaxy, and an efficient producer of ionizing photons ($\log(\xi_{ion}/{\rm erg^{-1} Hz})\sim25.5$). Its properties place CA4 at the poorly explored interface between massive stellar clusters and dwarf galaxies during the epoch of reionization. Moreover, CA4 shows large Ly$\alpha$ ($f_{esc}^{\rm Ly\alpha}\sim43\%$) and Lyman-continuum ($f_{esc}\sim47\%$) escape fractions, consistent with its small Ly$\alpha$ velocity offset ($\Delta v\sim100$ km/s) and extremely blue UV-continuum slope ($\beta=-3.10$). These characteristics suggest that such UV-faint, metal-poor galaxies may contribute significantly to cosmic reionization. We also confirm five additional systems at the redshift of the Cosmic Archipelago, magnified by factors up to 12.5. They are all young (mass-weighted ages $<11$ Myr) and metal-poor ($Z<0.05$ Z$_\odot$), spanning a wide range of stellar masses and SFRs. Given the large number of these bursty star-forming galaxies in a small cosmic volume, we estimate that the currently known members of the Cosmic Archipelago result in a significant overdensity at $z\sim6$ ($\Delta z\sim0.08$), with $\delta_{gal}=12.3^{+6.6}_{-4.6}$. These results highlight the Cosmic Archipelago as an unprecedented laboratory for studying the earliest groups of low-mass, low-metallicity galaxies during the epoch of reionization.

After four observational runs, the Ligo-Virgo-Kagra collaboration estimated a local binary black hole (BBH) merger rate density of $R_{0,\textrm{LVK}}\simeq 14-26\,\textrm{Gpc}^{-3}\,\textrm{yr}^{-1}$ within the 90% credible interval. Some previous studies already pointed out that, when a realistic evolution of the metallicity-dependent cosmic star formation rate density (SFRD) is adopted, theoretical models predict a local BBH merger rate density that exceeds the observed value by at least a factor of $\sim 10$ (Sgalletta et al. 2025). In this paper, we confirm and strengthen this claim by constructing an empirical model for the SFRD and metallicity evolution that includes a correction accounting for iron abundance. The adopted metallicity relation is flexible, enabling us to bracket the wide range of observational uncertainties. We show that, even under the most conservative assumptions regarding both the SFRD and the metallicity relation, the local BBH merger rate density is overestimated by a factor $> 10$. Attempts to reconcile the predicted and observed merger rates by modifying only the metallicity-dependent SFRD would require unrealistically high metallicities ($Z>Z_\odot$) even in low-mass galaxies at high redshift. This finding indicates that revisions to the treatment of stellar and binary evolution are necessary to achieve consistency between theoretical predictions and observations. We suggest that even a modest steepening of the delay-time distribution could help alleviate this tension.

Massive stars in binary systems that undergo mass transfer during their lifetime have a different evolution from that of single stars, possibly affecting their chemical yields. While massive stars produce most of the metals in the Universe, only few studies have investigated the effects of massive binary stars on the chemical evolution of the Milky Way. Following the most recent studies on massive binary-stripped star yields as functions of metallicity, we aim at improving previous results based on single-metallicity model grids. Here, by adopting a detailed model of chemical evolution for our Galaxy, we compute the evolution of 22 chemical species including C, N, O, $\alpha$-elements and Fe-peak elements, adopting novel prescriptions for single and binary massive star yields. Our main results can be summarised as follows: (i) consistently with previous predictions, we observe very small differences in both the predicted solar abundances and [X/Fe] vs [Fe/H] relations even when including massive binary yields depending on metallicity; (ii) when adopting the new set of stellar yields for massive single stars, as computed by Farmer et al. (2023), we are able to reproduce both the K solar abundance as well as the [K/Fe] vs [Fe/H] relation, without invoking ad hoc assumptions on nucleosynthesis prescriptions; (iii) our model adopting Farmer's yields both for single and binary massive stars is able to better reproduce the [X/Fe] versus [Fe/H] relation for both Mg and Ca, as compared with standard nucleosynthetic yields adopted in chemical evolution models; iv) we find that no models can well reproduce the [C/Fe] and [Ti/Fe] vs [Fe/H] when adopting the new yields as functions of metallicity.

We present a Bayesian framework to constrain {mass ($M$), metallicity ($Z$), stellar age ($\tau$), and the convective mixing length parameter ($\alpha_{\rm MLT}$)} in main-sequence (MS) detached eclipsing binaries (DEBs). These systems provide precise values of stellar mass and radius, offering stringent tests of stellar evolution models. We combine these with broadband magnitudes in the $B$ and $V$ bands and Gaussian priors on spectroscopic mass and metallicity, and perform Markov Chain Monte Carlo inference using a fast machine-learning surrogate for one-dimensional stellar evolution models computed with Modules for Experiments in Stellar Astrophysics. To make this approach computationally feasible, we implement an active learning strategy that adaptively selects new stellar models to evaluate, concentrating training data in regions of parameter space where the surrogate is most uncertain. Applying this framework to 38 stars in DEB systems, we recover ages more precise than previous isochrone-based determinations and obtain bounds on $\alpha_{\rm MLT}$ for a subset of lower-mass stars ($M \lesssim 1.5 M_\odot$), where convective envelopes provide sensitivity to the mixing length parameter. For several stars, the inferred $\alpha_{\rm MLT}$ values lie below the Solar-calibrated value, supporting previous indications that a universal mixing length parameter may not adequately describe convection across the main sequence. The active learning methods developed here provide a scalable route to Bayesian inference with stellar evolution models, with clear applications to additional stellar physics parameters and other precisely characterized stellar systems.

Dust structures in protoplanetary discs have been widely observed and their creation remains an active field of research. Several possible origins have already been explored, including magneto-hydrodynamics, shadows and planets-disc interactions. The goal of this paper is to investigate whether a single migrating planet in a low-viscosity disc, including radiative processes, is capable of generating observable dust structures. We aim to examine both the lifetime of such structures and potential asymmetries within them. We perform a set of high-resolution, two-dimensional hydrodynamic simulations of migrating planets using three different equations of state: isothermal, constant $\beta$-cooling and an adaptive $\beta$ model. Dust is included in all simulations and the resulting dust density profiles are then post-processed to create radiative transfer images. For all equations of state considered, the planet undergoes one or several migration jumps, each producing dust rings and gaps. The lifetime of these structures depends on the phase of slow migration preceding and occurring between jumps, but in all cases they remain visible for at least 400 kyr. We find that cooling has a deciding effect on the migration behaviour and the number of jumps, but no measurable influence on the lifetime of the dust structures. The structures exhibit relatively few asymmetries, and large-scale vortices persist for an average of only 90 kyr. Our models highlight the capacity of planets to open multiple gaps while migrating, and stress the importance of a realistic cooling model. Care should be taken when interpreting and comparing such models directly to observations.

Recent JWST observations reveal an unexpectedly slow evolution in ultraviolet luminosity functions (UV LFs) at redshifts $z > 10$. To investigate this phenomenon, we develop a semi-analytical model of the UV LF, calibrated against well-constrained measurements at $z \sim 2-10$. Our analysis identifies a transition in star formation modes across cosmic epochs: at $z \lesssim 5$, a longer characteristic star formation timescale with nearly constant star formation efficiency ($f_\star$) dominates, whereas at $6 \lesssim z \lesssim 10$, shorter timescales prevail without requiring an increase in $f_\star$. For $z > 10$, the slow UV LF evolution is best explained by a shift toward even shorter star formation timescales without changing the star formation efficiency. Dust-free conditions or a top-heavy initial mass function (IMF) alone cannot reproduce the observations at $z\sim 14$. By combining UV LF with stellar mass estimates from Prospector-based SED fitting, we try to break degeneracies between IMF variations and star formation histories. Our results indicate that evolving star formation timescales rather than IMF or dust changes are the primary drivers of the observed high-redshift UV LF evolution, reflecting changing physical conditions during the earliest phases of galaxy assembly. Additionally, we show that moderate AGN activity could further boost UV luminosities at $z \sim 14$, potentially explaining the observed UV LF without changes in stellar parameters.

As we enter the 2030s, the astronomical landscape will be dominated by large-scale infrared (IR) and optical surveys led by JWST, Euclid, and the Nancy Grace Roman Space Telescope. While these facilities provide unprecedented views of the dusty environments of nearby star-forming regions, they are fundamentally limited in their ability to probe the high-energy physics of accretion, magnetospheric activity, and disk photoevaporation. This white paper argues for the critical continued use of the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) and Cosmic Origins Spectrograph (COS) to bridge the "UV Gap." We demonstrate that UV spectroscopy is the only direct method for characterizing the feedback mechanisms that determine planet habitability and stellar maturation, serving as a mandatory scientific bridge toward the Habitable Worlds Observatory (HWO). The study of star formation stands at a critical intersection of multiple scientific disciplines, linking the high-energy physics of stellar birth to the chemical evolution of protoplanetary disks and the eventual habitability of exoplanets. As such, it represents one of the most compelling and essential science cases for the continued allocation of HST resources. Ensuring that HST provides high-resolution UV spectroscopic data now is a fundamental requirement for the success of future flagship missions, as these data provide the unique physical context that infrared observations alone cannot achieve.

The energy spectra for individual elements and/or for groups of elements in cosmic rays (CR) in the energy range between 100 $\times$ Z GeV and 10$^{3}$ $\times$ Z PeV (where Z is the charge number of the nucleus) have a number of features, including two steepenings ("knees") with the rigidity-dependent energies $E_{k1} \approx$ 15 $\times$ Z TeV and $E_{k2} \approx$ 3 $\times$ Z PeV and three hardenings ("ankles") at $E_{a1} \approx$ 500 $\times$ Z GeV; for protons $E_{a2-p} \approx$ 150 TeV and $E_{ a3-p} \approx$ 100 PeV. While the values of $E_{a1}$ for different nuclei are rigidity-dependent, the values of $E_{a2}$ (and probably of $E_{a3}$) are not: $E_{a2-He} \approx$ 1 PeV for Helium. The recent advances in precision measurements of the elemental CR spectra in the DAMPE and LHAASO experiments, and, to some extent, in IceTop and other experiments, make it possible, for the first time, to clarify the origin of the aforementioned spectral features. We show that the elemental CR spectra are reasonably well described with a sum of three components: 1) a low-energy Galactic component with a convex spectral shape reflecting the accelerated particle spectrum in the source; this component peters out after the TeV knee, 2) a high-energy Galactic component including the PeV knee, and 3) an extragalactic component. There is no need for any third, additional component of Galactic cosmic rays in the energy range between 10 PeV and 1 EeV.

A significant puzzle in extragalactic astronomy is the scarcity of Little Red Dots (LRDs) at $z < 3$, compared to their higher abundance at earlier epochs. To understand this transition, we investigate the cosmic evolution of LRD environments. We measure the overdensity for LRDs and the general galaxy population at $3<z<7$, and find that at $z > 4$, LRDs predominantly reside in under-dense regions relative to the general galaxy population. By $z \sim 3.5$, however, this environmental contrast roughly diminishes, and LRDs are found in regions of comparable density to typical galaxies. Simultaneously, the dark matter halo masses of LRDs, inferred from large-scale clustering, grow rapidly from $\lesssim 10^{10.1} \, M_{\odot}$ at $z \sim 7.5$ to $\sim 10^{11.3} \, M_{\odot}$ at $z \sim 3.5$, where the halo mass becomes close to that of normal galaxies at lower redshift. Applying an empirical stellar-to-halo mass scaling relation, we derive stellar masses for LRDs; these show that black hole masses remain over-massive relative to stellar mass at $z > 4$, but converge toward the local $M_* - M_{\rm BH}$ scaling relation by $z \sim 3.5$. The coherent evolution of LRDs' large-scale environments $-$ as expressed by their overdensity and halo mass $-$ points to a distinct evolutionary pathway from that of normal galaxies. The significantly increased halo masses of LRDs lead to larger galaxy sizes, driven primarily by the potential enhancement of halo spins. Consequently, these sources are no longer as compact as typical high-redshift LRDs. Meanwhile, the depletion of dense gas and/or elevated star formation in their host galaxies would also significantly alter the spectral energy distribution of LRDs.

I present EXOVEIL, a transit detection system that learns what a star's brightness should look like and flags when reality disagrees. Unlike existing systems that require phase-folded input, EXOVEIL operates on raw flux time series and can detect planets that transit only once.A Transformer world model, trained on 16,499 Kepler light curves with transit-masked self-supervised learning, predicts expected stellar flux. A matched-filter detector with variance weighting extracts transit signals from the prediction residuals. A learned classifier (XGBoost) separates planets from false positives, achieving AUC 0.938 on Kepler DR25. Applied to single-transit injection-recovery, EXOVEIL recovers 32% of transits at 1000 ppm depth a task where all classification-based systems score 0% by construction. A blind search of 3,737 Kepler stars yields 179 new transit-like signals not present in the DR25 TCE catalogue, including 46 monotransit candidates. Applied withoutretraining to 47 confirmed TESS planets in the PLATO LOPS2 field, EXOVEIL achieves 100% recovery, demonstrating zero-shot cross-mission transfer. At PLATO's 25-second cadence, detection reaches 100 ppm -- approaching the Earth-analog regime. I provide the first application of conformal prediction to transit detection (95.9% empirical coverage) and release the system as pip install exoveil with pretrained weights and a candidate catalogue.

Reconstructing the direction of incoming neutrinos in the IceCube Neutrino Observatory is an important problem in astrophysics. The public IceCube--Neutrinos in Deep Ice Kaggle competition provided 140 million simulated events to benchmark reconstruction techniques. To address this challenge from a novel perspective we introduce neutrino fingerprints compact $72 \times 72 \times 3$ images in which each pixel represents a single detector, with pulse timing and charge statistics encoded as color channels. This representation transforms sparse, irregular pulse data into dense images suitable for convolutional processing. Our ResNet18 model achieves a mean angular error of $1.10$ rad, indicating that convolutional networks trained on fingerprints rival more complex architectures while offering an effective, interpretable baseline for IceCube event reconstruction.

Molecular clouds are affected by dynamical processes such as cloud merging and stellar feedback that alter their topology. For this reason, the molecular clouds in the PHANGS-JWST catalogue are studied under the light of topological data analysis. This study shows correlations between physical characteristics of galaxies and topological summaries of molecular clouds.

Over the last decade of ALMA's operation the molecular inventory of protoplanetary disks has expanded rapidly, revealing a diverse set of nitrogen-bearing organics and carbon-chain molecules that trace both prebiotic chemistry and fundamental disk physics. Despite this progress, detections of larger species such as cyanopolyynes have remained limited, leaving larger carbon-chain chemistry in Class II disks largely unconstrained. Here, we report the first detection of HC5N toward the TW Hya protoplanetary disk, representing the largest cyanopolyyne identified to date in a Class II system. We derive a HC5N column density for two rotational transitions J = 41-40 and J = 37-36, N_T ~ 10^12 cm^-2 for assumed T_rot = 20-50 K and optically thin emission in LTE. We compare HC5N and HC3N formation mechanisms and analyze the HC3N/HC5N ratio. We use a chemical model to estimate the expected abundance and emitting layer of HC5N in a TW Hya-like disk. Although HC5N emission is spatially unresolved, measured column densities suggest an origin in the warm molecular layer where CN-based pathways are active. This detection extends the known carbon-chain chemistry in Class II disks and demonstrates that long cyanopolyynes can form and persist in planet-forming environments.

Nereid, Neptune's third largest moon, is considered to be a captured irregular satellite due to its highly eccentric orbit. However, among irregular satellites, Nereid is an outlier: it is the largest, the closest to its host planet, and the most eccentric. We present James Webb Space Telescope near-infrared spectroscopy of Nereid that demonstrates that its composition is inconsistent with its suggested captured origin. We then simulate Nereid's early orbital history subsequent to Triton's capture to demonstrate a plausible dynamical pathway for a regular satellite formed in-situ around Neptune to evolve to Nereid's present-day orbit. Based upon the available spectroscopic and dynamical evidence, we propose that Nereid is not a body captured from the Kuiper belt, but rather the sole surviving intact regular satellite of Neptune.

Wide-band correlators for radio astronomy interferometers demand accurate, scalable signal processing backends that sustain high aggregate throughput while preserving stable timing alignment across a large number of signal chains. Addressing these coupled constraints is challenging without a co-designed backplane architecture. We present a backplane system developed for the Control Readout System (CRS) Field Programmable Gate Array (FPGA) platform, extending its capabilities to support high channel count wideband radio correlators. The design and validation process are guided by the requirements of the Canadian Hydrogen Observatory and Radio-transient Detector (CHORD) telescope, which provides a representative use case for the system's performance evaluation. Each backplane hosts up to four CRS boards, and a single crate integrates four interconnected backplanes to accommodate sixteen CRS modules (for a total of 128 digitized inputs per crate) interconnected through 25 Gbps per-lane links and an on-backplane data shuffle network. Comprehensive validation demonstrates robust high-speed link performance, sub-sampling-level timing alignment stability, and stable thermal and power behavior across environmental variations. The architecture delivers observatory-scale scalability, providing a low-jitter and phase-consistent foundation for wideband digital correlators. By supporting expansion from single-crate to multi-crate configurations without firmware modification, the system offers a practical and flexible path toward next-generation interferometers requiring tightly synchronized, high-throughput digital backends.

We revisit the mass of the neutron star in the ultracompact binary 4U 1820--30 in light of a recently reported transient absorption feature at about 3.8 keV, interpreted as a gravitationally redshifted, highly ionized iron line and implying \(1+z\simeq1.72\), a very high stellar compactness. We examine whether the mass-radius locus implied by this interpretation can be made compatible with external EoS-informed benchmarks and timing-based estimates. We map the compactness implied by the redshift onto the mass-radius plane, including rotational effects, and compare the resulting region with an EoS-informed 95\% reference contour derived from NICER data of several neutron-star systems. While we do not perform a statistically self-consistent joint mass-radius inference for 4U 1820--30, we present a quantitative conditional consistency test in a common \(M-R\) framework, comparing published inputs under explicitly stated assumptions. We find that, if the maximum neutron-star mass is restricted to low values \((\leq 2.3\,M_{\odot})\), the redshift-implied locus shows at most marginal overlap with the EoS-informed contour, indicating substantial tension. Allowing a higher maximum mass enlarges the parameter space and can restore compatibility with that benchmark. However, such high masses remain in tension with previous touchdown-flux estimates, although they are not necessarily excluded by interpretations based on the highest detected quasi-periodic oscillation frequency. We conclude that the redshift interpretation of the 3.8 keV feature, the touchdown-flux estimates, and the QPO/ISCO interpretation do not naturally select the same mass-radius sector for this source under these assumptions. Reconciling them requires auxiliary assumptions with high leverage on the inferred compactness.

Cosmic birefringence, a signature of parity-violating physics, rotates the cosmic microwave background (CMB) polarization plane, generating correlations between CMB $E$- and $B$-mode anisotropies. Measuring this effect remains challenging due to degeneracies with spurious rotations from instrumental polarization angle miscalibration and limited knowledge of Galactic foreground $EB$ correlations. We present a blind, map-based approach based on a multi-Stokes hybrid internal linear combination (ILC) that breaks this degeneracy and disentangles correlated and uncorrelated CMB polarization components. By jointly combining $E$- and $B$-mode frequency maps, the method preserves achromatic birefringence-induced CMB anisotropies while downweighting foregrounds and chromatic CMB anisotropies resulting from instrumental miscalibration. This enables a direct spatial linear-regression estimator of the birefringence angle. Applied to LiteBIRD simulations, the method yields competitive constraints on birefringence. Applied to Planck PR4 data, we measure a birefringence angle $\beta \simeq 0.32^\circ \pm 0.12^\circ$, consistent with previous independent analyses and stable across sky fractions.

Forecasting seismic waveforms beyond observed data remains challenging due to the nonlinear, dispersive, and multi-scale nature of seismic wave propagation. In this work, we introduce \textsc{SeismoGPT}, a transformer-based autoregressive model designed to forecast three-component seismic waveforms directly in the time domain. Forecasting is formulated as a physically constrained continuation problem in which the model receives waveform context beginning at the P-wave arrival and extending a defined time beyond the S-wave arrival, after which future motion is generated recursively without access to ground-truth samples. Evaluation is performed on synthetic seismograms spanning source depths of 5--100\,km, epicentral distances of 10--90$^\circ$, and magnitudes $3 \leq M_w \leq 7$. To disentangle the effects of context length and prediction horizon, we define three evaluation configurations using a distance-normalized context ratio and fixed prediction horizons of 120 and 240\,s. Across all configurations, the model achieves median normalized cross correlation above 0.93. Analysis of representative forecasts shows that successful predictions preserve both phase coherence and spectral energy distribution. Where failure cases arise, this is primarily due to gradual phase drift during autoregressive rollout rather than unphysical signal generation. These results demonstrate that transformer-based sequence models can learn stable dynamical continuation of seismic wavefields, highlighting the potential of foundation-model approaches for physics-driven time-series forecasting. There are potential applications of this methodology in seismic warning and hazard mitigation, particularly for next-generation gravitational-wave observatories, such as the Einstein Telescope.

Context: For the typical modeling of neutron stars cooling after an accretion episode in Low-Mass X-ray Binaries, an extra heating source of unknown physical origin, \textit{the shallow heating}, is invoked in order to account for the inferred high effective temperatures of the star up to hundreds of days after the end of accretion. The amount of the shallow heating generated in the crust is usually taken to be proportional to the accretion rate, although the proportionality constant may change from source to source. Aims: In this paper, we intend to model the effective temperature data of eight outburst episodes from seven different sources (\mxb, \xte, \exo, \igr, \swift, \rxs\ and \ks) without {\it ad hoc} shallow heating but accounting for the presence of thermonuclear heating due to the burning of the accreted H/He. Methods: We employ the fully relativistic code \texttt{nscool}, which simulates both the crust and core of a neutron star, equipped with a new boundary condition at the envelope/crust transition which considers thermonuclear heating leakage from the envelope into the crust and depends on the mass accretion rate. Results: We find that the neutron star cooling for seven out of eight of these outbursts can be well explained with this new boundary condition and without the requirement of {\it ad hoc} shallow heating. While the qualitative features of \exo\ cooling curve can be explained, a good fitting still requires additional physics.

We examine how inferences of the neutron-star equation of state depend on mass and radius observations. We update previous results with recent measurements combined with theoretical input from chiral effective field theory and perturbative quantum chromodynamics. The revised constraints are consistent with, but tighter than, those obtained in earlier work. Isolating the effects of different classes of observations we find that the theoretical constraints, together with the requirement that the maximal neutron-star mass exceeds $2\,M_\odot$, dominate the equation-of-state inference over most densities. Radius measurements mainly refine the constraints at the low-density regime, $\rho \lesssim 2\rho_0$, whereas measurements of masses well above $2\,M_\odot$ improve the constraints over a wider density range. Finally, we explore the impact of possible future observations. The largest impact would arise from a measurement that refines the value of the maximal neutron star mass. It can be, e.g., a detection of an extremely massive neutron star or an improved upper limit. However, even a precise measurement a $2.5-2.6\,M_\odot$ NS will not alter our knowledge of the equation of state qualitatively. Conversely, observations lying well outside the present allowed region, would point to new physics in neutron-star cores and require a revision of the current framework.

As the Centaurs of the Outer Solar System have become better studied, their relationship with the Jupiter Family Comets and their connection to the primordial protoplanetary disk has come under deeper scrutiny: which properties of the comets observed closer to the Sun are original, and which were modified significantly en route during their Centaur phase? The active Jupiter co-orbital comet P/2019 LD2 (ATLAS) attracted significant attention after its discovery when it was realized that the object would transition between a Centaur and JFC orbit in 2063, the first time this change can be observed and monitored in real time. In this study, we present new ground-based and Hubble Space Telescope imaging of the single other Jupiter co-orbital comet, P/2023 V6 (PANSTARRS), throughout late 2024 and early 2025. V6 was not detected in ground-based imaging after early October, and deep imaging with HST taken in early December is consistent with a $m_V = 28.06 \pm 0.03$ point source at its expected location. This both implies that the object ceased activity sometime in late 2024, and is thus in a different thermal state than LD2 despite both having large active fractions, and that V6's diameter is approximately $D\sim340$ meters. This is likely the smallest object directly observed by HST beyond the Main Belt, and certainly the smallest Centaur yet discovered, highlighting the ability to detect active sub-km objects beyond Jupiter with current surveys and potentially probing smaller sizes with LSST.

We report JWST/NIRSpec integral field unit (IFU) observations of the quasar J1512$+$4422 at $z \sim 6.2$ from the Aether survey. At $\sim$900 Myr after the Big Bang, this object already lies on the $M_{\rm BH}$-$\sigma_\ast$ relation found in the local universe, with an $M_{\rm BH} \simeq 8.9\times10^8\,M_\odot$ and a stellar velocity dispersion $\sigma_\ast \simeq 288$ km s$^{-1}$. We detect an outflow with a velocity of $\sim$478 km s$^{-1}$ in the nuclear region, which likely extends to $\sim$3.2 kpc in projection and has a median velocity of $\sim$352 km s$^{-1}$. The outflow dynamical time scale ($\sim$ 9 Myr) is consistent with the time scale of the current quenching process based on the star formation history as reported previously. The total mass outflow rate (92.6$^{+92.6}_{-74.1}$ M$_{\odot}$ yr$^{-1}$) is larger than the current star formation rate (0.9$^{+3.8}_{-0.8}$ or 4.3$^{+5.8}_{-3.7}$ M$_{\odot}$ yr$^{-1}$), and the total kinetic energy outflow rate (0.6$^{+0.6}_{-0.5}$\% of quasar luminosity) meets the threshold for negative quasar feedback as suggested by simulations. These results suggest that the outflow is capable of suppressing/quenching the star formation activity within the host galaxy. Furthermore, J1512$+$4422 exhibits $\sigma_\ast$, stellar mass and size similar to those of $z \gtrsim$ 3 quiescent/post-starburst galaxies, implying a link between the two. Overall, for objects like J1512$+$4422, the evolution of their SMBHs and host galaxies appears to be tightly coupled within the first billion years. The quasar feedback likely plays a critical role in both placing them on the $M_{\rm BH}$--$\sigma_\ast$ relation and quenching.

This study conducts a comprehensive analysis of brightness and color variability in blazars, utilizing over six years of quasi-simultaneous g-band and r-band data from 1149 sources in the ZTF Data Release 22 (DR22), including 589 BL Lacs and 560 FSRQs. We quantify the amplitude of variability and the fractional root mean square (rms) variability for each source and statistically assess the overall and short-term color behaviors across different subclasses; examine the distribution of brightness variability characteristics across different blazar types and investigate how the extent of variability correlates with color trends. We found BL Lacs tend to exhibit a BWB (bluer when brighter) trend, while FSRQs display a RWB (redder when brighter) trend; BL Lacs with negligible host-galaxy contamination exhibit a BWB trend fraction of 14.7% (68/462) compared to 2.3% (11/462) for RWB trend, while FSRQs show 8.8% (49/560) BWB trend versus 14.1% (79/560) RWB trend. By statistically investigating how color behavior depends on brightness state across different timescales, we find that brighter states in both BL Lacs and FSRQs are more likely to exhibit BWB trend. Our results also show that BL Lacs with a BWB trend exhibit higher variability than those with a RWB trend, whereas FSRQs with a RWB trend display significantly greater variability than those with a BWB trend. These results suggest that blazar color variability depends jointly on source type, brightness state, and variability amplitude, highlighting the complexity of color evolution in blazars.

The primordial helium mass fraction, $Y_\mathrm{p}$, is a key observational pillar of Big Bang nucleosynthesis and a sensitive probe of early-Universe physics. Over the past several decades, numerous observational $Y_\mathrm{p}$ determinations have been published using a wide range of astrophysical tracers and cosmological techniques. Although recent measurements exhibit striking convergence and increasingly small uncertainties, the statistical and historical context of this consensus has not been examined systematically. Here, we compile and analyse a comprehensive dataset of observational $Y_\mathrm{p}$ determinations published between the late-1960s and 2022. The final sample comprises 143 reported values spanning multiple tracers. We find clear evidence for long-term convergence in published $Y_\mathrm{p}$ values, punctuated by statistically significant change points in the mid-2000s and early 2010s. Careful examination reveals that many extragalactic H{\sc ii}-region determinations are not fully independent, relying on re-analyses or partial reuse of a limited number of observational datasets. This reduces the effective number of independent constraints and provides important context for interpreting the precision of recent results. Our findings do not challenge the overall consistency of modern $Y_\mathrm{p}$ determinations with standard cosmology, but they underscore the importance of accounting for data dependence, methodological homogeneity and historical evolution when synthesising measurements.

We present a fast, interpretable machine learning framework to classify early- and late-type galaxies in the COSMOS2025 catalog at $0 < z < 3$, without relying on image-based training labels or computationally expensive structural fitting. Using the Santa Cruz Semi-Analytic Model, we generate a training set with secure morphological labels defined by bulge-to-total mass ratio and specific star formation rate. We bridge the simulation-to-observation domain gap by injecting realistic photometric noise derived from COSMOS2025. A CatBoostClassifier trained on 66 broadband colors achieves excellent performance in the simulated domain, recovering late-types with 98\% precision/recall and early-types with 91\% precision and 88\% recall. Applied to 44,132 COSMOS2025 galaxies, the model reveals a striking bimodality: only about 6\% of galaxies receive intermediate probabilities ($0.3 < P(\text{Early type}) < 0.7$) -- nearly identical to the fraction observed in the simulation. This demonstrates that broadband colors are a decisive morphological discriminant, with the remaining 94\% classified at high confidence. Validation against independent bulge+disk decompositions yields 70\% overall accuracy, with late-types identified at 78\% purity and 74\% completeness. The most important color feature, F277W-F444W, reflects the expected optical/NIR contrast between old and young stellar populations. The full pipeline completes in under 30 minutes on standard hardware, demonstrating that simulation-trained color-based classifiers offer a scalable, physically interpretable route to approximate morphology for large next-generation surveys.

We present the serendipitous discovery of a nine-member system comprised of protostellar and candidate prestellar sources in $\sim$350 au-resolution images from Complex Chemistry in hot Cores with ALMA (CoCCoA). The system is bound in a stability analysis, has a mean separation between pairs of 7930 au, and appears to have formed via the fragmentation of a single large-scale filamentary structure traced by 1.20\,mm continuum and H$^{13}$CO$^+$ J = 3-2 emission. Two multiples within the nine-member system, a triple and a binary, have properties consistent with formation by core fragmentation on $\sim$1500-1700 au scales. The hot core NGC 6334-43 is resolved into two components (ALMA2a/ALMA2b) separated by 618 au and driving a bipolar outflow traced by $^{12}$CO J = 2-1 and SiO J = 5-4 in $\sim$1250 au-resolution archival Atacama Large Millimeter/submillimeter Array (ALMA) data. Only one other source in the nine-member system is clearly protostellar: ALMA6a, which drives an outflow traced by $^{12}$CO. The outflow properties of ALMA2a/ALMA2b and ALMA6a are consistent with high-mass and low-mass Class 0 sources respectively. By fitting the CH$_{3}$CN J = 13-12 emission towards ALMA2a, ALMA2b and ALMA6a, we derive M$_{\rm vir}$ = 4.5, 5.4 and 2.6 M$_{\odot}$ respectively. The other six sources in the nine-member multiple have M$_{\rm gas}$ = 0.50-1.87 M$_{\odot}$ and appear young, as indicated by their sparse mm-wavelength line emission and non-detection in published cm continuum observations. Our results highlight the potential of serendipitous discoveries in ALMA surveys to add to the small observational sample of young high-mass protomultiple systems.

Sugars are essential biomolecules, serving as metabolic fuels, nucleic acid backbone components, and structural or energy-storage polymers. A central question in origin-of-life research is how monosaccharides formed on the primitive Earth, as laboratory experiments under prebiotic conditions yield insufficient concentrations. The detection of ribose, glucose and other monosaccharides in asteroids and meteorites suggests an exogenous origin, possibly in the interstellar medium (ISM) prior to meteoritic parent-body formation. However, no sugar has been observed in the ISM so far. We report the discovery of erythrulose, a chiral four-carbon ketose, in the ISM. The detection has been achieved thanks to ultrasensitive, broadband spectral surveys toward the Galactic Center molecular cloud G+0.693-0.027 obtained using the Yebes 40m and IRAM 30m telescopes. Erythrulose appears to be at least eight times more abundant than analogous three-carbon sugars, which remain undetected in our ultrasensitive observations. Quantum chemical and astrochemical models indicate that erythrulose forms efficiently on interstellar dust grains from simpler two-carbon aldehydes and alcohols. As ketoses readily isomerize into aldoses in aqueous conditions, interstellar erythrulose could have contributed to the sugar inventory available for early metabolic and replication processes.

A reduction mechanism of the theoretically predicted excessive abundance of 7Li via nucleons evaporated by primordial black holes is suggested. It is shown that the fraction of 7Li with respect to the number density of baryons can be diminished down to the observed value 7Li/B via the process of 7Li transformation into 8Li or 8Be that quickly decay into a pair of 4He nuclei.

We investigate the expected uncertainties in recovering galaxy cluster mass profiles from upcoming spectroscopic survey data using The Three Hundred Project. Using the caustic technique, which leverages galaxy positions and line-of-sight velocities, we assess the systematic errors introduced by assumptions regarding velocity anisotropy and demonstrate how an iterative correction method can minimize these errors. We also assess the impact of survey magnitude limits on cluster mass estimates, highlighting potential biases across different observational strategies. We focus the analysis on our own CATARSIS survey, which aims at obtaining redshift measurements for all galaxies with magnitudes mAB,r < 22 within 2xR200c of 16 galaxy clusters with redshifts 0.14 < z < 0.27 using the future 8 arcmin^2 field-of-view TARSIS integral-field spectrograph of the Calar Alto 3.5-m telescope. Such data will enable us to mitigate systematic errors in the determination of density profiles. CATARSIS aims at enhancing the precision of mass profile estimates by deepening our understanding of the dynamical states and physical characteristics of galaxy clusters.

The recent discovery of Little Red Dots (LRDs) by the James Webb Space Telescope has challenged traditional models of early galaxy and black hole co-evolution. The nature of these highly compact objects remains heavily debated, with explanations divided between dust-reddened active galactic nuclei (AGN) and extremely dense stellar populations. We perform high-resolution cosmological simulations to model the formation of LRD precursors. Motivated by recent high-redshift observations and theoretical results, we specifically explore environments characterized by high star formation efficiencies (30\% and 100\%) and confined feedback. Our simulations naturally produce highly compact galaxies with stellar masses of $10^7-6 \times 10^8 $\,M$_\odot$, with most of the mass concentrated within $200-300$ pc. We find that, in these dense environments, gas inflows, gravitational torques, and stellar dynamical friction operate on highly efficient timescales. Over a 10 Myr timescale, gas inflows can accumulate $\rm \sim 10^7 M_\odot$ at the galactic center, while gravitational torques and dynamical friction can contribute an additional $10^5-10^9$\,M$_\odot$ and $10^3-10^4$\, M$_\odot$ through the inward migration of massive stars. Assuming a conservative 10\% efficiency to account for feedback, this rapid mass accumulation can lead to the formation of a $\sim 10^6$\,M$_\odot$ central black hole, naturally giving rise to an AGN in these dense systems. Therefore, stellar and AGN interpretations of LRDs may not be mutually exclusive; rather, dense stellar systems are likely precursors to AGN.

Cosmological constraints on self-interacting neutrinos require a Boltzmann hierarchy in which the collision term is projected onto momentum-averaged multipoles. We revisit the collision kernel for neutrino-neutrino scattering mediated by a light scalar and derive an exact analytic expression for the multipole integral that determines the coefficients $\alpha_\ell$. The key idea is to express the integration kernel as angular derivatives of the Yukawa-potential $\frac{\mathrm{e}^{-P/2}}{P}$, move the derivatives onto Legendre polynomials, and reduce the remaining momentum integrals to a single base family obeying a first-order recurrence. This gives an exact rational-plus-$\pi^2$ representation for every multipole, together with a compact implementation based on exact rational arithmetic. We provide the recurrence relations, a closed form for the base integral, and an asymptotically constrained approximation suitable for Boltzmann codes such as CLASS. Our numerical implementation is publicly available in the Jupyter notebook this http URL.

The earliest massive black holes are often discussed in terms of heavy baryonic seeds, primordial black holes, or super-Eddington accretion. We develop a different possibility: a compact object on a hidden donor brane forms a common five-dimensional horizon whose intersection with our brane is observed as a black-hole seed. Donor-side matter accretes onto the common five-dimensional horizon, increases the horizon radius, and consequently enlarges its intersection with our brane. As a result, the gravitational mass inferred by an observer living on our brane grows. We slice the five-dimensional geometry onto each brane and show that the induced exterior on our brane has the usual Schwarzschild/Vaidya monopole form at leading order, with subleading Weyl/Kaluza-Klein corrections in the localized-feeding branch. We construct a perturbative gradient-expansion solution satisfying the regular bulk equations and brane junction conditions. The matter sector satisfies the null energy condition for positive mass growth. The linear perturbation stability is investigated, and for supermassive seeds with horizon radius far larger than the interbrane scale, the dangerous long-wavelength mode is absent. The primary observational consequences are overmassive high-redshift black holes in underdeveloped hosts, hidden mass growth relative to the luminous accretion budget, LISA-band heavy-seed mergers, and the absence of primordial fossils required by primordial-black-hole explanations.

We present an updated Rossiter-McLaughlin modelling framework in the exoplanet analysis code \textsc{TLCM}. We describe our model in detail. The model and the code were validated by nine systems where we use TESS photometric measurements and archive radial velocity data (WASP-15, HAT-P-1, HAT-P-3, HAT-P-6, HAT-P-7, HAT-P-11, HAT-P-14, HAT-P-20, HAT-P-32). In addition, new observations were obtained from HD 2685 = TOI-135 which is an evolved, hot ($T_\mathrm{eff}=6801$ K), single star hosting a $\sim 1.15$ Jupiter-mass transiting hot Jupiter in a $\sim 4.1$ days orbit. We obtained new HARPS radial velocity measurements in-transit and out-of-transit. Also, there are new photometric observations from six additional, yet not-analyzed TESS-sectors since the time of the discovery of its transits. This allowed us to refine the planetary, orbital and system parameters and to detect Rossiter-Mclaughlin effect in it. We find an intermediate sky-projected obliquity, $\lambda = \ang{55.6}^{+\ang{10.9}}_{-\ang{11.9}}$, for our fiducial spectroscopic \(V\sin I_\star\) prior. Tests with broader \(V\sin I_\star\) priors show that the central value of \(\lambda\) remains stable, although the uncertainty increases.

Little Red Dots (LRDs) are candidates for growing supermassive black holes newly discovered by the James Webb Space Telescope (JWST), characterized by compact rest-optical morphology, V-shaped spectra, and broad Hydrogen Balmer lines. While recently proposed BH-star/envelope models have made progress in explaining their optical features, their rest-UV emission, which is considered to originate from host galaxies, remains poorly investigated. In this paper, we present a comprehensive analysis of the UV emission, including continuum shapes, emission line strengths, and morphology, using $\sim100$ LRDs selected from the JWST spectral archive. Compared to star-forming galaxies at the same redshifts and UV magnitudes, LRDs show systematically redder UV slopes and more compact UV sizes, indicating that their UV emission cannot be explained solely by normal star-forming galaxies and requires a significant contribution from central red and compact emission. From stacked spectra, we find that the Balmer break strength, UV slope, downturn depth around Ly$\alpha$, and $\mathrm{Fe\, II}$ equivalent width are positively correlated, while the UV size is anticorrelated with the Balmer break strength, suggesting that diversity in the UV continuum shape reflects the varying dominance of the central emission relative to its host. We also measure $\mathrm{Fe\, II//Mg\, II}\sim8-10$, higher than in quasars at similar redshifts, further supporting a substantial contribution from the central component. Spectral modeling suggests that the observed red UV continuum cannot be reproduced by host galaxy emission alone, but requires an additional very red continuum source ($\beta_\mathrm{UV}\sim0$), possibly nebular continuum emission leaking from dense ionized gas through a clumpy or porous neutral gas envelope.

Non-dissipative, transonic, sub-Keplerian accretion flow onto black holes is characterized by two conserved parameters: specific energy and specific angular momentum of the flow. For certain range of these parameters, the accretion flow shows shock formation and the post-shock matter forms a boundary layer which is believed to shape the radiative properties of the accretion disk. In this work, we identify the parameter space for shock in such accretion flows using multi-dimensional numerical simulations around non-rotating black holes and demonstrate that the shock formation parameter space is much larger than the analytically calculated one. We also find the boundary layer to be dynamic for a significant part of this parameter space and self-consistently produce outflow from the accretion disk.

The Gaia/DR3 GSP-Spec module has published the atmospheric parameters of up to 5.6 million stars based on the analysis of their Radial Velocity Spectrometer spectra. By combining these spectroscopic parameters with Gaia parallax and photometric measurements, a large catalogue of interstellar colour excesses and extinctions, complemented with stellar luminosities, radii, and masses, was constructed without relying on any stellar evolution or structure models. This catalogue also contains the associated uncertainties estimated from Monte-Carlo realisations for about 4.6 million stars. We present a system of quality flags based on the GSP-Spec quality parameters, the achieved numerical precision, and the Gaia astrometric quality. Adopting these flags, we defined a subsample of high-accuracy and precision parameters of more than 1.5 million stars. The impact of possible GSP-Spec parameter inaccuracies on the derived extinctions, luminosities, radii, and masses was also explored and revealed that the mass is the most affected quantity. The radii and masses were validated by comparison with interferometric and asteroseismic data. This confirmed their high quality, even when the targets were highly extincted by the interstellar medium. We also emphasise that they are fully compatible and homogeneous with the GSP-Spec parameters. This allowed us to avoid systematics and biases that might be hidden when data from different (and potentially) heterogeneous catalogues are combined. Finally, we present some example applications of this catalogue: (i) exoplanet radii and masses, (ii) present-day mass distribution functions, (iii) identification of Galactic populations based on their mass distribution, and (iv) Galactic halo accreted stellar luminosities and masses that confirm their merger epochs

Context. Sulphur-bearing species play a key role in the chemical evolution of the interstellar medium and icy Solar System bodies such as the Jovian moons, yet the sulphur budget remains poorly constrained. Sulphur dioxide is considered one of the main sulphur reservoirs in icy environments, making its interaction with water ice surfaces highly relevant for astrochemical models. Aims. This work aims to extract adsorption energy distributions of SO2 on water ice substrates as a relevant model for astrophysical environments to better constrain its thermal behaviour and solid-gas exchange for astrochemical simulations. Methods. We performed a systematic experimental study of temperature-programmed desorption of SO2 deposited on three types of surfaces -- polycrystalline gold, compact amorphous solid water (c-ASW), and crystalline water under ultra-high vacuum conditions -- to then extract, using a Polanyi-Wigner model, the adsorption energy distributions of SO2 on each surface. Results. We performed the extraction of the adsorption energy distribution of SO2 deposited on water ice substrates. These exhibit a bimodal structure: a first physisorbed layer and a second, more strongly bound population. Only minor differences are observed between c-ASW and crystalline water ice in the behaviour of the distributions. We also provide mean values, most probable values, and width of the distribution. On average, the binding energy of SO2 on water ice surface is 439 +- 41 meV.

High-mass X-ray binaries serve as important laboratories for studying a broad range of fundamental astrophysical questions. These systems host two distinct types of astrophysical objects at different stages of stellar evolution: a massive donor star and a compact object. I will explore how our understanding of these systems has evolved over the past 50 years, from the dawn of the X-ray astronomy era to the present day. Along this historical journey, I will introduce the various classes and sub-classes of high-mass X-ray binaries and highlight their key observational characteristics.

C$_{11}$H$_9^+$ ion is the dominant fragment cation formed from methyl-naphthalene (MeNp) and dimethyl-naphthalene (diMeNp). Using the multiplex capabilities of PIRENEA, a setup dedicated to laboratory astrophysics, we studied the reactivity of the benzylium-like isomers of C$_{11}$H$_9^+$ with diMeNp under isolated conditions relevant to radiative association. Two reaction products are observed, C$_{12}$H$_{11}^+$ -- also formed in the reaction with MeNp -- and C$_{13}$H$_{13}^+$, with branching ratios that depend on the specific diMeNp isomer. The reaction products were subsequently exposed to UV-visible irradiation to gain insight into their structures. The acenaphthylene radical cation, C$_{12}$H$_{8}^{\bullet +}$, was identified as the most stable photofragment. We show that this experimental approach, supported by density functional theory calculations and molecular dynamics simulations, provides new constraints on the chemistry of benzylium-type species. We highlight the role that long-lived ion-molecule complexes can have in promoting C-C coupling and the formation of a pentagonal cycle. Moreover, the chemistry uncovered here highlights new pathways for the formation of pentagonal rings during PAH growth under low-pressure and cold conditions. In particular, it can lead to efficient formation of acenaphthylene-like species, recently detected in the TMC-1 cold cloud.

Type Ia supernovae (SNe Ia) are well-known standardisable candles, and are one of the main ways to measure the distance to their host galaxies. However, extinction due to interstellar dust causes objects to appear fainter and redder. Correcting for this requires estimating the amount of intervening material and how the extinction changes as a function of wavelength. We present and analyse optical and near-infrared data of the well-observed SN 2024gy and use these to compare different extinction estimation techniques, making use of photometric, spectroscopic, and polarimetric data. SN 2024gy is a normal SN Ia with high velocity (HV) components in Si II $\lambda6355$ (phase $<-10$ days) and a particularly strong HV feature in the Ca II near-infrared triplet (up to peak). Modelling SN 2024gy with TARDIS shows better matches with a double-detonation scenario compared to a delayed-detonation scenario due to a better match to the Ca II HV component. A measurement of the stable Ni/Fe ratio however favours a delayed-detonation scenario. Host extinction estimates range from $E(B-V)_{host}=0.12\pm0.02$ mag (narrow interstellar absorption lines) to $E(B-V)_{host}=0.24\pm0.06$ mag (Lira law) with a mean of $E(B-V)_{host}=0.22\pm0.04$ mag, assuming $R_V=3.1$. The spread between different methods highlights the challenge of accurately estimating the amount of extinction light suffers before being observed.

Dual active galactic nuclei (dual AGNs) are pairs of simultaneously accreting supermassive black holes in merging galaxies. We investigate dual AGNs to understand whether merger-induced accretion is a significant growth mechanism for supermassive black holes. Searching for such systems is favorable at close separations and high redshift (Cosmic Noon, $z \sim 2$) due to the expected combination of high galaxy merger rate and peak AGN activity which characterize this era of the Universe. The sample of nine dual AGN candidates is selected based on resolved optical dual detections with Gaia, whose angular separations are less than 1$' '$ and redshifts range between 1.5 and 2.8. Each pair is spatially coincident with a Sloan Digital Sky Survey quasar primary target. We aim to classify the secondary targets and other components in the radio regime using 2-band Very Large Array imaging (C and Ku-bands) to test for dual AGN presence. We identify two dual AGNs and three quadruply imaged gravitational lens AGNs, two out of which show evidence of radio flux anomaly. The two new dual AGNs add to the limited census of confirmed kpc-scale pairs at Cosmic Noon, while the radio flux anomalies in J0911+0550 and J1118+0745 provide independent evidence for substructure in their lensing potentials, consistent with microlensing on compact AGN emission regions. Besides one confirmed AGN-star pair, three candidates remain unclassified due to lack of radio detection for one or two components.

The discovery rate of fast radio bursts (FRBs) continues to increase with the advent of new radio facilities and yet extracting their astrophysical parameters such as scattering timescale ($\tau$) remains a significant bottleneck. Current $\tau$ measurement approaches like fitting analytic template models and scattering aware de-convolution are accurate but slow, sensitive to initialization, limited by low signal to noise and often require manual supervision. These limitations inspired us to explore fast, robust and scalable machine learning methods to estimate the astrophysical parameter value. We present a deep learning approach named Multimodal Transformer Based Generic Mixture Density Network (MT-GMDN) which ingests FRB dynamic spectrum and its corresponding timeseries profile through parallel transformer encoders, fuses their latent representations and predicts the distribution of $\tau$ with probabilistic output derived from generic mixture-density formulation. This formulation not only estimates the value of $\tau$ but also captures the (zero inflated) nature of FRB populations where a significant fraction of bursts exhibit unresolvable scattering. We trained MT-GMDN on $\sim3500$ FRBs from CHIME/FRB \cattwo while holding out some fraction of FRBs for validation during training and for testing after the training completes. The model achieves a coefficient of determination ($R^2$) value of $94\%$ on the expected value of $\tau$ for the events with measurable scattering with an excellent recall value of $90\%$ on the test data set. The model was also able to incorporate heteroskedastic errors enabling us the construction of a confidence interval for the predictions.

Simulations of intermediate-mass black holes (IMBH) in dwarf galaxies within 10 Mpc that host bright nuclear star clusters (NSCs), prime candidates for IMBH formation, using the High Angular Resolution Monolithic Optical and Near-infrared Integral (HARMONI) field spectrograph on the Extremely Large Telescope, probe black hole formation in the early Universe. Our approach combines observed surface brightness profiles from the Hubble Space Telescope (HST), synthetic stellar population spectra, and Jeans Anisotropic Modeling (JAM) for stellar dynamics. Mock HARMONI observations were generated with the HSIM simulator and analyzed in a Bayesian framework to infer IMBH masses down to 0.5% of the NSC mass. In this work, we extend these simulations by constructing improved stellar-mass models using SimCADO to simulate imaging with the Multi-AO Imaging Camera for Deep Observations (MICADO). The MICADO data are jointly analyzed with HARMONI kinematics via JAM to reassess IMBH masses and uncertainties. This combined framework enables us to examine how variations in the NSC inner surface-brightness slope influence IMBH mass estimates, providing tighter constraints on low-mass black holes and advancing models for IMBH detection in NSCs.

The significant discrepancy between early- and late-Universe measurements of the Hubble constant, known as the Hubble tension, remains one of the most pressing open questions in cosmology. Since both sides of the tension rely on model-dependent assumptions or multi-rung calibration chains, a cosmological-model-independent measurement of $H_0$ is essential to arbitrate this discrepancy. In this work, we combine 142 gravitational-wave standard siren events from the Fourth Gravitational-Wave Transient Catalog with the latest TDCOSMO2025 time-delay strong lensing data to constrain $H_0$ in a cosmological-model-independent framework based on the distance sum rule. Under the FullPop-4.0 population model with the TDCOSMO2025-only lensing configuration, we obtain $H_0 = 83.78^{+12.53}_{-10.23}\ {\rm km\,s^{-1}\,Mpc^{-1}}$, with a relative precision of $13.58\%$. We find that the $H_0$ precision is governed primarily by the mass-sheet transformation treatment on the strong-lensing side: replacing the conservative TDCOSMO2025 hierarchical framework with the H0LiCOW method tightens the constraint to $H_0 = 75.42^{+3.74}_{-4.66}\ {\rm km\,s^{-1}\,Mpc^{-1}}$, with a relative precision of $5.57\%$. At the current precision, all results are consistent with both the Planck and SH0ES values, and future improvements from more high-redshift dark siren events and more time-delay lens systems are expected to strengthen this model-independent approach.

We augment the published optical photometry of ultra-diffuse galaxy candidates in the SMUDGes catalog with UV and IR measurements to investigate the recent ($<1$ Gyr) star formation history of 966 galaxies. We find that 1) we classify star forming, post-starforming, and quenched galaxies with a precision that is comparable to that of spectroscopic studies, 2) the star forming systems are sub-normally efficient and would not have formed their current stellar mass at their current star formation rate over a Hubble time, 3) the sample is biased against more strongly star forming systems by the central surface brightness criterion of ultra-diffuse galaxies, 4) for galaxies that are not quenched, the timescale of star formation episodes in this sample is typically $\lesssim$ 1 Gyr, 5) post-starburst galaxies in the sample tend to be of lower stellar mass and star forming galaxies of higher stellar mass, suggesting that the star forming behavior of these galaxies does depend on mass, and 6) there is a marginal indication, with caveats, that star formation episodes increase galaxy size, as measured by the half-light radius, by about 8\%. In addition to providing a statistically-sized sample with which to explore the star formation behavior of these galaxies, this study also provides a way to select galaxies with specific recent star formation histories for spectroscopic follow-up.

We test how supermassive black holes are fed by combining new black hole mass-luminosity relations with physically motivated feeding models. We build a uniform sample of 1729 unobscured blue quasars at z>2 by cross-matching SDSS DRE16 with eROSITA, and augment it with hyperluminous quasars (WISSH, HYPERION) plus 49 JWST broad-line AGN at z>3.5. We find for the SDSS-eROSITA sample of blue quasars a near-linear scaling of bolometric luminosity with mass (slope 0.91+/-0.01) and a shallower hard-X-ray trend (slope 0.73+/-0.01). Classical hot-mode (Bondi) accretion underpredicts the observed luminosities by about 2 dex at the high-mass end and is inconsistent with the measured slopes. In contrast, Chaotic Cold Accretion (CCA) - in which multiphase gas condenses, collides, and rains onto the nucleus - consistently reproduces both the normalization and the near-linear slope expected from halo thermodynamics. The shallower X-ray relation points to a decreasing coronal power fraction with black hole mass. JWST broad-line AGN frequently appear X-ray weak or Halpha enhanced. The latter case can be due to contributions from collisional ionization and photoionization from star-formation to the broad Halpha emission, leading to overestimate AGN luminosities and black hole masses. In the former case, the X-ray weakness is consistent with coronal shielding or anisotropy at high accretion rates. Overall, the data favor CCA-driven, self-regulated feeding over local spherical capture across the BH mass range 1E7-1E10 solar masses, and motivate extending these tests to lower masses and higher redshifts.

We probe the color-flavor locked (CFL) pairing gap ($\Delta_{\rm CFL}^{*}$) and the unknown N$^3$LO constant $c_0$ in perturbative QCD (pQCD) with Bayesian inference of flexible dense-matter equations of state (EOSs) informed by current astrophysical observations. Our EOS model combines a Gaussian process parameterization with sampled hyperparameters at neutron star densities and a boundary-constrained feed-forward neural network representation extending to pQCD densities, retaining nonparametric flexibility while supporting efficient nested sampling. Matching to the pQCD$+$CFL prediction at $\mu_B=2.6$ GeV, we obtain $\Delta_{\rm CFL}^{*}=28^{+23}_{-20}$ MeV (90% credibility), corresponding to a 95% credible upper limit of $\approx 51$ MeV, which is a factor of $\sim 3$ tighter than previous record and challenges most microscopic models. The pairing power corrections thus contribute at most a few percent at $\mu_B = 2.6~\mathrm{GeV}$, and are not a major source of uncertainty for neutron-star matter inference. We also set a bound on the poorly-known N$^3$LO constant $c_0=-28^{+5}_{-7}$, using a loose prior from convergence analysis of the N$^3$LO pressure.

Recent observations, particularly from DESI, have provided intriguing hints of dynamical behaviour in late-time dark energy. Modified gravity theories offer a compelling framework for interpreting such phenomena, with $f(R)$ gravity emerging as one of the most extensively studied examples. A central challenge in these models, however, lies in determining the precise functional form of $f(R)$. Nevertheless, several viable models have been proposed that successfully reproduce the standard $\Lambda$CDM cosmology at high red shifts while generating late-time cosmic acceleration without an explicit dark energy component. Within this framework, the evolution of the linear matter density contrast becomes scale dependent, leading to a growth index that varies with both scale and redshift. In this work, we explore the capability of forthcoming 21 cm observations to constrain the growth index, as well as the combined neutral hydrogen (HI) bias and growth-rate parameter. Our results indicate that future 21 cm surveys can provide meaningful, though moderate, support for these modified gravity scenarios.

White dwarf-brown dwarf (WD+BD) binaries are rare laboratories for probing both substellar survival through post-main-sequence evolution and the physics of strongly irradiated atmospheres. We present time-resolved eclipse photometry and radial-velocity confirmation of J0404+1112, a compact ($P = 2.93$ hr), totally eclipsing WD+BD system initially reported in a Research Note of the AAS. New high-cadence observations resolve a total eclipse of the WD and, combined with spectroscopy, broadband photometry, and the Gaia parallax, yield a revised system architecture. We find a hot DA WD with $T_{\rm eff} \simeq 28{,}000$ K, $\log g \simeq 8.0$, $M_{\rm WD} \simeq 0.6 \rm{M}_\odot$, and $R_{\rm WD} \simeq 0.015 \rm{R}_\odot$, orbited by a $\sim40 \rm{M}_{\rm Jup}$ BD with radius $\sim0.9 \rm{R}_{\rm Jup}$. These parameters supersede earlier SED-based estimates in which the WD temperature, radius, distance, and extinction were strongly covariant. We break this degeneracy with normalized Balmer-line profile fitting and high-cadence eclipse photometry that constraints the WD's radius geometrically. The total eclipses enable isolation of the BD flux and constrain its nightside emission. With its short orbital period and strong irradiation, J0404+1112 provides a uniquely compact, high-sensitivity JWST benchmark for probing atmospheric heat redistribution and photochemistry in the temperature regime of the hottest ultra-hot Jupiters, spanning dayside and nightside brightness temperatures of $\sim3{,}600$ K and $\sim1{,}800$ K within a single $\sim$3 hr orbit.

While recent JWST observations of mature super-Earths and sub-Neptunes have frequently revealed featureless transmission spectra, their inflated progenitors offer a unique window into understanding their primordial compositions. As part of the KRONOS (Keys to Revealing the Origin and Nature Of sub-neptune Systems) JWST program, we present the NIRISS/SOSS transmission spectrum of V1298 Tau c, a $\sim$23 Myr super-Earth progenitor orbiting a young Solar analog. We detect H$_2$O in V1298 Tau c's atmosphere with a $\log_{10}$ volume mixing ratio of $-1.83^{+0.68}_{-0.77}$, but no additional molecules from these data alone. We find consistent results for the planetary atmospheric properties in both retrievals with and without informed priors on stellar heterogeneities based on the observed stellar spectrum. We infer an atmospheric metallicity [O/H] of $14.8^{+56.0}_{-12.28}\times$ the Solar value. This metallicity is similar to literature measurements for other young planets, including its massive outer companion V1298~Tau~b. In contrast, this measured metallicity is systematically lower than the metallicities of mature planets of similar mass and temperature. Altogether, these results provide tentative but growing evidence that the exoplanet mass--metallicity relation evolves with planetary age.

James Webb Space Telescope (JWST) surveys of [O III]-emitting galaxies are offering fresh insight into the connection between galaxies and the intergalactic medium at redshift z ~ 6. Recent measurements of the cross-correlation between [O III]-emitting galaxies and Ly $\alpha$ forest transmission present an apparent challenge to numerical models. Here we improve upon previous theoretical work by constructing an empirical model that connects haloes with the observed population of [O III] emitters and incorporates the geometry and depth of the JWST surveys into mock galaxy survey catalogues. We compare these mocks to recent measurements of [O III] emitter clustering and the one and two dimensional galaxy-Ly $\alpha$ transmission cross-correlation. The large scatter in our mock survey measurements of the cross-correlation enable a statistically good match to the observational data, albeit the peak of the one dimensional correlation in our mocks occurs at a scale $\approx$10 cMpc below that observed. The large scatter implies that, at present, current galaxy-IGM observations may struggle to rule out a broad range of ionising source models. We anticipate that further progress will strongly benefit from increased observational sample sizes, as well as simulations performed in box sizes >250 cMpc that use a variety of source models.

Next-generation gravitational-wave detectors such as the Einstein Telescope and Cosmic Explorer will be able to detect binary black-hole mergers out to the cosmic dawn. Mergers observed in the local Universe represent a mixture of systems formed across the entire cosmic history, spanning a wide range of astrophysical environments. Iron-group elements govern metallicity effects on stellar evolution, making metallicity a key tracer that leaves a strong imprint on the black-hole population. We introduce the concept of a "target" redshift, $z_t$, defined as the epoch at which more than 90% of stars form with metallicity $Z < 0.1\,Z_\odot$. This provides a straightforward way to isolate mergers originating from metal-poor environments. The determination of $z_t$ relies on the reconstruction of the cosmic star-formation rate density as a function of iron abundance. This reconstruction is not unique, as it depends on the combination of different empirical scaling relations. Consequently, $z_t$ spans a broad range, from $z_t \sim 4$ to $z_t > 10$, depending on the adopted model variation. We present a statistical framework that enables rapid tests of astrophysical predictions against forecasted observations from next-generation gravitational-wave detectors. By quantifying variations in the binary black-hole merger-rate density between the target redshift and the local Universe, our approach maps evolutionary trends across parameter space and estimates the detection statistics required to distinguish genuine astrophysical variations from statistical fluctuations.

In this study, a parameter-free group-finding method named GraphShed is introduced and evaluated using the IllustrisTNG100-1 simulation. The method utilizes top-down watershed segmentation applied to the set of separated Voronoi-induced graphs, facilitating the recognition of aggregations directly from the density field without tunable parameters or density thresholds. A galaxy group catalog constructed with GraphShed is compared with a Friends-of-Friends catalog generated from the same dataset. The $M_{200}$ distributions of the two catalogs are statistically consistent; nevertheless, other structural properties, including $R_{200}$, sphericity, compactness, spin, and centroid shift show significant differences, suggesting that GraphShed could improve several internal characteristics of the identified systems. Conversely, the two-point correlation function and the mass function of the identified galaxy systems, derived from the aforementioned methods, show consistency. A velocity-based classification of interacting pairs indicates that GraphShed provides improved separation of nearby over-densities which might otherwise be considered as components of a single larger system in position-only methods due to their positional proximity. These results demonstrate that GraphShed effectively preserves cosmological statistics while offering a more refined detection of galaxy systems and their dynamical interactions.

Silicon is a key refractory element in giant planet atmospheres, which governs the formation of magnesium-silicate clouds, and reflects the quantity of silicates accreted during formation. While observations of directly imaged giant exoplanets have focused on the measurement of volatile species (e.g. CO, H$_2$O), high-resolution spectroscopy with CRIRES+ M-band provides access to gas phase silicon chemistry in sub-stellar atmospheres, through the ro-vibrational band head of SiO at 4 $\mu$m. Here, we present the first results of the CRIMSON survey of silicon chemistry in directly imaged companions with CRIRES+ M-band. We report the strong detection of gaseous SiO (S/N = 7.5) in the directly imaged companion TWA 5 B, with an atmospheric abundance of log(SiO) = $-3.56^{+0.42}_{-0.32}$ VMR, providing access to the refractory content of the atmosphere. The high retrieved SiO abundance implies the absence of significant magnesium-silicate cloud condensation, and thus the atmospheric silicon abundance is contained almost entirely within the observed gas phase SiO. Using the detection of refractory silicon, together with strong detections of the volatile species CO (S/N = 9.1) and H$_2$O (S/N = 18.8), we measure a stellar C/O and a marginally sub-stellar O/Si and C/Si, but a super-stellar Si/H ([Si/H]$_{\star}$ = $1.41^{+0.42}_{-0.32}$). Collectively, these volatile-to-refractory ratios are consistent with formation through core-accretion beyond the CO snowline, or gravitational instability followed by substantial solid enrichment. Finally, we discuss how gas phase SiO provides a unique diagnostic of the cloud properties in hot gas-giants, and can be used to probe the dominant cloud species forming across the directly imaged planet and isolated brown dwarf populations.

Short-period white-dwarf (WD) binaries are post-common-envelope systems that constrain orbital shrinkage, envelope evolution, and the survival of low-mass companions. We report the discovery and confirmation of ten fully eclipsing short-period WD + cool M-dwarf binaries identified through a tailored search for minute-scale eclipses in Transiting Exoplanet Survey Satellite (TESS) high-cadence data and validated with SPECULOOS multi-band photometry. The systems have orbital periods of a few hours and companions with effective temperatures of 2700-3400 K. These discoveries demonstrate that TESS contains a previously underexplored population of compact WD binaries whose short-duration, high-frequency, and often diluted eclipse signals are not efficiently recovered by standard transit-search pipelines. Whereas the literature contained only one eclipsing WD+M binary reported as a TESS-based discovery, our pilot search of $\sim3.7\times10^4$ Gaia-selected WDs yields ten new confirmed systems, increasing the TESS-discovered sample by an order of magnitude. SPECULOOS follow-up confirms the eclipses occur on target and uses chromatic eclipse dilution to distinguish stellar from substellar companions. We combine multi-band eclipse photometry with Bayesian spectral energy distribution modeling to derive self-consistent WD and companion parameters. The resulting systems expand the known population of fully eclipsing WD+M binaries and notably double the number of systems in temperature regimes corresponding to M4 and M7 companions. This work establishes a scalable framework for identifying compact WD binaries in time-domain photometric surveys. Applied to TESS archival data across the full Gaia WD-candidate catalog ($\sim1.3\times10^6$ sources), this approach opens the prospect of assembling a population large enough to constrain post-common-envelope evolution and the stellar-substellar transition.

The modelling of the power spectrum of biased tracers has become a central topic in the analysis of modern cosmological galaxy surveys. Perturbative templates formulated in both Eulerian and Lagrangian frameworks have been extensively developed over the last decades, with their implementation in $\Lambda$CDM thoroughly investigated and validated. In parallel, approaches combining perturbation theory with the output of dark-matter-only simulations have emerged as powerful tools for modelling the nonlinear regime, most notably the Hybrid Effective Field Theory (HEFT) framework~\cite{Modi:2019qbt}. In this work, we discuss the perturbative biased expansion within the local Lagrangian bias scheme and its implementation in the HEFT framework for modified gravity cosmologies. We focus on $f(R)$ gravity, a theory characterized by scale-dependent growth and chameleon screening, making it one of the most challenging scenarios for the computation of Lagrangian Perturbation Theory growth functions and for the generation of accurate numerical simulations. We present a detailed overview of the ingredients required to compute loop-corrected biased power spectra analytically and compare these predictions against fully non-perturbative simulation results. Finally, we propose a strategy to extend existing HEFT-based $\Lambda$CDM emulators, such as \texttt{bacco} and \texttt{Aemulus}, to beyond-$\Lambda$CDM cosmologies.

Recent gamma-ray observations indicate that star clusters can be efficient particle accelerators. In particular, LHAASO has detected diffuse gamma-ray emission from Cygnus OB2 extending to $\gtrsim$ PeV energies, indicating that particles are accelerated to at least $\gtrsim$1 PeV. In this work, we study the gamma-ray emission from the Cygnus region assuming particle acceleration either at the termination shock of the cluster wind (WTS) or in an unspecified source at the bubble center, taken to be either steady or bursting. We numerically solve the transport equation for non-thermal particles in all scenarios and derive their spatial and spectral distributions throughout the bubble. We then calculate the gamma-ray emission from pp interactions, including the contribution from particles interacting with the surrounding molecular cloud, which may help explain the extended emission observed by LHAASO. We also include the penetration of Galactic cosmic rays (GCRs) and the resulting shock reacceleration. The predicted emission is compared with Fermi-LAT, HAWC and LHAASO observations. For three diffusion models, we find that a spatially dependent Bohm diffusion coefficient is required to reproduce both the spectrum and morphology in the cluster wind scenario. Penetrating GCRs can contribute significantly to the gamma-ray emission above $\sim$300 TeV. A suppressed diffusion coefficient with respect to the Galactic average in a region extending to at least 150 pc from the cluster center is needed to reproduce the LHAASO morphology. Our conclusion is that explaining both the spectrum and morphology of the $\sim$PeV emission with hadrons accelerated in a non-relativistic steady source requires extreme assumptions. We also speculate on the possibility that some of the highest-energy gamma rays may originate from sources behind the Cygnus association.

We present a comprehensive analysis of the longitudinal development of Extensive Air Showers (EAS) simulated with CORSIKA version 7.7500 for proton, helium, and iron primaries at energies of 10^15, 10^16, and 10^17 eV across zenith angles of 0, 30, and 45 degrees. For each combination of primary type, energy, and zenith angle, 50 independent showers were simulated, resulting in a total of 450 simulated showers. The Gaisser - Hillas function was fitted to extract the depth of shower maximum (Xmax) and the number of particles at maximum (Nmax). Our results confirm the expected logarithmic increase of Xmax with energy (about 10 g/cm^2 per decade), as well as systematically shallower Xmax for heavier primaries (iron vs. proton: Delta (Xmax) equal to about 160 g/cm^2 at 10^17 eV).The simulations also reproduce the expected sec (theta) scaling behavior. Multi-component analysis reveals distinct evolutionary patterns for electromagnetic, muonic, and hadronic components. These findings provide benchmark-level simulations for cosmic-ray composition studies and validate the CORSIKA framework for multi-parameter analyses of air-shower development.

The Small Magellanic Cloud (SMC) exhibits significant kinematic disequilibrium due to interactions with the Large Magellanic Cloud (LMC). Here, we investigate the two-dimensional stellar kinematics of the SMC to understand the dynamical effects of these interactions by exploiting the increased time baseline of 6-11 years from the VISTA Survey of the Magellanic Clouds (VMC) data release 7. We derive proper motions with a threefold improvement in precision compared to previous studies based on VMC data. We used a geometric framework accounting for perspective effects from line of sight motion to model the systemic motion across the SMC and construct a residual proper motion map. We further introduce an anisotropic linear velocity gradient model to quantify the stretching of the galaxy. For the first time across all stellar populations, the residual proper motion map reveals expansion along the south-east and north-west directions, consistent with LMC-induced tidal forces, detectable even in the central regions. The gradient-corrected residuals show predominantly radial motions towards the SMC centre with no evidence of rotation. Velocity maps for different stellar populations, without assuming a rotating-disk model, reveal a coherent northward motion away from the centre exclusively in older red giant branch stars, interpreted as a kinematic signature of a past (>2 Gyr ago) interaction. This study highlights the inadequacy of simple rotating-disk models in capturing the internal kinematics of the galaxy.

In the coming years, the number of discovered active galactic nuclei (AGN) is expected to increase significantly due to upcoming spectroscopic surveys. This growth will challenge current analysis and modeling techniques, requiring scalable methods for large, heterogeneous datasets with diverse signal-to-noise ratios, spectral resolutions, and host-galaxy contamination. We present SHEAP (Spectral Handling and Estimation of AGN Parameters), a spectral-fitting framework designed to analyze large AGN samples efficiently while preserving physical interpretability, reproducibility, and robust uncertainty estimation. SHEAP uses JAX, a Python GPU-powered framework, to implement a flexible model with modular components, including continuum, host galaxy, FeII pseudo-continuum, and multi-component emission lines, together with parameter tying and physically motivated constraints. By combining gradient-based optimization with automatic differentiation, vectorization, and just-in-time compilation, SHEAP achieves stable convergence in blended regions, such as H$\beta$, while substantially reducing runtime. We compare SHEAP measurements with literature results and public fitting pipelines across four samples covering the CIV, MgII, H$\beta$, and H$\alpha$ regions. We find good agreement for the main AGN spectral parameters, with $\sim85$--$100%$ of objects lying within the $\pm0.3$ dex band and reduced chi-square distributions close to unity. Relative to the runtime reported by \citet{2026Bernal} using \texttt{pPXF}, the fitting stage requires only $\sim1.7%$ of the computational time, corresponding to an improvement of approximately $100$ times. These results show that \texttt{SHEAP} delivers reliable AGN spectral decompositions at substantially lower computational cost, making it suitable for massive spectroscopic datasets.

The International Astronomical Union's Office of Astronomy for Development (IAU OAD) uses astronomy as a tool to address societal challenges and contribute to sustainable development. Building on more than a decade of project funding and implementation, the OAD has developed a portfolio of flagship projects that represent tested and scalable applications of Astronomy for Development across thematic areas including socio-economic development, science diplomacy, skills development, inequality reduction, and technology transfer. To support the growth and long-term sustainability of these initiatives, the OAD has established the Flagship Ecosystem, a framework built around four interconnected pillars: Resources, Training, Community, and Implementation. This paper presents an overview of the OAD Flagship projects, the structure and components of the Flagship Ecosystem, and explores how it supports the translation of astronomy-based interventions into sustainable development outcomes. The ecosystem provides open-access resources, capacity-building opportunities, communities of practice, funding mechanisms, and evidence-generation activities that enable individuals and organizations to implement and scale astronomy-for-development initiatives. Grounded in principles of inclusivity, openness, sustainability, participation, and evidence-informed practice, the ecosystem aims to strengthen the global impact of Astronomy for Development while fostering collaboration across diverse sectors and regions.

Although cosmic acceleration is well established, its physical origin remains contentious. Most explanations invoke either a non-zero vacuum energy, i.e. a cosmological constant, or new fields. We propose instead a mechanism arising purely from quantum mechanics, without additional constants or local sources. The key point is that quantum theory permits both initial and final boundary conditions on a state, here the wave function of the universe. Pre- and post-selected systems are familiar in laboratory quantum mechanics; we extend the idea to minisuperspace quantum cosmology. As a warm-up, we show that a free non-relativistic particle, initially in a semiclassical wave packet and conditioned on a final quantum state, can have an intermediate peak which accelerates even though the Hamiltonian is free. A semiclassical observer would infer a contrived classical force. We then implement the analogous construction in quantum cosmology using connection variables and unimodular time. A forward semiclassical packet, taken for simplicity to describe pure radiation, is post-selected by a normalizable Chern-Simons soliton. The resulting two-boundary amplitude has a peak which leaves the radiation trajectory and enters an accelerating regime, while the forward Hamiltonian has $\Lambda=0$. A classical model can mimic this trajectory only by introducing a contrived effective component: near the transition it resembles $w\simeq -1$, but when extrapolated it evolves towards strongly phantom behaviour, $w<-1$. The acceleration is therefore more naturally interpreted as a quantum boundary-condition effect than as a local classical source. We also discuss why the Chern-Simons soliton is a clean final state, the small overlap between initial and final states, and possible tell-tale signatures.

Within the frame of the GINGER project, aimed at installing an array of large frame ring laser gyroscopes for fundamental physics tests and as part of a geophysics observatory located in the underground laboratory at Gran Sasso, Italy (LNGS-INFN), we are developing a ring laser gyroscope design to reduce spurious rotation of instrumental origin and the ability to extend the cavity perimeter from 1.5 up to 5m, thanks to the implementation of suitable spacers. The new design led to a prototype, called TRIO, with a side length of 1.52 m, conceived as a transportable instrument. The present paper reports on several preliminary measurements of the Earth angular velocity carried out with TRIO. Results have the twofold objective to assess the instrument performance in the present geometrical configuration and to test validity of the design in view of the GINGER project. To this aim, data obtained with TRIO are compared to typical data acquired with other, previously made, gyroscope prototypes, including the large frame GINGERINO already in operation at the Gran Sasso underground site.

In decaying magnetohydrodynamic turbulence, energy can be transported from small to large scales, known as inverse transfer. We explore the mechanism behind this phenomenon using shell-to-shell transfer functions. Independent of magnetic net-helicity, large magnetic scales receive energy directly from the integral scale in both the magnetic and kinetic reservoirs, leading to increasingly non-local transfer for larger receiving scales. The resulting rate of energy increase in each receiving scale is proportional to its energy, resulting in self-similar, multiplicative growth. Even though the system is magnetically dominated, contributions from kinetic-magnetic and magnetic-magnetic energy-exchange are similar in magnitude. In the case of vanishing net-helicity, transfer functions between the positively and negatively helical parts of the field are computed. We find that inverse transfer only occurs within each helical sector, not across them. Our findings are consistent with the theory underlying the conservation of the Hosking integral, which explains inverse transfer as merging of local magnetic islands with equal-signed helicity.

We develop a new bootstrap strategy for cosmological correlators at loop level, which we call spectral dispersion. It is based on two conceptual observations that a correlator can be recovered from its on-shell data, also known as nonlocal signals, by analyticity up to local counterterms, and that the on-shell data for a loop process take the form of a discrete sum over quasinormal modes. Technically, our method combines the dS spectral decomposition with dispersion relations. Using this technique, we bootstrap new results in a simple and intuitive form for 3-point and 4-point correlators with 1-loop massive exchanges of scalar and vector bosons, either directly or derivatively coupled. Applications of this bootstrap technique to higher spins and higher-loop banana graphs with dS covariant dispersions but noncovariant couplings are also straightforward.

Metastable cosmic strings provide a cosmological interpretation of the nanohertz stochastic gravitational wave background reported by Pulsar Timing Array (PTA) experiments. We revisit this scenario in a minimal dark-sector gauge theory, in which a complex Higgs doublet breaks $\mathrm{SU}(2)\times\mathrm{U}(1)\to\mathrm{U}(1)$ at a single symmetry-breaking scale. This one-scale setup predicts metastable $Z$-strings whose endpoints are monopole-like defects, and whose zero-temperature decay rate is controlled by the gauge couplings and mass ratios. We show that, once the string-forming transition occurs in a thermal plasma, the dominant decay channel is not the zero-temperature monopole nucleation but thermally induced nucleation on the string worldsheet. We determine the nucleation temperature, $T_{\rm nuc}$, from the one-loop finite-temperature effective potential with daisy resummation, and use it to compute the string formation temperature throughout the model parameter space. Requiring both a viable first-order transition and a PTA-compatible gravitational wave signal selects a narrow region in the model parameter space, in the $(\sin^2\theta_w,\sqrt{\beta})$ plane, where $\theta_w$ is the dark-sector weak mixing angle and $\beta\equiv M_\Phi^2/M_{Z}^2$ is the squared Higgs-to-$Z$ mass ratio. Thermal effects modify the zero-temperature picture significantly, shifting the PTA-compatible region towards lower values of the dark fine-structure constant $\alpha'$ and larger values of the monopole-to-string-tension ratio $\kappa$.

We study quintessence in $\alpha$-attractor models in light of recent DESI indications for dynamical dark energy. We show that the \emph{knee} of the attractor potential provides an excellent approximation to the axion-like quintessence model used as a DESI benchmark. This leads to a simple relation between the axion decay constant $f_a$ and the attractor parameter $\alpha$, allowing the experimental constraints to be translated into a preference for $\alpha=\mathcal{O}(1)$, in agreement with string-motivated expectations. We solve the background dynamics numerically and find good agreement with the DESI-preferred evolution of $w(z)$ up to $z\sim\mathcal{O}(1)$. More generally, we point out that the agreement between axion-like and attractor potentials reflects a common requirement imposed by the data: today's potential energy and slope are both of order the Hubble scale in Planck units. We finally comment on the origin of the required initial conditions, which can naturally arise in multifield attractor scenarios.

We present a four-dimensional deconstruction of the extra-dimensional axion arising from a $U(1)$ gauge theory in a five-dimensional orbifold, where the axion is identified with the Wilson line of the $U(1)$ gauge field and its coupling to QCD is generated by a 5D Chern-Simons (CS) term. We construct the corresponding 4D moose (quiver) gauge theory with link scalar fields, in which the axion emerges as a collective pseudo-Nambu-Goldstone boson. The axion-gluon coupling is described by a gauged Wess-Zumino-Witten term, providing the 4D counterpart of the 5D CS term. We further analyze non-perturbative effects from zero-mode and ``fractional'' instanton configurations. While the latter is exponentially suppressed in the regime corresponding to the 5D description, ensuring consistency with the higher-dimensional picture, we point out that this suppression can break down for smaller instantons whose inverse size exceeds the 5D cutoff scale, leading to a potentially significant effect. We also study axion potentials induced by bulk matter fields and boundary-localized symmetry-breaking operators, reproducing the characteristic nonlocal suppression associated with propagation in the extra dimension. Our construction provides a renormalizable 4D framework with a transparent understanding of the axion shift symmetry and its quality.

We compute the (operator-valued) commutator of a massless scalar field $\phi$ coupled to gravity. We work in perturbations around Minkowski space, in transverse-traceless gauge at the lowest order in $G_N$. The commutator is composed of different operators, including terms with Dirac delta derivatives supported on the lightcone. These are responsible for ``bending" the Minkowski lightcone when evaluated on a classical/coherent state of gravitons, which allows to recover standard microcausality in the fixed-background limit. On more general gravitational states, metric fluctuations induce an uncertainty in the causal structure. We compute this effect on a thermal state of gravitons at temperature $T$ by evaluating the probability that $[\phi(t, \vec x), \phi(0)] \neq 0$. We find that the probability is Gaussian in $\vec x^{\, 2}$, centered on the lightcone and with time-growing variance $$ {\rm Var}( \vec x^{\, 2}) = \frac{16 \, G_N T t^3}{3}\, .$$ This result is obtained by subtracting a universal vacuum contribution, which is log-divergent in the UV and subleading in the large-time limit. As a source of finite size can effectively serve as a regulator in this case, the lightcone spread in the vacuum appears to be source-dependent.

In the context of grand unified theories, any cosmic strings present in the post-inflationary universe are likely to be metastable, with a decay rate set by the spontaneous creation of monopole pairs on the string. Determining this decay rate is crucial in understanding the phenomenology of the cosmic string network, including a potentially observable gravitational wave background. The bounce action governing this rate has so far only been determined using the thin string approximation or specific ansätze for the field profiles in the monopole formation process. Here we solve this problem using classical lattice simulations, relying only on the inherent symmetries of the problem. Our results indicate a suppression of the bounce action and hence a faster string decay compared to previous estimates.

We investigate the dynamics of charged particles around a Schwarzschild-like black hole sourced by a Kalb-Ramond field and immersed in a uniform external magnetic field. The Kalb-Ramond field introduces a Lorentz violation parameter $l$ that modifies the spacetime geometry, while the magnetic field profoundly influences the trajectories through the Lorentz force, leading to a rich variety of orbital behaviours including curled (epicyclic) motion and dramatic transitions between distinct energy boundary configurations. We derive the full equations of motion, the effective potential, and the fundamental frequencies of quasi-periodic oscillations, and perform a comprehensive Monte Carlo Markov Chain (MCMC) analysis using observational data from the microquasars GRO 1655-40, XTE 1550-564, and GRS 1915+105. The pure Schwarzschild model is statistically ruled out for all three sources. For GRO 1655-40 and XTE 1550-564, only the combined effect of the magnetic field and Lorentz violation yields statistically robust models, with best-fit values $\mathcal{B}\sim 0.03$-$0.04$ and $l\sim 0.08$--$0.10$. Remarkably, for GRS 1915+105, the most massive object in our sample, the Lorentz violation parameter alone is sufficient to model the QPO frequencies, yielding an optimal fit with $\Delta AIC = \Delta BIC = 0$. Across all three objects, a clear trend emerges: the required value of $l$ decreases as the mass of the astrophysical object increases, suggesting a mass-dependent scaling of the Kalb-Ramond parameter. These findings establish the combined KR and magnetic field framework as a viable and statistically robust scenario for modeling QPOs in microquasars, and indicate that Lorentz-violating modifications to gravity may leave observable imprints in the strong-field regime, offering new avenues for testing quantum-gravity phenomenology with current and next-generation X-ray missions.

Gravitational lensing of gravitational waves (GWs) can produce multiple images in the geometric optics limit. These lensed GW images arrive at different times, are amplified by different magnification factors, and are shifted by constant phases. With current understanding, the occurrence of lensed events stands at a few per thousand events, and the number of GW detections is a few hundred with the ground-based detector network. However, with the inclusion of the sub-threshold events, the total number of detections crosses a few thousand. Therefore, a search that includes both types of events yields a higher chance of lensing detection. In this work, we carry out the first model-independent lensing search using a cross-correlation-based technique GLANCE over the entire volume of the GWTC-4 strain data, containing $\sim 90$ super-events $\sim 800$ sub-events forming a total of $\sim 11,000$ event pairs with a higher False Alarm Rate (FAR) event rate allowing to search deep in the noise dominated regime. We further conduct their spectrogram checks to inspect data quality, sky-map overlap of the interesting pairs, and a Bayesian parameter exploration of the sub-event to make a robust lensing detection. Although the search indicated four pairs of potential events with cross-correlation significance $\geq 2\sigma$, none were above $3\sigma$ at both the LIGO-Hanford and LIGO-Livingston detectors. This makes it possible to strongly rule out the presence of any statistically significant sub-threshold lensed GW event in GWTC-4. The null detection translates to an upper bound on the lensing detection rate to be $\leq$ 1.5/yr with inclusion of the sub-threshold event candidates. In the future, with more observation time, the detection of lensed GW can be possible from the current generation of GW detectors.

The gravitino is a prominent example of a freeze-in dark matter candidate. Its relic abundance depends on the reheating temperature and on supersymmetry-breaking parameters, that is the universal gaugino mass, $M_{1/2}$, and the gravitino mass, $m_{3/2}$. As a consequence, the reheating temperature consistent with the observed dark matter abundance exhibits a maximum value, $T_{\rm reh}^{\rm reak}$, which decreases as $M_{1/2}$ increases. This behavior gives rise to a tension between prospective lower bounds on the gluino mass from future collider searches and the high reheating temperatures required for successful thermal leptogenesis. In this work, we investigate a nonstandard cosmological scenario in which the thermal bath is supplemented by an additional scalar field. We show that, for a matter-like equation of state, this component can induce a substantial dilution of the gravitino abundance, thereby allowing significantly larger values of the reheating temperature. In contrast, for a kination-like equation of state, the gravitino abundance is enhanced rather than diluted, leading to a reduction of the maximum allowed reheating temperature.

Ultralight dark matter (ULDM) coupled to the Standard Model may effectively induce coherent oscillations of fundamental constants and thereby generate narrow-band signals in precision interferometric experiments. Here we present a systematic study of how these oscillations leave distinctive imprints on space-based laser interferometers, including LISA and Taiji. Starting from the one-way inter-spacecraft link observables, we analyze several instrument-level effects induced by ULDM, including composition-dependent acceleration of test masses, laser-frequency variations associated with cavity-length modulation, refractive-index effects, and clock-related contributions. We then propagate these signals through the standard data processing chain, including time-delay interferometry and clock-noise elimination. We show that the observability of an ULDM-induced effect is determined by the structure of its single-link response. In particular, the ULDM-driven variation in laser frequency appears in the raw link observable with the same form as laser phase noise. As a consequence, it is strongly suppressed in the final interferometry channels. In contrast, signals that possess an explicit directional pattern are not eliminated by this procedure, such as the ULDM-induced oscillations of the test masses. We further construct a local observable that isolates the differential motion between the test mass and the optical bench, and derive its sensitivity to both the dilaton--gluon coupling $d_g$ and the dilaton--electron coupling $d_e$ for LISA, Taiji, and BBO. We find that the local observable yields sensitivities comparable to the standard Michelson interferometer for $d_g$, but better than Michelson channel by three orders of magnitude for $d_e$.

We study constraints on sub-GeV inelastic dark matter (iDM) from cosmic-ray (CR) cooling in the active galactic nucleus (AGN) NGC 1068. In dense dark matter (DM) spikes surrounding supermassive black holes, high-energy CR protons can efficiently lose energy through scatterings with dark matter particles. We consider a minimal vector-portal iDM framework and consistently include both elastic and deep inelastic scattering (DIS) contributions to the CR energy-loss rate. We find that DIS processes dominate at high momentum transfer and substantially enhance the DM-induced cooling effect. By requiring the resulting cooling timescale to remain compatible with the observed Standard Model cooling in NGC 1068, we derive constraints on the iDM parameter space. Our results demonstrate that AGN cosmic-ray cooling probes previously unexplored regions of sub-GeV iDM parameter space inaccessible to current direct-detection experiments.