Papers for Thursday, Jan 01 2026

The microscopic composition of neutron star interiors remains uncertain, with possible scenarios including nucleonic matter, hyperonic matter, dark matter admixed cores, and strange self-bound matter. Traditional constraints on the equation of state rely on Tolman Oppenheimer Volkoff modelling and comparison with multimessenger observations, but machine learning provides a complementary pathway by learning composition dependent patterns directly from astrophysically accessible observables. This work presents a compact supervised learning framework for EOS family classification using stellar properties derived from TOV modelling, asteroseismology, and gravitational wave descriptors. A labelled dataset of neutron star configurations spanning four EOS families (nucleonic, strange matter, dark matter admixed, and hyperonic) is constructed using seven input features: gravitational mass, radius, fundamental f mode frequency, quadrupole moment, redshift, damping time, and characteristic strain. A multilayer perceptron is trained to infer the underlying matter composition. On a held out test set, the classifier achieves an accuracy of 97.4 percent with strong class wise precision and recall. Permutation based feature importance analysis shows that oscillation related quantities, especially the f mode frequency and damping time, dominate the discriminatory power, while mass and radius provide secondary support. Residual misclassifications occur in physically intuitive regions where different EOS families produce partially overlapping macroscopic signatures. These results show that lightweight neural models can reliably identify EOS family fingerprints from a modest set of observables, providing a reproducible baseline for future extensions incorporating Bayesian uncertainty and observational posteriors from NICER and gravitational wave events.

Loops of cosmic string experience a recoil from anisotropic gravitational radiation, known as the rocket effect, which influences the extent to which they are captured by galaxies during structure formation. Analytical studies have reached different conclusions regarding loop capture in galaxies: early treatments argued for efficient capture, while later analyses incorporating the loop rocket force throughout halo formation found that capture efficiency is reduced and strongly dependent on loop size. In this work, we employ the N-body simulation code GADGET-4, introducing non-backreacting tracer particles subject to a constant recoil force to model cosmic string loops with the rocket effect. We simulate the formation of a Milky-Way-like halo from redshift $z=127$ to $z=0$, considering loop populations characterized by a range of length parameters $\xi$, inversely proportional to the rocket acceleration. We find that the number of captured loops exhibits a pronounced peak at $\xi_{\textrm{peak}}\simeq 12.5$, arising from the competition between rocket-driven ejection at small $\xi$ and the declining intrinsic loop abundance at large $\xi$. For fiducial string tensions, this corresponds to $\mathcal{O}(10^6)$ loops within the halo. We further find that loops with weak rocket forces closely trace the dark-matter distribution, while those subject to stronger recoil but still captured -- particularly the most abundant loops near $\xi_{\textrm{peak}}$ -- are preferentially concentrated toward the central regions of the halo.

We present the main results obtained from the COmpact BInary Pulsar search in the low-LAtitude NEighborhood (COBIPLANE), an optical photometric survey designed to find new `spider' binary millisecond pulsars. We conducted observations targeting 30 unidentified sources from the 4FGL-DR3 Fermi Large Area Telescope (Fermi-LAT) catalog, selected for their pulsar-like $\gamma$-ray properties. Extending to Galactic latitudes as low as $\pm3^{\circ}$, this survey reaches closer to the Galactic plane than its predecessor survey, the COmpact BInary PULsar SEarch (COBIPULSE). We report the discovery of five optical variables coincident with the localizations of 4FGL J0821.5-1436, 4FGL J1517.9-5233, 4FGL J1639.3-5146, 4FGL J1748.8-3915, and 4FGL J2056.4+3142. These systems show optical flux modulation at the presumed orbital periods of $0.41576(6) \ \mathrm{d}$, $0.305(2) \ \mathrm{d}$, $0.204(7) \ \mathrm{d}$, $0.3(2) \ \mathrm{d}$, and $0.4395(1) \ \mathrm{d}$, respectively, and photometric temperatures of $4000$--$6000 \ \mathrm{K}$, consistent with the companion stars of `redback' subtype of spider pulsar binaries. Based on their optical light curve shapes and X-ray properties characteristic for spider systems -- namely, a luminosity of $1.5 \times 10^{32} \ (D / 3.9 \ \mathrm{kpc})^2 \ \mathrm{erg} \ \mathrm{s}^{-1}$ ($0.3$--$10 \ \mathrm{keV}$) for 4FGL J1748.8-3915, and upper limits of $\sim10^{31}$--$10^{33} \ \mathrm{erg} \ \mathrm{s}^{-1}$ ($0.2$--$12 \ \mathrm{keV}$) for the others -- we classify these sources as new spider candidate systems.

Dynamics of stellar orbits in dense stellar systems and nuclear star clusters (NSC) with an embedded supermassive black hole (SMBH) is governed a complex interplay of different forces. In particular, star--star gravitational collisions (relaxation), physical collisions between stars, and the hydrodynamical interaction with any surrounding gaseous environment, such as an accretion disk. These processes influence the stellar distribution, the feeding of the central black hole, and the generation of observable phenomena. Furthermore, the self-gravity of the accretion medium modulates the long-term evolution, adding significant complexity to the system's dynamics. By employing elementary arguments we outline the mentioned influences in their mutual competition.

Although many globular clusters (GCs) have been identified in the Galaxy, their population is estimated to be incomplete, especially in regions with strong crowding and interstellar extinction such as the Galactic bulge and this http URL Lyrae stars, as bright standard candles and tracers of old stellar populations, are powerful tools for finding GCs in these regions, and large catalogs of such stars have recently become available. We aim to construct a sample of RR Lyrae stars with six-dimensional information (three-dimensional positions, proper motions, and metallicities) in the Galactic plane and bulge, and to exploit it using a hierarchical clustering algorithm to search for Galactic substructures. We build a sample of fundamental-mode RR Lyrae (RRab) stars with positions, distances, proper motions, and photometric metallicity estimates from Gaia and VVV data. Using a clustering algorithm calibrated to optimize GC recovery, we identify groups of RRab stars with similar locations in the six-dimensional parameter space. The most promising groups are selected by comparison with the properties of known GCs. We recover many RRab groups associated with known Galactic GCs and derive the first RR Lyrae-based distances for BH 140 and NGC 5986. We also detect small groups of two to three RRab stars at distances up to ~25 kpc that are not associated with any known GC, but display GC-like distributions in all six parameters. Several of these groups, mostly pairs, lie toward the Galactic bulge but show distinct proper motions or distances, suggesting they may not belong to the bulge population. Overall, our approach identifies dozens of GC-like RRab groups in the Galactic plane and bulge, which are excellent targets for follow-up observations. Future radial velocity measurements can test whether the RRab members of these groups are truly co-moving.

Study the ionized gas in metal-poor environments is key to understanding the mechanisms regulating galaxy evolution. However, most of the previous studies of extragalactic HII regions rely on unresolved observations of gaseous structures. We study the south-western, spatially resolved, HII region of Leo A, one of the most studied isolated dwarf galaxies in the Local Group. Using archival VIMOS-IFU/VLT data, we explored its gaseous structure through optical emission lines to gain insights into the present-day drivers of gas physics in this dIrr, and we place constraints on the chemical evolution scenario responsible for this low chemical enrichment. The emission line maps reveal that the strongest emission comes from the south-west region. A stratified distribution of ionic species was detected, likely powered by the young star cluster at the nebular centre. HST/ACS data show that the brightest star is in the centre of both the HII region and the star cluster. Photoionization production rates derived indicate that this star can sustain the ionization budget to power the HII region, although subject to the assumed electron density. Using the direct method, we derived a metallicity of $12+\log(\mathrm{O/H})=7.29\pm0.06$ dex, increasing to $7.46\pm0.09$ dex after correcting for temperature fluctuations, placing Leo A in the low-mass end of the MZR. Chemical evolution models suggest that, under constant accretion, the stellar mass growth and metal enrichment over the last 10 Gyr are successfully reproduced by both leaky-box and gas-regulator models. Those results are similar to those found in SagDIG, supporting a picture in which the present-day evolution of Leo A is dominated by stellar feedback processes. The combination of mass loss mechanisms and accretion events reproduces its chemical evolution, suggesting that Leo A has evolved under a gas equilibrium regime across its lifetime.

Extinction curves contain key information on interstellar dust composition and size distribution, with the 2175 Å bump being the most prominent feature. We analyze 20 sightlines toward M31 using HST/STIS UV spectroscopy combined with multi-band photometry to characterize this feature. The extinction curves show substantial diversity, from MW-like shapes to flatter profiles with $R_V$ reaching up to $\sim5.8$. The strength of the 2175 Å feature varies widely, including two sightlines where the bump is essentially absent. The bump central wavelength spans a broader range than previously reported, while its width remains consistent with earlier studies. A moderate positive correlation is found between bump strength ($c_3$) and width ($\gamma$). We derive an average UV extinction curve toward M31 with $R_V \approx 3.53$. These results provide new constraints on dust properties and their spatial variations in this galaxy.

We present Green's function solutions for a geometrically thin, one-dimensional Keplerian accretion disk that includes angular momentum extraction and mass loss due to magnetohydrodynamic (MHD) winds. The disk viscosity is assumed to vary radially as $\nu \propto r^{n}$. We derive solutions for three types of boundary conditions applied at the inner radius $r_{\rm in}$: (i) zero torque, (ii) zero mass accretion rate, and (iii) finite torque and finite accretion rate, and investigate the time evolution of a disk with an initial surface density represented by a Dirac-delta function. The mass accretion rate at the inner radius decays with time as $t^{-3/2}$ for $n = 1$ at late times in the absence of winds under the zero-torque condition, consistent with Lynden-Bell \& Pringle (1974), while the presence of winds leads to a steeper decay. All boundary conditions yield identical asymptotic time evolution for the accretion and wind mass-loss rates, though their radial profiles differ near $r_{\rm in}$. Applying our solutions to protoplanetary disks, we find that the disk follows distinct evolutionary tracks in the accretion rate-disk mass plane depending on $\psi$, a dimensionless parameter that regulates the strength of the vertical stress driving the wind, with the disk lifetime decreasing as $\psi$ increases due to enhanced wind-driven mass loss. The inner boundary condition influences the evolution for $\psi < 1$ but becomes negligible at higher $\psi$, indicating that strong magnetically driven winds dominate and limit mass inflow near the boundary. Our Green's function solutions offer a general framework to study the long-term evolution of accretion disks with magnetically driven winds.

Fast radio bursts (FRBs) are bright, mostly millisecond-duration transients of extragalactic origin whose emission mechanisms remain unknown. As FRB signals propagate through ionized media, they experience frequency-dependent delays quantified by the dispersion measure (DM), a key parameter for inferring source distances and local plasma conditions. Accurate DM estimation is therefore essential for characterizing FRB sources and testing physical models, yet current dedispersion methods can be computationally intensive and prone to human bias. In this proof-of-concept study, we develop and benchmark three deep-learning architectures, a conventional convolutional neural network (CNN), a fine-tuned ResNet-50, and a hybrid CNN-LSTM model, for automated DM estimation. All models are trained and validated on a large set of synthetic FRB dynamic spectra generated using CHIME/FRB-like specifications. The hybrid CNN-LSTM achieves the highest accuracy and stability while maintaining low computational cost across the investigated DM range. Although trained on simulated data, these models can be fine-tuned on real CHIME/FRB observations and extended to future facilities, offering a scalable pathway toward real-time, data-driven DM estimation in large FRB surveys.

We explore ion escape from, and solar ion deposition to, \hll{an unmagnetized Earth-like planet}. We use RHybrid, an ion-kinetic electron-fluid code to simulate the global plasma interaction of unmagnetized Earth with the solar wind. We vary the global ionospheric emission rate, and quantify the resultant planetary ion escape rates ($O^+$ and $H^+$) and the solar wind deposition rate ($H^+$). We use these results to compute the net mass flux to the atmosphere and find that the solar ion deposition rate could be comparable to planetary ion escape rates. For the emission rates simulated, our results show that under typical solar wind conditions ($v_{sw} = 400 \ km \ s^{-1}$, $n_{sw} = 5 \ cm^{-3}$), the mass of the atmosphere would decrease by less than 3\% over a billion years, indicating that Earth's intrinsic magnetic field may be unnecessary for retention of its atmosphere. Lastly, we present a hypothesis suggesting that ionospheric emission may evolve through time towards a critical emission rate that occurs at a net mass flux of zero.

Wide-field rapid sky surveys serve as critical observational methods for time-domain astronomical research. The Antarctic region, with several months of continuous dark nights annually, is an ideal site for time-domain astronomical observations. The Antarctic TianMu Staring Observation Project aims to deploy a fleet of small telescopes, adopting an array observation model to conduct time-domain optical observations in Antarctica, featuring wide-sky coverage, high-cadence sampling, long-period staring, and simultaneous multi-band measurements. Considering the severe challenges optical telescopes face in Antarctica, including extremely low temperatures, unattended operation, and limited power supply and network transmission, we have designed and developed the Antarctic TianMu prototype telescope based on drift-scan charge-coupled device technology. In October 2022, our prototype (with an aperture of 18 cm), named AT-Proto was transported to Zhongshan Station in Antarctica aboard China's 39th Antarctic Research Expedition. It has since operated stably and reliably in the frigid environment for over two years, demonstrating the significant advantages of this technology in polar astronomical observations. The experimental observation results of AT-Proto provide a solid foundation for the subsequent construction of a time-domain astronomy observation array in Antarctica.

This paper presents simulations of the synchrotron self-Compton (SSC) spectrum within the Internal-Collision-induced Magnetic Reconnection and Turbulence (ICMART) model. We investigate how key parameters like the magnetization $\sigma_0$ shape the broadband spectral energy distribution by regulating the electron distribution and magnetic field strength. The overall spectrum typically comprises two components: synchrotron radiation peaking at $E_{\rm p}$ with a low-energy spectral index $\alpha$ between -1 and -1.5, and an SSC component peaking at $E_{\rm ssc}$. At high energies, Klein-Nishina suppression causes an exponential cutoff. The flux ratio Y between these components is critical: when Y is small, the SSC peak can be suppressed. Spectral features of the synchrotron component reveal the underlying physical conditions: harder spectra with $\alpha\sim-1$ indicate a large Y parameter and strong KN suppression. We find a positive correlation between Y and $\sigma_0$, contrasting with internal shock model predictions. Applied to GRB 221009A, our model suggests $\sigma_0\leq20$ can reproduce the MeV-TeV observations. This study underscores the value of combined MeV-TeV observations in probing GRB emission mechanisms.

We present a comprehensive long-term, multi-epoch spectral and timing study of the Seyfert 1 Active Galactic Nucleus (AGN) Mrk~1040, utilizing X-ray observations spanning from 2009 to 2024 ($\sim$15 years). The source exhibits pronounced spectral and temporal variability, indicative of transitions between different accretion regimes in the vicinity of the central supermassive black hole. The earlier reported soft excess is re-examined within a uniform, physically motivated multi-epoch framework. We confirm the presence of this soft excess in the 2009 observation, where it is well described by a warm, extended Comptonizing corona with $kT_{\rm e,warm} \sim 0.26$~keV and a radial extent of $R_{\rm warm} \sim 30~r_g$. In subsequent epochs, the soft excess is not statistically significant, possibly due to a combination of enhanced ionized absorption, intrinsic weakening of the warm Comptonizing region, or partial truncation of the inner disc. A strong correlation between the soft and hard X-ray fluxes suggests a common physical origin for both components, likely within a multi-layered Comptonizing structure that evolved into a compact and thermally stable corona after 2013. The observed spectral variability, together with changes in the Fe~K$\alpha$ line strength, reflects the evolving coronal geometry and accretion flow dynamics. Variations in the intrinsic column density ($N_H$) further indicate that Mrk~1040 is embedded within a clumpy, dynamically variable absorber responding to changes in the accretion rate. Using the TCAF model, we estimate the black hole mass as $M_{\rm BH} = (4.50 \pm 1.62) \times 10^7~M_\odot$, consistent with previous estimates.

The origin and production mechanisms of high-energy astrophysical neutrinos remain open questions in multimessenger astronomy. Previous studies have hinted at a possible linear correlation between the hard X-ray and high-energy neutrino emission in active galactic nuclei. New \textit{NuSTAR} observations, first presented here, reveal that blazar PKS 1424+240, located within a prominent IceCube neutrino hotspot, is far fainter in hard X-rays than expected from this trend. Motivated by this apparent ambiguity, we identify the nearby Seyfert galaxy NGC 5610, also coincident with the hotspot, whose unabsorbed hard X-ray flux exceeds that of PKS 1424+240 by about an order of magnitude. When the local IceCube neutrino flux is apportioned between the two AGN in proportion to their hard X-ray emission, both align with the previously suggested X-ray-neutrino correlation. This suggests that certain IceCube hotspots may be unresolved blends of multiple AGN, and supports a multimessenger scenario in which high-energy neutrinos and hard X-rays originate from the same hadronic interactions, with the X-ray emission produced through cascade reprocessing.

Tidally tilted pulsators (TTPs), whose pulsation axis aligns with the binary's semi-major axis, represent a newly established class of oscillators in binary systems. While all previously known TTPs are either $\delta$ Scuti or subdwarf B-type stars, their existence has remained unidentified in more massive $\beta$ Cephei variables. Here, we report the discovery of tidally trapped pulsations in the massive ellipsoidal variable HD~329379, based on photometry from the Transiting Exoplanet Survey Satellite (TESS). Our analysis reveals a $\beta$ Cephei pulsator in a 2.25-day orbit whose pulsation mode amplitude is strongly modulated with the orbital frequency. Based on our analysis, we concluded that this modulation can be explained by pulsations with significantly larger amplitude near the star's two tidal poles (apsides). We interpret this as a tidally distorted quadrupole pulsation chariacteristiced by trapped two-pole pulsations, with a pulsation axis aligned with the tidal axis. This represents the first identification of such a pulsation mode in a $\beta$ Cephei star, which differs from single-sided pulsations observed in previous works, marking a rare and important discovery. Our work extends the family of TTPs beyond $\delta$ Scuti and subdwarf B-type stars to include more massive $\beta$ Cephei variables. In particular, the two-pole pulsator HD~329379 stands out as the prototype of a new class of TTPs in massive stars. These results not only provide a new insight to probe the interior structure and evolutionary state for massive stars but also offer a unique opportunity to study the interaction between pulsations and strong tidal distortions.

We outline a science case for next-generation wide-field spectroscopic surveys aimed at connecting the physics of the accretion disc and X-ray corona in active galactic nuclei (AGN) with the properties of their nebular regions and circumgalactic medium (CGM). We focus on the non-linear Lx-Luv relation and on deviations from this canonical coupling encoded in $\Delta \alpha_{OX}$, the offset of the optical-to-X-ray index from the mean relation, and propose to use broad and narrow line emission and CGM nebulae as calorimeters of the ionising SED to trace different accretion "states". We propose an observational strategy based on rest-frame UV/optical spectroscopy of $\sim 10^{4}-10^{5}$ AGN, a time-domain reverberation-mapping tier for a well-defined subsample, coordinated X-ray coverage, and wide-field IFU mapping of CGM emission (including H$\alpha$ and Ly$\alpha$). From these goals we derive requirements for a future ESO facility in the 2040s: a dedicated, wide-field, high-multiplex optical-NIR spectroscopic telescope with time-domain flexibility and arcmin-scale IFU capability.

Using the 1D Monte Carlo-based radiative transfer code TARDIS, we investigate the spectral evolution of the Type Iax supernova (SN) 2020rea from -7 days before to +21 days after maximum light. Our best-fit models indicate stratified, velocity-dependent abundances at early times, successfully reproducing most observed spectral features. As the SN evolves, the ejecta transition from a layered to a more homogeneous composition, posing an alternative to pure deflagration models that predict fully mixed ejecta. These results highlight the need for further investigation, as current pure deflagration models cannot fully explain the origin or spectral properties of Type Iax SNe like SN 2020rea.

PKS 0346-27 is a Low Synchrotron Peaked (LSP) blazar at redshift 0.991. The very-high-energy (VHE, E > 100 GeV) spectra of blazars are always affected by $\gamma\gamma$ absorption by the Extragalactic Background Light (EBL) and subsequently, no blazars have been detected in VHE $\gamma$-rays at redshifts exceeding 1. Extending the redshift range of VHE-detected blazars to $z \gtrsim 1$ will yield insights into the cosmological evolution of both the VHE blazar population and the EBL. This is the goal of a target-of-opportunity (ToO) programme by H.E.S.S. to observe flaring high-redshift ($z \gtrsim 1$) blazars. We report on H.E.S.S. ToO and multi-wavelength observations of the blazar PKS\,0346$-$27. Along with H.E.S.S., simultaneous data from {\it Fermi}-LAT, {\it Swift} (XRT and UVOT), and ATOM have been analysed and modelled using single-zone leptonic and hadronic models. PKS~0346-27 has been detected by H.E.S.S at a significance of 6.3$\sigma$ during one night, on 3 November 2021, while for other nights before and after this day, upper limits on the VHE flux are determined. No evidence for intra-night $\gamma$-ray variability has been found. A flare in high-energy (HE, $E > 100$~MeV) $\gamma$-rays detected by {\it Fermi}-LAT preceded the H.E.S.S. detection by 2 days. A fit with a single-zone emission model to the contemporaneous spectral energy distribution during the detection night was possible with a proton-synchrotron-dominated hadronic model, requiring a proton-kinetic-energy-dominated jet power temporarily exceeding the source's Eddington limit, although alternative (e.g. multi-zone) models can not be ruled out. A one-zone leptonic model is, in principle, also able to fit the flare-state SED, however, requiring implausible parameter choices, in particular, extreme Doppler and bulk Lorentz factors of $\gtrsim 80$.

Spectroscopic observations of the kilonova AT 2017gfo provide a unique opportunity to identify signatures from individual heavy elements freshly synthesised via the {\it r}-process, the nucleosynthetic channel responsible for producing $\sim$half of all trans-iron-group elements. Limitations in the available atomic data have historically hampered comprehensive line identification studies; however, renewed interest has led to the generation of improved (more complete and accurately calibrated) line lists for {\it r}-process species. Here we demonstrate the utility of such data, by exploiting newly generated line lists for the lanthanides to model the photospheric-phase 3.4d X-shooter spectrum of AT 2017gfo with the radiative transfer tool \textsc{tardis}. We find the data can only be reproduced by invoking a substantially diminished lanthanide mass fraction ($X_{\textsc{ln}}$) than that proposed by previous studies. Specifically, our model necessitates $X_{\textsc{ln}} \approx 2.5 \times 10^{-3}$, a value $20 \times$ lower than previously claimed. This substantial reduction in $X_{\textsc{ln}}$ is driven by our inclusion of much more complete lanthanide line information that enables better estimation of their total contribution to the observations. We encourage future modelling works to exploit all atomic data advances, and also encourage continued efforts to generate the necessary data for the remaining {\it r}-process species of interest.

From NBODY1 to NBODY6 : The Growth of an Industry is the title of a 1999 invited review by Sverre Aarseth, for Publications of the Astronomical Society of the Pacific (PASP). I took this as an inspiration for the title of this paper; it describes how Sverres NBODY Industry has further grown since 90s of the previous century, and how it is further flourishing and hopefully developing, in his spirit, even after the sad news of his passing away reached us. My contact and friendship with Sverre started a few decades ago being sent to Cambridge to learn NBODY5, counting input parameters, and learning about the fact that even a sophisticated code (which had already at that time quite a history) requires permanent maintenance and bug fixes. Managed by Sverre, who relentlessly ran his code and responded to the widely spread crowd of customer colleagues. There has been a phase of massive and fast development and improvements due to vectorization, parallelization, GRAPE and GPU acceleration, and Sverre has been always on top of it if not ahead, but also fully adopting ideas of collaborators, once they tested well. NBODY6++GPU and NBODY7 entered the scene, and also recent new competitors, such as PETAR or BIFROST . We all have learnt a lot from Sverre, and strive to continue in his open-minded spirit, for open source and exchange. A striking evidence for the further growth of the industry is the number of papers here (and two of them follow in this session, but also in other sessions) using and further developing the aforementioned codes, as well as the occurrence of new and competing codes, which keep the field alive.

We study the cosmological impact of a transient self-interaction phase in Ultra-Light Dark Matter (ULDM), focusing on its simultaneous effects on the sound horizon and the late-time growth of structure. In the presence of a quartic self-interaction, the scalar field undergoes a short-lived radiation-like phase before evolving into matter-like behaviour, inducing a localized modification of the expansion history at early times. We develop a perturbative and model-independent framework in which the self-interaction energy density is parametrized as a localized contribution to the total energy budget. Within this approach, the responses of the sound horizon and the linear growth factor can be expressed as weighted integrals over cosmic time, with distinct kernels encoding the temporal sensitivity of each observable. This structure leads to a simple analytic relation linking the corresponding early- and late-time responses, and naturally predicts correlated shifts in $H_0$ and $S_8$ whose sign and magnitude depend on the timing of the self-interaction episode. Our results show that a single transient modification of the expansion history can interpolate between early-time effects on the sound horizon and late-time suppression of structure growth within a unified physical framework, providing an analytical understanding of their joint response.

Based on the spatial distribution of objects in the solar neighbourhood with a radius of 20 parsecs, and after correcting for the incompleteness of observational data, an expression was obtained for estimating the probability of finding an object at a given distance from the Sun. According to these estimates, with a probability of about 0.5, there exists a brown dwarf in the immediate solar vicinity (< 1.2 pc). The possible multiplicity of this hypothetical object is discussed, as well as the reasons why it has not yet been detected.

In this thesis, we investigate the possibility that dark matter consists of ultra light spin-zero particles with mass $m \sim 10^{-22}\ \text{eV}$. We focus on the role of self-interactions, assuming all other non-gravitational couplings to Standard Model particles are negligible. Such ultra light dark matter (ULDM) is expected to form stable self-gravitating scalar field configurations (solitons), whose properties depend on the particle mass and self-coupling $\lambda$. Using solutions of the Gross-Pitaevskii-Poisson equations, we explore how galactic-scale observations can constrain $m$ and $\lambda$. We show that observational upper limits on the mass enclosed in central galactic regions can probe both attractive and repulsive self-interactions with strengths $\lambda \sim \pm 10^{-96} - 10^{-95}$. We further demonstrate that self-interactions can allow ULDM to describe observed rotation curves as well as satisfy an empirical soliton-halo mass relation in low surface brightness galaxies for $m \sim 10^{-22}\ \text{eV}$ and $\lambda \gtrsim 10^{-90}$. We also study tidal effects in satellite dwarf galaxies and find that attractive self-interactions can extend their lifetimes over cosmological timescales, allowing ULDM to evade recent constraints derived for the non-interacting case. Finally, we explore machine learning based inference of dark matter and baryonic parameters from galaxy rotation curves, showing that neural networks can recover parameters consistent with observations.

The late-time linear Integrated Sachs-Wolfe (ISW) effect directly probes the dynamics of cosmic acceleration and the nature of dark energy. Detecting these weak, secondary temperature anisotropy signals of the CMB requires accurate theoretical predictions of their amplitude across cosmological models. By extending the pyGenISW package, previously limited to $\Lambda$CDM, we aim to generate full-sky ISW maps for a suite of 791 $w$CDM cosmologies using the Gower Street N-body simulations, thereby enabling ISW analyses across a broader dark-energy parameter space. We make our code and ISW data publicly available. We compute the ISW signals by tracing the time evolution of the gravitational potential across large-volume simulations that span dark energy equation of state parameters from phantom to quintessence, $-1.79 \lesssim w \lesssim -0.34$. These data are projected onto the sphere using HEALPix to obtain full-sky temperature maps. We validate our pipeline by comparing the measured ISW angular power spectra and ISW-density cross-correlations against linear theory expectations ($2 \leq \ell \leq 200$) computed with benchmarks from the pyCCL library. The agreement is excellent across the multipole range where the ISW contribution is expected to dominate, confirming the reliability of our modelling of gravitational-potential evolution. With additional tests of the ISW signal's strength in density extrema, as well as comparing all models to a reference $\Lambda$CDM cosmology, we found that quintessence-like models ($w > -1$) show higher ISW amplitudes than phantom models ($w < -1$), consistent with enhanced late-time decay of gravitational potentials. The consistency of our $w$CDM ISW maps and their agreement with theory predictions confirm the robustness of our methodology, establishing it as a reliable tool for theoretical and observational ISW-LSS analyses.

We present multi-epoch, multi-band ALMA imaging of the new Class II millimeter methanol masers excited during the accretion outburst of the massive protostar G358.93-0.03 MM1. The highest angular resolution image (24 mas $\approx$ 160 au) reveals a nearly complete, circular ring of strong maser spots in the 217.2992 GHz ($v_t$=1) maser line that closely circumscribes the dust continuum emission from MM1. Weaker maser emission lies inside the eastern and southern halves of the maser ring, generally coincident with the centimeter masers excited during the outburst, but avoiding the densest parts of the hot core gas traced by high excitation lines of CH$_3$CN. Using a variety of fitting techniques on the image cubes of the two strongest maser lines, each observed over 3-4 epochs, we find the diameter of the ring increased by $\gtrsim$60% (from $\approx$1100 to $\approx$1800 au in the 217 GHz line) over 200 days, consistent with an average radial propagation rate of $\approx$0.01c, while the maser intensity declined exponentially. Fitting the angular extent of the millimeter masers versus time yields a power law of index 0.39$\pm$0.06, which also reproduces the observed extent of the 6.7 GHz masers in the first VLBI epoch of R. A. Burns et al. (2020). This exponent is consistent with the prediction of radius vs. time in the Taylor-von Neumann-Sedov self-similar solution for an intense spherical explosion from a point source ($R \propto t^{2/5}$). These results demonstrate the explosive nature of accretion outbursts in massive protostars and their ability to generate subluminal heat waves traceable by centimeter and millimeter masers for several months as the energy traverses the surrounding molecular material.

Star formation is governed by multiple physical processes, making it inherently complicated. One excellent example is the Canis Major OB1/R1 Association, whose complex history of star formation is related to different episodes. Three supernova (SN) events potentially altered the environment and impacted star formation and stellar evolution. Prior investigations revealed two stellar groups of different ages associated with GU CMa and Z CMa. This work focusses on identifying the low-mass young stellar population near FZ CMa, located between these two groups and spatially related to the H II region Sh 2-295. Our main goal is to verify whether this group is age-mixed and characterise its physical properties. We analysed multi-object spectroscopic data acquired with Gemini/GMOS to search for typical features of T Tauri stars (TTs) and to determine their spectral types. Lithium absorption line ($\lambda$ 6708 $\mathring{A}$) was used as a youth indicator, while H$\alpha$ emission was investigated to probe accretion activity. We also derived ages based on optical photometry from Gaia DR3 and compared the projected spatial distribution to diffuse infrared (IR) emission. We identified 29 TTs, including six new members of the association and three Classical TTs (CTTs). The equivalent width of the Li I absorption line suggests an age of $8.1^{+2.1}_{-3.8}$ Myr, while optical photometric data indicate stellar ages ranging from $\sim$1 to 14 Myr. Younger stars are concentrated around Sh 2-295, whereas the older ones are more widely dispersed. We increased the number of known TTs related to the CMa association. Our results support a scenario of multiple star-formation episodes, including a younger group that may have been triggered by the expansion of Sh 2-295. The influence of SN events appears limited in this context.

Foundation models build an effective representations of data that can be deployed on diverse downstream tasks. Previous research developed the OmniLearned foundation model for collider physics and showed that it could significantly advance discovery potential across collider experiments. In this paper we go beyond collider physics and show that Foundation Models trained on collider data can help improve the prediction of cosmological parameters and to predict halo and galaxy velocities in different datasets from CosmoBench. This is the first time a collider physics model is shown to generalize across scientific fields.

Collisionless fast-magnetosonic shocks are often treated as smooth, planar boundaries, yet observations point to organized corrugation of the shock surface. A plausible driver is upstream turbulence. Broadband fluctuations arriving at the front can continually wrinkle it, changing the local shock geometry and, in turn, conditions for particle injection and radiation. We develop a linear-MHD formulation that treats the shock as a moving interface rather than a fixed boundary. In this approach the shock response can be summarized by an effective impedance determined by the Rankine-Hugoniot base state and the shock geometry, while the upstream turbulence enters only through its statistics. This provides a practical mapping from an assumed incident spectrum to the corrugation amplitude, its drift along the surface, and a coherence scale set by weak damping or leakage. The response is largest when the transmitted downstream fast mode propagates nearly parallel to the shock in the shock frame, which produces a Lorentzian-type enhancement controlled by the downstream normal group speed. We examine how compression, plasma $\beta$, and obliquity affect these corrugation properties and discuss implications for fine structure in heliospheric and supernova-remnant shock emission.

One of the hallmarks of active galactic nuclei are that they are highly variable with time. In watching the spectra vary it has been observed that the emission-lines often appear to "reverberate" -- that is they vary in response to continuum variations assumed to originate close to the black hole. This critical observation underlies the reverberation mapping technique, an elegant physics experiment that has allowed us to characterize the environment around many supermassive black holes in nearby active galactic nuclei. Recent observations are of such quality that the response can be measured as a function of velocity across the emission-line, and in doing so we can construct velocity-delay maps that show the structure and physics of the gas in the broad-line region better than any other measurement to date. Unfortunately constructing such maps requires a deconvolution, and given that the data are often noisy and with gaps such deconvolutions are non-trivial. Here we present a novel deconvolution method for the recovery of velocity-delay maps using a custom convolutional neural network architecture, showcasing that such methods have great promise for the deconvolution of reverberation mapping data products. While we have designed this new method with the BLR in mind, in principle this technique could be applied to any reverberation deconvolution problem, including in the accretion disk and torus.

The Ultra-Violet Imaging Telescope (UVIT) is one of the five payloads onboard the first Indian multiwavelength astronomical observatory, AstroSat, launched by the Indian Space Research Organisation on 28 September 2015. UVIT, designed for simultaneous imaging in the far-ultraviolet (FUV; 1300-1800 Å) and near-ultraviolet (NUV; 2000-3000 Å) channels, has completed nine years in orbit in 2024 despite the failure of the NUV channel in 2018. As the FUV optics is subject to possible reduction in sensitivity due to microscopic amounts of contaminants, we used the FUV data acquired by UVIT over the past nine years on the open cluster NGC 188 and the white dwarf HZ 4 to study sensitivity variations in the UVIT FUV channel. Our findings indicate no significant reduction in the sensitivity of the FUV channel over the last nine years, with no significant episodic variations due to unknown causes.

Solar flares are the largest energy-release events in the Solar System, allowing us to study fundamental physical phenomena under extreme conditions. Those include magnetic reconnection, particle acceleration, radiation transport, and various plasma physics processes, all of which occur throughout the heliosphere and rest of the Universe. Flares and eruptive events are also components of geo-effective space weather. Their impacts from a space weather perspective are numerous, such as harm to satellites, disruption to GPS, communications and power systems, and impacts on passenger air travel. A comprehensive understanding of solar flares is therefore not just a compelling science problem, but also important for national security and infrastructure. This white paper (WP) addresses critical open science questions related to solar flares. Key observations and capabilities required to make significant advancements over the coming decade are identified. The UK has a robust and vibrant solar flare community. We are key partners in international collaborations, and also provide instrumentation for existing and upcoming ESA/NASA/JAXA space missions. Continuing this effort over the coming decade is vital to maintain UK leadership in this field, achieve Solar System Advisory Panel roadmap goals, and to work under the UK Space Agency's National Space Strategy Pillars. Several complementary WPs have been submitted that discuss instruments or concepts that would directly address the observational requirements we describe (including: SPARK, solar optimised IFUs, Solar-C/EUVST, and OSIRIS), as well as required numerical modelling efforts and infrastructure.

While solar flares are primarily associated with enhanced ultraviolet and X-ray emission, a subset of flares exhibit significant continuum brightening in visible light and are classified as white-light flares (WLFs). Despite extensive observational and modeling efforts, the physical mechanisms responsible for the compact, short-lived photospheric brightenings in WLF kernels observed during the impulsive phase of solar flares remain uncertain. Thick-target electron-beam models typically deposit energy in the upper chromosphere, and their ability to reproduce the magnitude and spatial localization of photospheric continuum enhancements observed in white-light flare kernels remains an open question. To investigate the role of realistic atmospheric structuring and multidimensional transport in flare energy deposition, we perform three-dimensional radiative MHD simulations of electron-beam heating using the StellarBox code for beam fluxes of $10^{12}$ erg\,s$^{-1}$\,cm$^{-2}$ and low-energy cutoffs of 10--25\,keV. We then compute Fe\,I 6173\,Å~Stokes profiles using the RH 1.5D radiative transfer code for direct comparison with Helioseismic and Magnetic Imager (HMI) observations. The simulations produce strong upper-chromospheric heating, multiple shock fronts, and continuum enhancements up to a factor of 2.5 relative to pre-flare levels, comparable to continuum enhancements observed during strong X-class white-light flares. Comparison with one-dimensional RADYN simulations highlights the influence of fine-scale structuring on flare dynamics and continuum emission that arises in three-dimensional geometry.

The recently initiated SPHEREx and 7DS surveys will deliver low-resolution spectra ($R\approx 30-130$) for hundreds of millions of galaxies over the optical to near-infrared range ($0.4-5.0\mu m$), covering a wide sky area without sample selection. These unique datasets will improve redshift estimation and provide a rich redshift catalog for the community. In this study, we forecast the performance of widely-used photometric redshift estimation methods using simulated SPHEREx and 7DS data. Four template-fitting approaches and two machine-learning (ML) methods are used to derive photometric redshifts from low-resolution spectrophotometric data. We measure redshifts using mock catalogs based on the GAMA and COSMOS galaxy samples and achieve high precision for bright (13 < i < 18) galaxies, with $\sigma_{NMAD}\lesssim 0.005$, bias $\lesssim 0.005$, and a catastrophic failure rate $\lesssim 0.005$ for all methods employed. We find that the combined SPHEREx + 7DS dataset significantly improves redshift estimation compared to using either the SPHEREx or 7DS datasets alone, highlighting the synergy between the two surveys. Moreover, we compare the redshift estimation performance across magnitude ranges for the different methods and examine the probability distribution functions (PDFs) produced by the template-fitting approaches. As a result, we identify some factors that can affect the redshift measurements, like treatments on dust extinction or inclusion of flux uncertainty in the ML model. We also show that the PDFs are relatively well calibrated, although the confidence intervals are generally underestimated, particularly for bright galaxies in the template-fitting methods. This study demonstrates the strong potential of SPHEREx and 7DS to deliver improved redshift measurements from low-resolution spectrophotometric data, underscoring the scientific value of jointly utilizing both datasets.

Current understanding suggests that as the Sun brightens in the far future, Earth's carbonate-silicate cycle will offset increasing temperatures by drawing CO$_2$ out of the atmosphere, ultimately leading to the extinction of all terrestrial plant life via either overheating or CO$_2$ starvation. Most previous estimates put the future lifespan of Earth's terrestrial biosphere at $\sim$1 billion yr, but recent work used a new coupled climate-continental weathering model with up-to-date parameter constraints to revise this estimate upward to 1.6-1.86 billion yr. In this study, we extend the model to examine the impacts of seafloor weathering and stochastic variations in CO$_2$ outgassing rates on the remaining lifespan of Earth's terrestrial biosphere. We find that if seafloor weathering has a stronger feedback than continental weathering and accounts for a large portion of global silicate weathering, then the remaining lifespan of the terrestrial biosphere can be shortened, but a lifespan of more than 1 billion yr (Gyr) remains likely. Similarly, stochastic fluctuations in outgassing rates can have a significant impact if the size of the fluctuations exceed those observed over the last 1 billion yr. The impact of weak seafloor weathering and lower variability stochasticity are minor. Our work provisionally supports a lengthened lifespan of Earth's terrestrial biosphere, suggests robustness of this lengthened lifespan to planetary parameters that may vary among exoplanets, and identifies seafloor weathering as a key process that requires further study and constraint.

GRB 161117A is a long-duration GRB with three main overlapping peaks. By analyzing the time-resolved spectra of its data observed with the Gamma-Ray Burst Monitor (GBM) on board the Fermi mission, we find that the spectral evolution shows a transition from thermal (single BB) to hybrid (PL$+$BB), and finally to non-thermal (Band and CPL) emissions. Such a transition suggests that the jet composition of GRB 161117A should be changed from a fireball to a Poynting-flux-dominated jet. The bulk Lorentz factor ($\Gamma_{\rm ph}$), radii ($R_{\rm ph}$ and $R_{0}$), magnetization factor at the central engine ($\sigma_0$), and dimensionless entropy ($\eta$) of the outflow can be inferred by invoking the observed quasi-thermal component within two models (e.g., pure fireball and hybrid). It is found that $\Gamma_{\rm ph}$ seems to be tracking with the light curve, and $R_{0}$ remains a constant at $\sim$ $10^{8}$ cm. The low magnetization ($1+\sigma_0 \sim$ 1) and high dimensionless entropy ($\eta \gg$ 1) during the first seven time-intervals suggest to be a pure fireball outflow. Moreover, we also estimate the lower limit of magnetization parameter at the photosphere radius ($\sigma_{\rm ph}\sim 1.4$ and 0.75) for late phase via the non-thermal spectra, and it indicates that the particle acceleration mechanism is dominated by internal shocks rather than magnetic dissipation processes. Finally, the $\nu \bar{\nu}$ annihilation mechanism of NDAF model to explain the thermal emission of GRB 161117A is also discussed.

The polarization of the Mg II h and k lines holds significant diagnostic potential for measuring chromospheric magnetic fields, which are crucial for understanding the physical processes governing the energy transport and dissipation in the solar upper atmosphere, as well as the subsequent heating of the chromosphere and corona. The Chromospheric Layer Spectropolarimeter was launched twice in 2019 and 2021, successfully acquiring spectropolarimetric observations across the Mg II h and k lines. The analysis of these observations confirms the capability of these lines for inferring magnetic fields in the upper chromosphere. In this review, we briefly introduce the physical mechanisms behind the polarization of the Mg II h and k lines, including the joint action of the Zeeman and Hanle effects, the magneto-optical effect, partial frequency redistribution, and atomic level polarization. We also provide an overview of recent progress in the interpretation of the Stokes profiles of the Mg II h and k lines.

Dust lifetime derived from an isolated supernova (SN) evolution in the interstellar medium is known to be an order of magnitude shorter than the time needed to replenish dust mass by its production in various Galactic sources. We show, using 3-D numerical hydrodynamical simulations, that destruction of dust in the case of multiple SNe in a star cluster is markedly different from that in an isolated SN. We find that the mass of dust destroyed in the bubble does not grow for a considerable time, while SNe continue to explode. This regime is attained at saturation timescale, which is proportional to SNe rate in cluster. We show that the mass of dust destroyed in bubble per SN decreases for higher SN rate. Thus, the destruction efficiency -- defined as the ratio of the the total mass of dust destroyed by clustered SNe to that destroyed by the same number of isolated SNe -- in bubbles evolved in a homogeneous medium drops for massive clusters, e.g. around clusters with $M_\ast > 4\times 10^4 M_\odot$ it is less $0.4$\%. For lower mass clusters, the efficiency is proportional to the average time delay between SNe. We found that each cluster with $M_\ast < 4\times 10^4 M_\odot$ destroys the same mass of dust as a single isolated SN. In a clumpy medium in bubbles formed around clusters with $M_\ast \sim 4\times 10^4 M_\odot$ and up to 4 times around $M_\ast \sim 8\times 10^5 M_\odot$. We argue that the interstellar dust swept up by multiple SNe almost completely survives in the shells of bubbles around such massive clusters. Therefore, the destruction of the interstellar dust is controlled by SNe in low-mass clusters. We point out that the interstellar dust lifetime for a given SN rate is at least a factor $\sim 10$ longer as compared to the estimates derived from an isolated SN. (abridged)

We develop an effective theory for biased tracers formulated at the level of the Boltzmann equation, providing a unified description of density and velocity bias. We introduce a general effective collision term in the tracer Boltzmann equation to encode tracer dynamics that are intrinsically different from those of dark matter. This collision operator leads to modified continuity and Euler equations, with source terms reflecting the collision-term physics. At linear order, this framework predicts time- and scale-dependent bias parameters in a self-consistent manner, encompassing peak bias as a special case while clarifying how velocity bias and higher-derivative effects arise. Applying the resulting bias model to redshift-space distortions, we show that the Boltzmann-equation approach reproduces the power spectrum of biased tracers obtained in the Effective Field Theory of Large-Scale Structure up to $k^4$ terms with fewer independent parameters.

Destruction of the interstellar dust proceeds primary behind supernova shocks. The previous estimates of the mass of the interstellar dust destroyed in the SN remnant do not take into account the physical properties of the ambient medium. Here we consider how some parameters, i.e. gas density and metallicity, can influence the destruction of the interstellar dust. We show that there are two regimes of the interstellar dust grains destruction in SN remnants: rapid and almost complete in compact low-mass SN remnants expanding in dense medium, and gradual and weak destruction in massive remnants evolving in the low-dense environment. When time for thermal sputtering is close to the dynamical one, i.e. to the SN remnant age, the mass of the interstellar dust destroyed in the SN remnant reaches its maximum value. We find that change of the ambient gas density results in the reduction of the dust mass logarithmically. We argue that dust cooling suppresses the interstellar dust destruction up to a factor of 1.6 by mass. This factor decreases for higher density of the ambient medium. We found that the dust mass depends linearly on gas metallicity as ${\rm log}~M_d \sim {\rm [Z/H]}$ or, in other words, on the dust-to-gas ratio as $M_d \sim \zeta_d$. In turn, the destruction efficiency is higher in low-metallicity environments due to relatively longer adiabatic phase. We point out that the mass of the interstellar dust destroyed per one SN in a high density environment of the high star formation regions like in local ultraluminous infrared and high-redshift massive galaxies is about several times smaller than that in the Milky Way diffuse medium.

In this work, we investigate how astrophysical observations from NICER and GW data constrain the matter properties at high densities, with a primary focus on the recent PSR J0614-3329 data. We have constructed three distinct classes of an ensemble of agnostic equation of state by speed of sound parametrisation. Bayesian inference is then employed to constrain the EoS construction parameters-namely, the squared speed of sound and chemical potential at each interpolation segment-using the observational data. Both the NICER and GW constraints hint towards a smoother EoS where PT occurs late, significantly reducing the maximum mass of NS. Also, the maximum-mass and maximum-compact sequences are distinctly different, as the former allows for the maximally stiff EoS to maximise the star mass. In contrast, the latter prefers a softer low-density and stiffer high-density EoS to maximise the compactness. The Bayesian analysis demonstrates that the observational bounds are effective in significantly constraining the low-density region of the equation of state. It is also seen that the astrophysical bound prefers the phase transition in the intermediate-density range and also prefers a small density jump for a discontinuous equation of state.

Powerful solar eruptions are known to produce fast and wide shock waves in the solar corona and inner heliosphere. The relationship between the coronal shock waves, solar energetic particles and different types of radio emission is a subject of long-lasting research activity. In this work, we perform a case study of 31 December 2023 eruption that occurred near eastern limb of the Sun. It produced a X5.0 class X-ray flare, a global EUV wave, a fast $\sim3000$ km/s Coronal Mass Ejection, strong radio emissions (including several type III and type II bursts), solar energetic particles in-situ, and long duration high-energy gamma-ray emission. We employ a technique that combines the reconstructed coronal shock from observations with background coronal MHD simulations to produce shock-mediated synthetic radio spectrum, assuming local emission at plasma frequency. We show that transient high Mach number and quasi-perpendicular coronal shock region explains both a ``hot flux tube'' precursor seen in EUV observations and reverse drifting radio spectral features observed by ground-based facilities. The occurrence of this evanescent strong shock patch was observed when it propagated across pseudo-streamer's cusp where the magnetic field was particularly low. We also find evidence that, at higher coronal altitudes, the low-frequency type II radio burst detected by several spacecraft, is triggered by the interaction of the shock with the heliospheric current sheet. This study provides additional evidence that high-$M_A$ regions of coronal shock surface are instrumental in energetic particle phenomenology.

We propose the Transformer-based Tidal disruption events (TDE) Classifier (\texttt{TTC}), specifically designed to operate effectively with both real-time alert streams and archival data of the Wide Field Survey Telescope (WFST). It aims to minimize the reliance on external catalogs and find TDE candidates from pure light curves, which is more suitable for finding TDEs in faint and distant galaxies. \texttt{TTC} consists of two key modules that can work independently: (1) A light curve parametric fitting module and (2) a Transformer (\texttt{Mgformer})-based classification network. The training of the latter module and evaluation for each module utilize a light curve dataset of 7413 spectroscopically classified transients from the Zwicky Transient Facility (ZTF). The \texttt{Mgformer}-based module is superior in performance and flexibility. Its representative recall and precision values are 0.79 and 0.76, respectively, and can be modified by adjusting the threshold. It can also efficiently find TDE candidates within 30 days from the first detection. For comparison, the parametric fitting module yields values of 0.72 and 0.40, respectively, while it is $>$10 times faster in average speed. Hence, the setup of modules allows a trade-off between performance and time, as well as precision and recall. \texttt{TTC} has successfully picked out all spectroscopically identified TDEs among ZTF transients in a real-time classification test, and selected $\sim$20 TDE candidates in the deep field survey data of WFST. The discovery rate will greatly increase once the differential database for the wide field survey is ready.

To enhance the efficiency, scalability, and cross-survey applicability of stellar parameter inference in large spectroscopic datasets, we present a modular, parallelized Python framework with automated error estimation, built on the LAMOST Atmospheric Parameter Pipeline (LASP) originally implemented in IDL. Rather than a direct code translation, this framework refactors LASP with two complementary modules: LASP-CurveFit, a new implementation of the LASP fitting procedure that runs on a CPU, preserving legacy logic while improving data I/O and multithreaded execution efficiency; and LASP-Adam-GPU, a GPU-accelerated method that introduces grouped optimization by constructing a joint residual function over multiple observed and model spectra, enabling high-throughput parameter inference across tens of millions of spectra. Applied to 10 million LAMOST spectra, the framework reduces runtime from 84 to 48 hr on the same CPU platform and to 7 hr on an NVIDIA A100 GPU, while producing results consistent with those from the original pipeline. The inferred errors agree well with the parameter variations from repeat observations of the same target (excluding radial velocities), while the official empirical errors used in LASP are more conservative. When applied to DESI DR1, our effective temperatures and surface gravities agree better with APOGEE than those from the DESI pipeline, particularly for cool giants, while the latter performs slightly better in radial velocity and metallicity. These results suggest that the framework delivers reliable accuracy, efficiency, and transferability, offering a practical approach to parameter inference in large spectroscopic surveys. The code and DESI-based catalog are available via \dataset[DOI: https://doi.org/10.12149/101679]{this https URL} and \dataset[DOI: https://doi.org/10.12149/101675]{this https URL}, respectively.

The Epoch of Reionization marks the last major phase transition in the early Universe, during which the majority of neutral hydrogen once filling the intergalactic medium was ionized by the first galaxies. The James Webb Space Telescope (JWST) is now identifying promising galaxy candidates capable of producing sufficient ionizing photons to drive this transformation. However, the fraction of these photons that escape into intergalactic space--the escape fraction--remains highly uncertain. Stellar feedback is thought to play a critical role in carving low-density channels that allow ionizing radiation to escape, but the dominant mechanisms, their operation, and their connection to observable signatures are not well understood. Local analogs of high-redshift galaxies offer a powerful alternative for studying these processes, since ionizing radiation is unobservable at high redshift due to intergalactic absorption. However, current UV space-based instrumentation lacks the spatial resolution and sensitivity required to fully address this problem. The core challenge lies in the multiscale nature of LyC escape: ionizing photons are generated on scales of 1--100 pc in super star clusters but must traverse the circumgalactic medium which can extend beyond 100 kpc. The proposed Habitable Worlds Observatory (HWO) will provide a platform for future UV instruments capable of resolving these scales. In this article, we present a science case for understanding how LyC photons escape from star-forming galaxies and define the observational requirements for future instruments aboard HWO, including a UV integral field spectrograph (IFS).

We study the cosmic evolution of an interacting scalar field radiation model, in which a minimally coupled scalar field exchanges energy with the radiation sector through an exponential coupling. Extending previous formulations, a non-relativistic matter component is included explicitly, which allows a self consistent description of cosmological dynamics from the radiation-dominated era to late-time acceleration. Analytical expressions for the background expansion are derived and characterized using kinematic diagnostics. We constrain the model using observational Hubble data, Type Ia Supernovae, baryon acoustic oscillations (including DESI DR2), and compressed cosmic microwave background distance information, performing a Bayesian MCMC analysis. The interaction parameter is found to be consistent with zero, though small deviations from standard radiation scaling are allowed. These deviations can partially alleviate the Hubble tension by modifying the sound horizon, but this is accompanied by correlated shifts in the matter density. The reconstructed expansion history remains close to LCDM at late times. Model comparison suggest that the interacting scenario is statistically competitive but not decisively preferred by current background data.

The search for ``dark galaxies,'' a key prediction of the lambda cold dark matter, has yielded few viable candidates. Recently, FAST J0139+4328 was reported as the first isolated dark galaxy in the nearby universe, based on a neutral hydrogen (HI) detection and a non-detection in the Pan-STARRS1 survey. To verify the nature of this candidate, we obtained deep optical imaging, using the $1.4\,\mathrm{m}$ \textit{Milanković} and $0.6\,\mathrm{m}$ \textit{Nedeljković} telescopes, and spectroscopic follow-up of the field. We report the unambiguous discovery of a low-surface-brightness (LSB) optical counterpart at the location of the HI cloud. Furthermore, the detection of H$\alpha$ emission via the $6\,\mathrm{m}$ Big Telescope Alt-Azimuthal (BTA) confirms that the stellar system lies at a redshift consistent with the HI source, establishing their physical association. Through detailed photometry and employing color-dependent mass-to-light scaling relations, we derive a total stellar mass of $M_\star = (7.2 \pm 3.7) \times 10^6\, M_{\odot}$, about an order of magnitude higher than the previously estimated upper limit. Using the literature HI mass, this implies a gas-to-stellar mass ratio of $M_{\mathrm{HI}} / M_{\star} = 11.5 \pm 6.4$. Our findings demonstrate that FAST J0139+4328 is not a dark galaxy but an extremely gas-rich LSB dwarf galaxy, whose stellar component was simply below the detection limit of the Pan-STARRS1 survey. This reclassification resolves the status of this prominent dark galaxy candidate and underscores the necessity of deep optical follow-up to classify faint HI-selected systems.

FRB 20240114A is extraordinarily active, and therefore presents an opportunity to search for the periodicity predicted by magnetar models of Fast Radio Bursts (FRB). Zhang, et al. (2025) observed 11,553 bursts, including 3196 on MJD 60381 (March 12, 2024). We find no significant peak in the periodogram of those bursts, which occur within 15628 s, short enough that even with a characteristic slowing age of 1 year a signal with period $\ge 0.1\,$s it would not significantly dephase within the observation. Introducing modulation artificially shows that an amplitude of 0.15 would have been detected robustly. Implications for magnetar models of FRB are briefly considered.

The recently reported Cosmic Himalayas (CH) -- an extreme quasar overdensity at z~2 -- poses an apparent challenge to the Lambda CDM framework, with a reported significance of 16.9-sigma under Gaussian assumptions. Such an event appears improbably rare, with a formal probability of P ~ 10^-68. In this work, we investigate whether CH-like structures can naturally arise in cosmological hydrodynamic simulations. Using the CROCODILE simulation, which self-consistently models galaxy-black hole coevolution, we examine quasar clustering through two complementary approaches: the count-in-cells (CIC) statistic, which probes large-scale overdensities, and the nearest-neighbor distribution (NND), sensitive to small-scale environments. CIC analysis reveals that the underlying distribution is heavy-tailed and non-Gaussian, and that conventional Gaussian-based evaluation substantially overestimates the significance of extreme events. When modeled with an asymmetric generalized normal distribution (AGND), the inferred rarity of the CH is substantially reduced and reconciled with standard Lambda CDM; for instance, regions appearing as 12-sigma outliers under Gaussian assumptions (P ~ 10^-33) are found to occur in the AGND regime with a probability of P ~ 10^-4. NND analysis further demonstrates that extreme overdense regions within the simulation can naturally sustain two-point correlation function values similar to those observed in the CH (r0 ~ 30 Mpc/h), suggesting that the strong clustering stems from sample selection biases and local environmental variations. These two analyses conclusively highlight the importance of adopting non-Gaussian statistics when quantifying extreme overdensities of quasars and establish that the CH is not an anomaly, but a natural outcome of structure formation in the Lambda CDM universe.

We present results from multi-epoch observations of the repeating fast radio burst FRB 20201124A with the upgraded Giant Metrewave Radio Telescope (uGMRT) during its active phase between 8 May and 28 May 2021. The bursts exhibit significant morphological diversity, including multiple sub-bursts, downward frequency drifts, and intrinsic widths ranging from 1.032 - 32.159 ms. Bursts were detected in both Band 4 (550 - 950 MHz) and Band 5 (1060 - 1460 MHz), with the last Band 5 burst occurring on 24 May, while Band 4 activity persisted until 28 May, indicating a frequency-dependent decline. Consecutive bursts were observed with separations of 16.7 - 291.5 ms, revealing short repetition intervals or potential sub-second quasi-periodicity. The waiting-time and energy distributions are bimodal, suggesting at least two distinct emission timescales and energy modes. Burst fluence ranges from 1.72 - 78.47 Jy ms, and the cumulative fluence distribution follows a broken power law. Multi-frequency analysis further shows closely spaced burst pairs across Band 4 and Band 5, with sub-second offsets of 1.08 - 1.15 s, and no strict simultaneity with contemporaneous FAST detections. These findings demonstrate that FRB 20201124A exhibits closely spaced, patchy, multi-frequency emission with frequency-dependent activity, highlighting the complex and dynamic nature of repeating FRBs.

Using the censored catalog of 103,169 resolved Gaia DR3 binary stars with accurate astrometric data for each component, a new observable, object-specific parameter is computed for each pair: the projected orbital momentum. This parameter is the product of four functions of physical characteristics: total mass, semimajor axis, eccentricity, and inclination angle. Using the previously estimated marginal probability densities of eccentricity and semimajor axis, and assuming an isotropic orientation of binary systems, the sample distribution of mass was adjusted using a concordance metric of the observed and synthetic distributions of orbital momenta and an ad hoc functional model. The best-fitting mass density model is found to faithfully reproduce the observed dependence of orbital momenta on apparent separation, although the absolute luminosity distributions indicate a tendency of the widest systems to more frequently include solar-type primaries. The anticipated manifestation of MOND is computed in the investigated parameter space \{separation, momentum\}. This effect is absent in the given data. The median total mass of the widest Gaia binaries is found to be somewhat higher than that of the tighter pairs, which is interpreted as a dynamical age effect.

Upcoming cosmological surveys will obtain numerous rest-frame ultraviolet (UV) observations of Type Ia supernovae (SNe Ia), yet there is concern about how standardizable SNe Ia are in the UV. In this work, we train a robust optical--UV SED model for SNe Ia (SALT3-UV) with the open-source model-training software $\texttt{SALTshaker}$. We incorporate a spectroscopic UV data sample from HST, including 67 UV spectra from 18 nearby SNe Ia. Unlike previous training spectra, the HST spectra have sufficiently precise calibration that they do not require additional warping to match coincident photometric data. Additionally, while including this new SN Ia sample necessitates incorporating auxiliary photometric data from ZTF and ATLAS that have insufficient calibration for cosmological analyses, the improvements in the calibration of these data is anticipated in the near future. Compared to the previous SALT3-K21 model, the SALT3-UV model shows a significant improvement in the UV down to $2000\mathring{\text{A}}$, with over a threefold improvement in model uncertainty and a more physically accurate continuum and line features. We further evaluate potential redshift evolution in the UV template by separating the UV training sample into low- and high-$z$ subsamples. Our results reveal a non-negligible $\gtrsim 0.05$ mag difference between low- and high-$z$ SALT3-UV models in the $g-$band at $z\gtrsim0.5$ and the $u-$band at $z\gtrsim0.2$. We demonstrate that, if confirmed, such evolution could lead to a few-percent bias in the measurement of $w$ if high-$z$ rest-frame UV data are included in future cosmological surveys such as LSST and $\textit{Roman}$.

We study central configurations in the four body problem, i.e., configurations in which the forces on all the bodies point to a fixed, single point in space. The newly formulated pair-space formalism yields a set of vectorial equations that fully characterize such configurations. We investigate a sub-class of solutions in which at least two pairs of inter-body distances are equal. The only such non-collinear configurations are the tetrahedron (the unique non-planar configuration), kites and the isosceles trapezium. The specific shapes (internal angles) are determined by the ratio of the masses of the bodies. Mathematical expression are given for all these relations.

We consider a novel scenario for a strongly coupled spectator sector during inflation, that of a higher dimensional conformal field theory with large anomalous dimensions -- ``unparticles" -- and compactify the extra dimensions. More specifically, we take generalized free fields in five dimensions, where the extra dimension is compactified to a circle. Due to the usual Kaluza-Klein mechanism, the resulting excitations carry properties of both particles and unparticles, so we dub this scenario ``gapped unparticles". We derive a two-point function of the gapped unparticles by performing dimensional reduction. We then compute, in the collapsed limit, the four-point correlation function of conformally coupled scalars exchanging a gapped unparticle, which are used as seed functions to obtain the correlation function of primordial density perturbations. The phenomenology of the resulting correlators presents some novel features, such as oscillations with an envelope controlled by the anomalous dimension, rather than the usual value of 3/2. Depending on the value of the five-dimensional scaling dimension and effective mass of the gapped unparticles, we find a clear strategy to distinguish gapped unparticles from heavy massive scalars. If we assume the interactions are localized on a brane, gapped unparticles with different effective masses will share a universal coupling, and their exchanges produce an interesting interference pattern.

The High Energy Particle Detector (HEPD-02) is a payload of the second China Seismo-Electromagnetic Satellite (CSES-02), designed and built by the Italian Limadou collaboration. Its purpose is to detect cosmic rays and trapped particles of radiation belts, in the kinetic energy range 3-100 MeV for electrons, 30-200 MeV for protons. HEPD-02 is the first space detector to use a tracking detector based on Monolithic Active Pixel Sensors (MAPS). The MAPS provides high spatial resolution, low noise, increased robustness, and low production costs. Operating MAPS in space presents a significant challenge due to strict power consumption requirements. To meet such constraints, a custom Tracker Data Acquisition (TDAQ) board and firmware have been designed and implemented, by using a commercial low-power Field Programmable Gate Array (FPGA). This paper addresses the design features of the TDAQ unit, enabling the tracking detector to be operated efficiently, with particular focus on the power consumption performance.

Motivated by the cosmological collider program, which aims to probe high-energy physics through inflation, we investigate the phase diagram of multi-flavor QCD in de Sitter spacetime with a flavor-universal axial chemical potential induced by a rolling inflaton coupled to fermions. We determine the first-order critical line and a critical point as functions of the Hubble parameter and the axial chemical potential, employing an effective description of chiral symmetry breaking within the framework of the Nambu--Jona-Lasinio model. We find that a first-order chiral phase transition may occur during inflation or at its end when the axial chemical potential is sufficiently large and crosses the critical line. This provides a cosmological collider analogue of the QCD phase diagram explored in heavy-ion colliders.

Magnetic reconnection is a ubiquitous process in astrophysical plasmas and an efficient mechanism for particle acceleration. Using 2.5D magnetohydrodynamic (MHD) simulations with a co-evolving fluid-particle framework, we investigate how particle feedback affects reconnection and acceleration. Our simulations demonstrate that particle feedback to the fluid amplifies shear flows within magnetic islands, which strengthens the convective electric field and thereby boosts particle acceleration. This mechanism results in a higher maximum particle energy and a harder non-thermal energy spectrum. The guide field suppresses both the increase in gas internal energy and particle acceleration. These findings highlight the complex interplay between feedback, guide fields, and reconnection dynamics.

The reported evidence for an isotropic gravitational-wave background (GWB) from pulsar timing array (PTA) collaborations has motivated searches for extrinsic and intrinsic anisotropies. Kinematic anisotropies may arise as a consequence of a boosted observer moving with respect to the frame in which the GWB appears isotropic. In this work, we present an analytical toolbox to describe the effects of kinematic anisotropies on the overlap reduction function. Our analytical results differ from previous findings at the quadrupole order and are detailed in three appendices. For the first time, we also derive the corresponding auto-correlation using two approaches, taking the pulsar distances to be infinite or finite, respectively. Our formulas can be used in forecasts or Bayesian analysis pipelines.

We study the impact of background-induced forces on dark matter (DM) annihilation and their implications for indirect detection. In the presence of a finite number density of background particles, loop-level interactions can generate an effective force that is significantly enhanced relative to the vacuum case. We construct a two-component DM model in which the dominant component is a fermionic particle $\chi$ and the subdominant component is an ultralight pseudoscalar particle $\phi$. The annihilation of $\chi$ proceeds through the p-wave channel and produces gamma-ray emission. The finite density of $\phi$ particles induces a background-enhanced force between $\chi$ particles, leading to a sizable Sommerfeld enhancement of the annihilation. We show that a viable region of parameter space in this model can account for the gamma-ray excess observed in the Galactic Center using Fermi-LAT data. The background-induced force substantially amplifies the Sommerfeld enhancement and thus enlarges the parameter space capable of explaining the excess, highlighting the importance of background effects in astrophysical environments.

We investigate the impact of pressure anisotropy on the structural and geometric properties of neutron stars within general relativity, focusing primarily on the phenomenological Bowers-Liang (BL) model, and comparing selected results with a quasi-local prescription. Using the SLy equation of state, we explore how anisotropic stresses modify global observables such as the mass-radius relation, moment of inertia, compactness, and tidal deformability over a broad range of anisotropy parameters. We find that moderate positive anisotropy can increase the maximum supported mass up to approximately $2.4\;M_\odot$ and enhance stellar compactness by up to $20\%$ relative to isotropic configurations, while remaining broadly consistent with current NICER and gravitational-wave constraints. To probe the internal gravitational field, we compute curvature invariants including the Ricci scalar, the Ricci tensor contraction, the Kretschmann scalar, and the Weyl scalar. We show that curvature measures directly tied to the matter distribution exhibit a strong sensitivity to anisotropy, whereas the Weyl curvature remains comparatively insensitive, reflecting its role as a measure of the free gravitational field. Within the phenomenological BL framework, the maximum compactness increases with anisotropy and reaches values as high as $\mathcal{C}_{\max}\approx 0.25$-$0.38$ for $\lambda_{\rm BL}\in[-4,+4]$, although the physical realizability of such highly compact configurations depends sensitively on the underlying anisotropy mechanism. A comparison with the quasi-local model highlights the strong model dependence of anisotropic effects, underscoring both the potential significance and the limitations of phenomenological anisotropy prescriptions in modeling strong-field neutron-star interiors.

This work presents the Trojan Horse Method (THM) as a powerful technique for measuring nuclear reaction cross sections at astrophysical energies. We then explore the impact of THM-derived reaction rates on the predictions of Standard Big Bang Nucleosynthesis (SBBN) using the PRIMAT code. Primordial abundances are shown for the single rate impact and, for the first time, also for all the THM rates together. The result shows significant differences with the use of THM rates, which in some cases goes in the direction of improving the agreement with the observations with respect to the use of only reaction rates from direct data, especially for the $^7$Li and deuterium abundances, which are still open issues for SBBN.

A theory of cosmic ray production within the solar system (not extra-galactic) is presented. The sun's time variable magnetic flux linkage makes the sun (as well, perhaps, as Jupiter) a natural, all-purpose, betatron storage ring, with semi-infinite acceptance aperture, capable of storing and accelerating counter-circulating, opposite-sign, colliding beams. The puzzle of how positrons and anti-protons can be well represented at all energies, is explained, initially, by the low energy capture of particles of either sign by the sun's magnetic dipole field. Later, as the magnetic field bending has become negligible compared to the gravitational bending, both positive and negative beams will have survived the gradual transition from predominantly magnetic to predominantly gravitational bending. Later, anti-particles produced in QED beam-beam collisions of sufficiently high energy, are also accelerated. The high quality of cosmic ray data collected over recent decades, at steadily increasing energies, especially by the International Space Station (ISS), make the study of cosmic ray production mechanisms both timely and essential. The paper describes how longitudinal electric fields, explained by the Parker solar wind theory can enable the sun to serve as a ``booster'' accelerator of cosmic rays, increasing the maximum cosmic ray energies enough to produce the observed 13 orders of magnitude maximum particle energy and the energy flux needed to maintain the observed cosmic ray atmosphere equilibrium within the solar system. A steady state mechanism is described, based on semi-quantitative discussion of a relativistic Hamilton-Jacobi formalism, according to which the highest energy cosmic rays observed can have been produced by the Parker longitudinal electric field component, during fractionally brief, but periodic, circular or semi-circular turns centered on the sun.

I present some memories of my Ph.D supervisor and, later, collaborator but always encouraging supporter Prof. G. Lazarides. Some of his contributions to our common and related scientific activities on the phenomenology of MSSM and inflation are also summarized.

We study Higgs-like inflation in the framework of scalar-torsion gravity, focusing on the general class of $f(T,\phi)$ theories in which gravitation is mediated by torsion rather than curvature. Motivated by the increasing precision of cosmic microwave background and large-scale-structure observations, we examine whether Higgs-like inflation remains compatible with current data in this extended gravitational setting. Working within the slow-roll approximation, we analyze the inflationary dynamics both analytically and numerically. In the dominant-coupling regime we derive closed-form expressions for the scalar spectral index and the tensor-to-scalar ratio as functions of the number of e-folds, and we subsequently relax this assumption by numerically solving the slow-roll equations. Confrontation with the latest constraints from Planck 2018, ACT DR6, DESI DR1, and BICEP/Keck shows that Higgs-like inflation in $f(T,\phi)$ gravity is fully consistent with current bounds, naturally accommodating the preferred shift in the scalar spectral index and leading to distinctive tensor-sector signatures.

In this study we obtain interior solutions and investigate structural properties of isotropic compact stars in the framework of four-dimensional regularized Einstein-Gauss-Bonnet (4DEGB) gravity. For stellar matter content, we adopt a widely used quark-matter model that approximates a realistic equation of state (EoS). By numerically integrating the modified Tolman-Oppenheimer-Volkoff equations, we obtain interior solutions for static, spherically symmetric fluid spheres. The resulting sequences are compared directly with the predictions of General Relativity (GR). Our analysis focuses on three diagnostic indicators: (i) the mass-radius profiles under GR and three representative choices of the Gauss-Bonnet coupling; (ii) the stellar compactness factor, $C \equiv M/R$; and (iii) the relation between stellar mass and central energy density. Recent observational studies suggest that the maximum masses inferred from the mass-radius relation may be larger than previously expected. To address this, we include a comparative set of constraints from multi-messenger astrophysical observations, including gravitational-wave event GW190814, as well as X-ray measurements from NICER for PSR~J0740+6620 and PSR~J0030+0451. These data provide stringent, astrophysically grounded tests of the viability of the models discussed here. Our results indicate that compact stars within 4DEGB gravity are systematically less compact and achieve moderately higher maximum masses compared to the GR case. This trend is consistent with recent theoretical analyses of compact stars in higher-curvature gravity theories and with constraints from multi-messenger astrophysics. Together, these findings suggest that regularized Gauss-Bonnet corrections constitute a plausible extension of GR in the strong-field regime.

We examine Sommerfeld enhancement in dark matter annihilation as a potential origin of the halo-like gamma-ray excess near $E_\gamma \simeq 20$ GeV reported by Totani. A minimal model with a light CP-even scalar mediator naturally produces a velocity-dependent annihilation cross section consistent with thermal freeze-out, the Milky Way excess, and limits from dwarf spheroidal galaxies.

We calculate the $f$-mode frequency and tidal overlap of quark stars using the full general relativity method. We verify the universal relations obtained from conventional neutron stars in the case of quark stars and explore the cases with different values of parameters of the quark star equation of state. Since quark stars have significantly smaller radii compared to neutron stars in the low mass range, the relation between the tidal defomability and $f$-mode frequency times radius is different for neutron stars and quark stars. This difference has an impact on dynamical tide, which is the lowest-order effect we know of that can distinguish quark stars and neutron stars from the gravitational wave during the inspiral phase. We calculate the tidal dephasing caused by this effect in the post-Newtonian method and find that it can not be detected even by the next-generation gravitational wave detectors.

Gravitational wave echoes offer a unique probe of the near-horizon structure of astrophysical black holes, beyond the standard ''black hole spectroscopy''. Theoretical waveform predictions, however, remain uncertain, motivating robust searches that avoid specific echo modeling. We present a model-independent search framework targeting long-lived quasinormal modes (QNMs) expected from strong interior reflection. By employing a generalized phase-marginalized likelihood that coherently combines data for each QNM across a detector network, our method enhances sensitivity to the signals. To handle real detector noise, we implement an optimized notching procedure to suppress instrumental spectral lines and refine the Bayesian parameter settings. We validate the performance of this framework using injection studies on O1 background data, demonstrating reliable signal recovery in realistic noise conditions. We then apply this method to three binary black hole merger events with high ringdown signal-to-noise ratios (SNR) from observing runs O1 to O4: GW150914, GW231226, and the recently detected GW250114. No statistically significant evidence for postmerger echoes is found. Consequently, we derive 90% upper limits on the network SNR and the average amplitude of the long-lived QNMs, setting the first model-independent constraints on late-time echo signatures from LVK data.

Primordial black holes (PBHs) provide a well-motivated non-particle candidate for dark matter, requiring an enhancement of curvature perturbations on small inflationary scales consistent with observational constraints. In this work we study PBH production within Horndeski gravity, accounting for compatibility with the GW170817 constraint on the gravitational-wave speed and imposing a constant coupling to the Ricci scalar. Under these conditions, and assuming an inflaton field characterised by a canonical kinetic term and a smooth potential, the inflationary dynamics is controlled by the cubic Horndeski interaction. We show that a suitable kinetic dependence of the latter enhances the effective friction acting on the inflaton, inducing a transient ultra-slow-roll phase embedded in an otherwise standard slow-roll evolution. Interestingly, this mechanism amplifies the curvature power spectrum on small scales without introducing any feature in the potential. For representative parameter choices we find that pronounced peaks in the scalar power spectrum are generated, leading to the formation of asteroid-mass PBHs with masses of order $\mathcal{O}(10^{-16})\,M_\odot$, which can account for a substantial fraction of the dark matter abundance, reaching $f_{\rm PBH}\simeq 0.9$, while satisfying current observational constraints. The resulting sharp features in the scalar power spectrum also imply potentially observable scalar-induced gravitational-wave signatures.