Papers for Wednesday, May 29 2024

Gravitational lensing occurs as the path of light from distant celestial bodies is distorted due to gravitational attraction by other celestial bodies, whose mass is partly invisible, being so-called dark matter. When observed through a gravitational lens, distant galaxies appear distorted. A lot of research activity goes into mapping the dark matter in the universe through graviational lensing. However, the mathematical models are complicated, and calculations both time consuming and tideous, if manual. In this paper we discuss how we may combine the Roulette formalism due to Clarkson with machine learning for automatic, local estimation of the lense potential in strong lenses. We also present a framework of open source software for generating datasets and validating results. -- Gravitasjonslinsing er fenomenet der ljos frå fjerne himmellegeme vert avbøygd av tyngdekraften frå andre himmellegeme, som ofte ikkje er fullt synlege fordi mykje av massen er mørk materie. Observert gjennom ei gravitasjonslinse, framstår fjerne galaksar som forvrengde. Der er mykje forskingsaktivitet som freistar å karleggja mørk materie ved å studera linseeffektar, men dei matematiske modellane er kompliserte og utrekningane krev i dag mykje manuelt arbeide som er svært tidkrevjande. I denne artikkelen drøftar me korleis me kan kombinera rouletteformalismen åt Chris Clarkson med maskinlæring for automatisk, lokal estimering av linsepotentialet i sterke linser, og me presenterer eit rammeverk med programvare i open kjeldekode for å generera datasett og validera resultat.

Using data from the Chandra X-Ray Observatory, we revisited the reverse shock in the supernova remnant (SNR) Cassiopeia A.Based on the spectroscopic of a series of annuli in the northwest (NW) and southeast (SE), we get the radial profiles of the S/Si K-alpha line flux ratio and Fe K-alpha line centroid energy. They both show monotonic increase, confirming that the Si- and Fe-rich ejecta are heated by the reverse shock.The abrupt change of the S and Si line flux ratio is clearly observed in Cassiopeia A, leading to the determination of the reverse shock location (~1.71+-0.16 arcmin and ~1.35+-0.18 arcmin in the NW and SE, with respect to the central source). By comparing the radial profiles of S and Si line flux, we find that the reverse shock is moving outward in the frame of the observer, and the velocities are ~3950+-210 km/s and ~2900+-260 km/s in the NW and SE, respectively. In contrast, the velocities become ~1150 km/s (NW) and ~1300 km/s (SE) in the ejecta frame. Our measured reverse shock velocities are quite consistent with those obtained from the X-ray and/or optical images. It therefore supplies a crosscheck of the accuracy for the two available methods to measure the reverse shock velocity in SNRs. Both the location and the velocity of the reverse shock show apparent asymmetry, suggesting that the asymmetric explosion of the progenitor plays a key role in the interaction between the reverse shock and the ejecta, ultimately shaping complex features observed in SNRs.

We empirically assess estimates from v3.0 of the JWST NIRCam Exposure Time Calculator (ETC) using observations of resolved stars in Local Group targets taken as part of the Resolved Stellar Populations Early Release Science (ERS) Program. For bright stars, we find that: (i) purely Poissonian estimates of the signal-to-noise ratio (SNR) are in good agreement between the ETC and observations, but non-ideal effects (e.g., flat field uncertainties) are the current limiting factor in the photometric precision that can be achieved; (ii) source position offsets, relative to the detector pixels, have a large impact on the ETC saturation predictions and introducing sub-pixel dithers in the observation design can improve the saturation limits by up to ~1 mag. For faint stars, for which the sky dominates the error budget, we find that the choice in ETC extraction strategy (e.g., aperture size relative to point spread function size) can affect the exposure time estimates by up to a factor of 5. We provide guidelines for configuring the ETC aperture photometry to produce SNR predictions in line with the ERS data. Finally, we quantify the effects of crowding on the SNRs over a large dynamic range in stellar density and provide guidelines for approximating the effects of crowding on SNRs predicted by the ETC.

The magnetic fields that emerge from beneath the solar surface and permeate the solar atmosphere are the key drivers of space weather and, thus, understanding them is important to human society. Direct observations, used to measure magnetic fields, can only probe the magnetic fields in the photosphere and above, far from the regions the magnetic fields are being enhanced by the solar dynamo. Solar gamma rays produced by cosmic rays interacting with the solar atmosphere have been detected from GeV to TeV energy range, and revealed that they are significantly affected by solar magnetic fields. However, much of the observations are yet to be explained by a physical model. Using a semi-analytic model, we show that magnetic fields at and below the photosphere with a large horizontal component could explain the $\sim$1 TeV solar gamma rays observed by HAWC. This could allow high-energy solar gamma rays to be a novel probe for magnetic fields below the photosphere.

The term 'active galactic nuclei' (AGN) subtends a huge variety of objects, classified on their properties at different wavelengths. Peaked sources (PS) represent a class of AGN at the first stage of evolution, characterised by a peaked radio spectrum. Among these radio sources, low-luminosity compact (LLC) sources can be identified as PS accreting with a high Eddington rate, harbouring low-power jets and hosting low-mass black holes. These properties are also shared by narrow-line Seyfert 1 galaxies (NLS1s). In 2016, LLCs were hypothesised to be the parent population of NLS1s with a flat radio spectrum (F-NLS1s), suggesting the former to be the same objects as the latter, seen at higher inclination. Based on radio luminosity functions and optical spectra analysis, 10 LLCs were identified as valid candidates for F-NLS1s. To account for the missing puzzle piece, verifying if these LLCs could be hosted in late-type galaxies as NLS1s, we performed the photometric decomposition of their Pan-STARRS1 images in all five filters. We used the 2D fitting algorithm GALFIT for the single-band analysis, and its extension GALFITM for the multi-band analysis. Considering that the morphological type and the structural parameters of the host can be dependent on the wavelength, we found six out of ten LLCs hosted in late-type galaxies, probably with pseudo-bulges, three point-like sources and one object of uncertain classification. Although this study is based on a small sample, it represents the first morphological analysis of LLC host galaxies. The results confirm the trend observed in NLS1s, indicating late-type/disc-like host galaxies for LLCs and supporting the validity of the parent population scenario.

Models of interacting dark radiation have been shown to alleviate the Hubble tension. Extensions incorporating a coupling between dark matter and dark radiation (DM-DR) have been proposed as combined solutions to both the Hubble and $S_8$ tensions. A key feature of these extended models is a break in the matter power spectrum (MPS), suppressing power for modes that enter the horizon before the DM-DR interactions turn off. In scenarios with a massless mediator, modes that enter before matter-radiation equality get suppressed, whereas for massive mediators, the break is determined by the mediator mass, a free parameter. In this work, we test these models against probes of LSS: weak lensing, CMB lensing, full-shape galaxy clustering, and eBOSS measurements of the 1D Ly$\alpha\,$ forest flux power spectrum. The latter are the most constraining since they probe small scales where many models predict the largest deviations. In fact, already within $\Lambda{\rm CDM}\,$, the eBOSS Ly$\alpha\,$ data are in significant tension with Planck CMB data, with the Ly$\alpha\,$ data preferring a steeper slope of the MPS at $k \sim h \mathrm{Mpc}^{-1}$. We find that the simplest dark radiation models, which improve the Hubble tension, worsen the fit to the Ly$\alpha\,$ data. However, models with DM-DR interactions can simultaneously address both tensions.

The discovery of a kilonova associated with the GW170817 binary neutron star merger had far-reaching implications for our understanding of several open questions in physics and astrophysics. Unfortunately, since then, only one robust binary neutron star merger was detected through gravitational waves, GW190425, and no electromagnetic counterpart was identified for it. We analyze all reported electromagnetic followup observations of GW190425 and find that while the gravitational-wave localization uncertainty was large, most of the 90% probability region could have been covered within hours had the search been coordinated. Instead, more than 5 days after the merger, the uncoordinated search covered only 50% of the probability, with some areas observed over 100 times, and some never observed. We further show that, according to some models, it would have been possible to detect the GW190425 kilonova, despite the larger distance and higher component masses compared to GW170817. These results emphasize the importance of coordinating followup of gravitational-wave events, not only to avoid missing future kilonovae, but also to discover them early. Such coordination, which is especially important given the rarity of these events, can be achieved with the Treasure Map, a tool developed specifically for this purpose.

We present optical follow-up of IGR J16194-2810, a hard X-ray source discovered by the INTEGRAL mission. The optical counterpart is a $\sim500\,L_\odot$ red giant at a distance of $2.1$ kpc. We measured 16 radial velocities (RVs) of the giant over a period of $\sim 300$ days. Fitting these RVs with a Keplerian model, we find an orbital period of $P_{\rm orb} = 192.73 \pm 0.01$ days and a companion mass function $f(M_2) = 0.361 \pm 0.005 \,M_{\odot}$. We detect ellipsoidal variability with the same period in optical light curves from the ASAS-SN survey. Joint fitting of the RVs, light curves, and the broadband SED allows us to robustly constrain the masses of both components. We find a giant mass of $M_\star = 1.02\pm 0.01\,M_{\odot}$ and a companion mass of $M_{2} = 1.35^{+0.09}_{-0.07}\,M_{\odot}$, implying that the companion is a neutron star (NS). We recover a $4.06$-hour period in the system's TESS light curve, which we tentatively associate with the NS spin period. The giant does not yet fill its Roche lobe, suggesting that current mass transfer is primarily via winds. MESA evolutionary models predict that the giant will overflow its Roche lobe in $5$-$10$ Myr, eventually forming a recycled pulsar + white dwarf binary with a $\sim 900$ day period. IGR J16194-2810 provides a window on the future evolution of wide NS + main sequence binaries recently discovered via Gaia astrometry. As with those systems, the binary's formation history is uncertain. Before the formation of the NS, it likely survived a common envelope episode with a donor-to-accretor mass ratio $\gtrsim 10$ and emerged in a wide orbit. The NS likely formed with a weak kick ($v_{\rm kick}\lesssim 100\,\rm km\,s^{-1}$), as stronger kicks would have disrupted the orbit.

Massive stars in the red supergiant (RSG) phase are known to undergo strong mass loss through winds and observations indicate that a substantial part of this mass loss could be driven by localised and episodic outflows. Various mechanisms have been considered to explain this type of mass loss in RSGs, but these models often focus on single-star evolution. However, massive stars commonly evolve in binary systems, potentially interacting with their companions. Motivated by observations of the highly asymmetric circumstellar ejecta around the RSG VY~CMa, we investigate a scenario where a companion on an eccentric orbit grazes the surface of a red supergiant at periastron. The companion ejects part of the outer RSG envelope, which radiatively cools, reaching the proper conditions for dust condensation and eventually giving rise to dust-driven winds. Using simple treatments for radiative cooling and dust-driven winds, we perform 3D smoothed particle hydrodynamics simulations of this scenario with a $20\,M_\odot$ RSG and a $2\,M_\odot$ companion. We follow the evolution of the binary throughout a total of 14 orbits and observe that the orbit tightens after each interaction, in turn enhancing the mass loss of subsequent interactions. We show that one such grazing interaction yields outflows of $3\times10^{-4}\,M_\odot$, which later results in wide asymmetric dusty ejecta, carrying a total mass of $0.185\,M_\odot$ by the end of simulations. We discuss the implications for the evolution of the binary, potential observational signatures, as well as future improvements of the model required to provide sensible predictions for the evolution of massive binaries.

Different models of dark matter can alter the distribution of mass in galaxy clusters in a variety of ways. However, so can uncertain astrophysical feedback mechanisms. Here we present a Machine Learning method that ''learns'' how the impact of dark matter self-interactions differs from that of astrophysical feedback in order to break this degeneracy and make inferences on dark matter. We train a Convolutional Neural Network on images of galaxy clusters from hydro-dynamic simulations. In the idealised case our algorithm is 80% accurate at identifying if a galaxy cluster harbours collisionless dark matter, dark matter with ${\sigma}_{\rm DM}/m = 0.1$cm$^2/$g or with ${\sigma}_{DM}/m = 1$cm$^2$/g. Whilst we find adding X-ray emissivity maps does not improve the performance in differentiating collisional dark matter, it does improve the ability to disentangle different models of astrophysical feedback. We include noise to resemble data expected from Euclid and Chandra and find our model has a statistical error of < 0.01cm$^2$/g and that our algorithm is insensitive to shape measurement bias and photometric redshift errors. This method represents a new way to analyse data from upcoming telescopes that is an order of magnitude more precise and many orders faster, enabling us to explore the dark matter parameter space like never before.

A wide range of astrophysical sources exhibit extreme and rapidly varying electromagnetic emission indicative of efficient non-thermal particle acceleration. Understanding these sources often involves comparing data with a broad range of theoretical scenarios. To this end, it is beneficial to have tools that enable not only fast and efficient parametric investigation of the predictions of a specific scenario but also the flexibility to explore different theoretical ideas. In this paper, we introduce \texttt{Tleco}, a versatile and lightweight toolkit for developing numerical models of relativistic outflows, including their particle acceleration mechanisms and resultant electromagnetic signature. Built on the Rust programming language and wrapped into a Python library, \texttt{Tleco} offers efficient algorithms for evolving relativistic particle distributions and for solving the resulting emissions in a customizable fashion. \texttt{Tleco} uses a fully implicit discretization algorithm to solve the Fokker-Planck (FP) equation with user-defined diffusion, advection, cooling, injection, and escape, and offers prescriptions for radiative emission and cooling. These include, but are not limited to, synchrotron, inverse-Compton, and self-synchrotron absorption. \texttt{Tleco} is designed to be user-friendly and adaptable to model particle acceleration and the resulting electromagnetic spectrum and temporal variability in a wide variety of astrophysical scenarios, including, but not limited to, gamma-ray bursts, pulsar wind nebulae, and jets from active galactic nuclei. In this work, we outline the core algorithms and proceed to evaluate and demonstrate their effectiveness. The code is open-source and available in the GitHub repository: \href{this https URL

Eventual presence of diamond carbon allotrope in space is discussed in numerous theoretical and experimental studies. The review summarises principal mechanisms of nanodiamond formation and experimental results of spectroscopic and structural investigations of nano- and microdiamonds extracted from meteorites. Size dependence of diamond spectroscopic properties is discussed. Infrared spectroscopy allows detection of C-H bonds on surfaces of hot nanodiamond grains. Spectroscopic observation of nitrogen-related point defects in nanodiamonds is very challenging; moreover, such defects were never observed in nanodiamonds from meteorites. At the same time, photoluminescence and, eventually, absorption, of some impurity-related defects, in particular, of silicon-vacancy (SiV) center, observed in real meteoritic nanodiamonds, opens a possibility of diamond detection in astronomical observations.

The spin evolution of stars in close binary systems can be strongly affected by tides. We investigate the rotational synchronisation of the stellar components for 69 SB1 systems and 14 SB2 B-type systems in the 30 Doradus region of the Large Magellanic Cloud using observations from the VFTS and BBC surveys. Their orbital periods range from a few to a few hundred days, while estimated primary masses for these systems are in the range 5-20 Msun with mass ratio ranges of approximately q=0.03-0.5 and q=0.6-1.0 for the SB1 and SB2 systems, respectively. Projected rotational velocities of the stellar components have been compared with their synchronous velocities derived from the orbital periods. We find that effectively all systems with orbital period of more than 10 days must be asynchronous, whilst all the systems with periods of less than 3 days are likely synchronised. In terms of the stellar fractional radius (r), our results imply that all systems with r<0.1 are asynchronous, with those having r>0.2 probably being synchronised. For the apparently synchronised systems our results are more consistent with synchronisation at the mean orbital angular velocity rather than with that at periastron.

An electron-multiplying charge-coupled device (EMCCD) is often used for taking images with space telescopes and other devices. Photons hit the pixels and photo-electrons are created, and these are multiplied via impact ionization as they travel through the gain register from one gain stage to the next. A high gain means a high multiplication factor, and this is achieved through a high voltage difference across a gain stage. If the gain is high enough, the chance of clock-induced charge production in the gain register increases. The probability distribution function governing the gain process in the literature only accounts for charge multiplication if one or more electrons enters the gain register. I derive from first principles the modified probability distribution that accounts for clock-induced charge production in the gain register. I also examine some EMCCD data and show through maximum likelihood estimation that the data conform better to the modified distribution versus the usual one in the literature. The use of the modified distribution would in principle improve the accuracy of signal extraction from a frame.

Gamma Ray Bursts (GRBs) bridge relativistic astrophysics and multi-messenger astronomy. Space-based gamma/X-ray wide field detectors have proven essential to detect and localize the highly variable GRB prompt emission, which is also a counterpart of gravitational wave events. We study the capabilities to detect long and short GRBs by the High Energy Rapid Modular Ensemble of Satellites (HERMES) Pathfinder (HP) and SpIRIT, namely a swarm of six 3U CubeSats to be launched in early 2025, and a 6U CubeSat launched on December 1st 2023. We also study the capabilities of two advanced configurations of swarms of >8 satellites with improved detector performances (HERMES Constellations). The HERMES detectors, sensitive down to ~2-3 keV, will be able to detect faint/soft GRBs which comprise X-ray flashes and high redshift bursts. By combining state-of-the-art long and short GRB population models with a description of the single module performance, we estimate that HP will detect ~195^{+22}_{-21} long GRBs (3.4^{+0.3}_{-0.8} at redshift z>6) and ~19^{+5}_{-3} short GRBs per year. The larger HERMES Constellations under study can detect between ~1300 and ~3000 long GRBs per year and between ~160 and ~400 short GRBs per year, depending on the chosen configuration, with a rate of long GRBs above z>6 between 30 and 75 per year. Finally, we explore the capabilities of HERMES to detect short GRBs as electromagnetic counterparts of binary neutron star (BNS) mergers detected as gravitational signals by current and future ground-based interferometers. Under the assumption that the GRB jets are structured, we estimate that HP can provide up to 1 (14) yr^{-1} joint detections during the fifth LIGO-Virgo-KAGRA observing run (Einstein Telescope single triangle 10 km arm configuration). These numbers become 4 (100) yr^{-1}, respectively, for the HERMES Constellation configuration.

Looking at the well-known Hubble tension as a tension in the calibrators of the cosmic distance ladder, i.e. the absolute magnitude $M$ of standard candles such as supernovae of Type Ia (SNIa) and the standard ruler represented by the comoving sound horizon at the baryon-drag epoch, $r_d$, we propose a model-independent method to measure these distance calibrators independently from the cosmic microwave background and the first rungs of the direct distance ladder. To do so, we leverage state-of-the-art data on cosmic chronometers (CCH), SNIa and baryon acoustic oscillations (BAO) from various galaxy surveys. Taking advantage of the Gaussian Processes Bayesian technique, we reconstruct $M(z)$, $\Omega_k(z)$ and $r_d(z)$ at $z\lesssim2$ and check that no significant statistical evolution is preferred at 68\% C.L. This allows us to treat them as constants and constrain them assuming the metric description of gravity, the cosmological principle and the validity of CCH as reliable cosmic clocks, and SNIa and BAO as optimal standard candles and standard rulers, respectively, but otherwise in a model-independent way. We obtain: $\Omega_k=-0.07^{+0.12}_{-0.15}$, $M=(-19.314^{+0.086}_{-0.108})$ mag and $r_d=(142.3\pm 5.3)$ Mpc. At present, the uncertainties derived are still too large to arbitrate the tension but this is bound to change in the near future with the advent of upcoming surveys and data.

White dwarfs (WDs) polluted by exoplanetary material provide the unprecedented opportunity to directly observe the interiors of exoplanets. However, spectroscopic surveys are often limited by brightness constraints, and WDs tend to be very faint, making detections of large populations of polluted WDs difficult. In this paper, we aim to increase considerably the number of WDs with multiple metals in their atmospheres. Using 96,134 WDs with Gaia DR3 BP/RP (XP) spectra, we constructed a 2D map using an unsupervised machine learning technique called Uniform Manifold Approximation and Projection (UMAP) to organize the WDs into identifiable spectral regions. The polluted WDs are among the distinct spectral groups identified in our map. We have shown that this selection method could potentially increase the number of known WDs with 5 or more metal species in their atmospheres by an order of magnitude. Such systems are essential for characterizing exoplanet diversity and geology.

We present new Chandra X-ray observations of TAP 26, a ~17 Myr old magnetically-active weak-lined T Tauri star that has been reported to host a massive planet in a 10.8 day orbit. At a separation of a = 0.097 AU the planet will be exposed to intense X-ray and UV radiation from the star. The first observation caught the star in a state of elevated X-ray emission with variability on a timescale of a few hours and an X-ray temperature kTx ~ 2 - 4 keV. Two subsequent observations 5-10 days later showed slow variability and a lower X-ray flux and temperature (kTx ~ 1 keV). We characterize the X-ray emission and estimate the X-ray ionization and heating rates that will need to be incorporated into realistic models of the planet's atmosphere.

We present a new simulated galaxy cluster catalog based on the IllustrisTNG simulation. We use the Mulguisin (MGS) algorithm to identify galaxy overdensities. Our cluster identification differs from the previous FoF cluster identification in two aspects; 1) we identify cluster halos based on the galaxy subhalos instead of unobservable dark matter particles, and 2) we use the MGS algorithm that separates galaxy overdensities hosted by massive galaxies. Our approach provides a cluster catalog constructed similar to the observed cluster catalogs using spectroscopic surveys. The MGS cluster catalog lists 303 halos with M$_{200} > 10^{14}$ M$_{\odot}$, including $\sim 10\%$ more than the FoF. The MGS catalog includes more systems because we separate some independent massive MGS cluster halos that are bundled into a single FoF algorithm. These independent MGS halos are apparently distinguishable in galaxy spatial distribution and the phase-space diagram. Because we constructed a refined cluster catalog that identifies local galaxy overdensities, we evaluate the effect of MGS clusters on the evolution of galaxies better than using the FoF cluster catalog. The MGS halo identification also enables effective identifications of merging clusters by selecting systems with neighboring galaxy overdensities. We thus highlight that the MGS cluster catalog is a useful tool for studying clusters in cosmological simulations and for comparing with the observed cluster samples.

The redshifted 21 cm line signal is a powerful probe of the cosmic dawn and the epoch of reionization. The global spectrum can potentially be detected with a single antenna and spectrometer. However, this measurement requires an extremely accurate calibration of the instrument to facilitate the separation of the 21 cm signal from the much brighter foregrounds and possible variations in the instrument response. Understanding how the measurement errors propagate in a realistic instrument system and affect system calibration is the focus of this work. We simulate a 21 cm global spectrum observation based on the noise wave calibration scheme. We focus on how measurement errors in reflection coefficients affect the noise temperature and how typical errors impact the recovery of the 21 cm signal, especially in the frequency domain. Results show that for our example set up, a typical vector network analyzer (VNA) measurement error in the magnitude of the reflection coefficients of the antenna, receiver, and open cable, which are 0.001, 0.001, and 0.002 (linear), respectively, would result in a 200 mK deviation on the detected signal, and a typical measurement error of 0.48 degree, 0.78 degree, or 0.15 degree in the respective phases would cause a 40 mK deviation. The VNA measurement error can greatly affect the result of a 21 cm global spectrum experiment using this calibration technique, and such a feature could be mistaken for or be combined with the 21 cm signal

The details of the dynamo process in the Sun are an important aspect of research in solar-terrestrial physics and astrophysics. The surface part of the dynamo can be constrained by direct observations, but the subsurface part lacks direct observational constraints. The torsional oscillations, a small periodic variation of the Sun's rotation with the solar cycle, are thought to result from the Lorentz force of the cyclic magnetic field generated by the dynamo. In this study, we aim to discriminate between three Babcock-Leighton (BL) dynamo models by comparing the zonal acceleration of the three models with the observed one. The property that the poleward and equatorward branches of the torsional oscillations originate from about $\pm 55^\circ$ latitudes with their own migration time periods serves as an effective discriminator that could constrain the configuration of the magnetic field in the convection zone. The toroidal field, comprising poleward and equatorward branches separated at about $\pm 55^\circ$ latitudes can generate the two branches of the torsional oscillations. The alternating acceleration and deceleration bands in time is the other property of the torsional oscillations that discriminate between the dynamo models. To reproduce this property, the phase difference between the radial ($B_{r}$) and toroidal ($B_{\phi}$) components of the magnetic field near the surface should be about $\pi/2$.

Identifying sources exhibiting ellipsoidal variability in large photometric surveys is becoming a promising method to search for candidate detached black holes in binaries. This technique aims to exploit the orbital-phase dependent modulation in optical photometry caused by the black hole distorting the shape of the luminous star to constrain the mass ratio of the binary. Without understanding if, or how much, contamination is present in the candidate black hole samples produced by this new technique it is hard to leverage them for black hole discovery. Here, we follow up one of the best candidates identified from Gaia Data Release 3, Gaia DR3 4042390512917208960, with a radial velocity campaign. Combined photometric and radial velocity modelling, along with spectral disentangling, suggests that the true mass ratio (mass of the unseen object divided by the mass of the luminous star) is an order of magnitude smaller than that inferred assuming the modulations arise from ellipsoidal variability. We therefore infer that this system is likely a contact binary, or on the boundary of both stars nearly filling their Roche lobes, however, further observations are required to confidently detect the secondary. We find that the well-known problem of discriminating between ellipsoidal and contact binary light curves results in a larger contamination from contact binaries than previously suggested. Until ellipsoidal variables can be reliably distinguished from contact binaries, samples of black hole candidates selected based on ellipsoidal variability are likely to be highly contaminated by contact binaries or similar systems.

Owing to the broad energy coverage of Insight-HXMT in the hard X-ray band, we detected the highest energy of pulsation exceeding 200 keV around the 2017-2018 outburst peak of the first Galactic pulsating ultraluminous X-ray source (PULX) Swift J0243.6+6124, which is the highest energy detected from PULXs to date. We also obtained the highest energy of pulsation of every exposure during the outburst in 2017-2018, and found the highest energy is roughly positively correlated with luminosity. Using our newly developed method, we identified the critical luminosity being $4\times 10^{38}\, \rm erg\,s^{-1}$ when the main peaks of the low and high energy pulse profiles became aligned, which separates the fan-beam dominated and pencil-beam dominated accretion regimes. Above the critical luminosity, the phase of the main peak shifted gradually from 0.5 to 0.8 until the outburst peak in all energy bands is reached, which is in agreement with the phase shift found previously at low energies. Our result is consistent with what is derived from spectral analysis.

Context. About 25% -- 50% of white dwarfs are found to be contaminated by heavy elements, which are believed to originate from external sources such as planetary materials. Elemental abundances suggest that most of the pollutants are rocky objects and only a small fraction of white dwarfs bear traces of volatile accretion. Aims. In order to account for the scarcity of volatile pollution, we investigate the role of the white dwarfs' magnetospheres in shielding the volatile content of icy objects. Methods. We estimated the volatile sublimation of inward-drifting exocomets. We assume the orbits of the exocomets are circularized by the Alfven wing drag that is effective for long-period comets. Results. Volatile material can sublimate outside the corotation radius and be shielded by the magnetic field. {The two conditions for this volatile-shielded mechanism are that the magnetosphere radius must be larger than the corotation radius and that the volatiles are depleted outside the corotation radius, which requires a sufficiently slow orbital circularization process.} We applied our model to nine white dwarfs with known rotational periods, magnetic fields, and atmosphere compositions. Our volatile-shielded model may explain the excess of volatile elements such as C and S in the disk relative to the white dwarf atmosphere in WD2326+049 (G29-38). Nevertheless, given the sensitivity of our model to the circularization process and material properties of icy objects, there remains considerable uncertainty in our results. Conclusions. Our work suggests a possible explanation for the scarcity of volatile-accretion signatures among white dwarfs. We also identify a correlation between the magnetic field strength, the spin period, and the composition of pollutants in white dwarf atmospheres.

Gravitational radiation alone is not efficient in hardening the orbit of a wide binary black hole (BBH). By employing a toy model for the interstellar medium (ISM) surrounding BBHs, here we discuss the effect of this baryonic medium on BBH dynamics. Depending on the BBH's mass, we show that a binary surrounded by an isotropic cold neutral medium (i.e., an asymptotic temperature $T_{\infty} \approx 100$ K) with a time-averaged particle density of $\langle n_H \rangle = \mathcal{O}(1)$ cm$^{-3}$ can play a significant role in hardening the binary orbit over a $\mathcal{O}(10^9)$ yr time scale. Additionally, this causes the black hole's mass to grow at a rate $\propto m^2$. We thus discuss the impact of the ISM on the LIGO-Virgo-KAGRA (LVK) observables and quantify the properties of the ISM under which the latter could act as an additional important pathway for driving a subset of LVK's BBH mergers.

Binary systems made by a low-mass CO WD and a He-donor represent possible progenitors of explosive events via He-detonation, producing low-luminosity thermonuclear Supernovae with a peculiar nucleosynthetis. Recently, the binary system PTF J223857.11+743015.1 has been suggested as one. We investigate the evolution of the PTF J223857.11+743015.1 system, composed by a 0.75Msun CO WD and a 0.390Msun subdwarf, capped by a thin H-rich layer, considering rotation of the WD component. We compute the evolution of two stars simultaneously, accounting for the possible evolution of the orbital parameters, as determined by mass transfer between components and by mass ejection from the system during RLOF episodes. We consider that the WD gains angular momentum due to accretion and we follow the evolution of the angular velocity profile as due to angular momentum transport via convection and rotation-induced instabilities. As the donor H-rich envelope is transferred, the WD experiences recurrent very strong H-flashes triggering RLOF episodes during which the entire accreted matter is lost from the system. Due to mixing of chemicals by rotation-induced instabilities during the accretion phase, H-flashes occur inside the original WD. Hence, pulse-by pulse, the accretor mass is reduced down to 0.7453Msun. When He-rich matter is transferred, He-detonation does not occur in the rotating WD, which undergoes 6 very strong He-flashes and subsequent RLOF episodes. Also in this case, due to rotation-induced mixing of the accreted layers with the underlying core, the WD is eroded. Finally, when the mass transfer rate from the donor decreases, a massive He-buffer is piled-up onto the accretor which ends its life as a cooling WD. The binary system PTF J2238+743015.1 as all those binaries having similar components masses and orbital parameters are not good candidates as thermonuclear explosions progenitors.

We present a pipeline to infer the equation of state of neutron stars from observations based on deep neural networks. In particular, using the standard (deterministic), as well as Bayesian (probabilistic) deep networks, we explore how one can infer the interior speed of sound of the star given a set of mock observations of total stellar mass, stellar radius and tidal deformability. We discuss in detail the construction of our simulated dataset of stellar observables starting from the solution of the gravitational equations, as well as the relevant architectures for the deep networks, along with their performance and accuracy. We further explain how our pipeline is capable to detect a possible QCD phase transition in the stellar core. Our results show that deep networks offer a promising tool towards solving the inverse problem of neutron stars, and the accurate inference of their interior from future stellar observations.

The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both $\textit{light}$ and $\textit{heavy}$ seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between $\textit{light}$ and $\textit{heavy}$ seeds with $\textit{light}$ at one end and $\textit{heavy}$ at the other that instead a continuum exists. $\textit{Light}$ seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the $\textit{heaviest}$ seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that $\textit{light}$ seeds must be at least $10^{3}$ to $10^{5}$ times more numerous than $\textit{heavy}$ seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes $\textit{heavy}$ seeds ($\rm{M_{seed}} > 10^3$ M$_{\odot}$) a significantly more likely pathway given that $\textit{heavy}$ seeds have an abundance pattern than is close to and likely in excess of $10^{-4}$ compared to $\textit{light}$ seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.

One of the biggest challenges in understanding Magnetohydrodynamic (MHD) turbulence is identifying the plasma mode components from observational data. Previous studies on synchrotron polarization from the interstellar medium (ISM) suggest that the dominant MHD modes can be identified via statistics of Stokes parameters, which would be crucial for studying various ISM processes such as the scattering and acceleration of cosmic rays, star formation, dynamo. In this paper, we present a numerical study of the Synchrotron Polarization Analysis (SPA) method through systematic investigation of the statistical properties of the Stokes parameters. We derive the theoretical basis for our method from the fundamental statistics of MHD turbulence, recognizing that the projection of the MHD modes allows us to identify the modes dominating the energy fraction from synchrotron observations. Based on the discovery, we revise the SPA method using synthetic synchrotron polarization observations obtained from 3D ideal MHD simulations with a wide range of plasma parameters and driving mechanisms, and present a modified recipe for mode identification. We propose a classification criterion based on a new SPA+ fitting procedure, which allows us to distinguish between Alfvén mode and compressible/slow mode dominated turbulence. We further propose a new method to identify fast modes by analyzing the asymmetry of the SPA+ signature and establish a new asymmetry parameter to detect the presence of fast mode turbulence. Additionally, we confirm through numerical tests that the identification of the compressible and fast modes is not affected by Faraday rotation in both the emitting plasma and the foreground.

Coronal Mass Ejections (CMEs) are the main drivers of the disturbances in interplanetary space. Understanding the CME interior magnetic structure is crucial for advancing space weather studies. Assessing the capabilities of a numerical heliospheric model is crucial, as understanding the nature and extent of its limitations can be used for improving the model and the space weather predictions based on it. The present paper aims to test the capabilities of the recently developed heliospheric model Icarus and the linear force-free spheromak model that has been implemented in it. To validate the Icarus space weather modeling tool, two CME events were selected that were observed by two spacecraft located near Mercury and Earth, respectively. This enables testing the heliospheric model computed with Icarus at two distant locations. The source regions for the CMEs were identified, and the CME parameters were determined and later optimized. Different adaptive mesh refinement levels were applied in the simulations to assess its performance by comparing the simulation results to in-situ measurements. The first CME event erupted on SOL2013-07-09T15:24. The modeled time series were in good agreement with the observations both at MESSENGER and ACE. The second CME event started on SOL2014-02-16T10:24 and was more complicated, as three CME interactions occurred in this event. It was impossible to recover the observed profiles without modeling the other two CMEs that were observed, one before the main CME and one afterward. For both CME studies, AMR level 3 was sufficient to reconstruct small-scale features near Mercury, while at Earth, AMR level 4 was necessary due to the radially stretched grid that was used.

Since molecules are ubiquitous in space, the study of the 'Molecular Universe' could unfold the mystery of the existing Interstellar medium. Star formation is linked to the chemical evolution processes. Thus, an analysis of the formation of stars coupled with the chemical evolution would give a clear insight into the entire process. For example, various evolutionary stages of star formation could be probed by observing various molecules. Chemical diagnostics of these regions could be used to extract the physical properties (e.g., density, temperature, ionization degree, etc.) of these regions. Radiative transfer calculations are worthwhile in estimating physical parameters of the region where molecules are detected. However, the radiative transfer calculations are limited due to insufficient molecular data, such as spectroscopic information or collisional excitation probabilities of many interstellar species. Complex organic molecules are detected in various environments ranging from the cold gas in prestellar cores to the warm gas on solar system scales close to individual protostars. A comparative study of the relative abundances of molecules could provide insights into the beginning of chemical complexity and the link to our solar system. In my thesis, I would mainly investigate the physical properties and kinematics of different star-forming regions using radiative transfer modeling. The observed spatial differentiation between various key molecules is used to explain their physical structure or evolution and various microphysical effects. In addition, some key molecules are used to study the various evolutionary phases. This simulated data is useful for interpreting the observed data of different telescopes like IRAM 30m, GBT, ALMA, Herschel, SOFIA, etc.

We studied the influence of a massive star on a mid-infrared bubble and its surrounding gas in the IRAS\,16489-4431 star-forming region using multi-wavelength data. The {\it Spitzer} mid-infrared band images revealed the shocked nature of the bubble. Analyses showed that the bubble is developed by a massive star owing to its strong radiation pressure. Evidence of collected material along the edge of the bubble was noted by the cold gas tracer line observed using Atacama Millimeter/submillimeter Array (ALMA). The presence of dense dust cores with bi-polar outflows and young stellar objects toward the collected material is suggestive of active star formation possibly influenced by the expansion of the radiation driven bubble.

Edge-on galaxies act as the best laboratories to understand the origin of thin and thick discs in galaxies. Measurement of spatially resolved stellar population properties in such galaxies, particularly age, metallicity and [$\alpha$/Fe], are crucial to understanding the formation and evolution of disc galaxies. Such measurements are made possible from stellar population model fits to deep integral field spectroscopic (IFU) observations of resolved galaxies. We utilise archival MUSE IFU observations of the edge-on galaxy ESO 544-27 to uncover the formation history of its thin and thick discs through its stellar populations. We find the thin disc of the galaxy is dominated by an old ($>9$ Gyr) low [$\alpha$/Fe] metal-rich stellar population. Its outer thick disc is dominated by an old ($>9$ Gyr) high [$\alpha$/Fe] metal-rich component that should have formed with higher star-formation efficiency than the Milky Way thick disc. We thus find [$\alpha$/Fe] dichotomy in ESO 544-27 with its thin and thick discs dominated by low and high [$\alpha$/Fe] stellar populations respectively. However, we also find a metal-rich younger ($<2$ Gyr old) stellar population in ESO 544-27. The galaxy was nearly quenched until its star-formation was reignited recently first in the outer and inner thick disc ($\sim$1 Gyr ago) and then in the thin disc ($\sim$600 Myr ago). We thus find that both the low [$\alpha$/Fe] thin and high [$\alpha$/Fe] thick discs of ESO 544-27 are inhabited primarily by similarly old metal-rich stellar populations, a contrast to that of other galaxies with known thin and thick disc stellar population properties.

Ground-based large-aperture telescopes, interferometers, and future Extremely Large Telescopes equipped with adaptive-optics systems provide angular resolution and high-contrast performance that are superior to space-based telescopes at thermal-infrared wavelengths. Their sensitivity, however, is critically limited by the high thermal background inherent to ground-based observations in this wavelength regime. We aim to improve the subtraction quality of the thermal-infrared background from ground-based observations, using Principal Component Analysis (PCA). We use data obtained with the Nulling-Optimized Mid-Infrared Camera on the Large Binocular Telescope Interferometer as a proxy for general high-sensitivity, AO-assisted ground-based data. We apply both a classical background subtraction -- using the mean of dedicated background observations -- and a new background subtraction based on a PCA of the background observations. We compare the performances of these two methods in both high-contrast imaging and aperture photometry. Compared to the classical background subtraction approach, PCA background subtraction delivers up to two times better contrasts down to the diffraction limit of the LBT's primary aperture (i.e., 350 mas in N band), that is, in the case of high-contrast imaging. Improvement factor between two and three are obtained over the mean background retrieval within the diffraction limit in the case of aperture photometry. PCA background subtraction significantly improves the sensitivity of ground-based thermal-infrared imaging observations. When applied to LBTI's nulling interferometry data, we expect the method to improve the sensitivity by a similar factor 2-3. This study paves the way to maximising the potential of future infrared ground-based instruments and facilities, such as the future 30m-class telescopes.

[Abridged] In recent years, conflicting results have provided an uncertain view of the dust-attenuated properties of $z>4$ star-forming galaxies (SFGs). To solve this, we used the deepest data publicly available in COSMOS to build a mass-complete ($>10^{9.5}\,M_{\odot}$) sample of SFGs at $4<z<5$ and measured their dust-attenuated properties by stacking all archival ALMA band 6 and 7 observations available. Combining this information with their rest-frame ultraviolet emission from the COSMOS2020 catalog, we constrained the IRX ($\equiv L_{\rm IR}/L_{\rm UV}$)--$\beta_{\rm UV}$, IRX--$M_\ast$, and SFR--$M_\ast$ relations at $z\sim4.5$. Finally, using these relations and the stellar mass function of SFGs at $z\sim4.5$, we inferred the unattenuated and dust-attenuated SFRD at this epoch. SFGs at $z\sim4.5$ follow an IRX--$\beta_{\rm UV}$ relation that is consistent with that of local starbursts, while they follow a steeper IRX--$M_\ast$ relation than observed locally. The grain properties of dust in these SFGs seems thus similar to those in local starbursts but its mass and geometry result in lower attenuation in low-mass SFGs. SFGs at $z\sim4.5$ lie on a linear SFR--$M_\ast$ relation, whose normalization varies by 0.3 dex, when we exclude or include from our stacks the ALMA primary targets. The cosmic SFRD$(>M_\ast)$ converges at $M_\ast<10^{9}\,M_\odot$ and is dominated by SFGs with $M_\ast\sim10^{9.5-10.5}\,M_\odot$. The fraction of the cosmic SFRD that is attenuated by dust, ${\rm SFRD}_{\rm IR}(>M_\ast)/ {\rm SFRD}(>M_\ast)$, is $90\pm4\%$ for $M_\ast\,=\,10^{10}\,M_\odot$, $68\pm10\%$ for $M_\ast=10^{8.9}\,M_\odot$ (i.e., $0.03\times M^\star$; $M^\star$ being the characteristic stellar mass of SFGs) and this value converges to $60\pm10\%$ for $M_\ast=10^{8}\,M_\odot$. Even at this early epoch, the fraction of the cosmic SFRD that is attenuated by dust remains thus significant.

We consider the motion of a circularly-moving perturber in a self-gravitating, collisional system with spherically symmetric density profile. We concentrate on the singular isothermal sphere which, despite its pathological features, admits a simple polarization function in linear response theory. This allows us to solve for the acoustic wake trailing the perturber and the resulting dynamical friction, in the limit where the self-gravity of the response can be ignored. In steady-state and for subsonic velocities $v_p<c_s$, the dynamical friction torque $F_\varphi\propto v_p^3$ is suppressed for perturbers orbiting in an isothermal sphere relative to the infinite, homogeneous medium expectation $F_\varphi\propto v_p$. For highly supersonic motions, both expectations agree and are consistent with a local approximation to the gravitational torque. At fixed resolution (a given Coulomb logarithm), the response of the system is maximal for Mach numbers near the constant circular velocity of the singular isothermal profile. This resonance maximizes the gravitational wave (GW) emission produced by the trailing acoustic wake. For an inspiral around a massive black hole of mass $10^6 M_\odot$ located at the center of a (truncated) isothermal sphere, this GW signal could be comparable to the vacuum GW emission of the black hole binary at sub-nanohertz frequencies when the small black hole enters the Bondi sphere of the massive one. The exact magnitude of this effect depends on departures from hydrostatic equilibrium and on the viscosity present in any realistic astrophysical fluid, which are not included in our simplified description.

Chemical cartography of the Galactic disk provides insights to its structure and assembly history over cosmic time. In this work, we use chemical cartography to explore chemical gradients and azimuthal substructure in the Milky Way disk with giant stars from APOGEE DR17. We confirm the existence of a radial metallicity gradient in the disk of $\Delta$[Fe/H]/$\Delta$R $\sim -0.066 \pm 0.0004$ dex/kpc and a vertical metallicity gradient of $\Delta$[Fe/H]/$\Delta$Z $\sim -0.164 \pm 0.001$ dex/kpc. We find azimuthal variations ($\pm0.1$ dex) on top of the radial metallicity gradient that have been previously established with other surveys. The APOGEE giants show strong correlations with stellar age and the intensity of azimuthal variations in iron; older stellar populations show the largest deviations from the radial metallicity gradient. Beyond iron, we show that other elements (e.g., Mg, O) display azimuthal variations at the $\pm0.05$ dex-level across the Galactic disk. We illustrate that moving into the orbit-space could help constrain the mechanisms producing these azimuthal metallicity variations. These results suggest that the spiral arms of the Galaxy are not solely responsible for azimuthal metallicity variations and other Galactic processes are at play.

Primordial black holes could constitute part or all of dark matter but they require large inhomogeneities to form in the early universe. These inhomogeneities can strongly backreact on the large scale dynamics of the universe. Stochastic inflation provides a way of studying this backreaction and getting an estimation of the abundance of primordial black holes. Because stochastic inflation focuses on large scale dynamics, it rests on the separate universe approach. However, the validity of this approach has only been checked in single field models, but not in multifield models in which we expect strong boosts in the power spectrum, leading to the formation of primordial black holes. We will check the validity of a separate universe approach in multifield models by matching it with a complete cosmological perturbation theory approach at large scales. In particular, we wish to compare these two paradigms and their differences in the adiabatic and entropic directions of the phase space. This will give us a range of validity and conditions one needs to verify in order to apply the separate universe approach and stochastic inflation in multifield models.

In this paper we present the publicly available open-source spectral energy distribution (SED) fitting code SMART (Spectral energy distributions Markov chain Analysis with Radiative Transfer models). Implementing a Bayesian Markov chain Monte Carlo (MCMC) method, SMART fits the ultraviolet to millimetre SEDs of galaxies exclusively with radiative transfer models that currently constitute four types of pre-computed libraries, which describe the starburst, active galactic nucleus (AGN) torus, host galaxy and polar dust components. An important novelty of SMART is that, although it fits SEDs exclusively with radiative transfer models, it takes comparable time to popular energy balance methods to run. Here we describe the key features of SMART and test it by fitting the multi-wavelength SEDs of the 42 local ultraluminous infrared galaxies (ULIRGs) that constitute the HERschel Ultraluminous Infrared Galaxy Survey (HERUS) sample. The Spitzer spectroscopy data of the HERUS ULIRGs are included in the fitting at a spectral resolution, which is matched to that of the radiative transfer models. We also present other results that highlight the performance and versatility of SMART. SMART promises to be a useful tool for studying galaxy evolution in the JWST era. SMART is developed in PYTHON and is available at this https URL.

The long-term evolution of astrophysical systems is driven by a Hamiltonian that is independent of the fast angle. As this Hamiltonian may contain explicitly time-dependent parameters, the conservation of mechanical energy is not guaranteed in such systems. We derive how the semi-major axis evolves in these cases. We analyze two astrophysically interesting examples, those of the harmonic and quadrupole perturbations.

In recent years, the study of the Milky Way has significantly advanced due to extensive spectroscopic surveys of its stars, complemented by astroseismic and astrometric data. However, it remains disjoint from recent advancements in understanding the physics of the Galactic interstellar medium (ISM). This paper introduces a new model for the chemical evolution of the Milky Way that can be constrained on stellar data, because it combines a state-of-the-art ISM model with a Milky Way stellar disc model. Utilizing a dataset of red clump stars from APOGEE, known for their precise ages and metallicities, we concentrate on the last 6 billion years -- a period marked by Milky Way's secular evolution. We examine the oxygen abundance in the low-$\alpha$ disc stars relative to their ages and birth radii, validating or constraining critical ISM parameters that remain largely unexplored in extragalactic observations. The models that successfully reproduce the radius -- metallicity distribution and the age -- metallicity distribution of stars without violating existing ISM observations indicate a need for modest differential oxygen enrichment in Galactic outflows, meaning that the oxygen abundance of outflows is higher than the local ISM abundance, irrespective of outflow mass loading. The models also suggest somewhat elevated ISM gas velocity dispersion levels over the past 6 billion years compared to galaxies of similar mass. The extra turbulence necessary could result from energy from gas accretion onto the Galaxy, supernovae clustering in the ISM, or increased star formation efficiency per freefall time. This work provides a novel approach to constraining the Galactic ISM and outflows, leveraging the detailed insights available from contemporary Milky Way surveys.

Particle acceleration and pitch-angle anisotropy resulting from magnetic reconnection are investigated in highly magnetized ion-electron plasmas. By means of fully kinetic particle-in-cell simulations, we demonstrate that magnetic reconnection generates anisotropic particle distributions $f_s \left( {|\cos \alpha|,\varepsilon} \right)$, characterized by broken power laws in the particle energy spectrum $f_s (\varepsilon) \propto \varepsilon^{-p}$ and pitch angle $\langle \sin^2 \alpha \rangle \propto \varepsilon^m$. Their characteristics are determined by the ratio of the guide field to the reconnecting field ($B_g/B_0$) and the plasma magnetization ($\sigma_0$). Below the break energy $\varepsilon_0$, ion and electron energy spectra are extremely hard ($p_<\lesssim 1$) for any $B_g/B_0$ and $\sigma_0 \gtrsim 1$, while above $\varepsilon_0$, the spectral index steepens ($p_> \gtrsim 2$), displaying high sensitivity to both $B_g/B_0$ and $\sigma_0$. The pitch angle displays power-law ranges with negative slopes ($m_<$) below and positive slopes ($m_>$) above $\varepsilon_{\min \alpha}$, steepening with increasing $B_g/B_0$ and $\sigma_0$. The ratio $B_g/B_0$ regulates the redistribution of magnetic energy between ions ($\Delta E_i$) and electrons ($\Delta E_e$), with $\Delta E_i \gg \Delta E_e$ for $B_g/B_0 \ll 1$, $\Delta E_i \sim \Delta E_e$ for $B_g/B_0 \sim 1$, and $\Delta E_i \ll \Delta E_e$ for $B_g/B_0 \gg 1$, with $\Delta E_i/\Delta E_e$ approaching unity when $\sigma_0 \gg 1$. The anisotropic distribution of accelerated particles results in an optically thin synchrotron power spectrum $F_\nu(\nu) \propto\nu^{(2-2p+m)/(4+m)}$ and a linear polarization degree $\Pi_{\rm lin} = (p+1)/(p+7/3+m/3)$. Pitch-angle anisotropy also induces temperature anisotropy and eases synchrotron cooling, along with producing beamed radiation, potentially responsible for frequency-dependent variability.

The identification of substructures within halos in cosmological hydrodynamical simulations is a fundamental step to identify the simulated counterparts of real objects, namely galaxies. For this reason, substructure finders play a crucial role in extracting relevant information from the simulation outputs. They are based on physically-motivated definitions of substructures, performing multiple steps of particle-by-particle operations, thus computationally expensive. The purpose of this work is to develop a fast algorithm to identify substructures in simulations. The final aim, besides a faster production of subhalo catalogues, is to provide an algorithm fast enough to be applied with a fine time-cadence during the evolution of the simulations. We chose to apply the architecture of a well known Fully Convolutional Network, U-Net, to the identification of substructures within the mass density field of the simulation. We have developed SubDLe (Substructure identification with Deep Learning), an algorithm which combines a 3D generalization of U-Net and a Friends-of-Friends algorithm, and trained it to reproduce the identification of substructures performed by the SubFind algorithm in a set of zoom-in cosmological hydrodynamical simulations of galaxy clusters. For the feasibility study presented in this work, we have trained and tested SubDLe on galaxy clusters at $z=0$, using a NVIDIA P100 GPU. We focused our tests on the version of the algorithm working on the identification of purely stellar substructures, stellar SubDLe. Our stellar SubDLe is capable of identifying the majority of galaxies in the challenging high-density environment of galaxy clusters in short computing times. This result has interesting implications in view of the possibility of integrating fast subhalo finders within simulation codes, that can take advantage of accelerators available on state-of-art computing nodes.

Turbulence, magnetic fields and radiation feedback are key components that shape the formation of stars, especially in the metal-free environments at high redshifts where Population III stars form. Yet no 3D numerical simulations exist that simultaneously take all of these into account. We present the first suite of radiation-magnetohydrodynamics (RMHD) simulations of Population III star formation using the adaptive mesh refinement (AMR) code FLASH. We include both turbulent magnetic fields and ionizing radiation feedback coupled to primordial chemistry, and resolve the collapse of primordial clouds down to few au. We find that dynamically strong magnetic fields significantly slow down accretion onto protostars, while ionizing feedback is largely unable to regulate gas accretion because the partially ionized \ion{H}{ii} region gets trapped near the star due to insufficient radiative outputs from the star. The maximum stellar mass in the HD and RHD simulations that only yield one star exceeds $100\,\rm{M_{\odot}}$ within the first $5000\,\rm{yr}$. However, in the corresponding MHD and RMHD runs, the maximum mass of Population III star is only $60\,\rm{M_{\odot}}$. In other realizations where we observe widespread fragmentation leading to the formation of Population III star clusters, the maximum stellar mass is further reduced by a factor of few due to fragmentation-induced starvation. We thus conclude that magnetic fields are more important than ionizing feedback in regulating the mass of the star, at least during the earliest stages of Population III star formation, in typical dark matter minihaloes at $z \approx 30$.

The evolution and fate of massive stars are thought to be affected by rotationally induced internal mixing. The surface boron abundance is a sensitive tracer of this in early B-type main sequence stars. We test current stellar evolution models of massive main sequence stars which include rotational mixing through a systematic study of their predicted surface boron depletion. We construct a dense grid of rotating single star models using MESA, for which we employ a new nuclear network which follows all the stable isotopes up to silicon, including lithium, beryllium, boron, as well as the radioactive isotope aluminium-26. We also compile the measured physical parameters of the 90 Galactic early B-type stars with boron abundance information. We then compare each observed stars with our models through a Bayesian analysis, which yields the mixing efficiency parameter with which the star is reproduced the best, and the probability that it is represented by the stellar models. We find that about two-thirds of the sample stars are well represented by the stellar models, with the best agreement achieved for a rotational mixing efficiency of ~50% compared to the widely adopted value. The remaining one third of the stars, of which many are strongly boron depleted slow rotators, are largely incompatible with our models, for any rotational mixing efficiency. We investigate the observational incidence of binary companions and surface magnetic fields, and discuss their evolutionary implications. Our results confirm the concept of rotational mixing in radiative stellar envelopes. On the other hand, we find that a different boron depletion mechanism, and likely a different formation path, is required to explain about one-third of the sample stars. The large spread in the surface boron abundances of these stars may hold a clue to understanding their origin.

Differentiating between real transit events and false positive signals in photometric time series data is a bottleneck in the identification of transiting exoplanets, particularly long-period planets. This differentiation typically requires visual inspection of a large number of transit-like signals to rule out instrumental and astrophysical false positives that mimic planetary transit signals. We build a one-dimensional convolutional neural network (CNN) to separate eclipsing binaries and other false positives from potential planet candidates, reducing the number of light curves that require human vetting. Our CNN is trained using the TESS light curves that were identified by Planet Hunters citizen scientists as likely containing a transit. We also include the background flux and centroid information. The light curves are visually inspected and labeled by project scientists and are minimally pre-processed, with only normalization and data augmentation taking place before training. The median percentage of contaminants flagged across the test sectors is 18% with a maximum of 37% and a minimum of 10%. Our model keeps 100% of the planets for 16 of the 18 test sectors, while incorrectly flagging one planet candidate (0.3%) for one sector and two (0.6%) for the remaining sector. Our method shows potential to reduce the number of light curves requiring manual vetting by up to a third with minimal misclassification of planet candidates.

Single-dish far-infrared (far-IR) and sub-millimetre (sub-mm) point source catalogues and their connections with catalogues at other wavelengths are of paramount importance. However, due to the large mismatch in spatial resolution, cross-matching galaxies at different wavelengths is challenging. This work aims to develop the next-generation deblended far-IR and sub-mm catalogues and present the first application in the COSMOS field. Our progressive deblending used the Bayesian probabilistic framework known as XID+. The deblending started from the Spitzer/MIPS 24 micron data, using an initial prior list composed of sources selected from the COSMOS2020 catalogue and radio catalogues from the VLA and the MeerKAT surveys, based on spectral energy distribution modelling which predicts fluxes of the known sources at the deblending wavelength. To speed up flux prediction, we made use of a neural network-based emulator. After deblending the 24 micron data, we proceeded to the Herschel PACS (100 & 160 micron) and SPIRE wavebands (250, 350 & 500 micron). Each time we constructed a tailor-made prior list based on the predicted fluxes of the known sources. Using simulated far-IR and sub-mm sky, we detailed the performance of our deblending pipeline. After validation with simulations, we then deblended the real observations from 24 to 500 micron and compared with blindly extracted catalogues and previous versions of deblended catalogues. As an additional test, we deblended the SCUBA-2 850 micron map and compared our deblended fluxes with ALMA measurements, which demonstrates a higher level of flux accuracy compared to previous results.We publicly release our XID+ deblended point source catalogues. These deblended long-wavelength data are crucial for studies such as deriving the fraction of dust-obscured star formation and better separation of quiescent galaxies from dusty star-forming galaxies.

The standard LambdaCDM cosmology passes demanding tests that establish it as a good approximation to reality. It is incomplete, with open questions and anomalies, but the same is true of all our physical theories. The anomalies in the standard cosmology might guide us to an even better theory. It has happened before.

Supermassive Black Holes (SMBHs) are commonly found at the centers of massive galaxies. Estimating their masses ($M_\text{BH}$) is crucial for understanding galaxy-SMBH co-evolution. We present WISE2MBH, an efficient algorithm that uses cataloged Wide-field Infrared Survey Explorer (WISE) magnitudes to estimate total stellar mass ($M_*$) and scale this to bulge mass ($M_\text{Bulge}$), and $M_\text{BH}$, estimating the morphological type ($T_\text{Type}$) and bulge fraction ($B/T$) in the process. WISE2MBH uses scaling relations from the literature or developed in this work, providing a streamlined approach to derive these parameters. It also distinguishes QSOs from galaxies and estimates the galaxy $T_\text{Type}$ using WISE colors with a relation trained with galaxies from the 2MASS Redshift Survey. WISE2MBH performs well up to $z\sim0.5$ thanks to K-corrections in magnitudes and colors. WISE2MBH $M_\text{BH}$ estimates agree very well with those of a selected sample of local galaxies with $M_\text{BH}$ measurements or reliable estimates: a Spearman score of $\sim$0.8 and a RMSE of $\sim$0.63 were obtained. When applied to the ETHER sample at $z\leq0.5$, WISE2MBH provides $\sim$1.9 million $M_\text{BH}$ estimates (78.5\% new) and $\sim$100 thousand upper limits. The derived local black hole mass function (BHMF) is in good agreement with existing literature BHMFs. Galaxy demographic projects, including target selection for the Event Horizon Telescope, can benefit from WISE2MBH for up-to-date galaxy parameters and $M_\text{BH}$ estimates. The WISE2MBH algorithm is publicly available on GitHub.

High fidelity separation of astrophysical foreground contributions from the cosmic microwave background (CMB) signal has been recognized as one of the main challenges of modern CMB data analysis, and one which needs to be addressed in a robust way to ensure that the next generation of CMB polarization experiments lives up to its promise. In this work we consider the non-parametric maximum likelihood CMB cleaning approach recently proposed by some of the authors which has been shown to match the performance of standard parametric techniques for simple foreground models, while superseding it in cases where the foregrounds do not exhibit a simple frequency dependence. We present a new implementation of the method in pixel space, extending its functionalities to account for spatial variability of the properties of the foregrounds. We describe the algorithmic details of our approach and its validation against the original code as well as the parametric method for various experimental set-ups and different models of the foreground components. We argue that the method provides a compelling alternative to other state-of-the-art techniques.

We present the first JWST/NIRCam observations of the directly-imaged gas giant exoplanet $\beta$ Pic b. Observations in six filters using NIRCam's round coronagraphic masks provide a high signal-to-noise detection of $\beta$ Pic b and the archetypal debris disk around $\beta$ Pic over a wavelength range of $\sim$1.7-5 $\mu$m. This paper focuses on the detection of $\beta$ Pic b and other potential point sources in the NIRCam data, following a paper by Rebollido et al. which presented the NIRCam and MIRI view of the debris disk around $\beta$ Pic. We develop and validate approaches for obtaining accurate photometry of planets in the presence of bright, complex circumstellar backgrounds. By simultaneously fitting the planet's PSF and a geometric model for the disk, we obtain planet photometry that is in good agreement with previous measurements from the ground. The NIRCam data supports the cloudy nature of $\beta$ Pic b's atmosphere and the discrepancy between its mass as inferred from evolutionary models and the dynamical mass reported in the literature. We further identify five additional localized sources in the data, but all of them are found to be background stars or galaxies based on their color or spatial extent. We can rule out additional planets in the disk midplane above 1 Jupiter mass outward of 2 arcsec ($\sim$40 au) and away from the disk midplane above 0.05 Jupiter masses outward of 4 arcsec ($\sim$80 au). The inner giant planet $\beta$ Pic c remains undetected behind the coronagraphic masks of NIRCam in our observations.

Gamma-ray bursts (GRBs) are powered by ultra-relativistic jets. The launching sites of these jets are surrounded by dense media, which the jets must cross before they can accelerate and release the high energy emission. Interaction with the medium leads to the formation of a mildly relativistic sheath around the jet resulting in an angular structures in the jet's asymptotic Lorentz factor and energy per solid angle, which modifies the afterglow emission. We build a semi-analytical tool to analyze the afterglow light curve and polarization signatures of jets observed from a wide range of viewing angles, and focus on ones with slowly declining energy profiles known as shallow jets. We find overall lower polarization compared to the classical top-hat jet model. We provide an analytical expression for the peak polarization degree as a function of the energy profile power-law index, magnetic field configuration and viewing angle, and show that it occurs near the light curve break time for all viewers. When applying our tool to GRB 221009A, suspected to originate from a shallow jet, we find that the suggested jet structures for this event agree with the upper limits placed on the afterglow polarization in the optical and X-ray bands. We also find that at early times the polarization levels may be significantly higher, allowing for a potential distinction between different jet structure models and possibly constraining the magnetization in both forward and reverse shocks at that stage.

Gravitational wave (GW) detection has enabled us to test General Relativity in an entirely new regime. A prominent role in tests of General Relativity takes the detection of the Quasi-normal modes (QNMs) that arise as the highly distorted remnant formed after the merger emits GWs until it becomes a regular Kerr BH. According to the no-hair theorem, the frequencies and damping times of these QNMs are determined solely by the mass and spin of the remnant BH. Therefore, detecting the QNMs offers a unique way to probe the nature of the remnant BH and to test General Relativity. We study the detection of a merging binary black hole (BBH) in the intermediate mass range, where the inspiral-merger phase is detected by space-based laser interferometer detectors TianQin and LISA while the ringdown is detected by the ground-based atom interferometer (AI) observatory AION. The analysis of the ringdown is done using the regular broadband mode of AI detectors as well as using the resonant mode where the detection band is optimized to the frequencies of the QNMs predicted from the inspiral-merger phase. We find that using the regular broadband mode allows constraining the parameters of the BBH with relative errors of at most $10^{-6}$ from the ringdown while the frequencies and the damping times of the QNMs can be determined with total errors below $0.2\,{\rm Hz}$ and $115\,{\rm \mu s}$, respectively. Furthermore, we find that using the resonant mode can improve the parameter estimation for the BBH from the ringdown by up to one order of magnitude. Utilizing the resonant mode significantly limits the detection of the frequency of the QNMs but improves the detection error of the damping times by one to four orders of magnitude.

We present a new numerical model for solving the Chew-Goldberger-Low system of equations describing a bi-Maxwellian plasma in a magnetic field. Heliospheric and geospace environments are often observed to be in an anisotropic state with distinctly different parallel and perpendicular pressure components. The CGL system represents the simplest leading order correction to the common isotropic MHD model that still allows to incorporate the latter's most desirable features. However, the CGL system presents several numerical challenges: the system is not in conservation form, the source terms are stiff, and unlike MHD it is prone to a loss of hyperbolicity if the parallel and perpendicular pressures become too different. The usual cure is to bring the parallel and perpendicular pressures closer to one another; but that has usually been done in an ad hoc manner. We present a physics-informed method of pressure relaxation based on the idea of pitch-angle scattering that keeps the numerical system hyperbolic and naturally leads to zero anisotropy in the limit of very large plasma beta. Numerical codes based on the CGL equations can, therefore, be made to function robustly for any magnetic field strength, including the limit where the magnetic field approaches zero. The capabilities of our new algorithm are demonstrated using several stringent test problems that provide a comparison of the CGL equations in the weakly and strongly collisional limits. This includes a test problem that mimics interaction of a shock with a magnetospheric environment in 2D.

Sub-GeV dark matter (DM) particles produced via thermal freeze-out evade many of the strong constraints on heavier DM candidates but at the same time face a multitude of new constraints from laboratory experiments, astrophysical observations and cosmological data. In this work we combine all of these constraints in order to perform frequentist and Bayesian global analyses of fermionic and scalar sub-GeV DM coupled to a dark photon with kinetic mixing. For fermionic DM, we find viable parameter regions close to the dark photon resonance, which expand significantly when including a particle-antiparticle asymmetry. For scalar DM, the velocity-dependent annihilation cross section evades the strongest constraints even in the symmetric case. Using Bayesian model comparison, we show that both asymmetric fermionic DM and symmetric scalar DM are preferred over symmetric fermionic DM due to the reduced fine-tuning penalty. Finally, we explore the discovery prospects of near-future experiments both in the full parameter space and for specific benchmark points. We find that the most commonly used benchmark scenarios are already in tension with existing constraints and propose a new benchmark point that can be targeted with future searches.

We propose a novel scenario where thermally under-abundant dark matter (DM) can be revived with a first-order phase transition (FOPT). In the absence of FOPT, thermal DM abundance remains suppressed due to efficient annihilation via mediators. A FOPT brings sharp change to the mass of the mediator at the nucleation temperature such that the final DM relic agrees with observations. We implement this idea in a scenario where DM interacts via a mediator whose initial mass is of same order as DM mass keeping DM annihilation either in allowed or forbidden ballpark. As the mediator mass decreases sharply at the nucleation temperature of the FOPT, the frozen out DM suffers further depletion while keeping final relic within observed limits. DM with sizeable interactions with a light mediator can also give rise to the required self-interactions necessary to solve the small scale structure issues of cold dark matter. While the mechanism is generic to any thermal DM mass, choosing it in the GeV ballpark forces the FOPT to MeV scale which predicts stochastic gravitational waves with nano-Hz frequencies within reach of pulsar timing array (PTA) based experiments like NANOGrav. The existence of light scalar mediator and its mixing with the Higgs keep the scenario verifiable at different particle physics experiments.

Relative motion effects have long been known to ``contaminate'' the observations. In fact, when looking back to the history of astronomy, one finds a number of examples where relative motions have led to a gross misinterpretation of reality. Using relativistic cosmological perturbation theory it was shown that observers living inside bulk-flow domains that expand slightly slower than their surroundings, can have the illusion of cosmic acceleration, while the host universe is actually decelerating. This claim was originally based on studies of a perturbed tilted Einstein-de Sitter model, primarily for mathematical simplicity. Nevertheless, nothing really changed when the background universe was replaced by a Friedmann cosmology with nonzero pressure and spatial curvature. This raised the possibility that the peculiar-motion effect on the deceleration parameter, as measured locally by the bulk-flow observers, may be generic and independent of the specifics of the host universe. Here, we investigate this possibility, by extending the earlier studies to perturbed Bianchi cosmologies. We find that the picture remains unchanged, unless the Bianchi background has unrealistically high anisotropy. The peculiar-motion effect on the deceleration parameter, as measured by the relatively moving observers, is essentially the same with that reported earlier in a perturbed Einstein-de Sitter universe and in the rest of its Friedmann counterparts.

We examine how the existence of a population of primordial black holes (PBHs) influences cosmological gravitational particle production (CGPP) for spin-0 and spin-1 particles. In addition to the known effects of particle production and entropy dilution resulting from PBH evaporation, we find that the generation of dark matter (DM) through CGPP is profoundly influenced by a possible era of PBH matter domination. This early matter dominated era results in an enhancement of the particle spectrum from CGPP. Specifically, it amplifies the peak comoving momentum $k_\star$ for spin-1 DM, while enhancing the plateau of the spectrum for minimally coupled spin-0 particles for low comoving momenta. At the same time, the large entropy dilution may partially or completely compensate for the increase of the spectrum and strongly mitigates the DM abundance produced by CGPP. Our results show that, in the computation of the final abundance, CGPP and PBH evaporation cannot be disentangled, but the parameters of both sectors must be considered together to obtain the final result. Furthermore, we explore the potential formation of PBHs from density fluctuations arising from CGPP and the associated challenges in such a scenario.

Over the past decade, neutrino astronomy has emerged as a new window into the extreme and hidden universe. Current generation experiments have detected high-energy neutrinos of astrophysical origin and identified the first sources, opening the field to discovery. Looking ahead, the authors of this Perspective identify seven major open questions in neutrino astrophysics and particle physics that could lead to transformative discoveries over the next 20 years. These multi-disciplinary questions range from understanding the vicinity of a black hole to unveiling the nature of neutrino mass, among other topics. Additionally, we critically review the current experimental capabilities and their limitations and, from there, discuss the interplay between different proposed neutrino telescope technologies and analysis techniques. The authors firmly believe that achieving the immense discovery potential over the next two decades demands a model of global partnership and complementary specialized detectors. This collaborative neutrino telescope network will pave the way for a thriving multi-messenger era, transforming our understanding of neutrino physics, astrophysics, and the extreme universe. \end{abstract}

Antiquark nuggets are hypothetical compact composite objects conjectured to account for a significant fraction of dark matter in the Universe. In contrast to quark nuggets, these objects consist of antimatter. They may remain undetected if they possess a sufficiently small cross section relative to their mass. In this paper, we investigate the allowed region in the parameter space of this model that is consistent with the observed neutrino flux from the Sun and the Earth, and the non-observation of seismic events with specific signatures of dark matter particles. We found the allowed values of the antibaryon charge number in this model to be in the interval $2\times 10^{24}<A<8\times 10^{25}$, while the probability of nucleon annihilation upon collisions with the antiquark core is constrained by $0.1\lesssim \kappa<0.25$. Although very large values of the antibaryon charge, $A>10^{33}$, are not fully excluded by the present study, we show that they conflict with the non-observation of rare catastrophic explosion-like events on the Earth.

We present a detailed exposition of a statistical method for estimating cosmological parameters from the observation of a large number of strongly lensed binary-black-hole (BBH) mergers observable by third-generation gravitational-wave (GW) detectors. This method, first presented in $\href{this https URL}{[1]}$, compares the observed number of strongly lensed GW events and their time delay distribution (between lensed images) with observed events to infer cosmological parameters. We show that the precision of the estimation of the cosmological parameters does not have a strong dependance on the assumed BBH redshift distribution model. An incorrect model for the distribution of lens properties and redshifts can lead to a biased cosmological inference. However, Bayesian model selection can assist in selecting the right model from a set of available parametric models for the distribution of lens redshift and properties. We also present a way to incorporate the effect of contamination in the data due to the limited efficiency of lensing identification methods, so that it will not bias the cosmological inference.

Using tremendous photon statistics gained with the stray light aperture of the NuSTAR telescope over 11 years of operation, we set strong limits on the emission of close to monochromatic photons from the radiative decays of putative dark matter sterile neutrinos in the Milky Way. In the energy range of 3-20 keV covered by the NuSTAR, the obtained limits reach the edge of theoretical predictions of realistic models leaving only a small room left to explore.

We present the model we developed to reconstruct the CUORE radioactive background based on the analysis of an experimental exposure of 1038.4 kg yr. The data reconstruction relies on a simultaneous Bayesian fit applied to energy spectra over a broad energy range. The high granularity of the CUORE detector, together with the large exposure and extended stable operations, allow for an in-depth exploration of both spatial and time dependence of backgrounds. We achieve high sensitivity to both bulk and surface activities of the materials of the setup, detecting levels as low as 10 nBq kg$^{-1}$ and 0.1 nBq cm$^{-2}$, respectively. We compare the contamination levels we extract from the background model with prior radio-assay data, which informs future background risk mitigation strategies. The results of this background model play a crucial role in constructing the background budget for the CUPID experiment as it will exploit the same CUORE infrastructure.

Machine learning (ML) methods are having a huge impact across all of the sciences. However, ML has a strong ontology - in which only the data exist - and a strong epistemology - in which a model is considered good if it performs well on held-out training data. These philosophies are in strong conflict with both standard practices and key philosophies in the natural sciences. Here, we identify some locations for ML in the natural sciences at which the ontology and epistemology are valuable. For example, when an expressive machine learning model is used in a causal inference to represent the effects of confounders, such as foregrounds, backgrounds, or instrument calibration parameters, the model capacity and loose philosophy of ML can make the results more trustworthy. We also show that there are contexts in which the introduction of ML introduces strong, unwanted statistical biases. For one, when ML models are used to emulate physical (or first-principles) simulations, they introduce strong confirmation biases. For another, when expressive regressions are used to label datasets, those labels cannot be used in downstream joint or ensemble analyses without taking on uncontrolled biases. The question in the title is being asked of all of the natural sciences; that is, we are calling on the scientific communities to take a step back and consider the role and value of ML in their fields; the (partial) answers we give here come from the particular perspective of physics.

Matching gravitational-wave observations of binary neutron stars with theoretical model predictions reveals important information about the sources, such as the masses and the distance to the stars. The latter can be used to determine the Hubble Constant, the rate at which the Universe expands. One general problem of all astrophysical measurements is that theoretical models only approximate the real underlying physics, which can lead to systematic uncertainties introducing biases. However, the extent of this bias for the distance measurement due to uncertainties of gravitational waveform models is unknown. In this study, we analyze a synthetic population of 38 binary neutron star sources measured with Advanced LIGO and Advanced Virgo at design sensitivity. We employ a set of four different waveform models and estimate model-dependent systematic biases on the extraction of the Hubble Constant using the bright siren method. Our results indicate that systematic biases are below statistical uncertainties for the current generation of gravitational wave detectors.

Motivated by the null results of current dark matter searches and the small-scale problems, we study a dark sector charged by a spontaneous broken gauge $U(1)'$. To explore the parameter space of this model, in addition to the consideration of the small-scale data, we also consider the theoretical bounds on the dark Higgs mass, with the upper bound coming from the tree-level perturbative unitarity and the lower bound from the one-loop Linde-Weinberg bound. We deeply examine the dependence of the Linde-Weinberg bound on gauge choice and energy scale. Combining the theoretical and observational constraints, we obtain the following ranges for the parameter space: the dark matter mass is 10-500 GeV, the mediator (dark photon) mass is 0.5-5 MeV, the dark Higgs mass is 0.05-50 MeV, the dark fine-structure constant is 0.001-0.5. We conclude that the dark Higgs in this model cannot be ignored in the phenomenological study of the dark sector.

We study cold strange quark stars employing an enhanced version of the quark-mass density-dependent model which incorporates excluded volume effects to address non-perturbative QCD repulsive interactions. We provide a comparative analysis of our mass formula parametrization with previous models from the literature. We identify the regions within the parameter space where three-flavor quark matter is more stable than the most tightly bound atomic nucleus (stability window). Specifically, we show that excluded volume effects do not change the Gibbs free energy per baryon at zero pressure, rendering the stability window unaffected. The curves of pressure versus energy density exhibit various shapes -- convex upward, concave downward, or nearly linear -- depending on the mass parametrization. This behavior results in different patterns of increase, decrease, or constancy in the speed of sound as a function of baryon number density. We analyze the mass-radius relationship of strange quark stars, revealing a significant increase in maximum gravitational mass and a shift in the curves towards larger radii as the excluded volume effect intensifies. Excluded volume effects render our models compatible with all modern astrophysical constraints, including the properties of the recently observed low-mass compact object HESSJ1731.

We complete the perturbative program for equilibrium thermodynamics of cosmological first-order phase transitions by determining the finite-temperature effective potential of gauge-Higgs theories at next-to-next-to-next-to-next-to-leading order (N$^4$LO). The computation of the three-loop effective potential required to reach this order is extended to generic models in dimensionally reduced effective theories in a companion article. Our N$^4$LO result is the last perturbative order before confinement renders electroweak gauge-Higgs theories non-perturbative at four loops. By contrasting our analysis with non-perturbative lattice results, we find a remarkable agreement. As a direct application for predictions of gravitational waves produced by a first-order transition, our computation provides the final fully perturbative results for the phase transition strength and speed of sound.

The radio astronomy community is rapidly adopting deep learning techniques to deal with the huge data volumes expected from the next generation of radio observatories. Bayesian neural networks (BNNs) provide a principled way to model uncertainty in the predictions made by such deep learning models and will play an important role in extracting well-calibrated uncertainty estimates on their outputs. In this work, we evaluate the performance of different BNNs against the following criteria: predictive performance, uncertainty calibration and distribution-shift detection for the radio galaxy classification problem.