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Physics Astrophysics

astro-ph Watch Astrophysics

Friday 24 April

Astrophysics of Galaxies

The abundance and radial distribution of faint and ultra-faint dwarfs in galaxy clusters

Pradyumna Sadhu, Laura V. Sales, Julio F. Navarro et al. (+3 more)

Cosmological simulations of galaxy clusters are unable to resolve dwarf galaxies due to limited numerical resolution which drives the artificial disruption of dark matter substructures. We address these limitations by combining the results of the cosmological hydrodynamical simulation TNG50 in $\Lambda$CDM with an empirical model of tidal evolution of cluster galaxies calibrated using high-resolution idealized N-body simulations. Applied to the three most massive clusters in TNG50, our model allows us to study the stellar mass and radial distribution of dwarfs well below the formal resolution limit of the parent simulation. We find that, at $z=0$, clusters with virial mass $M_{200} \sim 10^{14}~\mathrm{M_\odot}$ host a vast population of dwarf galaxies within the virial radius, amounting to $2000$-$7000$ systems with $M_* > 100~\mathrm{M_\odot}$. Taken together, these satellites follow a radial distribution that matches the underlying dark matter profile of the host. However, applying a minimum mass or luminosity threshold for detection, as expected in observational studies, tends to exclude the most heavily-stripped objects, which tend to populate the inner regions. Future surveys targeting ultra-faint galaxies in group and cluster environments, such as those made possible by the Euclid, Rubin, or Roman telescopes, will be fundamental to refute or confirm this prediction.
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All authors Pradyumna Sadhu, Laura V. Sales, Julio F. Navarro, Raphaël Errani, Jose Benavides, Eric W. Peng

Cosmology and Nongalactic Astrophysics

Diffusion-based Galaxy Simulations for the Roman High Latitude Survey

Diana Scognamiglio, Jake H. Lee, Eric Huff et al. (+2 more)

Future weak lensing analyses with the Nancy Grace Roman Space Telescope will require highly realistic image simulations to control shear systematics at unprecedented precision. A key limitation of existing approaches is their reliance on analytic light-profile models, which cannot fully capture the complex, non-parametric morphologies revealed by high-resolution observations. We present a diffusion-based framework for generating realistic galaxy image simulations tailored to the weak lensing requirements of the Roman High Latitude Survey. We construct Roman-like galaxy images from multi-band JWST/NIRCam observations in the GOODS-S and GOODS-N fields, transforming them into the Roman observing regime through point-spread-function matching, pixel-scale conversion, and interloper masking that preserves correlated noise properties. These data are used to train a denoising diffusion probabilistic model to generate multi-band galaxy postage stamps in the Roman Y, J, and H filters. We validate the generated sample against an independent dataset using a consistent photometric pipeline, comparing key galaxy observables including magnitude, size, ellipticity, peak surface brightness, and three-band colors. The generated galaxies reproduce both the marginal distributions and the covariance structure of these properties, with only modest deviations in low-occupancy regions of parameter space. These results demonstrate that diffusion models provide a scalable and physically motivated alternative to analytic simulations, enabling high-fidelity galaxy populations for Roman weak lensing calibration and, more generally, for survey preparation in upcoming cosmological experiments.
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All authors Diana Scognamiglio, Jake H. Lee, Eric Huff, Sergi R. Hildebrandt, Shoubaneh Hemmati

High Energy Astrophysical Phenomena

IXPE Polarizations of the Lighthouse Pulsar, Trail, and Filament

Jack T. Dinsmore, Roger W. Romani, S. Zhang et al. (+9 more)

The Lighthouse pulsar (PSR J1101$-$6101) sports a bright X-ray trail and filament. The synchrotron emission from both structures is expected to be polarized, with electric vector position angle (EVPA) perpendicular to the magnetic field direction and polarization degree (PD) indicating the local degree of magnetic turbulence. We present a 1 megasecond Imaging X-ray Polarimetry Explorer (IXPE) observation of the Lighthouse complex. At the 99% confidence level, we detect the filament polarization with PD $55 \pm 18\%$ and EVPA indicating a magnetic field parallel to the filament axis. The large PD implies a turbulent magnetic field weaker than the background field, in conflict with some existing models. We also detect polarization from the pulsar and trail. The trail's X-ray polarization is nearly orthogonal to the radio polarization, suggesting spatial separation between the X-ray- and radio-emitting leptons. The pulsar polarization is well-fit by the rotating vector model.
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All authors Jack T. Dinsmore, Roger W. Romani, S. Zhang, C.-Y. Ng, Stefano Silvestri, Oleg Kargaltsev, Niccolo' Bucciantini, Philip Kaaret, Josephine Wong, Patrick Slane, Paolo Soffitta, Martin C. Weisskopf

Solar and Stellar Astrophysics

The Effects of Accretion Feedback on Stellar Evolution in AGN Disks

Alexander J. Dittmann and Matteo Cantiello

Stars embedded in the accretion disks of active galactic nuclei (AGN) can accrete rapidly from their surroundings, dramatically altering their structure and evolution. However, feedback from the release of gravitational potential energy and radiative enthalpy by accreting gas can limit accretion rates, as recently demonstrated in radiation hydrodynamics simulations. To determine the importance of these effects neglected in earlier stellar evolution calculations, we incorporate these feedback processes into a semi-analytical model of stellar structure and evolution and conduct a suite of calculations spanning a broad parameter space of AGN disk conditions drawn from $\alpha$-disk models with central black hole masses $M_\bullet/M_\odot \in [10^6, 10^9]$. We find that accretion feedback limits stellar accretion rates below $\sim 10^{-1}\,M_\odot\,\mathrm{yr}^{-1}$, reducing the sensitivity of stellar evolution on disk properties. This suppression eliminates runaway accretion in models where it would otherwise occur, broadening the parameter space over which stars can reach long-lived “immortal” equilibria between accretion and mass loss. When gap opening is also accounted for, accretion feedback significantly alters stellar properties: it can reduce accretion and mass-loss rates by over an order of magnitude, reducing the strength of accretion shocks and thereby increasing equilibrium stellar masses and radii. These higher masses correspond to higher intrinsic luminosities, suggesting that neglecting accretion feedback may lead to an underestimate of disk chemical enrichment rates. Additionally, accretion feedback is important for predicting the properties of stellar populations within AGN disks, and associated transient phenomena.
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Earth and Planetary Astrophysics

Substructures Induced by Dust Drag in Protoplanetary Disks

Jiaqing Bi, Mario Flock, Dominik Ostertag et al. (+2 more)

Dust substructures observed in protoplanetary disks are commonly attributed to embedded planets; however, intrinsic gas-dust interactions can also generate complex morphologies. We performed two-dimensional, axisymmetric simulations of gas and dust that include dust back-reaction and parameterized turbulence to investigate how the streaming instability (SI) and vertical shear instability (VSI) shape dust distributions. With moderate viscosity and sufficiently high metallicity, we identify a characteristic shuttlecock-shaped dust substructure composed of a dense, vertically settled "head" and a vertically extended "tail." This morphology arises from nonlinear SI driven by marginally coupled grains and the associated modification of gas flows. The dust scale height in the tail exceeds predictions based on the simple diffusion-settling balance, indicating strong self-generated turbulence. With lower viscosity, VSI becomes more vigorous, disrupts midplane structures, and increases vertical stirring; nevertheless, for dust grains with Stokes numbers around 0.01, SI can still attain dust-to-gas ratios of up to 20-50, potentially approaching the Hill density for gravitational binding. Our results demonstrate that intrinsic gas-dust interactions can generate prominent dust substructures even in disks with finite viscosity and, under favorable conditions, concentrate dust to levels relevant for planetesimal formation.
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All authors Jiaqing Bi, Mario Flock, Dominik Ostertag, Neele Lüttkemöller, Sebastian Wolf

Instrumentation and Methods for Astrophysics

Describing the swdatatoolkit: A Space Weather Data Analysis Library

Dustin Kempton, Griffin Goodwin, Tarun Kumar Reddy Thippareddy et al. (+3 more)

swdatatoolkit is a Python-based scientific software library designed to support the acquisition, preprocessing, and analysis of solar and space weather data. The toolkit consolidates functionality across multiple domains, including data downloading from established heliophysics sources, image preprocessing, edge detection, image texture quantification, magnetic field analysis, and the derivation of higher-level parameters commonly used in solar physics research. Its modular structure reflects the heterogeneous nature of space weather data and enables reproducible, extensible workflows for both exploratory analysis and machine-learning-driven studies. This paper presents an overview of the library's available capabilities, its scientific motivations, and its role in the broader space weather research ecosystem.
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All authors Dustin Kempton, Griffin Goodwin, Tarun Kumar Reddy Thippareddy, Reet Gupta, Viacheslav Sadykov, Rafal Angryk

Cosmology and Nongalactic Astrophysics

On the redshift evolution of the spin parameter in cosmological simulations

Tomas Riera, Alexander Knebe, Chris Power et al. (+2 more)

Although the spin parameter of dark matter halos is well known to follow a log-normal distribution at fixed epoch, its quantitative redshift evolution - encompassing both the mean and the dispersion - remains only partially explored. Prior studies either lack the mass resolution required to establish reliable evolutionary trends or do not provide analytical relations that enable forward modelling. Using a suite of LCDM N-body simulations with controlled resolution across the redshift range 0 < z < 5, we characterise the evolution of the mean and dispersion of the Peebles (lambda) and Bullock (lambda') definitions of spin. We find a mild but statistically robust linear evolution for ln(lambda) and a non-monotonic trend with a turnover at z ~ 1 - 2 for ln lambda', which we verify are unaffected by mass resolution of choice of halo definition. We provide closed-form fitting functions for these trends that allow modellers to draw physically motivated spin values at any redshift within our range of validity. This is a practical, redshift-dependent alternative to the common assumption of a constant spin distribution, and provides a useful input to semi-empirical and semi-analytic models of galaxy formation.
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All authors Tomas Riera, Alexander Knebe, Chris Power, Robert Adriel Mostoghiu Paun, Adam Ussing

Cosmology and Nongalactic Astrophysics

Precision Analysis for $\boldsymbol{H_0}$ Using Upcoming Multi-band Gravitational Wave Observations

Setabuddin, Md Riajul Haque, Ratna Koley et al. (+1 more)

We investigate how multi-band gravitational wave (GW) observations can constrain the uncertainties in the Hubble parameter ($H_0$) using primordial black holes (PBHs) as possible sources. Our framework combines scalar-induced and merger-induced GWs from PBHs, and forecasts on a combination of two future detectors Square Kilometre Array (SKA) and the Einstein Telescope (ET), enabling a multi-band analysis. We perform a statistical forecast of the PBH parameters, $M_{\rm PBH}$ and $f_{\rm PBH}$, using signal-to-noise ratio (SNR) estimates and Fisher matrix analysis. Imposing $\mathrm{SNR} \geq 1$, we identify the accessible PBH parameter space and propagate these uncertainties to estimate the corresponding uncertainties in $H_0$. For $\delta \theta_i/\theta_i \leq 0.1$, with $\theta_i \equiv M_{\rm PBH}(f_{\rm PBH})$, we find $\delta H_0 \lesssim 2~{\rm km\,s^{-1}\,Mpc^{-1}}$ in a conservative approach, improving to $\delta H_0 \lesssim \mathcal{O}(0.1)~{\rm km\,s^{-1}\,Mpc^{-1}}$ for $\delta \theta_i/\theta_i \leq 0.01$ for an optimistic approach of precision measurement. The results are further found to be largely insensitive to the fiducial choice of the $H_0$, with only moderate dependence on the PBH collapse efficiency. These findings demonstrate that multi-band GW observations provide an independent and complementary approach to constraining the uncertainties in $H_0$, with the potential to provide a novel, cosmic distance ladder-independent measure of the Hubble parameter.
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All authors Setabuddin, Md Riajul Haque, Ratna Koley, Supratik Pal

Solar and Stellar Astrophysics

Simulation of a protoplanetary disk accretion activity due to a collision with a gas stream

Vitaliy Grigoryev and Tatiana Demidova

The consequences of a protoplanetary disk collision with a gas stream are being studied using three-dimensional numerical gas-dynamic simulation. The influence of orbital parameters and the stream mass on the accretion activity of the star is examined. It is shown that the orbital inclination and the initial mass of the infalling material are the most influential parameters in determining the accretion rate. The obtained accretion rate dependencies are compared with actual observational data for two FU~Ori type stars. It turns out that not only is the maximum accretion rate consistent with observational estimates, but the behavior of the accretion rate over time is very similar to available long-term light curves.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Gauge-independent approach to inflation in quadratic gravity

Adrian Palomares, Ying-li Zhang and Jinsu Kim

We investigate the scalar sector of linear cosmological perturbations in quadratic gravity. Working in the Einstein frame, we derive the equations of motion in a gauge-independent manner and express them in terms of three sets of gauge-invariant variables. This approach allows us to distinguish genuine physical effects from gauge artefacts, which is particularly relevant for assessing the stability of perturbations in this theory. In the superhorizon limit, we obtain the leading-order behaviour of the relevant gauge-invariant variables and analyse the perturbations in commonly used gauges. We find that the Newtonian gauge exhibits an apparent instability, characterised by the exponential growth of the metric perturbations. However, this growth is non-generic and gauge-dependent; in the other gauges analysed in this work, the perturbations remain well behaved within the perturbative regime. Our analysis also demonstrates how the evolution behaviour of a gauge-invariant variable changes under the frame transformation and clarifies the relation between results obtained in the Jordan and Einstein frames.
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Cosmology and Nongalactic Astrophysics

Reionization, UV Luminosity and 21$\,$cm Sensitivity to Primordial Magnetic Fields: Impact of Energy Losses

Gaétan Facchinetti, Alexander Korochkin, Laura Lopez-Honorez et al. (+1 more)

Magnetic fields with field strengths between $10^{-17}\,$G and a few Nanogauss are expected to exist today in the intergalactic medium (IGM). Their origin is unknown, but may be of primordial nature, in which case they would have influenced the thermal and ionization history of the IGM as well as the growth of small-scale matter perturbations. In this work, we revisit constraints on Primordial Magnetic fields (PMFs) by consistently accounting for their energy losses through ambipolar diffusion and decaying turbulences from recombination through the epoch of reionization, which progressively reduces the magnetic field strength over time. We implement these effects in ${\tt HyRec}$ and ${\tt exo21cmFAST}$ to model the interplay between PMFs and astrophysical processes up to reionization. Using a neural-network emulator (${\tt NNERO}$), we perform a MCMC analysis that combines late-time probes of the reionization history and galaxy UV luminosity functions. We find that including PMF energy losses significantly relaxes previous bounds, as the reduced field strength suppresses their imprint on observables. Employing a Fisher matrix analysis, we estimate the sensitivity of the 21$\,$cm signal experiment HERA to the PMFs' imprint on intergalactic medium perturbations and show that 21$\,$cm cosmology could significantly improve on current bounds, depending on assumptions on the astrophysics. Our results highlight the importance of modeling PMF evolution self-consistently with the IGM evolution to extract current bounds and future sensitivities.
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All authors Gaétan Facchinetti, Alexander Korochkin, Laura Lopez-Honorez, Justus Schwagereit

Astrophysics of Galaxies

First Statistical Study of Over 100 Magnified Stellar Events at Redshift $z \approx 0.725$ with JWST

J. M. Palencia, Fengwu Sun, J. M. Diego et al. (+25 more)

Highly magnified stars at cosmological distances ($z \gtrsim 0.7$) become detectable thanks to microlensing by intracluster stars near the critical curves of galaxy clusters. Multi-epoch photometric campaigns targeting caustic crossing galaxies magnified by massive galaxy clusters enable the detection of these objects as transient events. Such stars provide unique opportunities to study stellar populations at early cosmic times, probe the nature of dark matter, reveal small-scale structure in the cluster, and improve lens models. To date, only a few dozen high-redshift stars have been reported, with a single lensed galaxy, the Dragon, holding the current record of 44 detections. These numbers, however, remain insufficient to exploit their full potential. In this paper, owing to the inclusion of new observations, we report the identification of more than 100 magnified stellar events in the Dragon, behind the massive galaxy cluster Abell 370. The relatively low redshift of the Dragon ($z\approx0.725$) facilitates the detection of its most massive stars. Using imaging data from three different cycles (2022–2024) with the James Webb Space Telescope, we apply a time-domain technique to identify flux variations associated with caustic-crossing events. From the spatial distribution of stellar events we constrain the high-end slope of the stellar luminosity function, finding $\beta=2.18^{+0.20}_{-0.30}$. Alternatively, assuming a fixed slope, we constrain the microlens surface mass density. In addition, we examine the parity asymmetry of the detected caustic-crossing events, a proposed probe of wave dark matter, and find that it remains present. We also use the events to trace the regions of highest magnification, offering an alternative way to map the system critical curves.
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All authors J. M. Palencia, Fengwu Sun, J. M. Diego, Yoshinobu Fudamoto, Anton M. Koekemoer, Christopher N. A. Willmer, Eduardo Iani, Xiaojing Lin, Justin D. R. Pierel, Alfred Amruth, Tom Broadhurst, W. Chen, Liang Dai, Daniel Espada, Alexei V. Filippenko, Seiji Fujimoto, Patrick L. Kelly, Mingyu Li, Sung Kei Li, Ashish Kumar Meena, Jordi Miralda-Escudé, P. Morilla, Mitchell F. Struble, Hayley Williams, Rogier A. Windhorst, E. Zackrisson, Ruwen Zhou, Adi Zitrin

Instrumentation and Methods for Astrophysics

Forecasting the occupancy of satellite megaconstellations in SKA observations

Nicolas Cerardi, Emma Tolley and Federico di Vruno

The Square Kilometre Array (SKA) is expected to start science operations in 2030 and by that time there could be up to 10$^5$ artificial satellites in Earth's orbit, comprising an increase of an order of magnitude compared to 2024. Most of these new satellites will belong to satellite megaconstellations aimed at providing communication services all over Earth. These satellites create radio frequency interference (RFI) that can impact the observations of modern radio telescopes. In this Letter, we forecast the amount of observing time for which the SKA interferometers will be exposed to satellites, risking RFI contamination. We employed an analytical model and considered two cases of exposure to satellites; (1) satellites that only lie in the main beam and (2) satellites that lie in the main beam or the first sidelobe. We show that for SKA-Low, the exposure is high, with satellites in the beam for 30% of the observation time across half of the frequency range, rising up to 100% below 100 MHz. For SKA-Mid, high frequencies are mostly spared, but observations below 1 GHz could also end up seeing satellites for at least 30% of the time. We conclude that satellites will be unavoidable during SKA observing conditions, risking a strong impact on the RFI environment. This will necessitate a concerted effort to obtain accurate measurements of satellite RFI and to improve our understanding of the impact on various science cases. Finally, new mitigation techniques that are less data-destructive than simple flagging must be introduced.
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Instrumentation and Methods for Astrophysics

WAsp: The Wideband (W) Adaptive-Scale Pixel (Asp) Deconvolution Algorithm for Interferometric Imaging

M. Hsieh, S. Bhatnagar and U.Rau

This paper introduces the Wide-band Asp-Clean (WAsp) algorithm, a novel scale-sensitive image reconstruction method tailored for wide-band imaging applications. This algorithm is particularly beneficial for thermal noise-limited imaging with aperture synthesis telescopes, where joint spatio-frequency modeling of the sky brightness distribution is critical. The WAsp algorithm replaces the use of the MS-Clean algorithm in the MS-MFS algorithm with the Asp algorithm \citep{Asp_Clean}, which itself has been improved for both imaging and runtime performance. With the high sensitivity of current and next-generation telescopes, spatio-frequency modeling in a scale-sensitive basis becomes crucial for ensuring that residuals align with the noise model across the frequency band. Although existing wide-band scale-sensitive algorithms have demonstrated superior performance over scale-insensitive counterparts, they often suffer from well-documented deficiencies, leading to significant wide-scale residuals in Stokes-I at low levels and consequently significant relative errors in spectral index maps. The WAsp algorithm addresses these limitations while maintaining computational efficiency. The implementation can be configured to support narrow-band and wide-band scale-sensitive imaging, spectral-cube imaging applications and joint single-dish and interferometer imaging. To demonstrate improved imaging performance, we show comparison with existing algorithms via carefully developed simulations for stress-testing the algorithms. We also present results from its application to real-world wide-band data, underscoring its effectiveness in practical imaging scenarios.
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Instrumentation and Methods for Astrophysics

CosmicDancePro – Measuring LEO satellite's orbital decay and network connectivity implications during solar storms

Suvam Basak, Amitangshu Pal and Debopam Bhattacherjee

The May 2024 solar superstorm highlighted the vulnerability of rapidly expanding low Earth orbit (LEO) satellite networks to severe space weather events. To systematically evaluate LEO network resilience, we introduce an open-source tool, CosmicDancePro. It enables a comprehensive analysis of the effects of solar storms in the LEO satellite network. It integrates real-world multimodal datasets, including space weather measurements from several satellites, upper-atmospheric density conditions from data-driven and high-fidelity physics-based models, and LEO satellite trajectory and LEO network measurement traces to quantify orbital decay driven by enhanced atmospheric density and network connectivity degradation. We utilize CosmicDancePro to analyze the Starlink constellation's behavior during two recent major solar storms. First, we identify the specific fleet management strategies Starlink adopts during the May 2024 solar superstorm and how they differ from its regular orbit-correction strategy. Second, we identify the mechanisms driving the previously unexplained 'W'-shaped altitude variation pattern across orbital planes of LEO constellations. Finally, our network-layer analysis quantifies the connectivity degradation during these storms, revealing transient disruptions that include repetitive short-lived outages, reconfiguration latency spikes above 500 ms, up to 60% increase in uplink loss, distorted diurnal latency patterns, and a 10+ Mbps drop in end-user data rates during storm peaks.
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High Energy Astrophysical Phenomena

Dense Matter and Compact Stars in Strong Magnetic Fields

Monika Sinha and Vivek Baruah Thapa

Compact stars serve as natural systems where matter exists at densities far beyond those achievable in laboratory experiments. Among them, magnetars are expected to possess interior magnetic fields that may reach values of the order of $10^{17}-10^{18}$ G. These extreme conditions are expected to alter the microscopic and macroscopic properties of dense matter. In this review, we examine how strong magnetic fields affect fermionic matter through mechanisms such as Landau quantization and anomalous magnetic moment interactions. We further discuss the behaviour of magnetized hadronic matter within relativistic mean-field approaches and consider the possible emergence of additional degrees of freedom, including hyperons, $\Delta$ resonances, meson condensates and quark matter. The consequences of these effects for neutron-star structure and observational constraints are also briefly outlined.
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High Energy Astrophysical Phenomena

Exploring the diversity of kilonovae with 3D radiative transfer I. The polar direction

Christine E. Collins, Luke J. Shingles, Vimal Vijayan et al. (+7 more)

We present 3D kilonova radiative transfer simulations for a series of binary neutron star merger models. The masses of the neutron stars are varied as well as the total mass of the system and two different equations of state were used (SFHO and DD2), producing a range in dynamical ejecta masses and elemental abundance patterns. In this paper, we focus on the bolometric light curves and spectra in the polar direction for comparison with observations of the kilonova AT2017gfo. We calculate line-by-line opacities and include new calibrated lanthanide atomic data. All of the simulated spectra show strong features from Sr II, La III, Gd III and Ce III, which appear to correspond to features identified in AT2017gfo, although the simulated features are generally more blueshifted. The models with the lowest lanthanide fraction in the polar direction also show a Y II feature. Ce III, Ce II, Nd III and Nd II play an important role in shaping the spectral continuum. While the bolometric luminosities in the polar direction vary with the ejecta mass of each model, we find only little sensitivity of the spectral properties to the merger configuration. Our study demonstrates that dynamical ejecta alone can reproduce (although at earlier times) many spectral properties of AT2017gfo, suggesting dynamical ejecta may have a strong impact on the early spectral evolution. However, future simulations are needed to also elucidate the role of other ejecta components for shaping the kilonova spectrum.
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All authors Christine E. Collins, Luke J. Shingles, Vimal Vijayan, Andreas Floers, Oliver Just, Fiona McNeill, Zewei Xiong, Andreas Bauswein, Kate Maguire, Stuart A. Sim

Astrophysics of Galaxies

The Sound of the Universe: A Resonant Gravitational Instability Driven by Baryon-Dark Matter Relative Drift

Mohamad Shalaby and Avery Broderick

Dark matter and baryons acquire a relative velocity after decoupling in the early Universe. Baryons are gravitationally unstable only above their Jeans scale, while cold dark matter (CDM) is unstable on all scales. We show for the first time that their relative drift triggers a resonant gravitational instability that drives sound waves in baryons. When the projected DM drift is subsonic, the stable oscillatory branch of baryons resonates with the Doppler-shifted DM mode, producing exponentially growing perturbations whose growth rates exceed the intrinsic CDM growth rate. The instability peaks below the baryon Jeans scale and, in baryon-dominated environments, opens a window of complete stability between the Jeans scale and the resonance. Supersonic drift suppresses growth, as previously noted. The resonant coupling also transfers momentum between the species, creating a non-viscous, collisionless drag. We derive an accurate analytical approximation for the growth rate at resonance and show that the associated timescales range from years to tens of millions of years across diverse environments – planets, protoplanetary disks, stars, molecular clouds, galaxies, and galaxy clusters – typically much shorter than their ages. In an expanding FLRW universe, the instability enhances baryon density perturbations at different redshifts for appropriately oriented modes while suppressing the growth of those aligned with the DM stream. The universe thus sings across all scales, and this resonant mechanism provides the means to listen: it offers a novel probe of dark matter through its seismic imprint on astrophysical objects and may explain long-standing puzzles such as the persistence of spiral arms and the heating of the intracluster medium in galaxy clusters.
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Solar and Stellar Astrophysics

From core to envelope: revealing the deep dynamics of stars with two convective zones

Sylvain N. Breton, Allan Sacha Brun and Rafael A. García

On the Hertzsprung-Russell diagram, F-type solar pulsators connect the Sun to intermediate mass stars located on the instability strip. With respect to lower mass stars, they are structurally peculiar in the sense that they are constituted of three distinct dynamical layers: a small convective core, a deep radiative interior, and a shallow convective envelope. Current asteroseismic techniques only provide limited information on the interior dynamics of these stars. Indeed only gravity modes (g modes), for which unambiguous characterisation is lacking, are able to probe the deep stellar layers. A better understanding of the excitation and behaviour in F-type solar pulsators is therefore necessary in order to consider their detection. In this work, we simulate for the first time the global stellar structure of an F-type star (core, radiative interior, envelope). We show that the contribution of the core strongly affects the spectrum of excited g modes, with low-order high-degree modes unable to form due to their interaction with the turbulent convection of the core. Finally, by computing the disc-integrated signature of the modes, we are able to demonstrate that they preserve their integrity up to the top of the convective envelope, which is a strong argument in favour of their detectability with spaceborne photometry.
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High Energy Astrophysical Phenomena

Radiative feedbacks as drivers for quasi-periodic-oscillation activity in black-hole X-ray binaries

Apostolos Mastichiadis

Black-hole X-ray binaries (BHXRBs) in the hard and hard-intermediate spectral states commonly exhibit prominent type-C quasi-periodic oscillations (QPOs) in their X-ray power spectra. Despite extensive observational and theoretical efforts, the physical mechanism responsible for these oscillations has not yet been firmly established. The disk-corona system in BHXRBs is radiatively coupled, as hard X-ray emission from the corona can be reprocessed by the accretion disk and re-emitted as soft photons that contribute to cooling the coronal electrons. Aim of the present study is to examine whether this feedback can give rise to limit cycles having the spectro-temporal properties of QPOs. We model the coronal emission using a one-zone radiation framework and solve the time-dependent kinetic equations for electrons and photons. Electrons are energized by some unspecified process and cool via inverse Compton scattering of soft photons originating from (i) the accretion disk and (ii) disk reprocessing of the hard radiation produced in the corona. When electron cooling is dominated by soft photons reprocessed in the accretion disk, the disk-corona system undergoes limit-cycle oscillations. For a subset of the model parameters, these oscillations reproduce key properties of type-C QPOs observed in BHXRBs. The oscillation frequency depends on the coronal radius and on the energization timescale, while the resulting X-ray spectra are well described by power laws extending up to energies of ~ 10-100 keV. These calculations confirm and extend earlier semi-analytical results obtained with simplified treatments. Owing to the scale-invariant nature of the model, the results can be readily extrapolated to other accreting systems, such as Active Galactic Nuclei.
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Astrophysics of Galaxies

Variability of Sagittarius A* at 3 GHz on minute-scale with MeerKAT

K. Kaur, I. Rammala-Zitha, A. Basu et al. (+21 more)

The supermassive black hole Sagittarius A* (Sgr A*) exhibits temporal and spectral variability across the electromagnetic spectrum. However, variability at radio frequencies below ~ 5 GHz for timescales shorter than a day remains largely unexplored. We investigate the variability of Sgr A* at 2.79 GHz on short timescales (1 min), to probe an under-explored regime of its emission process. Through point-source model fitting in the uv-domain, we analyse the flux density variation of Sgr A* over an 8 h observation. We detect flux variation on a few tens of minute timescale with a modulation index of 6.11 %, a mean flux density of ($827 \pm 0.1_{\mathrm{stat}} \pm 33_{\mathrm{sys}}) \, \mathrm{mJy}$, and a mean spectral slope of $0.08\pm0.03$. Furthermore, we measure the slope of the structure function of the observed light curve as $0.81 \pm 0.05$ with a characteristic timescale of about 120 min. Our study at low radio frequencies is a critical step toward constraining the physical mechanisms that drive Sgr A*'s variable emission and its spectral energy distribution. Our study suggests that variability at centimetre and millimetre wavelengths is likely more closely related than previously thought.
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All authors K. Kaur, I. Rammala-Zitha, A. Basu, G. Witzel, M. Wielgus, V. Balakrishnan, E.D. Barr, A. Brunthaler, S. Buchner, D.J. Champion, M. Hoeft, S. Khan, H.-R. Klöckner, C. König, M. Kramer, V. Venkatraman Krishnan, Y.K. Ma, S.A. Mao, P.V. Padmanabh, S. Ranchod, S.S. Sridhar, J.D. Wagenveld, R.S. Wharton, O. Wucknitz

Cosmology and Nongalactic Astrophysics

Constraints on the Primordial Black Hole Abundance using Pulsar Parameter Drifts

Yan-Chen Bi, Yu-Mei Wu and Qing-Guo Huang

Primordial black holes (PBHs) provide a compelling interpretation for the binary black holes (BBHs) observed by ground-based gravitational-wave (GW) detectors, especially for those BBHs in the theoretical mass gap. In the early Universe, the scalar perturbations required to produce such PBHs inevitably generate scalar-induced GWs (SIGWs). These SIGWs peak in the sub-nanohertz band, and manifest secularly as measurable jerk-like drifts in the second derivative of pulsar spin periods. In this Letter, we perform the first search for SIGWs using pulsar parameter drifts, and place a 95% confidence-level upper limit on the PBH abundance of $f_{\mathrm{PBH}} < 10^{-10}$ over the mass range $[3 \times 10^{-1}, 4 \times 10^{4}] M_{\odot}$. Our results strongly disfavor a PBH origin for the BBHs currently detected by the LIGO-Virgo-KAGRA (LVK) Collaborations.
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High Energy Astrophysical Phenomena

Ultra-high-energy $\gamma$-ray imprints from PeV particles accelerated by supernova remnants

Zhen Cao, F. Aharonian, Y.X. Bai et al. (+325 more)

The quest for the origin of cosmic ray (CRs) is a fundamental issue in astrophysics. Shocks of supernova remnants (SNRs) have been considered as the dominant contributors to Galactic CRs below the spectral knee near $\sim 3$ petaelectronvolt (PeV). Whether SNRs are efficient accelerators of particles beyond PeV energies has long been debated. Here we report observations of very-high-energy $\gamma$-ray emission up to hundreds of TeV from two middle age shell-type SNRs, G150.3$+$4.5 and $\gamma$-Cygni, with the Large High Altitude Air Shower Observatory (LHAASO). Two (or three) distinct morphological/spectral components with convex spectral shapes are observed in both sources, with the low-energy one being more extended than the high-energy one. %Although it is possible that these high-energy components may be driven by powerful pulsars, The likely association of the high-energy component with molecular clouds at similar distances, and the weakness/absence of pulsar wind nebulae (PWNe) inside these SNRs clearly indicate for the first time that the highest energy emission is produced by collision of hadronic CRs up to PeV energies with the clouds. These results are compatible with the classic model prediction that PeV particles accelerated near the end of the free expansion phase of SNR evolution can illuminate nearby molecular clouds (MCs) to produce strong $\gamma$-ray emission.
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All authors Zhen Cao, F. Aharonian, Y.X. Bai, Y.W. Bao, D. Bastieri, X.J. Bi, Y.J. Bi, W. Bian, J. Blunier, A.V. Bukevich, C.M. Cai, Y.Y. Cai, W.Y. Cao, Zhe Cao, J. Chang, J.F. Chang, E.S. Chen, G.H. Chen, H.K. Chen, L.F. Chen, Liang Chen, Long Chen, M.J. Chen, M.L. Chen, Q.H. Chen, S. Chen, S.H. Chen, S.Z. Chen, T.L. Chen, X.B. Chen, X.J. Chen, X.P. Chen, Y. Chen, N. Cheng, Q.Y. Cheng, Y.D. Cheng, M.Y. Cui, S.W. Cui, X.H. Cui, Y.D. Cui, B.Z. Dai, H.L. Dai, Z.G. Dai, Danzengluobu, Y.X. Diao, A.J. Dong, X.Q. Dong, K.K. Duan, J.H. Fan, Y.Z. Fan, J. Fang, J.H. Fang, K. Fang, C.F. Feng, H. Feng, L. Feng, S.H. Feng, X.T. Feng, Y. Feng, Y.L. Feng, S. Gabici, B. Gao, Q. Gao, W. Gao, W.K. Gao, M.M. Ge, T.T. Ge, L.S. Geng, G. Giacinti, G.H. Gong, Q.B. Gou, M.H. Gu, F.L. Guo, J. Guo, K.J. Guo, X.L. Guo, Y.Q. Guo, Y.Y. Guo, R.P. Han, O.A. Hannuksela, M. Hasan, H.H. He, H.N. He, J.Y. He, X.Y. He, Y. He, S. Hernández-Cadena, B.W. Hou, C. Hou, X. Hou, H.B. Hu, S.C. Hu, C. Huang, D.H. Huang, J.J. Huang, X.L. Huang, X.T. Huang, X.Y. Huang, Y. Huang, Y.Y. Huang, A. Inventar, X.L. Ji, H.Y. Jia, K. Jia, H.B. Jiang, K. Jiang, X.W. Jiang, Z.J. Jiang, M. Jin, S. Kaci, M.M. Kang, I. Karpikov, D. Khangulyan, D. Kuleshov, K. Kurinov, Cheng Li, Cong Li, D. Li, F. Li, H.B. Li, H.C. Li, Jian Li, Jie Li, K. Li, L. Li, R.L. Li, S.D. Li, T.Y. Li, W.L. Li, X.R. Li, Y. Li, Zhe Li, Zhuo Li, E.W. Liang, Y.F. Liang, S.J. Lin, B. Liu, C. Liu, D. Liu, D.B. Liu, H. Liu, J. Liu, J.L. Liu, J.R. Liu, M.Y. Liu, R.Y. Liu, S.M. Liu, W. Liu, X. Liu, Y. Liu, Y. Liu, Y.N. Liu, Y.Q. Lou, Q. Luo, Y. Luo, H.K. Lv, B.Q. Ma, L.L. Ma, X.H. Ma, I.O. Maliy, J.R. Mao, Z. Min, W. Mitthumsiri, Y. Mizuno, G.B. Mou, A. Neronov, K.C.Y. Ng, M.Y. Ni, L. Nie, L.J. Ou, Z.W. Ou, P. Pattarakijwanich, Z.Y. Pei, D.Y. Peng, J.C. Qi, M.Y. Qi, J.J. Qin, D. Qu, A. Raza, C.Y. Ren, D. Ruffolo, A. Sáiz, D. Savchenko, D. Semikoz, L. Shao, O. Shchegolev, Y.Z. Shen, X.D. Sheng, Z.D. Shi, F.W. Shu, H.C. Song, Yu.V. Stenkin, Y. Su, D.X. Sun, H. Sun, J.X. Sun, Q.N. Sun, X.N. Sun, Z.B. Sun, N.H. Tabasam, J. Takata, P.H.T. Tam, H.B. Tan, Q.W. Tang, R. Tang, Z.B. Tang, W.W. Tian, C.N. Tong, L.H. Wan, C. Wang, D.H. Wang, G.W. Wang, H.G. Wang, J.C. Wang, K. Wang, Kai Wang, Kai Wang, L.P. Wang, L.Y. Wang, L.Y. Wang, R. Wang, W. Wang, X.G. Wang, X.J. Wang, X.Y. Wang, Y. Wang, Y.D. Wang, Z.H. Wang, Z.X. Wang, Zheng Wang, D.M. Wei, J.J. Wei, Y.J. Wei, T. Wen, S.S. Weng, C.Y. Wu, H.R. Wu, Q.W. Wu, S. Wu, X.F. Wu, Y.S. Wu, S.Q. Xi, J. Xia, J.J. Xia, G.M. Xiang, D.X. Xiao, G. Xiao, Y.F. Xiao, Y.L. Xin, H.D. Xing, Y. Xing, D.R. Xiong, B.N. Xu, C.Y. Xu, D.L. Xu, R.F. Xu, R.X. Xu, S.S. Xu, W.L. Xu, L. Xue, D.H. Yan, T. Yan, C.W. Yang, C.Y. Yang, F.F. Yang, L.L. Yang, M.J. Yang, R.Z. Yang, W.X. Yang, Z.H. Yang, Z.G. Yao, X.A. Ye, L.Q. Yin, N. Yin, X.H. You, Z.Y. You, Q. Yuan, H. Yue, H.D. Zeng, T.X. Zeng, W. Zeng, X.T. Zeng, M. Zha, B.B. Zhang, B.T. Zhang, C. Zhang, H. Zhang, H.M. Zhang, H.Y. Zhang, J.L. Zhang, J.Y. Zhang, Li Zhang, P.F. Zhang, R. Zhang, S.R. Zhang, S.S. Zhang, S.Y. Zhang, W. Zhang, W.Y. Zhang, X. Zhang, X.P. Zhang, Yi Zhang, Yong Zhang, Z.P. Zhang, J. Zhao, L. Zhao, L.Z. Zhao, S.P. Zhao, X.H. Zhao, Z.H. Zhao, F. Zheng, T.C. Zheng, B. Zhou, H. Zhou, J.N. Zhou, M. Zhou, P. Zhou, R. Zhou, X.X. Zhou, X.X. Zhou, B.Y. Zhu, C.G. Zhu, F.R. Zhu, H. Zhu, K.J. Zhu, Y.C. Zou, X. Zuo, Y. Li

Astrophysics of Galaxies

MUSE-DARK III: The evolution of the radial acceleration relation at intermediate redshifts

B. I. Ciocan, N. F. Bouché, J. Fensch et al. (+5 more)

The radial acceleration relation (RAR) is a tight empirical correlation between the observed radial acceleration (a_tot) and the baryonic radial acceleration (a_bar) measured across galaxy radii: these two accelerations start to deviate significantly from each other below a characteristic acceleration scale, a0. So far, observational studies of the RAR have predominantly focused on galaxies in the local Universe, leaving its evolution with cosmic time largely unexplored. Using high signal-to-noise data from the MUSE Hubble Ultra Deep Field survey, we investigate the RAR with a sample of 79 star-forming galaxies (complete above M* >10^8.8 Msun) at intermediate redshifts (0.33 <z <1.44). We estimate the observed intrinsic acceleration and the baryonic acceleration from a disk-halo decomposition that incorporates stellar, gas, and dark matter components, with corrections for pressure support, using 3D forward modelling. We find a RAR in our intermediate-z sample offset from the local relation, with a higher characteristic acceleration scale, a0(z~1) = 2.38+/-0.1* 10^-10 m/s^2, and a larger intrinsic scatter (~0.17 dex). Dividing the sample into redshift bins and refitting the RAR in each bin, we find a characteristic acceleration scale that systematically increases with z. Parametrizing the z-dependence as a0(z)= a0(0) + a1 * z, we obtain a1 = 1.59+/-0.1 *10^-10 m/s^2, providing evidence for a z-evolution. We find similar results using various dark matter halo profiles as well as the Modified Newtonian Dynamics framework in our 3D forward modelling. Our results show that the RAR persists at intermediate redshift, with statistically significant redshift evolution of the characteristic acceleration, pointing to a possible evolution of the baryon-missing mass connection over cosmic time.
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All authors B. I. Ciocan, N. F. Bouché, J. Fensch, D. Krajnović, J. Freundlich, H. Desmond, B. Famaey, R. Techi

Solar and Stellar Astrophysics

The Effect of Mass Loss and Convective Overshooting on the Pre-Collapse Structure, Composition, and Neutrino Emission of Red Supergiants

McKenzie A. Myers, Claire B. Campbell, Kelly M. Patton et al. (+6 more)

Prior to core collapse, the neutrino emission from red supergiants (RSGs) is so large that a nearby ($\lesssim1\:$kpc) RSG will become visible in current and near-future neutrino detectors. The rate of emission and the spectra of the pre-supernova (pre-SN) neutrinos from RSGs are sensitive to the temperature, density, and detailed isotopic composition of the core. During the last year of the star's life, these properties change considerably as the nuclear burning accelerates and deleptonization begins. Uncertainties in stellar evolution modeling - including the treatment of mass loss and convective overshooting - alter the thermal conditions and composition of the RSG core as it approaches collapse, and thus one expects a consequent effect upon the pre-SN emission. In this paper we present the first study of how varying the treatment of mass loss and convective overshooting together affects the pre-collapse core properties and neutrino emission of RSGs. We use the stellar evolution instrument MESA and construct a grid of 32 RSG models with zero-age main sequence masses of $\{ 12, 15, 18, 20\}$ M$_\odot$, apply the so-called "Dutch" mass-loss scheme with wind efficiencies of $\{0.2, 0.4, 0.8, 1.0\}$, and consider two convective overshooting schemes. Our models use a large 206-isotope nuclear network in order to accurately compute the structure and composition of the star. We find that varying the treatment of mass loss and overshooting results in significant differences in core properties and the strength and timing of shell burning episodes, and that the onset of silicon shell burning leads to a localized peak in the pre-SN neutrino event rate observed by a JUNO-like detector $\sim 10$ hours to $\sim 1$ hour prior to collapse.
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All authors McKenzie A. Myers, Claire B. Campbell, Kelly M. Patton, Segev BenZvi, Marta Colomer Molla, Alec Habig, James P. Kneller, Dan Milisavljevic, Jeffrey Tseng

High Energy Astrophysical Phenomena

Synchrotron polarization of anisotropic electron distribution in GRB prompt emission

Kang-Fa Cheng, Kai-Xian Luo, Xiao-Hong Zhao et al. (+7 more)

In gamma-ray bursts (GRBs), the electron pitch angle ($\alpha$) is usually assumed to be isotropically distributed. However, recent numerical simulations indicate that only the high-energy electrons (with Lorentz factors $\gamma>\gamma_{iso}$) are distributed isotropically, whereas the low-energy electrons (with $\gamma<\gamma_{iso}$) follow an energy-dependent anisotropic distribution during magnetic reconnection. The mean value of $\sin^2 \alpha$ approximately follows the relation $\langle \sin^2 \alpha \rangle \propto \gamma^{m}$ for $\gamma<\gamma_{iso}$. In principle, polarization measurements may help us constrain the pitch-angle distribution of electrons in GRBs, since different pitch-angle distributions produce distinct synchrotron polarization signatures. The polarization of GRBs produced by isotropically distributed electrons has been extensively studied. In this paper, we investigate synchrotron polarization produced by anisotropically distributed electrons within a globally toroidal magnetic field in GRB prompt emission. Our results show that the synchrotron PDs in the $\gamma$-ray and X-ray bands produced by anisotropically distributed electrons are systematically lower than those produced by isotropically distributed electrons, while the PD in the optical band could be either lower or higher than that of isotropically distributed electrons, depending primarily on the value of the energy slope $m$. In addition, we compared our numerical results with observational data, and the comparison suggests that an anisotropic distribution of electrons may offer a potential explanation for the PD and spectral data of some GRBs.
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All authors Kang-Fa Cheng, Kai-Xian Luo, Xiao-Hong Zhao, Jirong Mao, Hong-Bang Liu, Yu-Hang Mo, Jin-Rong Huang, Rong-Li Weng, Wen-Jie Xie, Gao-Jin Yu

Astrophysics of Galaxies

A homogeneous three-dimensional view of Molecular Cloud kinematics out to 2.5 kpc. Using Young Stellar Objects and Open Clusters as complementary tracers

Xabier Pérez-Couto, Santiago Torres, Nuria Miret-Roig et al. (+4 more)

Understanding the large-scale dynamics of molecular clouds (MCs) is crucial for constraining the processes that govern star formation and the structure and evolution of the Galaxy. While gas tracers have traditionally been used to map MC kinematics, stellar tracers such as young stellar objects (YSOs) and open clusters (OCs) provide a complementary approach that enables direct comparisons between the stellar and gaseous components. We aim to validate OCs as complementary tracers by testing whether they retain the same bulk kinematic imprint as YSOs, and to reconstruct the three-dimensional (3D) motions of the main MC complexes within 2.5 kpc of the Sun using YSOs and young OCs as tracers. Using Gaia DR3 astrometry together with complementary spectroscopic surveys for radial velocities, we compiled a unified sample of 24,732 stellar tracers. We applied robust clustering in proper motion space to identify co-moving YSOs and derived cloud-averaged motions via Monte Carlo sampling. These were compared with the kinematics of OCs younger than 30 Myr. Finally, we performed orbital integrations in a realistic Galactic potential to trace the past evolution of the clouds and quantify their expansion and rotation. We derive homogeneous 3D kinematics for 15 MC complexes within 2.5 kpc. YSOs and OCs exhibit strongly consistent kinematics, with a median spatial velocity offset of $\simeq 2$ km s$^{-1}$, confirming that both populations trace the bulk motion of their parent clouds. The resulting cloud kinematics show a median peculiar velocity of $\simeq 8.7$ km s$^{-1}$ with respect to Galactic rotation. We trace back the Solar System's voyage through the Orion cloud and the common origin of Lupus, Ophiuchus, and Corona Australis in Sco-Cen. Internally, we detect significant expansion in Orion and Ophiuchus ($5\sigma$) and coherent rotation in at least seven complexes.
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All authors Xabier Pérez-Couto, Santiago Torres, Nuria Miret-Roig, Friedrich Anders, Alexander J. Mustill, Eva Villaver, Minia Manteiga

Astrophysics of Galaxies

A Quasar–Companion System Without AGN Outflow at $z \sim 6$: The Case of PSO J083+11

Muhammad Akmal Husain, Irham Taufik Andika and Mochamad Ikbal Arifyanto

PSO J083.8371+11.8482, a quasar at $z = 6.34$ with a nearby companion galaxy, provides an opportunity to study the impact of active galactic nucleus (AGN) activity on the surrounding environment during the epoch of reionization. We analyze ALMA observations of the [C\,ii] 158~$\mu$m emission line and the far-infrared (FIR) continuum, which trace cold interstellar gas and dust-reprocessed radiation from star formation and AGN heating. The quasar host shows star formation rates (SFRs) of $544$–$3764~\mathrm{M_{\odot}~yr^{-1}}$ from [C\,ii] and $1861$–$2932~\mathrm{M_{\odot}~yr^{-1}}$ from FIR emission, while the companion galaxy exhibits lower SFRs of $21$–$145$ and $76$–$211~\mathrm{M_{\odot}~yr^{-1}}$ from the same diagnostics. Both galaxies follow typical $L_{\mathrm{[C\,II]}}/L_{\mathrm{FIR}}$ ratios observed in star-forming galaxies and show no evidence for a [C\,ii] deficit, indicating that stellar heating dominates the interstellar medium energetics. The [C\,ii] moment maps reveal compact emission with centrally peaked intensity and ordered rotational kinematics in both systems. Velocity dispersions remain well below values associated with powerful AGN-driven outflows, and no significant morphological asymmetries or disturbed velocity fields indicative of AGN feedback or major mergers are detected, although marginal kinematic substructure in the quasar's high-velocity channels warrants further investigation. Although the companion lies at a projected distance of $18.248 \pm 0.277$~kpc within the quasar proximity zone, neither morphological nor kinematic signatures indicate AGN-driven outflows affecting the circumgalactic medium. We therefore interpret this system as being observed in a pre-outflow accretion phase, where rapid supermassive black hole growth precedes the development of large-scale AGN feedback.
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Solar and Stellar Astrophysics

Radial evolution of Alfvén wave Parametric Decay Instability in the near-Sun solar wind: Effects of Temperature Anisotropy

Hayato Saguchi, Yohei Kawazura, Munehito Shoda et al. (+1 more)

Parametric decay instability (PDI) of Alfvén wave is thought to play an important role in the dissipation of the large-amplitude Alfvén waves and in the heating of magnetized plasmas. Temperature anisotropy is frequently observed by spacecraft, including Parker Solar Probe (PSP), in the near-Sun solar wind, yet its impact on PDI in the near-Sun solar wind has been understudied. We calculate the maximum growth rates of PDI, $\gamma_{\max}/\omega_{0}$, where $\omega_0$ is the frequency of the parent wave, by solving the linear dispersion relation of Chew-Goldberger-Low (CGL) equations under several expanding background models. To assess the effect of temperature anisotropy, the growth rate is compared with that derived from ideal magnetohydrodynamics (MHD). From $R_0$ ($ = 1.02R_\odot$) to $30R_0$, we consider three expansion cases: (i) spherically symmetric adiabatic expansion with constant wind speed, (ii) Multi-source observation- and model-constrained expansion, and (iii) a PSP-constrained profile of $(\beta_{\parallel},\xi)$, where $\beta_\parallel=8\pi p_{\parallel0}/B_0^2$ is the parallel plasma beta and $\xi=T_{\perp0} / T_{\parallel0}$ is the temperature anisotropy, that includes Parker-spiral effects. We find that temperature anisotropy increases $\gamma_{\max}/\omega_{0}$ for $\beta\lesssim 0.1$ in the near-Sun solar wind: in the case of (iii), temperature anisotropy with $T_{\perp0} > T_{\parallel0}$ increases $\gamma_{\max}/\omega_{0}$ by factors of $\sim 1.5$ over $R\simeq 1$–$10\,R_0$, whereas temperature anisotropy with $T_{\parallel0}>T_{\perp0}$ decreases $\gamma_{\max}/\omega_{0}$ at larger $R$. Our results suggest that the temperature anisotropy plays an important role in the onset of PDI even in low-$\beta$ regimes, such as the near-Sun solar wind.
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All authors Hayato Saguchi, Yohei Kawazura, Munehito Shoda, Yuto Katoh

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Machine Learning for Multi-messenger Probes of New Physics and Cosmology: A Review and Perspective

Andrea Addazi, Konstantin Belotsky, Vitaly Beylin et al. (+18 more)

The multi-messenger exploration of dark matter and physics beyond the Standard Model has emerged as a central direction in modern astro-particle physics, particularly following the discovery of gravitational waves. In this work, we present a comprehensive review and forward-looking perspective on machine-learning-enhanced multi-messenger approaches, combining information from gravitational waves, cosmic rays, gamma rays, neutrinos, and collider experiments. We summarize the current state of the field, discuss recent methodological developments, and outline a coherent research program aimed at integrating heterogeneous datasets within a unified inference framework. Our collaboration proposes here a plan for forthcoming analyses aiming at extracting information on the properties and interactions of dark matter, and finally on its genesis, combining multi-messenger astronomy techniques and inputs from laboratory physics. The main objectives planned in this line of research comprise: i) the multi-messenger analysis of new physics in cosmology, including mainly, but not only, several different models of dark matter; ii) the phenomenology of new physics signatures in ground-based cosmic rays experiments, with cross-correlation to the corresponding physical, astrophysical and cosmological observations; iii) the development of machine learning methods for data analysis in ground-based cosmic rays experiments, in light of the new physics signatures. We note that several groups have explored the use of multi-messenger observations, including gravitational waves, to probe alternative dark matter candidates. The present work builds on these developments by focusing on the role of machine learning in integrating heterogeneous datasets. We foresee that such a cross-fertilizing approach will represent the right path to extract information about the main questions left in fundamental physics.
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All authors Andrea Addazi, Konstantin Belotsky, Vitaly Beylin, Timur Bikbaev, Deen Chen, Filippo Fabrocini, Stefano Giagu, Krid Jinklub, Artem Kharakhashyan, Maxim Khlopov, Vladimir Korchagin, Maxim Krasnov, Atharv Mahajan, Antonino Marciano, Andrey Mayorov, Antonio Morais, Roman Pasechnik, Jackson Levi Said, Danila Sopin, Viktor Stasenko, Oem Trivedi