Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Black Holes as Frequency-Dependent Filters of Stochastic Gravitational Waves
Sefi Katznelson, Aidan Minger and Stefano Profumo
Black holes ring when perturbed, whereas their response to a stationary gravitational-wave background is a real-frequency scattering problem, not a source of additional quasi-normal-mode lines. We make this standard distinction quantitative by treating a black hole as a frequency-, angle-, and polarization-dependent filter. For an isotropic stationary background around Schwarzschild holes, elastic scattering produces no net monopole signal, so horizon absorption is the only population-level spectral distortion. We calculate this transfer function for Schwarzschild holes in detail, identify its absorptive and phase-delay signatures, and connect the stationary response to the causal ringdown excited by a finite wave packet. We then promote the single-hole result to an angular and polarization transport kernel for a cosmological population. The resulting optical depth is negligible for realistic black-hole populations, including asteroid-mass primordial black holes comprising all dark matter. We then extend the analysis to Kerr holes, for which superradiance allows genuine amplification in selected co-rotating modes, but isotropic incidence and random
spin orientations strongly dilute the diffuse signal. Observable effects are therefore more likely in rare, nearby, aligned, rapidly spinning, or transiently illuminated systems than through cumulative cosmological propagation.
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Cosmology and Nongalactic Astrophysics
Hunting Thermal Relics in the DESI DR1 Ly$\alpha$ Forest
Emanuelly Silva, Artur Ladeira, Rafael C. Nunes et al. (+1 more)
We investigate constraints on additional relativistic species and thermal sterile
neutrinos using the DESI DR1 one-dimensional Lyman-$\alpha$ forest power spectrum, combined with Planck 2018 CMB and DESI DR2 BAO measurements. We consider both the $\Lambda$CDM+$N_{\rm eff}$ extension and a thermal with a different-temperature sterile-
neutrino (DTS) scenario, in which the sterile relic can be colder than the standard
neutrino background. We first validate the DESI two-parameter $P_{\rm 1D}$ compression for the DTS model, finding that the residual cosmological dependence not captured by the compressed parameters remains below 0.15%. No significant evidence for additional radiation or a sterile component is found. For $\Lambda$CDM+$N_{\rm eff}$, we obtain $N_{\rm eff}<3.41$ at 95% credibility from CMB+DESI-BAO+DESI-$P_{\rm 1D}$. In the DTS scenario, the full CMB+DESI-BAO+DESI-$P_{\rm 1D}$ combination yields the stringent bound $m_s^{\rm eff}<0.061\,{\rm eV}$, highlighting the complementarity of BAO and Lyman-$\alpha$ information in constraining the massive sterile abundance. We further interpret the allowed $\Delta N_{\rm eff}$ in terms of thermal light relics, deriving lower limits on their decoupling temperatures that reach the QCD epoch.
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All authors Emanuelly Silva, Artur Ladeira, Rafael C. Nunes, Eleonora Di Valentino
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
The Deep Learning Halo Definer: A Multimodal Framework for Halo Mass and Gas Fraction Inference on Galaxy Groups and Clusters
Caleb Ogle, Kalvyn N. Poncelet Adams, Benjamin D. Oppenheimer et al. (+5 more)
Accurately inferring dark matter
halo properties like the total
halo mass (M_{
halo}) and gas fractions (f_{gas}) remains particularly challenging at group scales, where low member counts, shallow potential wells, and AGN feedback-driven baryon expulsion introduce significant observational scatter. As large-scale surveys begin to provide unprecedented multi-wavelength data, there is a pressing need for methods that can jointly leverage diverse observables to overcome these uncertainties. We introduce the Deep Learning
Halo Definer (DLHD), a
multimodal deep learning framework that simultaneously processes
galaxy catalogues and X-ray imaging through the combination of a Deep Sets and a Convolutional Neural Network (CNN) to improve M_{
halo} and f_{gas} estimation for
galaxy groups and clusters. Using mock
datasets derived from the IllustrisTNG300 hydrodynamic simulation, we demonstrate that the DLHD outperforms each of its component networks individually, achieving RMSE improvements in M_{
halo} of 1.9x over Deep Sets and 1.3x over the CNN alone. For the gas fraction enclosed within R_{200c}, DLHD reduces RMSE by 2.0x relative to Deep Sets and 1.1x relative to the CNN alone, with consistent improvements across other apertures. These results highlight a novel ability to leverage multi-band information inaccessible to single-modality methods, positioning DLHD as a promising tool for next-generation survey analyses.
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All authors Caleb Ogle, Kalvyn N. Poncelet Adams, Benjamin D. Oppenheimer, Naomi Gluck, Matthew Ho, Daisuke Nagai, Joseph N. Burchett, Mohammadreza Ayromlou
Cosmology and Nongalactic Astrophysics
Axio-Dilaton Dark Energy: A Dynamical Systems and Bayesian Inference Analysis
Mario Ramos-Hamud, Gabriela García-Arroyo, Fernando Quevedo et al. (+1 more)
We initiate a systematic cosmological investigation of an axio-dilaton system governed by a curved field-space metric as generically motivated by supergravity and string compactifications. The scalar sector consists of a light scalar dilaton field evolving along an asymptotically exponential potential and a pseudoscalar field spanning an essentially flat direction, kinetically coupled through an exponential field-space metric. Deviations from the asymptotic regime are incorporated by introducing a generalised Albrecht-Skordis potential containing a
polynomial factor. Utilising a dynamical systems approach alongside numerical
evolution and
Bayesian inference, we constrain the model using Type Ia
Supernovae (SNe Ia), Baryon Acoustic Oscillations (BAO) and Planck 2018 distance-prior data. We identify a parameter degeneracy indicating that steeper potentials demand stronger field-space kinetic couplings to sustain late-time
cosmic acceleration. Finally, a joint likelihood analysis reveals that while the model successfully accounts for dark energy dynamics, it is only slightly statistically favoured over $\Lambda$CDM by current observations.
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All authors Mario Ramos-Hamud, Gabriela García-Arroyo, Fernando Quevedo, J. Alberto Vázquez
Cosmology and Nongalactic Astrophysics
Stress-testing the spatially flat Universe: nonparametric spatial curvature determination from DESI DR2
Hannah C. Turner, Suhail Dhawan, Sunny Vagnozzi et al. (+2 more)
We present a nonparametric determination of spatial
curvature using only late-time geometrical probes. Under a Gaussian Process smoothness prior, we jointly constrain the dimensionless expansion history and $\Omega_K$, combining three Type Ia
Supernovae (SNeIa) samples with either DESI DR2 line-of-sight baryon acoustic oscillations (BAO) or
cosmic chronometers (CC) data. From our baseline SNeIa+BAO analyses we find $\Omega_K=0.219^{+0.110}_{-0.111}$, $\Omega_K=0.330^{+0.098}_{-0.150}$ and $\Omega_K=0.260^{+0.124}_{-0.127}$ for the PantheonPlus, DES Dovekie and Union3 SNeIa samples respectively. These nonparametric results mildly favour an open Universe, supporting recent hints in this direction, and improve on the sensitivity of a previous application of the method by up to a factor of $\sim 2.5$. We find consistent constraints combining SNeIa and CC, whereas restricting SNeIa data to the
redshift range covered by BAO somewhat weakens the constraints and shifts the PantheonPlus central value to $\Omega_K<0$. Our results depend only on late-time relative distances and expansion rates, making them insensitive to the absolute distance scale calibration, while relying neither on
Cosmic Microwave Background data nor on a parametric dark energy model.
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All authors Hannah C. Turner, Suhail Dhawan, Sunny Vagnozzi, Alice Townsend, Peter Massey
Cosmology and Nongalactic Astrophysics
Model-Independent Measurement of Baryon Gas Fractions through Galaxy-Galaxy Lensing and the Kinematic Sunyaev-Zel'dovich Effect
R. Henry Liu, Uroš Seljak, Simone Ferraro et al. (+52 more)
Baryon feedback is a leading source of systematic uncertainty for cosmology from weak
lensing, but measurements of the gas distribution around
galaxies have largely relied on parametric profile models or simulation-calibrated frameworks. We present model independent measurements of the radial gas fraction profile around
galaxies, combining
galaxy-
galaxy lensing and kinematic Sunyaev-Zel'dovich (kSZ) effect. We introduce a method that applies the same radial $\Delta\Sigma$ aperture filter to both the
galaxy-
galaxy lensing shear field and the velocity-weighted kSZ temperature maps; their ratio directly yields $\Delta\Sigma$ filtered gas fraction $f_{\rm gas}(R)$, the ratio of ionized gas to total matter as a function of projected radius. We apply this approach to DESI DR2 Bright
Galaxy Survey (BGS, $\bar{z} \approx 0.26$) and Luminous Red
Galaxy (LRG, $0.4 < z < 1.1$) samples, using ACT DR6 component-separated CMB maps for kSZ, and the HSC Year 3 shear catalog for weak
lensing. After correcting for ACT beam suppression using a simulation-calibrated compensation factor, we detect baryon depletion relative to the
cosmic mean baryon fraction at SNR = 17.2 (BGS) and SNR = 13.8 (LRG bin 1). Comparison with six hydrodynamical simulations from the Illustris, IllustrisTNG, SIMBA, and FLAMINGO suites shows that the fiducial FLAMINGO run most closely tracks the observed radial gas distribution in both samples, with Illustris-1 and TNG300-1 bracketing the data from below and above at small radii. We find a mild discrepancy between the kSZ measurements in the South and North Galactic Caps in one LRG
redshift bin, which may indicate residual systematics. We show that the ratio is robust to splits by stellar mass and to the removal of close pairs. These results establish $\Delta\Sigma$ filtering of kSZ versus weak
lensing signal as a model-independent probe of the baryon distribution around
galaxies.
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All authors R. Henry Liu, Uroš Seljak, Simone Ferraro, Boryana Hadzhiyska, Frank J. Qu, Bernardita Ried Guachalla, Emmanuel Schaan, Jessica Nicole Aguilar, Steven Ahlen, Anton Baleato Lizancos, Florian Beutler, Davide Bianchi, David Brooks, Aurelio Carnero Rosell, Francisco Javier Castander, Todd Claybaugh, Andrei Cuceu, Axel de la Macorra, Jaime E. Forero-Romero, Enrique Gaztañaga, Satya Gontcho A Gontcho, Gaston Gutierrez, Klaus Honscheid, Dragan Huterer, Mustapha Ishak, Stephanie Juneau, Tanveer Karim, David Kirkby, Anthony Kremin, Ofer Lahav, Martin Landriau, Laurent Le Guillou, Martine Lokken, Marc Manera, Aaron Meisner, Ramon Miquel, John Moustakas, Seshadri Nadathur, Jeffrey A. Newman, Hernan Enrique Noriega, Will Percival, Ignasi Pérez-Ràfols, Francisco Prada, Corentin Ravoux, Graziano Rossi, Lado Samushia, Eusebio Sanchez, Christoph Saulder, David Schlegel, Michael Schubnell, Hee-Jong Seo, Małgorzata Siudek, Gregory Tarlé, Benjamin Alan Weaver, Rongpu Zhou
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
The ALMA View of High-Redshift Galaxy Formation
Renske Smit and Rebecca A.A. Bowler
The advent of routine operations with the Atacama Large Millimeter/submillimeter Array (ALMA) in the last decade has led to a revolution in the direct study of the interstellar medium (ISM) in `normal' high-
redshift galaxies in the rest-frame far-infrared (FIR). This review summarizes the observational literature on z>6.5 sources observed with ALMA and NOEMA (NOrthern Extended Millimeter Array). The main findings are as follows: Cool gas consistently scales with
star-formation in a wide range of
galaxy environments, similar to local relations, suggesting fundamental processes of
star-formation stay relatively constant over 13 billion years of
cosmic time. Significant metal enrichment is present in
galaxies just 300-400 million years after the Big Bang. There is a trend to higher obscured fraction of
star formation with stellar mass and SFR already in place at z~7, with measurements of the
cosmic SFR density showing that >10 percent of the SFR density is obscured at this epoch. The estimated dust masses compared to the stellar mass suggest that rapid dust enrichment occurs, likely from
supernova with little dust destruction and/or rapid growth in the ISM, which is in agreement with maximal predictions from models. In individual sources cold disks are already in existence, with their gas disks being more extended and smooth than their observed stellar counterparts.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Non-Perturbative Modulus Decay and Multi-Component Dark Matter
Gordon Kane, Leia Price, Luis Rufino et al. (+2 more)
Non-thermal cosmological histories rest on the assumption that scalars displaced during inflation undergo coherent oscillations, dominate the energy density of the universe before Big Bang Nucleosynthesis, and decay perturbatively through gravitationally suppressed interactions. In addition, usually a single dark matter component is assumed. This early matter-dominated era is the basis for the usual predictions of non-thermal WIMP production,
axion dark matter,
entropy generation, and dark radiation. This paper examines whether this picture is dynamically robust against non-perturbative decay of the modulus condensate. In this work, we study non-perturbative particle production from oscillating moduli using the effective field theory appropriate to $G_2$ compactifications. We find that non-perturbative production of Wino-like
fermions is strongly suppressed in the relevant parameter regime. In contrast, a modulus-dependent
axion kinetic term admits narrow instability bands with growth rates that can exceed the Hubble rate. A linear Floquet analysis alone, however, cannot determine whether these bands significantly deplete the modulus condensate, since
cosmic expansion, backreaction, rescattering, and higher-order operators in the effective theory can become important. As a result, the conventional modulus-dominated cosmology remains robust against Wino and gauge-field preheating, while the
axion channel provides a potentially important modification that requires nonlinear study. If sufficiently efficient,
axion production can alter the division of dark matter between Winos and
axions and enhance the dark-radiation abundance.
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All authors Gordon Kane, Leia Price, Luis Rufino, Scott Watson, Fred Adams
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Resonant Gravitational Production of Chiral Dark Photons
Leah Jenks, Marc Kamionkowski and Edward W. Kolb
Vector fields with a chiral, parity-odd coupling to a pseudoscalar field are known to undergo resonant amplification. In this work, we study this phenomenon in the context of cosmological gravitational particle production during early-universe inflation. We consider a massive vector (dark
photon) field with a parity-odd coupling to the inflaton. There are two regimes of production, delineated by the relative size of the coupling and the dark
photon mass, arising from a tachyonic instability, and a parametric resonance, respectively. As a result of the coupling, the transverse modes, subdominant in both the minimally and nonminimally coupled theories, can dominate the total late-time abundance. The viable parameter space for dark-
photon dark matter is thus widened. Furthermore, in the tachyonic case, the production is dominated by a single helicity mode, leading to a population of chiral dark
photons that can lead to potential parity-violating observational signatures. We further explore the dependence of the production on the reheating history, and find that information about reheating is encoded in the number density spectrum.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Resurrecting Electroweak Dark Matter via Type-II Seesaw in light of recent LZ Event
Partha Kumar Paul, Sujit Kumar Sahoo, Narendra Sahu et al. (+1 more)
The recent observation of the high-energy nuclear recoil event LZ230616 with a recoil energy around 248 keV provides an interesting possibility to probe inelastic doublet dark matter (iDM). However, the electroweak doublet DM scenarios face strong constraints from solar DM capture for DM masses around the TeV scale which give rise to correct thermal relic density. In this work, we revive the inelastic doublet DM (iDM) scenario via type-II seesaw. In particular, we consider an inert lepton doublet (ILD) DM. While the minimal ILD scenario gives the correct relic abundance around the TeV scale, it is strongly constrained by direct detection and solar DM capture. In the type-II seesaw, the presence of the scalar triplet generates the required mass splitting and provides additional annihilation channels, allowing the correct relic abundance for much larger DM masses. The larger DM mass also helps evade the solar capture and indirect detection constraints. Additionally, the scalar triplet gives sub-eV
neutrino masses required by the oscillation data.
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All authors Partha Kumar Paul, Sujit Kumar Sahoo, Narendra Sahu, Shashwat Sharma
Cosmology and Nongalactic Astrophysics
Non-linear halo bias for accurate modelling of cosmic infrared background anisotropies
Baptiste Jego, Matthieu Béthermin, Katarina Kraljic et al. (+3 more)
Halo models provide the standard framework for interpreting
cosmic infrared background (CIB) anisotropies and inferring the connection between dusty
star-forming
galaxies and their host dark matter
halos. Recent studies have shown that inaccuracies in the modelling of
halo clustering may bias the inferred parameters governing
star formation in dark matter
halos. In this work, we investigate whether a more detailed description of
halo clustering can alleviate these shortcomings. We incorporate a scale-dependent, non-linear correction to the
halo bias within a
halo-model framework based on a simple SFR-
halo mass parametrisation. We consider both a full mass-dependent implementation and a computationally efficient approximation. We also investigate the impact of updated (sub)
halo mass functions. We validate the revised framework using mock observations derived from a dedicated simplified version of the SIDES-Uchuu simulation, combining the SIDES empirical
galaxy model with the Uchuu N-body simulation, specifically designed to match the SFR prescriptions adopted in our
halo-model. The corrections modify the predicted CIB clustering by up to 30% on intermediate scales, while the effective implementation reproduces the full treatment at the sub-percent level. The updated model removes the scale-dependent discrepancies previously identified and accurately reproduces the measured power spectra over the full multipole range. In MCMC analyses, the input SFR parameters are recovered with substantially reduced biases, with all input parameters recovered within their $1\sigma$ confidence intervals. Our results demonstrate that accurately modelling non-linear
halo clustering is essential not only to reproduce CIB anisotropies, but also to reliably recover the underlying
galaxy-
halo connection. The framework presented here provides a validated foundation for future analyses of observational data.
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All authors Baptiste Jego, Matthieu Béthermin, Katarina Kraljic, Athanasia Gkogkou, Guilaine Lagache, Abhishek S. Maniyar
Cosmology and Nongalactic Astrophysics
Modified Gravity from growth data: goodness-of-fit and gravitational coupling
Manoel V. S. Filho, Fernanda Oliveira, Wiliam S. Hipólito-Ricaldi et al. (+2 more)
While background expansion data alone cannot discriminate among cosmological models, the growth of large-scale structures directly probes the underlying theory of
gravity, offering a path to distinguish General Relativity from its modifications. In this work, we constrain three representative $F(R)$ modified
gravity models (Starobinsky, Hu-Sawicki, and $R^2$-corrected Appleby-Battye) using measurements of the growth rate $f(z)$ and the matter fluctuation amplitude $\sigma_8(z)$. Our analyses combine MCMC parameter estimation, Gaussian Process reconstructions, and goodness-of-fit statistics including Akaike information criterion (AIC) and
Bayesian information criterion (BIC). All investigated models provide statistically comparable fits to the current growth data, with information criteria differences too small to establish a preference for any particular scenario. To overcome this degeneracy, we reconstruct the effective gravitational coupling $\mu(z)$ from the MCMC posterior samples, providing a physically motivated diagnostic that complements standard goodness-of-fit criteria. The Starobinsky and Hu-Sawicki models predict moderate departures from General Relativity, remaining compatible with constraints on both $\mu(z)$ and $S_8$. In contrast, the $R^2$-AB model predicts $\mu_0 \sim 3.5$ and $S_8 = 0.638$, a $3.2\sigma$ tension with Planck 2018, rendering it physically disfavored despite its competitive statistical performance.
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All authors Manoel V. S. Filho, Fernanda Oliveira, Wiliam S. Hipólito-Ricaldi, Felipe Avila, Armando Bernui
Cosmology and Nongalactic Astrophysics
A two-component profile of baryonic feedback: hydrostatic and diffuse gas
Kaitlyn Shavelle, Jared Siegel, Leah Bigwood et al. (+2 more)
Baryonic feedback processes redistribute gas within and beyond dark matter
halos, however, the resulting gas distribution remains highly uncertain, limiting predictions of the matter distribution for precision cosmology. We introduce a physically motivated approach to modelling the gas distribution that decomposes it into an approximately hydrostatic inner component and a diffuse outer component. This approach takes advantage of the growing observational landscape: X-ray measurements primarily probe the dense inner
halo, while the kinetic Sunyaev-Zel'dovich (kSZ) effect is sensitive to diffuse ionized gas extending to larger radii. We implement this two-component profile within the baryonification framework, though we note that it is applicable to any model of the large-scale gas distribution. We jointly fit X-ray gas-fraction measurements from the HSC-XXL and eROSITA samples with stacked kSZ effect measurements of BOSS CMASS
galaxies from the Atacama Cosmology
Telescope, demonstrating that the proposed profile retains sufficient flexibility. This proof-of-concept shows that a decomposition between hydrostatic and diffuse gas provides a simple, physically interpretable framework for connecting complementary observations of the gas distribution, and a foundation for future models of baryonic feedback.
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All authors Kaitlyn Shavelle, Jared Siegel, Leah Bigwood, Alexandra Amon, Romain Teyssier
Cosmology and Nongalactic Astrophysics
Intrinsic Tidal Shear at the Largest Scales: Galaxy Multiplet Alignment in DESI DR2
C. Lamman, J. Aguilar, S. Ahlen et al. (+45 more)
We measure the intrinsic
alignment (IA) of
galaxy multiplets with the large-scale tidal field traced by
galaxy positions in DESI Data Release 2. Using the BGS, LRG, and ELG samples spanning $0.01 < z < 1.6$, we optimize the scales which define multiplets in each sample to minimize measurement noise. We measure multiplet tidal
alignment $\mathcal{E}_+$ on scales beyond 100 $h^{-1}$Mpc in all samples, and detect
alignment over 200 $h^{-1}$Mpc, up to 4.5$\sigma$ in the highest LRG
redshift bin. We additionally present the multiplet shape-shape autocorrelation, $\mathcal{E}_{++}$, which is independent of
galaxy bias and provides a consistency check of our NLA (nonlinear
alignment) model. We do not detect a baryon acoustic feature in the projected
estimator. We also find the
alignment strength of multiplets is correlated with
redshift and
galaxy morphology. Multiplet
alignment offers direct access to the tidal shear field in all
galaxy samples, even where individual
galaxy alignment cannot, and extends IA detection to the largest scales yet probed.
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All authors C. Lamman, J. Aguilar, S. Ahlen, A. Aviles, D. Bianchi, D. Brooks, A. Carnero Rosell, F. J. Castander, T. Claybaugh, A. de la Macorra, D. Eisenstein, A. Font-Ribera, J. E. Forero-Romero, C. Garcia-Quintero, E. Gaztañaga, G. Gutierrez, K. Honscheid, M. Ishak, S. Juneau, T. Karim, D. Kirkby, O. Lahav, M. Landriau, M. E. Levi, M. Manera, A. Meisner, R. Miquel, S. Nadathur, H. E. Noriega, N. Palanque-Delabrouille, W. J. Percival, M. Perdomo, F. Prada, I. Pérez-Ràfols, C. Ravoux, A. J. Ross, G. Rossi, R. Ruggeri, L. Samushia, E. Sanchez, C. Saulder, D. Schlegel, M. Schubnell, J. Silber, M. Siudek, G. Tarlé, R. Vaisakh, B. A. Weaver
Cosmology and Nongalactic Astrophysics
FLUMEN: Neural Emulator of an Advanced Stochastic Weak Lensing Model
Galymzhan Baltabay and Ville Vaskonen
Weak gravitational
lensing by intervening structure magnifies distant sources and induces scatter in their luminosity distances. We develop an improved
stochastic model for the distribution of weak
lensing magnifications, $\textrm{d} P/\textrm{d}\mu$, that resolves individual lenses down to $10^7\,M_\odot$ and, besides field
halos and filaments, includes subhalos and large-scale clustering of the lens population. Both extensions broaden the distribution, and the resulting scatter in the luminosity distances agrees with the
halo-model prediction from the nonlinear matter power spectrum and exceeds that obtained from $N$-body ray tracing, which we attribute to the finite mass resolution and box size of the simulations. Building on this model, we develop FLUMEN, a conditional normalizing-flow emulator that predicts $\textrm{d} P/\textrm{d}\mu$ as a function of the source
redshift up to $z_s=12$ and six cosmological parameters $\{h,\Omega_M,\Omega_B,\sigma_8,n_s,z_{\rm eq}\}$. The emulator enforces the empty-beam cutoff and the fold-caustic power-law tail analytically, and reproduces the Monte Carlo distributions on held-out cosmologies with a median Kullback–Leibler divergence of $0.0048$ at negligible cost. Our results provide a fast and flexible framework for incorporating the full magnification distribution into cosmological analyses of standard sirens,
supernovae, and other point sources.
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Cosmology and Nongalactic Astrophysics
High Resolution Grid-based Simulations of the Warm-Hot Intergalactic Medium
Lile Wang and Renyue Cen
We present high-resolution cosmological hydrodynamic simulations of the Warm-Hot Intergalactic Medium (WHIM) using the GPU-optimized grid-based hydrodynamic code Kratos. Employing a uniform 4096^3 grid in a (100 h^-1 Mpc)^3 comoving volume, we achieve a spatial resolution of ~24.5 h^-1 kpc, sufficient to resolve the Jeans scale of gas at T ~ 10^4 K and n_H ~ 10^-3 to 10^-2 cm^-3. This calculation ranks among the largest grid-based cosmological hydrodynamic simulations performed to date. We find that ~23.4% of
cosmic baryons reside in the WHIM phase (T = 10^5 - 10^7 K) at z = 0, significantly below the 40-50% found in earlier, lower-resolution simulations. Through a suite of lower-resolution simulations, we demonstrate that spatial resolution plays a pivotal role in determining the WHIM fraction: resolving gas near its Jeans scale allows it to reach higher densities, where enhanced radiative cooling transfers a substantial fraction of baryons out of the WHIM temperature range. The remaining WHIM resides predominantly in filaments and
accretion-shock structures in the vicinity of
halos, where hierarchical structure formation and ongoing hydrodynamic
accretion provide continued shock heating. Synthetic observations of Lyman-alpha, O VI, O VII, and O VIII emission reveal distinct morphological and kinematic signatures, with O VI tracing filament-
halo interfaces and the X-ray lines probing hotter gas associated with massive
halos. These predictions underscore the importance of current and future missions such as XRISM, ATHENA, and HUBS for mapping WHIM thermodynamics and kinematics.
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Cosmology and Nongalactic Astrophysics
Lens Modeling and Cosmological Inference from an Impure Sample of Galaxy-Galaxy Strong Lenses
Philip Holloway, Aprajita Verma, Philip J. Marshall et al. (+7 more)
The start of the Legacy Survey of Space and Time marks a new era for strong
lensing science, where the number of strong lenses identified is expected to increase to $\mathcal{O}(10^5)$. In this paper we use a neural network to determine the precision with which lens parameters can be determined, using realistic simulated LSST lensed systems. We find that the Einstein radius can be measured with a mean precision of $3.7\%$ with calibrated uncertainties accurately reflecting the corresponding measurement error. Based on the performance of current strong lens classifiers, the $\sim 100,000$ detectable strong lenses are expected to be accompanied by a similar or larger number of false positives (non-lenses). In readiness for this we introduce a formalism, termed `
COSMIC-BEAMS', to infer cosmological parameters while accounting for contamination by false positives. As a proof-of-concept, using simulated LSST measurements of the Einstein radii of a realistic and impure sample of photometric lens systems, i.e. those without spectroscopic confirmation, we find that the cosmological parameters $\Omega_m$, $\Omega_\Lambda$, and $w$ can be measured to a precision of $0.1$, $0.03$ and $0.15$ respectively for a $w$CDM cosmology. We demonstrate that unbiased cosmological parameters can be inferred even in strong lens samples contaminated by $50\%$ false positives, and that the photometric
dataset of $100\,000$ strong lenses will provide equivalent $w$-precision to $2500-3500$ spectroscopic systems.
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All authors Philip Holloway, Aprajita Verma, Philip J. Marshall, Padmavathi Venkatraman, Sydney Erickson, Tian Li, Simon Birrer, Steven Dillmann, Thomas E. Collett, the LSST Dark Energy Science Collaboration
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.IM
Combining astrometry with pulsar timing: the first joint analysis of very low frequency gravitational waves
Lorenzo Filipello, William Beordo, Volodymyr Akhmetov et al. (+2 more)
The pHz to sub-nHz GW regime remains largely unexplored but is crucial for mapping the early inspiral stage of SMBHBs and probing early-Universe physics. Astrometry and
pulsar timing offer orthogonal and deeply complementary secular observables to investigate this frequency band. We aim to present the first joint data analysis combining real astrometric proper motions with binary
pulsar timing, to search for and constrain continuous gravitational waves (CWs) sourced by SMBHBs in the ultra-low-frequency regime ($10^{-12} \le f_{GW} \le10^{-9} Hz$). We employ a
Bayesian model selection and upper limit estimation framework to combine apparent proper motion displacements of $\sim 1.5 \times 10^6$
quasars from the Gaia CRF3 catalog with the line-of-sight orbital period derivatives ($\dot{P}_b$) of 11 high-precision binary
pulsars. To prevent spurious detections, we heavily model instrumental and astrophysical systematics: we propagate the Galactic potential uncertainty for
pulsars via Monte Carlo simulations and perform a Vector Spherical Harmonics (VSH) decomposition up to the octupole order (l=3) for
quasars. We find no statistically significant evidence for a CWs signal in the joint analysis ($\ln B_{joint} = -0.42 \pm 0.03$). In the absence of detection, we set the tightest constraints to date on CW strain in the pHz band, yielding a 95% upper limit of $h_0\le6.4x10^{-11}$ at a reference frequency of $f_{ref} = 4 \times 10^{-10}$ Hz. The combined
dataset achieves full sky coverage and improves single-
dataset upper limits by 20%-30%. Combining orthogonal observables successfully breaks spatial degeneracies intrinsic to isolated searches. Furthermore, forecasts from inj.-rec. indicate that with the extended temporal baseline and reduced uncertainties of the upcoming Gaia DR4, this joint framework is poised to break the $h_0 < 10^{-11}$ upper limit barrier for sub-nHz CWs.
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All authors Lorenzo Filipello, William Beordo, Volodymyr Akhmetov, Mariateresa Crosta, Mario Gilberto Lattanzi
Cosmology and Nongalactic Astrophysics
A note on oscillons: non-negligible metric fluctuations during preheating
Daniel del-Corral, Paolo Gondolo, K. Sravan Kumar et al. (+1 more)
The dominant
lattice approach to post-inflationary preheating and oscillon formation evolves an inhomogeneous inflaton field on a spatially homogeneous Friedmann-Lemaître-Robertson-Walker background, whose expansion is sourced by a volume-averaged energy density, while metric perturbations are neglected. We examine the consistency of this approximation with General Relativity. Using the linearized Einstein constraints, we show that the suppression of the Bardeen potential, characteristic of slow-roll inflation, disappears during preheating: once the first slow-roll parameter becomes of order unity, the metric and inflaton fluctuations enter at the same perturbative order. We further show that the scalar-field equation evolved in the fixed-FLRW prescription omits leading-order contributions generated by metric fluctuations. We then derive the proper-volume average of the ADM
Hamiltonian constraint and show that it does not reduce to the Friedmann equation used in
lattice simulations: the exact averaged constraint contains additional contributions from the spatial
curvature, the variance of the local expansion, the shear, and metric corrections to the local energy density. Finally, we illustrate numerically, for Starobinsky and $\alpha$-attractor models, that the metric contribution becomes comparable to the scalar-field contribution during the amplification stage. These results directly affect the standard
lattice description of oscillon formation and motivate numerical relativity as a consistent framework for the nonlinear preheating problem.
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All authors Daniel del-Corral, Paolo Gondolo, K. Sravan Kumar, João Marto
Cosmology and Nongalactic Astrophysics
21-cm Constraints on S-wave Dark Matter Annihilation with Subhalo-enhanced Effects
Zixuan Xu and Sibo Zheng
Observations of the 21-cm signal can probe energy injection into the intergalactic medium arising from dark matter annihilation during
cosmic dawn and reionization. For s-wave annihilation, the annihilation rate depends on the squared dark matter density, making the 21-cm signal sensitive to dark matter
halo substructure. In this work, we extend the numerical method of DM21cm to address spatially inhomogeneous s-wave annihilation including subhalo effects, using semi-analytical treatment of SASHIMI-C. Our numerical results show that the projected HERA limit for the $\gamma\gamma$ annihilation channel is stronger than the Leo~T bound within the dark matter mass range of $m_{\chi}\leq 3\,{\rm keV}$, whereas the projected HERA limit for the $e^+e^-$ annihilation channel is the strongest among the existing bounds for $m_\chi\sim 0.1$–$1\,{\rm GeV}$.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
The high-velocity dark matter halo of the Milky Way in light of the LZ 248 keV event
Ciaran A. J. O'Hare
The interpretation of high-energy nuclear recoil events in direct-detection experiments can depend sensitively on the poorly understood high-speed tail of the Galactic dark matter velocity distribution. This fact has been brought into sharper focus recently by an anomalous nuclear-recoil event at $E_R\approx248~\mathrm{keV}$ observed by the LZ experiment. If interpreted as caused by a dark-matter-induced recoil, kinematic constraints on many models imply this particle would have to emerge from the high-speed tail. Here, we re-assess this astrophysical uncertainty using Milky Way analogues from the IllustrisTNG and FIRE simulations. We find that the maximum laboratory-frame DM speed on June 16, when the event was observed, is $792.7^{+82.9}_{-95.6}\, \mathrm{km/s}$ (median and 95% containment across simulations), with a median very close to the fiducial SHM value. Modelling the tail of the velocity distribution in three dimensions is complicated by the fact that these simulated dark matter
halos are anisotropic and are generically seen to
spin in the same direction as the baryonic disk. However, we find that this does not reduce the maximum laboratory-frame DM speed because the approximately Gaussian azimuthal velocity distribution is negatively skewed by this co-rotation, rather than shifted by it. We illustrate these results in the context of an inelastic dark matter interpretation of the LZ event.
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