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Physics Astrophysics Cosmology and Nongalactic Astrophysics

astro-ph.CO Watch Cosmology and Nongalactic Astrophysics

Thursday 13 August

Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

Abundant Heavy Black Hole Seeds from Moderate Lyman-Werner Radiation

Ryan Hazlett, Eli Visbal, Greg L. Bryan et al. (+1 more)

The existence of high-redshift quasars may indicate that massive black hole seeds formed via supermassive Population III stars in atomic-cooling halos with large gas inflow rates; however, the dependence of this process on halo assembly rate and radiative background remains poorly constrained. We present a large suite of 65 high-resolution cosmological zoom-in simulations of 15 pristine halos spanning a wide range of Lyman-Werner radiation backgrounds and halo assembly histories. We introduce a novel method to estimate the final Population III stellar mass from radial gas infall profiles at the onset of runaway collapse and validate it against simulations from the literature that explicitly follow protostellar accretion with sink particles, reproducing protostellar masses to within a factor of $\sim2$. We find a clear transition in gas inflow rates between halos exposed to $J_{\rm 21} \lesssim 1$ and $J_{\rm 21} \gtrsim 10$, with the latter frequently sustaining inflow rates above the adopted threshold for supermassive star formation and producing estimated stellar masses up to $10^{5} \, M_{\odot}$. In contrast, the halo assembly timescale, $M_{\rm Halo}$/$\dot{M}_{\rm Halo}$, shows no statistically significant correlation with predicted stellar mass, despite halo assembly rates spanning $0.01$-$7 \, M_{\rm \odot} \, {\rm yr}^{-1}$. The Lyman-Werner radiation field therefore is a stronger predictor of sustained high accretion within our parameter space. Finally, a semi-analytic model applied to cosmological volumes shows that halos exposed to intermediate Lyman-Werner backgrounds ($1 \lesssim J_{\rm 21} < 10$) are orders of magnitude more common than those in the high-$J_{\rm 21}$ tail. If sustained high accretion extends into this intermediate regime, heavy black hole seeds may form in substantially more common environments than required by classical direct-collapse scenarios.
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All authors Ryan Hazlett, Eli Visbal, Greg L. Bryan, Mihir Kulkarni

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

Axion Isocurvature Perturbations Survive the Scaling Evolution of Axion Domain Walls

Naoya Kitajima, Junseok Lee, Kai Murai et al. (+2 more)

We revisit the evolution of axion domain walls seeded by inflationary fluctuations. In our previous work, we showed that such domain-wall networks retain superhorizon correlations even after entering the scaling regime. We extend our previous analysis to the case with large initial fluctuations, where many minima of the axion potential are already populated when the axion starts to oscillate. Although the conventional misalignment contribution can have suppressed long-wavelength isocurvature perturbations when many vacua are averaged over, axions produced by domain-wall collapse provide an additional contribution that can dominate when the walls enter the scaling regime before annihilation. In particular, the biased vacuum energy released during wall annihilation inherits the superhorizon correlations of the inflationary fluctuations and transfers them to the axion energy density. We find that sizable isocurvature perturbations can therefore survive even after the walls annihilate. We also discuss generic isocurvature constraints on dark matter produced by domain-wall collapse.
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All authors Naoya Kitajima, Junseok Lee, Kai Murai, Fuminobu Takahashi, Wen Yin

Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.HE

A binary black hole merger rate comparison within the same metallicity-star formation rate framework

Lumen Boco, Michela Mapelli, Michele Bosi et al. (+2 more)

Recent studies have suggested that binary population synthesis models, when coupled with observationally based, metallicity-dependent SFRD, overpredict the observed local BBH merger rate density. The significance of this tension might vary depending on the specific code and parameters adopted. Thus, a more extensive exploration of the parameter space is required. Here, we perform such an extended analysis. We first carry out a comprehensive analysis by using a large set of BBH merger efficiencies across a wide range of physical assumptions, parameters, and initial conditions. We combine these efficiencies with an observationally motivated SFRD and explore 18 metallicity variations to encompass observational uncertainties. We find that the tension between predicted and observed BBH merger rate density persists: in 17 out of 18 metallicity variations none of the models considered predicts a local BBH merger rate within or below the observed 90% credible interval. Even in the most favorable metallicity variation, only <10% of the models are consistent with the observational constraints. Then, we perform a full calculation, including a self-consistent delay time distribution, for the models yielding the lowest BBH merger rate densities. This analysis confirms that even the most conservative models overpredict the observed local BBH merger rate for almost all the metallicity variations. We show that the inclusion of the low-metallicity tail contributed by low-mass galaxies and starbursts, together with a treatment of iron rather than oxygen abundance, systematically shift the predicted rates toward higher values. Consequently, even literature models that predict moderate BBH merger rates can instead produce substantially higher rates when coupled to an observationally motivated SFRD.
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All authors Lumen Boco, Michela Mapelli, Michele Bosi, Cecilia Sgalletta, Amedeo Romagnolo

Cosmology and Nongalactic Astrophysics · Cross-listed from physics.data-an

Unknown Unknowns: Model Misspecification in Machine Learning for Physics

Juan Cruz-Martinez, Carolina Cuesta-Lazaro, Alexander Held et al. (+1 more)

Machine learning is now a central tool for solving inverse problems in particle physics and astronomy. Models are trained on simulation and deployed on real data, raising the question not just of whether they fit, but of whether they are wrong in ways we did not anticipate: the unknown unknowns. This challenge of model misspecification is not unique to machine learning. In physics, misspecification is sometimes exactly what we want to find: new discoveries appear as failures of existing models. At other times, we want such effects absorbed into the analysis without biasing the measurement. A robust analysis is one that absorbs the misspecifications we are not interested in, while preserving sensitivity to the ones we are. Machine learning can both amplify misspecification and provide new tools to address it. We discuss the challenges of model misspecification, diagnostics for detecting it, and strategies for mitigation. No single diagnostic can confirm that a model is correctly specified: detection and mitigation are two halves of an iterative loop, in which a battery of complementary diagnostics is applied, the model is updated, and the process repeated. Robustness against unknown unknowns is ultimately less about any single technique than about a disposition: a willingness to suspect one's own model, and to design analyses that can survive being wrong in ways one did not anticipate.
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All authors Juan Cruz-Martinez, Carolina Cuesta-Lazaro, Alexander Held, Michael Kagan

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Vector Perturbations in Ghost-Free Quasidilaton Massive Gravity

Ekapob Kulchoakrungsun and Daris Samart

We study transverse vector perturbations in ghost-free extended quasidilaton massive gravity without a quasidilaton kinetic term, in the presence of minimal matter. In vacuum, we recover the known result that the kinetic coefficient $K_V$ of the gravitational vector modes vanishes on the self-accelerating branch $J=0$, so those modes are infinitely strongly coupled at linear order. We then add a canonical scalar field and a single Abelian vector (Maxwell or Proca). After integrating out the auxiliary shift, we find the same $K_V$ as in vacuum. The scalar matter has no transverse perturbation; it enters the unsimplified shift constraint, but those terms cancel once the Friedmann equation is used. A Maxwell or Proca field with vanishing isotropic background does not mix with the gravitational vectors at quadratic order. Minimal matter therefore leaves $K_V=0$ on Branch II. We do not claim that the modes are absent from the nonlinear theory. We do conclude that ordinary minimal matter is not enough to make the vector sector perturbatively healthy on this branch. If we need healthy gravitational vector modes at the linear level, Branch I is the branch to use.
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Cosmology and Nongalactic Astrophysics

Higher-Order Analytical Expansion of Thawing Dark Energy with an Exponential Potential

Naoto Maki and Kazunori Kohri

Motivated by recent DESI results suggesting dynamical dark energy, we investigate the thawing scenario in quintessence with an exponential potential, $V=V_0e^{-\lambda\phi/m_{\mathrm{pl}}}$, by analytically expanding the deviation of the equation of state parameter $w_{\phi}$ from $-1$ in powers of $\lambda$. In addition to the previously known leading-order result at $O(\lambda^2)$, we derive the $O(\lambda^4)$ correction as a function of the density parameter $\Omega_\phi$. We show that a consistent determination of the redshift dependence of $w_\phi$ through $O(\lambda^4)$ requires corrections to the background expansion. We obtain the required correction by expanding $\Omega_\phi$ in powers of $\lambda$ around its $\Lambda\mathrm{CDM}$ value. Comparison with numerical solutions demonstrates that the $O(\lambda^4)$ expansion provides a more accurate approximation than the leading-order result. Our analytical approximation, which consistently incorporates the $O(\lambda^4)$ correction, will provide a potentially useful tool for distinguishing the exponential quintessence model from other dark energy models in future observations.
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Cosmology and Nongalactic Astrophysics

The Most Probable Outer Density Profile from Excursion Set Theory

Ericka Florio and Vasiliki Pavlidou

Measurements of the turnaround radius around galaxy clusters can be used to break the degeneracy between measurements of the present day energy density of matter and dark energy. Korkidis & Pavlidou showed that the turnaround radius coincides with the first point of deviation between outer density profiles in N-body simulations and the analytic profile predicted by excursion set theory. However, their analytic profile relied on a number of simplifying assumptions, which may each introduce systematic error. We evaluate the effect of these assumptions on the shape of the analytic profile and its correspondence with simulated outer density profiles. We relax the key simplifying assumptions and re-derive the mode of the outer density profile from excursion set theory. We then numerically resolve the double distribution (DD) across a range of masses and clustering parameters, and compare the numerical mode estimate to the re-derived analytic profile. We find excellent agreement between our analytic profile and the numerically-realized DD. However, our analytic profiles diverge from N-body profiles, and this divergence grows as we relax successive assumptions. We relate this mismatch to the differing window functions used in the analytic and simulation-based approaches, which respectively yield Markovian and correlated density trajectories. We conclude that the analytic profile proposed by Korkidis & Pavlidou should only be used as a few-parameter effective description of the most-probable outer density profile, with parameters fitted to results of cosmological simulations.
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Cosmology and Nongalactic Astrophysics

Automatic detection of fast oscillations of dark matter scalar field and updated cosmological constraints on QCDM

Amin Aboubrahim and Pran Nath

It is well known that a scalar field dark matter with a quadratic potential undergoes fast oscillations when the time period represented by the mass scale in the Klein-Gordon equation becomes much smaller than that set by the Hubble parameter. This makes a solution to the equation numerically intractable. Many works in the literature have addressed the problem by either switching between solving the Klein-Gordon equation in the well-behaved regime to solving the fluid equations at the onset of oscillations, or by introducing a new set of variables that can absorb these oscillations. Despite being successful, these techniques rely on an estimate of when the oscillations start. For large scale scans of a model's parameter space, this can become cumbersome. Furthermore, the techniques have been used mainly for non-interacting dark matter models. In this work, we introduce an averaging technique with an automatic detection of the onset of oscillations, capable of capturing the non-interacting as well as the interacting dark matter scenarios. The technique, implemented in CLASS, is tested on the QCDM model and shows excellent detection and averaging abilities. We also update the cosmological constraints on the model using the most recent public data.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.IM

Optical concept model of the future cosmology project BISOU

Morgane Loquet Le Gall, Bruno Maffei, Pierre Guiot et al. (+2 more)

We present an optical analysis of BISOU (Balloon Interferometer for Spectral Observations of the primordial Universe), an astronomical balloon-borne pathfinder spectrometer developed as part of a preparatory study for a future space mission aiming at measuring spectral distortions of the cosmic microwave background (CMB). The BISOU optical system is based on a differential polarizing Fourier Transform Spectrometer (FTS) that receives inputs from both a sky-facing telescope and an internal calibration source. The FTS focal planes are equipped with bolometric detectors coupled to multimode feed horns, with distinct focal planes dedicated to the low (90 - 300GHz) and high (0.3 - 1.5THz) frequency bands. The optical analysis first relies on ray-tracing simulations to establish the overall configuration of the system, before proceeding to more advanced Gaussian beam and physical optics analyses.
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All authors Morgane Loquet Le Gall, Bruno Maffei, Pierre Guiot, Creidhe O'Sullivan, Neil Trappe

Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.IM

Optical development of the BISOU breadboard

Morgane Loquet Le Gall, Creidhe O'Sullivan, Bruno Borgo et al. (+4 more)

BISOU (Balloon Interferometer for Spectral Observations of the primordial Universe) is an astronomical balloon-borne pathfinder developed as part of a preparatory study for a future space mission aimed at measuring spectral distortions of the cosmic microwave background (CMB). A laboratory breadboard of the instrument is being developed at the Institut d'Astrophysique Spatiale (IAS), enabling the characterization of subsystems and instrument systematic effects, particularly in the optical system. The optical system is based on a differential polarizing Fourier Transform Spectrometer (FTS) that receives inputs from both a sky-facing telescope and an internal calibration source. The FTS focal planes include sub-K detectors coupled to multimode feed horns. The full spectral band, spanning between 90 and 1500 GHz, is sub-divided into two frequency sub-bands, thanks to the use of a dichroic. The optical analysis first relies on ray-tracing simulations to establish the overall configuration of the system, before proceeding to more advanced Gaussian beam and physical optics analyses.
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All authors Morgane Loquet Le Gall, Creidhe O'Sullivan, Bruno Borgo, Clémence De Jabrun, Valentin Sauvage, Neil Trappe, Bruno Maffei

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Long-term 3+1 simulations of primordial black hole formation during radiation domination

Zhuan Ning, Rong-Gen Cai, Shao-Jiang Wang et al. (+1 more)

We develop an efficient three-dimensional numerical-relativity framework for primordial black-hole (PBH) formation from superhorizon curvature perturbations in a radiation-dominated Universe. We implement flux-conservative relativistic hydrodynamics in the adaptive-mesh-refinement code GRChombo and introduce a cosmologically scaled Gamma-driver that allows the cosmic-time step to grow in proportion to the scale factor. For a representative long-term simulation, the scaled driver preserves the apparent-horizon mass evolution and constraint behavior while reducing the number of coarse-level advances by a factor of approximately $94$ relative to the standard driver. We also construct a conformal-time version of the moving-puncture gauge as an independent check. Applying the framework to a spherical Gaussian curvature profile, we find a collapse threshold $0.79578 < \mu_c < 0.79580$ and a critical exponent $\gamma \simeq 0.3559$, consistent with previous spherically symmetric results. We further fit the late-time PBH mass growth to the Zel'dovich–Novikov accretion law, demonstrating that the code can follow both near-critical collapse and long-term post-formation evolution in three dimensions. The framework provides a foundation for future studies of PBH formation beyond spherical symmetry.
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All authors Zhuan Ning, Rong-Gen Cai, Shao-Jiang Wang, Chul-Moon Yoo

Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.IM

FOSSIL's preliminary thermal architecture

Valentin Sauvage, Clémence de Jabrun, Anaïs Besnard et al. (+6 more)

FOSSIL (FTS fOr CMB Spectral diStortIon expLoration) is a proposed ESA M8 mission tailored to measure the spectral distortions monopole of the Cosmic Microwave Background (CMB) with a sensitivity three orders of magnitude beyond the COBE/FIRAS legacy measurement. Achieving this sensitivity demands an extraordinarily challenging cryogenic architecture: the scientific instrument must be maintained at 4.5 K, while the detector focal plane assembly operates at 50 mK. This paper presents an overview of the preliminary thermal architecture of the FOSSIL payload, from the spacecraft service module at 293~K down to the sub-kelvin detector stage. The design draws on heritage from the Planck and ARIEL missions and relies on a staged passive cooling chain comprising a multi-layer insulation blanket, three V-groove radiators (operating at approximately 130 K, 90 K, and 50 K), and a 25 K actively cooled shield fed by an ESA-provided 4 K mechanical cryocooler. Sub-kelvin temperatures are achieved via a multi-stage adiabatic demagnetisation refrigerator (ADR) developed for NewAthena/X-IFU, providing continuous cooling at 1.8 K and 350 mK, and 50 mK with an 80% duty cycle. The Focal Plane Assembly (FPA), housing four Kinetic Inductance Detector (KID) arrays at 50 mK, is thermally isolated from the 4.5 K bench via a carbon-fibre reinforced polymer (CFRP) hexapod with staged heat interception. We outline the staged cooling concept and show that the architecture closes with positive thermal margins at every stage; the detailed steady-state thermal budget will be presented in a forthcoming dedicated paper.
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All authors Valentin Sauvage, Clémence de Jabrun, Anaïs Besnard, Bruno Borgo, Ivan Charles, Jean-Marc Duval, Bruno Maffei, Sylvain Martin, Nabila Aghanim

Cosmology and Nongalactic Astrophysics

Cosmography with DESI-DR1 Cosmic Chronometers: Direct H(z) measurements from Luminous Red Galaxy ages

Carlos A. Álvarez, Marcos M. Cueli, Balakrishna S. Haridasu et al. (+6 more)

Providing robust redshift estimates for almost 3 million luminous red galaxies (LRGs), the Dark Energy Spectroscopic Instrument (DESI) offers a unique opportunity to test the expansion rate of the Universe with independent approaches. We apply the cosmic chronometer method to derive new, independent constraints on the Hubble parameter at 0.3<z<1.2 from the differential age evolution of DESI LRGs. We select spectra applying spectroscopic cuts to ensure sample purity and remove contamination by star-forming objects, then build a robust sample of cosmic chronometers (CCs) by stacking to obtain stable, high signal-to-noise (S/N) spectra, which also serves as a democratic binning choice for the $t-z$ plane. Ages are estimated by measuring Lick indices on the stacked spectra and fitting them with a theoretical stellar population model. We obtain $t-z$ relations from which we derive $H(z)$ constraints via two independent approaches: a fit with a pivotal-redshift cosmography, and a direct estimate from the original CC method. The cosmographic fit yields posteriors for the kinematic parameters $\{H_{z_0}, q_{z_0}, j_{z_0}\}$ compatible with currently considered cosmologies, giving a precision-level estimate of $H(z)$. We provide the maximum-a-posteriori (MAP) $H(z)$ estimate, an array of the median confidence region in the $H-z$ plane, and its covariance matrix. We also leverage the redshift distributions of the $t-z$ relation for different velocity dispersion groups to obtain two independent local measurements using the discrete approximation $H(z) \approx -\Delta z/[\Delta t (1+z)]$; the one from the reddest envelope of CCs gives $H(z \approx 0.61) = 88.5^{+6.7}_{-12.6}$ (stat.) $\pm 8.1$ (syst.) km s$^{-1}$ Mpc$^{-1}$. Systematic uncertainties for both the cosmographic and discrete $H(z)$ measurements come from a comprehensive analysis of all methodological choices in the data treatment.
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All authors Carlos A. Álvarez, Marcos M. Cueli, Balakrishna S. Haridasu, Michele Moresco, Martina Torsello, Alessandro Bressan, Lumen Boco, Luigi Danese, Andrea Lapi

Cosmology and Nongalactic Astrophysics

Forecast for the detectability of patchy hydrogen reionization in WEAVE-QSO measurements of the Lyman-$\alpha$ forest power spectrum at redshift $z \geq 4$

Ke Ma, James S. Bolton, Vid Iršič et al. (+9 more)

We present the first detailed forecasts for the detectability of patchy hydrogen reionization in the one-dimensional Ly$\alpha$ forest power spectrum to be measured by the WEAVE-QSO survey. Using the Sherwood-relics reionization simulations and a WEAVE-QSO survey configuration, we generate mock spectra in four redshift bins, $z=4.0,4.2,4.4,$ and $4.6$, in which relic ionization and temperature fluctuations from patchy hydrogen reionization enhance the Ly$\alpha$ forest power spectrum on large scales (i.e., at wavenumber $k\sim 10^{-3},\mathrm{s\,km^{-1}}$). Our Ly$\alpha$ forest pipeline forecasts the power spectrum covariance by considering sample size, spectral resolution, noise subtraction, continuum placement, metal contamination, and damping wings from high-column density absorbers. Applying our covariance forecast within a Bayesian parameter inference framework, we find that the signature of patchy hydrogen reionization should be detectable at a significance of $\simeq 4.5\sigma$. The forthcoming WEAVE-QSO 1D power spectrum measurements should therefore be able to directly detect and characterize the large-scale relic imprint of patchy hydrogen reionization in the Ly$\alpha$ forest power spectrum at $z\geq 4$.
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All authors Ke Ma, James S. Bolton, Vid Iršič, Prakash Gaikwad, Matthew M. Pieri, Trystyn A. M. Berg, Rajeshwari Dutta, Matteo Fossati, Michele Fumagalli, Emanuel Gafton, Ignasi Pérez Ràfols, Francesco Pistis

Cosmology and Nongalactic Astrophysics

Cosmic Structures in CDM and SIDM

Sut-Ieng Tam

The standard $\Lambda$ Cold Dark Matter ($\Lambda$CDM) model has achieved remarkable success in explaining the formation and evolution of cosmic structures on large scales, supported by a wide range of observations, including the cosmic microwave background, large-scale structure surveys, and galaxy clusters. However, discrepancies between theoretical predictions and observations on small scales, have motivated the exploration of alternative dark matter models, including the self-interacting dark matter (SIDM) scenario. This review provides an overview of the theoretical foundations of CDM structure formation, the small-scale challenges, and the solutions proposed within the SIDM framework. We summarize recent theoretical developments in the SIDM framework and discuss current observational constraints on the dark matter self-interaction cross-section with particular emphasis on galaxy clusters.
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Cosmology and Nongalactic Astrophysics

X-ray signals converted from high-frequency gravitational waves emitted by spinning light primordial black hole dark matter

Asuka Ito and Kazunori Kohri

We investigate the detectability of high-frequency gravitational waves from the superradiance of light primordial black hole dark matter through photons converted in the Galactic magnetic field. We find that the signal is significantly enhanced in the X-ray frequency range around $10^{18}$Hz. For clustered initial conditions, future X-ray observations may detect the converted photons from primordial black holes in the mass range $10^{-15}M_{\odot} \sim 10^{-13}M_{\odot}$. Our results indicate that future X-ray observations could provide a new probe of light primordial black hole dark matter through high-frequency gravitational waves.
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Cosmology and Nongalactic Astrophysics

Waterfall-modulated $\alpha$-attractors

Renata Kallosh, Andrei Linde and Yusuke Yamada

Hybrid $\alpha$-attractor models \cite{Kallosh:2022ggf} can have significantly greater values of $n_{s}$ and smaller $r$, while preserving the relation $r\cong 3\alpha (1-n_s)^2$, which is valid for exponential T- and E-models at large values of the inflaton field. Here we study single-field $\alpha$-attractors with features inspired by hybrid models: one can uplift the potential, and one can also have a waterfall regime that leads to a premature termination of inflation near the critical point $\varphi_c$. This allows one to increase the effective number of e-foldings $N_c$ in formulas like $n_s\simeq 1-{2\over N_c}$, $r\simeq {12 \alpha\over N_c^2}$. By changing the waterfall's steepness and location, one can continuously move the predictions along the curves with $r\cong 3\alpha (1-n_s)^2$ as $n_s$ increases and $r$ decreases. We also study the effect of waterfall insertions and uplift on $n_s$ in quintessential $\alpha$-attractors that describe inflation and dynamical dark energy.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Scalar induced gravitational waves as probes of dark QCD

Wan-Zhe Feng, Ao Li and Jing-Zhi Zhou

We investigate scalar induced gravitational waves (SIGWs) as probes of a dark QCD crossover. Motivated by twin Higgs and asymmetric twin baryon dark matter scenarios, we consider a dark QCD sector with a confinement scale approximately 5.5 times the Standard Model (SM) QCD scale. We construct the effective energy and entropy degrees of freedom for the SM supplemented by dark QCD sectors containing either three light dark quark flavors or all six dark quark flavors. The resulting equation of state parameter and sound speed are then used to solve the first-order scalar perturbations and the second-order SIGWs through the SM and dark QCD crossover epochs. For a monochromatic primordial curvature power spectrum, we first demonstrate that the realistic SM thermal history modifies the SIGW spectrum relative to the idealized radiation-dominated case. We then show that a dark QCD crossover generates an additional frequency-shifted distortion when the enhanced scalar mode reenters the horizon near the dark confinement scale. This distinctive feature can therefore serve as a characteristic signature of the dark QCD sector. Our results demonstrate that SIGWs provide a complementary cosmological probe of hidden confining sectors, with characteristic spectral features shifted to higher frequencies relative to the SM QCD imprint. The analysis developed in this work can also be extended to other well-motivated theories containing different dark confining sectors.
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Wednesday 12 August

Cosmology and Nongalactic Astrophysics

CosmoFit: A Graphical User Interface for Bayesian Cosmological Parameter Estimation with User-Defined H(z) Models

Giovany Cruz

We present CosmoFit, a desktop graphical interface for Bayesian parameter inference in background cosmology. The application is designed to simplify cosmological analyses by reducing the need to manually program each step, while maintaining the transparency and reproducibility of the results. Users can define an expansion history H(z), specify fixed and sampled parameters, assign prior ranges and proposal scales, select the available observational likelihoods, and run Markov chain Monte Carlo analyses from a unified graphical interface. CosmoFit uses Cobaya for Bayesian sampling and GetDist for posterior analysis and visualization. The current version supports cosmic-chronometer data and the official Pantheon+, Pantheon+SH0ES, and Union3 supernova likelihoods available through Cobaya. For each run, the application stores the configuration files, metadata, execution logs, chains, and numerical summaries required to inspect and reproduce the analysis. The performance of CosmoFit was evaluated through unit tests, a parameter-recovery test using synthetic data, and an independent comparison with an analysis performed directly in Cobaya. The posterior mean values obtained with both procedures agree to within less than one percent. In addition, the synthetic-data test recovers the fiducial parameters within the expected credible regions. As an illustrative example, we perform a spatially flat wCDM analysis using Pantheon+SH0ES and obtain marginalized constraints and triangle plots directly from the interface. Within its current scope, CosmoFit provides an accessible, transparent, and reproducible tool for research and academic applications involving explicit models of the background cosmological expansion.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

Gaia parallax bias via spherical harmonics: A Python tool and discussion of possible causes

Valeri V. Makarov and Ciprian T. Berghea

Parallaxes in Gaia DR3 are known to suffer from a complex set of sky-correlated and magnitude-dependent offsets or biases at the level of a few tens of $\mu$as. Estimated from a sample of one million distant quasars and AGNs from the CRF catalog, the average offset is negative, but the actual distribution of this important parameter shows significant variations on the sky. We propose a practical method to evaluate the parallax correction as a function of sky position and, optionally, of $G$ magnitude using a spherical harmonic series, and supply a tested Python tool varpi3.py available on Zenodo\footnote{ https://zenodo.org/records/21708614}. We find that only the constant $Y_{00}$ term is significantly dependent on magnitude, while the other 80 harmonic terms are either close to zero or flat with magnitude. The directions of the smallest and largest parallax offsets are $(l,b)\simeq(220\degr,+43\degr)$ and $(l,b)\simeq(45\degr,-45\degr)$, which are close to the orientation of the quasar density dipole reported in recent publications. Motivated by this curious coincidence, we review possible physical effects resulting in a negative bias of measured parallaxes, including an anisotropic universe with a positive curvature and an orbital aberration component. The proposed method of parallax correction is tested using independent asteroseismology data for four different areas on the sphere. Finally, we show that the parallax zero-point propagates into the CRF proper-motion field through the parallax–proper-motion covariance, biasing the vector spherical harmonic determination of the secular-aberration glide, and hence the Galactocentric acceleration, at the microarcsecond-per-year level.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Spontaneous Scoto-leptogenesis

Arghyajit Datta, Hyun Min Lee and Jun-Ho Song

We propose a low-scale spontaneous leptogenesis scenario within the dynamical minimal scotogenic model for accommodating neutrino masses and inert scalar dark matter simultaneously. Thus, we dub the mechanism Spontaneous Scoto-leptogenesis. In this setup, a rolling Majoron arising from the global $U(1)_{B-L}$ symmetry breaking induces an effective chemical potential for the $B-L$ charge in the presence of $B-L$ violating interactions that allow for the efficient decays and inverse decays of right handed neutrinos (RHN), so it gives rise to the observed baryon asymmetry of the Universe through the electroweak sphaleron conversion. The mechanism becomes effective in the strong washout regime and successfully lowers the viable mass scale of the lightest RHN to the range of TeV scales, thereby making the thermal scotogenic leptogenesis with two hierarchical RHNs accessible to direct tests. We identify the roles of the $\lambda_5$ coupling for spontaneous leptogenesis and inert scalar dark matter through the efficient erasure of the inert scalar asymmetry. We also explore the regime for Majoron dark matter from the kinetic misalignment, showing that a multicomponent dark sector comprising the inert scalar and the Majoron can be realized in the model. The resulting framework provides a unified origin for low-scale baryogenesis, neutrino masses, and multicomponent dark sector, so it can be tested by complementary experimental probes through direct detection experiments, collider searches for inert scalars, and future detection of Majoron dark matter or dark radiation.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Singlet-Doublet fermion origin of dark matter, neutrino mass and inverse first-order electroweak phase transition

Debasish Borah, Indrajit Saha, Sujit Kumar Sahoo et al. (+2 more)

We study the possibility of an inverse first-order electroweak phase transition (IFOEWPT) and observable gravitational waves (GW) in a radiative neutrino mass model of scotogenic type where singlet-doublet (SD) fermions, the lightest of whom is the dark matter (DM) candidate, generate the necessary seesaw at one-loop level. Considering the possibility of light neutrinos being Dirac for simplicity and additional detection prospects, we extend the standard model (SM) with two generations of $SU(2)_L$ singlet and doublet fermions, one singlet scalar, and three right-handed neutrinos (RHNs). While RHNs provide the right chiral parts of light Dirac neutrinos, the SD fermions and the scalar singlet facilitate the one-loop neutrino mass diagram. The neutral component of the lighter SD fermion, stabilized under a residual $Z_2$ symmetry plays the role of DM while the heavier SD fermions strongly couple to the Higgs leading to an IFOEWPT where the Universe undergoes two different first-order phase transition as it goes from the symmetric to the final broken Higgs phase. We constrain the parameter space from the requirements of generating the correct neutrino mass, DM relic as well as IFOEWPT while incorporating the existing constraints from different experiments. The final allowed parameter space of the model can be probed at collider, direct-detection, GW and cosmic microwave background (CMB) experiments in near future.
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All authors Debasish Borah, Indrajit Saha, Sujit Kumar Sahoo, Narendra Sahu, Shashwat Sharma

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Thermal false vacuum decay near black holes is aspherical

D. S. Gorbunov, D. G. Levkov and V. E. Maslov

We study decay of a scalar field false vacuum near a (3+1)-dimensional Schwarzschild black hole equilibrated at Hawking temperature with the environment. Our scalar field model has negative quartic self-coupling and thereby resembles Higgs sector of the Standard Model in the large-field limit. We demonstrate that if the black hole is not too small, the false vacuum in this model decays aspherically with regard to the black hole center: via formation of expanding true vacuum bubbles emerging on the outer side of the event horizon. More specifically, we identify three regimes of the decay. For the largest and coldest black holes, the main mechanism is quantum tunneling described by an infinitesimally thin bounce sitting at some point of the horizon. In the intermediate-mass regime, the vacuum is destroyed by thermal fluctuations creating aspherical critical bubbles in the horizon vicinity. Finally, near the smallest black holes thermal fluctuations still guide the decay but the dominant critical bubble is spherically symmetric and covers the entire horizon.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

Evidence for the First Globular Cluster Stellar Stream beyond the Milky Way

Julie Kiel Holm, Sarah Pearson, Jacob Nibauer et al. (+5 more)

The dark matter content of ultra-diffuse galaxies is the subject of considerable debate. Stellar streams, which form when a host galaxy tidally strips stars from an orbiting stellar system, provide a powerful technique to constrain the dark matter content of external galaxies. The stripped stars form long, thin leading and trailing tidal arms that persist for billions of years. Stellar streams from globular clusters are particularly sensitive probes of dark matter halos and substructure. Globular cluster streams are expected to exist in a variety of host galaxy types, but so far, they have only been observed in the Milky Way. We present evidence for the first extragalactic globular cluster stellar stream, identified in deep Hubble Space Telescope imaging of the ultra-diffuse galaxy, UGC9050-Dw1. The stream's morphology, colour, and apparent association with a compact source support the globular cluster progenitor interpretation observationally, and we reproduce the observed surface brightness with simulated globular cluster stellar populations. We use generative stream modelling, which fits dynamical models directly to the stream morphology, to constrain the mass of the progenitor and present the first stream-based halo constraint for an ultra-diffuse galaxy. The stream models point to a globular cluster origin and suggest a massive dark matter host halo. By extending the reach of globular cluster stream analysis to external galaxies, this work opens a new chapter in dark matter science.
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All authors Julie Kiel Holm, Sarah Pearson, Jacob Nibauer, David J. Sand, Adrian M. Price-Whelan, Tjitske Starkenburg, David Hendel, Catherine Fielder

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Robustness of the primordial power spectrum in hybrid loop quantum cosmology to approximations near the bounce

Kristina Giesel, Almudena Guillén, Guillermo A. Mena Marugán et al. (+1 more)

We prove the robustness of the analytic approximation used in (hybrid) loop quantum cosmology to compute the primordial power spectrum of the cosmological perturbations for a recently proposed vacuum state (the non-oscillatory state with asymptotic Hamiltonian diagonalization). To investigate this, we study different approximations to the effective mass of these perturbations near the bounce, showing that the Pöschl-Teller potential employed in previous works leads to indistinguishable power spectra compared to other estimations of the mass, provided that they successfully capture the characteristic scale of the bounce, which translates into a scale of power suppression.
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All authors Kristina Giesel, Almudena Guillén, Guillermo A. Mena Marugán, Leonardo Ricci

Cosmology and Nongalactic Astrophysics

CIBER $\times$ galaxy cross-correlations reveal a bright, low-redshift NIR background

Richard M. Feder, Grigory Heaton, James J. Bock et al. (+7 more)

We perform the first tomographic analysis of near-IR extragalactic background light (EBL) anisotropies, cross-correlating CIBER 1.1 and 1.8 $\mu$m imager data with photometric galaxy catalogs from DESI Legacy Survey DR8 and Hyper-Suprime-Cam Ultra-Deep Survey. We measure significantly higher cross-power than expectations from an integrated galaxy light (IGL) model on scales $\ell < 2000$, concentrated at low redshift ($z\lesssim 0.6$). Cluster member galaxies and associated structure account for 15-20% of the large-angle cross-power, indicating that group- and galaxy-scale halos contribute the bulk of the signal. Through a parametric halo model decomposition, we detect two-halo and one-halo clustering in cross-power at high significance, with amplitudes that decline smoothly across $z=0{-}1$. The inferred one-halo cross-power is of similar amplitude between DESI-LS and the deeper HSC catalog, implying a scenario in which low-redshift EBL fluctuations are amplified by contributions from lower-mass halos with satellites and/or diffuse intra-halo light (IHL). Converting our two-halo fits into estimates of $b_I \times dI/dz$, we find that standard IGL predictions underestimate our measurements, even when assuming an intensity bias as high as 3, similar to that of large SZ clusters, suggesting that a higher $dI/dz$ is required to reconcile observed discrepancies. Lastly, we find that correlated large-scale structure (LSS) at $z<1$ accounts for a substantial fraction of the CIBER auto-power reported in earlier work. These results identify low-redshift LSS as a significant and previously unappreciated contributor to near-IR EBL fluctuation measurements, setting the stage for cross-correlation science with CIBER-2, SPHEREx and a variety of LSS tracers.
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All authors Richard M. Feder, Grigory Heaton, James J. Bock, Yun-Ting Cheng, Yi-Kuan Chiang, Phillip M. Korngut, Shuji Matsuura, Jordan Mirocha, Kohji Tsumura, Michael Zemcov

Cosmology and Nongalactic Astrophysics

MeerKAT Reveals Evidence of a Radio Megahalo at GHz Frequency

Swarna Chatterjee and Kenda Knowles

Radio megahalos are recently discovered large-scale diffuse synchrotron sources identified through LOFAR observations. We present MeerKAT L-band observations of the massive galaxy cluster RXC~J0528.9$-$3927, that reveals faint emission surrounding its central radio halo. At 1.28 GHz, the known $\sim1.14$ Mpc halo is embedded within previously unreported low-surface-brightness emission extending to $\sim2$ Mpc. The surface-brightness profile of the emission shows a distinct flattening beyond $\sim0.55R_{500}$, suggesting that the outer emission forms an additional component. These properties make the cluster a candidate megahalo system and potentially the first detected at GHz frequencies, although deeper multi-frequency observations are required for confirmation.
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Tuesday 11 August

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Torsional pseudo-inflation beyond Einstein-Cartan

Fernando Izaurieta, Samuel Lepe and Cristian Quinzacara

Torsion entered early-universe cosmology twice: through the nonsingular Einstein–Cartan bounce, where the quantum spin of fermions halts the contraction, and through the proposal that the expansion following that bounce could take over the duties of cosmic inflation. We revisit the second idea in a constructive spirit. First we compute its budget: for a Weyssenhoff spin fluid with barotropic source, $w\in\left[0,1\right]$, the accelerated window that follows the bounce spans $N_e=\ln\left[4/\left(1+3w\right)\right]/3\left(1-w\right)\leq\tfrac{1}{3}\ln4\simeq0.46$ e-folds, and positive spatial curvature only shrinks it. The mechanism is sound; its torsional “fuel” dilutes as $a^{-6}$, and the engine stops two orders of magnitude short of inflationary needs. We then ask what torsion would need in order to sustain a quasi-de Sitter phase, and give a two-branch answer in Riemann–Cartan cosmology with nonminimal couplings, where torsion is fed by the couplings rather than by spin. The vectorial branch reproduces Palatini inflation, observationally alive. On the axial branch we exhibit an exact de Sitter solution sustained by a torsion condensate: constant axial torsion $f_{0}$, a linear Gauss–Bonnet coupling, and a potential fixed to $V_{0}=6f_{0}^{2}+\tfrac{5}{2}v^{2}$ by the Friedmann constraint. The solution is an attractor of the homogeneous dynamics, with eigenvalue exactly $-3H$. The phase ends when the slope $U^{\prime}$, a decreasing function of the roll speed at fixed flat potential, drifts down to the floor $5/16V_{0}$ and the condensate switches itself off; consistency of the effective theory pins the whole episode near the Planck scale, $H\gtrsim0.3$ in reduced Planck units. We studied this branch at background level; its perturbation spectrum remains open.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

Magnetic fields in extreme primordial halos: turbulent collapse and implications for early quasar formation

V.B. Díaz, D.R.G. Schleicher, M.A. Latif et al. (+1 more)

It is sometimes suggested that the most massive quasars at high redshift may have formed from rare high-sigma peaks in the cosmic density field. We explore here the evolution in a massive primordial halo corresponding to one of these rare sigma peaks, employing cosmological high-resolution magneto-hydrodynamical zoom-in simulations with initial field strength of $10^{-14}-10^{-8}$ G. The dark matter halo forms at the intersection of strongly convergent flows, leading to the formation of highly supersonic turbulence already on intergalactic scales, with turbulent Mach numbers of order $10-20$ also within the halo. Turbulent magnetic field amplification has never been explored in this regime and we therefore investigate whether this gives rise to effects similar to those observed in more typical halos. While the weaker initial field is somewhat more strongly amplified as a result of the shear flows, overall the evolution in the different simulations is rather similar and the flows are dominated by supersonic turbulence. We show in particular that the turbulent Jeans mass always dominates over the thermal and magnetic Jeans masses, and only on scales of $10^{-2}-10$ pc, the magnetic Jeans mass may become comparable to the thermal one. Our simulations thus strongly suggest the evolution to be dominated by the large-scale dynamics. As established in previous work, we thus expect the formation of central massive objects of a few times $10^4$ M$_\odot$ also in the presence of magnetic fields. The situation is somewhat different from more typical atomic cooling halos, where previous results have indicated a larger relevance of the magnetic Jeans mass on intermediate scales, potentially enhancing the mass of the massive object.
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All authors V.B. Díaz, D.R.G. Schleicher, M.A. Latif, R. Banerjee

Cosmology and Nongalactic Astrophysics

A new measurement of the FRB DM-galaxy cross correlation and a first joint analysis with the kinematic SZ effect

Samuel McCarty, Liam Connor, Kritti Sharma et al. (+8 more)

Understanding the distribution of cosmic baryons is crucial for advancing cosmology and galaxy formation. Localized Fast Radio Bursts (FRBs) are a promising new probe of the diffuse gas, but measurements thus far have been limited by small sample size. In this work, we measure the FRB dispersion measure (DM)-galaxy cross correlation with 130 localized FRBs, including new spectroscopic host redshifts from the DSA-110, and the DESI Legacy Survey Bright Galaxy Sample. We detect this signal at the highest significance to date ($6.5\sigma$) in both configuration and harmonic space. By comparing to simulations and a halo model, we demonstrate that this statistic can constrain the strength of baryonic feedback. Our measurements disfavor a no-feedback scenario in which gas traces the underlying dark matter at $\sim\,9\sigma$. In addition to small scale feedback, this represents one of the first direct measurements of the clustering of electrons on scales larger than a few Mpc. We compare our measurement to recent kinematic Sunyaev-Zeldovich effect (kSZ) studies, which show good agreement despite the differences in observational methods and sample selection. Finally, we make a first attempt at breaking the kSZ optical depth degeneracy with FRBs, jointly measuring the growth rate of large-scale structure $f\sigma_8$. With future samples, FRB two-point statistics will provide precision constraints on the distribution of cosmic baryons and complement other probes.
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All authors Samuel McCarty, Liam Connor, Kritti Sharma, Simone Ferraro, Vikram Ravi, Elisabeth Krause, Boryana Hadzhiyska, Vishnu Balakrishnan, Casey Law, Pranav Sanghavi, Kaitlyn Shin