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Physics Astrophysics Cosmology and Nongalactic Astrophysics

astro-ph.CO Watch Cosmology and Nongalactic Astrophysics

Tuesday 1 September

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

Higgsino Dark Matter Interpretation of the LUX-ZEPLIN 248 keV Nuclear-Recoil Event

Katherine Freese and Dionysios P. Theodosopoulos

We propose Higgsino dark matter as a potential interpretation of the $248~\mathrm{keV}$ nuclear-recoil event of interest reported by the LUX-ZEPLIN (LZ) experiment. LZ studied several rare background processes and detector effects in detail, but did not identify any as a likely explanation of the event. A nearly pure Higgsino naturally realizes inelastic dark matter through the off-diagonal $Z$ coupling of two nearly degenerate neutral Majorana states separated by a mass splitting $\delta$. The same electroweak interaction fixes the inelastic Higgsino-nucleon scattering cross section, rather than leaving it as a free parameter. We show that the predicted Higgsino inelastic scattering cross section approaches the published LZ two-sided 90% confidence interval for a Higgsino mass $m_{\widetilde H}\sim1~\mathrm{TeV}$ and a mass splitting $\delta\sim350~\mathrm{keV}$.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Gravitational Waves from Reheating beyond Instantaneous Thermalization

Kyohei Mukaida and Tenta Tsuji

We study gravitational-wave production during perturbative reheating without assuming instantaneous thermalization of the inflaton decay products. The injected energetic particles thermalize through an in-medium cascade of nearly collinear splittings subject to the Landau-Pomeranchuk-Migdal effect and are ultimately isotropized by elastic scatterings near the thermal scale. The non-thermal hard population present before complete thermalization produces an additional gravitational-wave component through hard-soft scatterings, with $\Omega_{\mathrm{GW}}\propto f^{1/2}$ below the injection-scale turnover. The same isotropization erases the directional information underlying the vacuum $1/k$ bremsstrahlung soft pole, changing the deep-infrared spectrum from $\Omega_{\mathrm{GW}}\propto f$ to $\Omega_{\mathrm{GW}}\propto f^3$.
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Cosmology and Nongalactic Astrophysics

Energy deposited by black holes in the hot X-ray gas of elliptical galaxies, groups and clusters

A. Cattaneo and S. Ettori

Galaxy groups show entropy excesses $\Delta S$ with respect to theoretical expectations from models and simulations with purely gravitational heating. We determine the heat $Q_{\rm heat}\simeq T\Delta S$ deposited by non-gravitational sources into the hot gas of elliptical galaxies, groups and clusters, and to compare it with the energy output of their central black holes (BHs). We adopt a simple model for the hot gas with only one free parameter: the core entropy. We calibrate the core entropy on the observed relation between X-ray luminosity and halo mass, and we use it to determine the entropy $S$ of the hot gas. We determine $\Delta S=S-S_0$ by taking the difference between $S$ and the entropy $S_0$ found in cosmological adiabatic simulations for haloes of the same mass. The temperature $T$ of the hot gas during the heating phase is determined from semi-analytic/semi-empirical modelling by assuming that heat absorption traces the accretion histories of supermassive BHs. Our findings suggest that supermassive BHs thermalise 1 to $3\%$ of their energy output in the surrounding gas. Our results suggest two regimes: (i) in elliptical galaxies and groups, active galactic nuclei (AGN) heat the gas much more rapidly than it can cool, generating the observed entropy excesses and quenching star formation when the accumulated heat is large enough to unbind the gas reservoir in the host halo; (ii) in galaxy clusters (at $M_{200}>10^{14}{\rm\,M}_\odot$), heating and cooling are in self-regulated equilibrium.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Gravitational-wave signatures of primordial black hole clusters and the imprint of an early dense-core collapse

Marc Barceló-Sastre and Juan García-Bellido

Primordial black holes (PBHs) are expected to be born essentially non-spinning and, if the primordial curvature fluctuations possess non-Gaussian tails, strongly clustered. Any spin measured in a PBH population must therefore be dynamically generated. Using direct $N$-body simulations with nbody6++gpu, modified to treat nearly parabolic dynamical-capture mergers, we quantify the conditions under which an initially non-spinning PBH cluster develops the spin, mass and stochastic-background signatures that gravitational-wave observations are now sensitive to. We find a sharp tension: producing a root-mean-square spin $\chi_{\rm rms}\sim0.1 - 0.2$ in the $30 - 50\,M_\odot$ range requires initial Plummer radii of order $10^{-5}\,{\rm pc}$, whereas survival over cosmological times requires parsec-scale clusters. This tension is resolved naturally if PBHs form with a compact, short-lived core embedded in an extended halo, and we therefore simulate the two regimes as independent blocks. The core block ($4000$ PBHs, Plummer radii $3\times10^{-6} - 10^{-4}\,{\rm pc}$) collapses in days to years, producing a burst of mergers whose orbits are strongly non-circular ($e\to1$) and of low dimensionless orbital angular momentum, so that remnant spins are systematically below the quasi-circular value $\chi\simeq0.7$. Redshifted from their formation epoch, the core mergers deposit a stochastic background peaking in the $10^{-6}$–$10^{-4}\,{\rm Hz}$ band accessible to LISA. The picture predicts a specific division of labour between observables, spins set in the primordial collapse, detectable mergers set by the long-term halo, and a two-component stochastic background, and, in particular, that both the spin and the mass data favour a primordial mass function truncated near $50\,M_\odot$.
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Cosmology and Nongalactic Astrophysics

First tomographic measurements of the angular clustering and bias of photometric quasars from S-PLUS

Maria Lopes, Felipe Avila, Armando Bernui et al. (+1 more)

We investigate the quasar clustering in the QuCatS photometric catalog, constructed from the fourth data release of the Southern Photometric Local Universe Survey (S-PLUS). The quasar sample for this study consists of $23,402$ quasars, spanning the redshift interval $1.1 \leq z_{\rm phot} \leq 2.6$, which we divided into four bins for our tomographic analyses. In each bin, we measured the two-point angular correlation function and compared it with theoretical predictions for the clustering of dark matter in the flat-$\Lambda$CDM cosmological model. We then estimate the effective linear bias in each bin that best fits the data, obtaining $b_{Q}(z_{\rm eff}=1.26)=2.17^{+0.30}_{-0.35}$, $b_{Q}(z_{\rm eff}=1.63)=2.67^{+0.36}_{-0.42}$, $b_{Q}(z_{\rm eff}=2.04)=3.29^{+0.52}_{-0.62}$, and $b_{Q}(z_{\rm eff}=2.38)=4.05^{+0.71}_{-0.86}$. These measurements are consistent with previous analyses in the literature. Moreover, the evolution of the bias agrees well with the $b(z)$ parameterization proposed by \cite{laurent2017}. Our measurements constitute the first cosmological study of the tomographic clustering of photometric quasars provided by the S-PLUS dataset, contributing to the mapping of the evolution of linear bias and paving the way for future analyses of data releases with larger datasets. In addition, our study also serves as a consistency test for the calibration procedure of the photometric redshift probability distributions of the quasars in the QuCatS catalog.
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All authors Maria Lopes, Felipe Avila, Armando Bernui, Lilianne Nakazono

Cosmology and Nongalactic Astrophysics

Angular power spectrum of induced gravitational waves: breaking model and parameter degeneracies in PTA observations

Peng-Yu Wu, Di Wu and Jing-Zhi Zhou

Large primordial curvature and tensor perturbations on small scales can generate second-order tensor-scalar induced gravitational waves (TSIGWs) through scalar-scalar, tensor-scalar, and tensor-tensor source terms. TSIGWs are recognized as one of the principal contributors to the stochastic gravitational wave background (SGWB) observations. We explore the energy density spectrum of second-order TSIGWs in the presence of non-Gaussian primordial curvature perturbations. Furthermore, we present the first calculation of the anisotropic angular power spectrum associated with second-order TSIGWs, which provides a promising tool to discriminate them from other SGWB sources.
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Cosmology and Nongalactic Astrophysics

The cosmic multipoles: a consistency test for the Szekeres cosmological model

Marie-Noëlle Célérier

Some of the properties of the Szekeres solutions which have never been used in a cosmological context are known for long. In this letter, the total and unique decomposition of its matter energy density into a monopole and dipole moment is recalled and specialized to the axially symmetric quasi-spherical subclass of the model. All the model special features – axial symmetry, spherical quasi-symmetry, location of the observer – are observationally justified. Then, a consistency test of the model involving its no-high-multipole-in-mass-density property is proposed.
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Cosmology and Nongalactic Astrophysics

Quantifying Sky Map Resolution Requirements for Beam Chromaticity Correction in Sky-Averaged 21 cm Experiments

Aleksandra Dragović, Dominic Anstey, Harry T. J. Bevins et al. (+1 more)

The 21 cm hyperfine transition of neutral hydrogen provides one of the few direct probes of the early cosmic history. High-redshift detections of this signal could shine light on the poorly understood epochs of the Dark Ages and Cosmic Dawn, periods that remain among the least understood in the Universe's history. However, this signal is masked by bright foregrounds and is distorted by the chromaticity of the antenna used to detect it. Correcting for the chromaticity requires an accurate representation of the radio sky across relevant frequencies. However, base sky maps used for this correction, such as instances of the Global Sky Model (GSM), are limited by resolution, calibration and extrapolation uncertainties, especially when scaled to lower frequencies relevant for Cosmic Dawn studies. This work quantifies how accurately the base map must represent the true sky to produce a reliable beam correction. Using simulated sky data, we generate beam chromaticity corrections generated from progressively degraded versions of the base map, and compare how well they do in comparison to a correction based on the full-resolution map. We find that degradation in map resolution of $\sim 1^\circ$ does not introduce measurable increases in the amplitude of the residuals when correcting for the chromaticity and subtracting three different foreground models (two polynomials and a power law expansion). These results provide practical constraints on the required resolution and accuracy of sky models used in beam correction pipelines, informing future design and calibration strategies for global 21 cm experiments, and future efforts to map the low frequency sky.
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All authors Aleksandra Dragović, Dominic Anstey, Harry T. J. Bevins, Eloy de Lera Acedo

Cosmology and Nongalactic Astrophysics

A Class of Exact Single-Field Inflationary Solutions beyond Slow Roll

Jia-Wei Zhang, Bai-Cian Ke, Yao Yu et al. (+2 more)

We construct exact solutions for single-field inflaton dynamics without invoking the slow-roll approximation. A suitable change of variables reduces the background equation to an Abel equation of the first kind. Although a generic Abel equation is not analytically solvable, we identify a class of inflaton potentials for which the transformed equation admits exact solutions. The resulting framework contains constant-roll inflation as a special case and also accommodates solutions with a constant second Hubble-flow parameter. We analyze the linear local attractor behavior and superhorizon evolution of these rolling backgrounds. Using the public joint CMB likelihood contours in the $(n_s,r)$ plane, we identify compatible parameter regions and show that one rolling branch can also yield $50\leq N_*<60$. Direct numerical evolution of the scalar and tensor modes at representative points validates the local-index predictions to better than $7\times10^{-4}$ in $n_s$ and $2\times10^{-6}$ in $r$. The exact family extends beyond slow roll, although the observationally selected regions displayed here lie close to the slow-roll regime.
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All authors Jia-Wei Zhang, Bai-Cian Ke, Yao Yu, Dong-Ze He, Shou-Jia Wang

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

Dissipative Multi-Field Dynamics from Non-Hermitian Inflationary Potentials

S. D. Campos

In this work, we develop a perturbative framework for inflation driven by a complex inflaton with non-minimal gravitational coupling and a non-Hermitian potential. During the observable cosmic microwave background radiation era, the dynamics reduce to an effectively conservative two-field model, preserving the predictions of the $\alpha$-attractor class and satisfying Planck 2018 and BICEP/Keck constraints on $n_s$, $r$, and $f_{\mathrm{NL}}$. Near the end of inflation, trajectory bending activates the non-Hermitian sector, triggering geometric reheating. The resulting non-unitary evolution modifies the curvature spectrum and stochastic gravitational-wave background through a calculable damping factor determined by the complex mass eigenvalues. While cosmic microwave background-scale observables remain essentially unchanged, a distinctive suppression emerges in the high-frequency gravitational-wave spectrum ($f > 10^2$ Hz), potentially testable by future detectors such as the Einstein Telescope and the Big Bang Observer.
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Cosmology and Nongalactic Astrophysics

Combining Systematic Effects in CMB Polarization Experiments through map-based simulations: application to LiteBIRD's HWP non-idealities and detectors non-linearity

Silvia Micheli, Francesco Piacentini, Tommaso Ghigna et al. (+10 more)

We quantify the impact of coupled instrumental systematics on next-generation CMB polarization experiments targeting primordial $B$-mode polarization, with a focus on the forthcoming LiteBIRD satellite mission. We study the interplay between the non-linear response of Transition-Edge Sensor (TES) bolometers and Half-Wave Plate (HWP) non-idealities, in particular synchronous signals arising from differential emissivity. We develop a map-based formalism that captures the resulting intensity-to-polarization leakage by explicitly solving the binning map-making equations, avoiding the need for computationally expensive time-ordered data simulations. We apply this framework to LiteBIRD, adopting its baseline scanning strategy and frequency configuration, and perform analyses at both single- and multi-frequency levels, including Galactic foregrounds and blind component separation. We find that while detector non-linearity and HWP non-idealities individually induce negligible bias on the tensor-to-scalar ratio $r$, their coupling can generate non-trivial contamination, driven by large signals such as the solar dipole and amplified in high-frequency channels by foreground leakage. From these results, we derive joint requirements on detector non-linearity and HWP differential emission, and discuss their implications for the instrument design and calibration strategy of LiteBIRD and future CMB polarization missions targeting $r \lesssim 10^{-3}$.
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All authors Silvia Micheli, Francesco Piacentini, Tommaso Ghigna, Alessandro Carones, Alessandro Novelli, Giampaolo Pisano, Giulia Barbieri Ripamonti, Alessandro Coppolecchia, Paolo de Bernardis, Silvia Masi, Andrea Occhiuzzi, Alessandro Paiella, Simone Stellati

Cosmology and Nongalactic Astrophysics

Baryonic feedback suppression of the matter power spectrum: a three-parameter fitting formula and its single-parameter reduction

Pengjie Zhang

Baryonic feedback can suppress matter clustering by $\sim 10\%$ at $k\sim 1h$/Mpc and $z\sim 1$, and is therefore a major source of systematic errors in weak lensing cosmology. We investigate this effect through the ratio $S(k,z)\equiv P_{\rm hydro}(k,z)/P_{\rm DMO}(k,z)$ measured in the FLAMINGO, IllustrisTNG, and Illustris hydrodynamical simulation suites, together with the one-parameter-at-a-time (1P) variation runs of CAMELS-TNG and CAMELS-SIMBA. We present a three-parameter fitting formula that reproduces all but one of these runs with maximum error less than $0.03$ (and typical error less than $0.01$) at $k\leq 3h/$Mpc and $z\leq 2$; the only exception is a run with unrealistically low $\Omega_m=0.1$. Each of the three parameters ($B_0$, $n$, and $a$) has a clear physical interpretation: $B_0$ sets the characteristic scale of the suppression at $z=0$, corresponding to a gas particle displacement scale of $B_0^{1/2}$; $n$ sets the suppression floor $(1-\Omega_b/\Omega_m)^n$; and $a$ sets the redshift $z_B$ at which the suppression peaks. Furthermore, we find that $B_0$ and $z_B$ are significantly correlated for most runs. Also, $n\simeq 1$ for FLAMINGO, TNG and CAMELS-TNG. For these simulations, the description reduces to a single parameter formula with maximum error less than $0.03$. The formulas remain accurate at max$(|\Delta S|)<0.03$ (and typical error less than $0.01$) for cosmologies well away from the calibration cosmology, spanning the range $\Omega_m\in [0.2,0.5]$, $\Omega_b\in [0.029,0.069]$ and $\sigma_8\in [0.6,1.0]$. These results imply that, despite the diversity of baryonic physics implementations, an accurate description of $S(k,z)$ requires at most three effective degrees of freedom. Therefore the impact of feedback on weak lensing cosmology can in principle be mitigated internally without significant loss of cosmological constraining power.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Status of the strong $CP$ problem

Wen-Yuan Ai

The strong $CP$ problem remains one of the major open questions in the Standard Model of particle physics. Its best-known solution is the Peccei–Quinn mechanism, which predicts a new pseudoscalar boson, the QCD axion. In recent years, alternative solutions and new perspectives on the foundations of the strong $CP$ problem have also received renewed attention. In this review, we provide a pedagogical account of the underlying physics and summarise the current theoretical and phenomenological status of the problem.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.HE

Nanohertz Gravitational-Wave Constraints on Supermassive Binary Black Holes at Cosmic Dawn

Yiqin Chen, Shi-Yi Zhao, Xingjiang Zhu et al. (+16 more)

Standard continuous gravitational-wave searches with pulsar timing arrays (PTAs) neglect cosmological redshift, restricting their applicability to the local Universe. We introduce a redshift-aware PTA framework and apply it to the Parkes PTA Data Release 3, deriving the first direct constraints on supermassive binary black holes (SMBBHs) at the cosmic dawn. Evaluating our limits across a broad redshift range, we observationally establish the non-monotonic mass-redshift exclusion boundary driven by the theoretical “redshift bias", demonstrating how PTAs can effectively probe sources at extreme distances. Redshift-aware targeted searches toward high-redshift systems, including the ultraluminous quasar J0100+2802 ($z=6.327$) and the JWST-discovered galaxy JADES-GS-z14-0 ($z=14.32$), rigorously exclude SMBBHs with chirp masses $\mathcal{M}_c \gtrsim 10^{10} M_\odot$ across the nanohertz frequency band. Finally, we demonstrate that high-redshift binaries can be robustly detected and localized, allowing for the accurate measurement of their intrinsic properties. Our results provide the tightest constraints to date on SMBBHs at $z > 6$ and establish a practical framework for probing early-Universe black hole assembly.
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All authors Yiqin Chen, Shi-Yi Zhao, Xingjiang Zhu, N. D. Ramesh Bhat, Jacob Cardinal Tremblay, Małgorzata Curyło, Valentina Di Marco, George Hobbs, Wenhua Ling, Rami F. Mandow, Richard N. Manchester, Saurav Mishra, Daniel J. Reardon, Sparrow Roch, Christopher J. Russell, Ryan M. Shannon, Jingbo Wang, Shuangqiang Wang, Andrew Zic

Monday 31 August

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

Formation of Heavy Seed Black Holes and Little Red Dots-like Compact Clusters in Metal-enriched Star-forming Regions

Sunmyon Chon, Shingo Hirano, Ke-Jung Chen et al. (+1 more)

The origin of supermassive black holes (SMBHs) in the early Universe remains uncertain. While the classical direct-collapse scenario requires pristine gas exposed to intense Lyman-Werner (LW) radiation, recent JWST observations suggest that early growing BHs may reside in compact, metal-enriched environments. We investigate early BH formation using a cosmological radiation-hydrodynamic simulation that self-consistently follows the formation and evolution of rapidly accreting supermassive stars (SMSs). We find that intense LW radiation develops in clustered star-forming regions; by the time the first heavy seed forms, the mass-weighted internal intensity has reached $J_{21}\sim1000$. Most seeds form in weakly metal-enriched gas with [Z/H]$\sim-3$ to $-2$, because the strongest LW fields occur in regions already enriched by previous stellar feedback. All halos above $10^9M_\odot$ in our zoom-in region host a BH more massive than $10^5M_\odot$. We construct stellar spectra using MIST/PHOENIX libraries for normal stars and $6000~\mathrm{K}$ blackbody spectra for bloated SMSs. Five of eight massive clusters with stellar masses larger than $10^6~M_\odot$ exhibit intrinsically V-shaped spectra similar to those of Little Red Dots (LRDs). In the most prominent cases, luminous SMSs dominate the red optical emission, although Balmer breaks in normal stellar populations also contribute. We also identify off-center LRD-like systems in our simulation resembling those recently reported in strongly lensed observations. Our results suggest that heavy-seed formation, compact-cluster formation, and LRD-like continuum emission are linked outcomes of clustered, weakly metal-enriched, strongly irradiated environments.
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All authors Sunmyon Chon, Shingo Hirano, Ke-Jung Chen, Volker Springel

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

Radiative Corrections and Reheating in Supergravity Models of Inflation

John Ellis, Tony Gherghetta, Kunio Kaneta et al. (+2 more)

We consider the effects of radiative corrections in Starobinsky-like models of inflation, concentrating on models of inflation formulated in N=1 no-scale supergravity. Inflaton couplings to matter fields are necessary for reheating and these have an impact on loop corrections to the inflaton potential. Whilst corrections due to the supergravity couplings of the inflaton to Standard Model (MSSM) fields are negligible, we use Planck data to obtain interesting constraints on GUT bilinear couplings, vevs, and gauge boson masses that could be sharpened by future CMB measurements.
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All authors John Ellis, Tony Gherghetta, Kunio Kaneta, Wenqi Ke, Keith A. Olive

Cosmology and Nongalactic Astrophysics

TDCOSMO XXVIII. The Hubble constant from the quadruply lensed quasar J1537$-$3010 with precise time delays

A. Galan, A. G. Schweinfurth, S. H. Suyu et al. (+21 more)

We present the first measurement of the Hubble constant ($H_0$) from the quadruply-lensed quasar J1537$-$3010, which has optically-measured time delays at $\sim2 \%$ precision. We combine these delays with multi-band imaging data from the Hubble Space Telescope (HST) and model the system with two independent software and teams. We adopt a mass profile that is maximally degenerate with $H_0$ to fully incorporate the mass-sheet degeneracy in the error budget, with nuisance parameters constrained by spatially resolved stellar kinematics from the Multi Unit Spectroscopic Explorer (MUSE) and a line-of-sight (LoS) analysis using the Euclid Flagship simulation. The entire analysis is performed blindly to $H_0$, distances and mass density slope of the main deflector. After unblinding, we measure $H_0 = 75.5^{+9.3}_{-5.8}\ {\rm km\,s^{-1}\,Mpc^{-1}}$, corresponding to a $10\%$ precision measurement from a single system. This precision is driven by conservative lens modeling assumptions including differences between lens modeling methods and the limited stellar kinematics constraints, from which we infer a total mass-sheet parameter $\lambda\equiv(1-\kappa_{\rm ext})\lambda_{\rm int} = 0.89^{+0.11}_{-0.06}$ ($\lambda_{\rm int}=0.89^{+0.09}_{-0.07}$) that is consistent with current results for elliptical galaxies ($\lambda \approx 1$). Our lensing constraints, stellar kinematic measurements and LoS characterization will be included in subsequent population-level measurements of $H_0$. Moreover, our lens models combined with future near-infrared spectroscopy and imaging from the James Webb Space Telescope will further reduce the uncertainties on $H_0$ from J1537$-$3010 alone, bringing it closer to the few percents precision of the time delays.
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All authors A. Galan, A. G. Schweinfurth, S. H. Suyu, D. P. Johnson, A. Chawla, D. Sluse, G. V. Kharchilava, E. Buckley-Geer, H. Lin, S. Knabel, W. Sheu, S. Ertl, T. Anguita, S. Birrer, F. Courbin, F. Dux, M. Millon, V. Motta, S. Schuldt, T. Treu, D. M. Williams, M. Cappellari, K. C. Wong, D. Eckert

Cosmology and Nongalactic Astrophysics

Extended radio emission in and around the merging cluster A520 as seen by MeerKAT

S. Giacintucci, W. D. Cotton, M. Markevitch et al. (+3 more)

We present results from a deep MeerKAT 1.28 GHz observation of Abell 520, a galaxy cluster in the middle of a merger and a treasure trove of merger-generated phenomena. MeerKAT's combination of high angular resolution and sensitivity to extended radio emission lets us uncover unprecedented detail of the cluster's giant halo and puzzling features beyond the halo. We find that the main radio halo is sharply bounded along the direction of the NE-SW merger axis by the two X-ray shock fronts. In the perpendicular direction, the halo wings smoothly span over 2 Mpc, with the spectrum steepening in the outskirts. We detect faint radio emission upstream of the main (SW) bow shock; the emissivity jump across this shock can be used to constrain the physical mechanisms at work there. We discover a tail of radio emission extending past the NE shock to the gas-poor, high-entropy “dark subcluster” in the NE outskirts. The tail and subcluster have a higher radio/X-ray brightness ratio than the main halo's, suggesting efficient reacceleration of cosmic rays. We also discover two peripheral radio relics beyond the cluster virial radius, and a faint, $\sim2$ Mpc long, broad radio bridge connecting the dark subcluster to one of the relics along the direction perpendicular to the merger axis. The spectral slopes of the dark subcluster and the bridge are consistent with that of the main halo. This bridge and both relics may be caused by another giant merger-generated shock front at the virial radius.
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All authors S. Giacintucci, W. D. Cotton, M. Markevitch, T. Venturi, T. E. Clarke, H. Bourdin

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

Early Supermassive Black Holes and Little Red Dots Require Free-Fall Growth

Junehyoung Jeon, Volker Bromm, Michael Boylan-Kolchin et al. (+1 more)

Supermassive black holes/active galactic nuclei (SMBHs/AGN), forming only a few hundred million years after the Big Bang as observed with the James Webb Space Telescope (JWST), challenge theoretical understanding. How could they grow so massive $(M_{\rm BH} > 10^6 {\rm \,M}_\odot)$ so quickly after initial seeding? Is this rapid growth related to the numerous and enigmatic Little Red Dots (LRDs), compact sources with AGN-like characteristics, discovered by JWST? To address these mysteries, we consider the first-order constraint on SMBH growth: enough baryonic material has to reach the vicinity of the SMBH seed, located near the bottom of the gravitational potential well of the host dark matter halo. We specifically examine cold-mode accretion, where gas from the cosmic environment flows into the virialized halo in cold streams without being shock-heated, efficiently reaching the center on a free-fall timescale. We find that cold mode accretion is necessary to supply material for the SMBHs to reach the observed masses, whereas for shock-heated gas inflow the required amount could only be supplied by implausibly rare halos. Moreover, cold-mode inflow in rare $(\sim1$ Gpc$^{-3}$) halos matches the mass and number of the massive quasars, and halos able to support super-Eddington accretion for massive SMBHs ($\sim10^7$ M$_\odot$) match LRD number densities. The decreasing LRD abundance at lower redshifts may then reflect the termination of cold-mode accretion in the growing host halos. The populations of massive SMBHs and LRDs at early times may thus arise naturally from cosmological structure formation, based on the abundance of halos capable of supplying sufficient material through cold accretion.
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All authors Junehyoung Jeon, Volker Bromm, Michael Boylan-Kolchin, Julian B. Muñoz

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

Evolution of Cosmic String Loops under Gravitational Backreaction

Lasse Gerblich, Richard A. Battye and E.P.S. Shellard

Nambu-Goto cosmic string loops generically develop cusps, points where the string momentarily reaches the speed of light. These cusps produce strong gravitational wave bursts with a characteristic strain spectrum $\tilde{h}(\omega)\propto (G\mu)\,\omega^{-4/3}$, making them prime targets for gravitational wave searches, where $\mu$ is the string mass per unit length. However, this picture is modified when one accounts for gravitational backreaction. Using a convenient gauge, we reformulate the Nambu-Goto equations of motion for a loop moving in its own dynamically sourced gravitational field, enabling the first continuous numerical evolution of loops under this backreaction. A key finding is that locally cusps survive backreaction. Nevertheless, the gravitational waveform calculated in this formalism is significantly modified, weakening the cusp burst and introducing a high-frequency cutoff at $f_c\propto(G\mu)^{-3/2}$. This suppression above $f_c$ reduces the expected signal-to-noise ratio in current and near-future detectors relative to unperturbed waveform predictions.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.IM

Agentic research is oxymoronic

Natalie B. Hogg

The use of agentic large language models obviates human interpretation of scientific results, and will lead to substantial distrust in the literature.

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

Ad Astra White Paper: A Pitch for the Next 25 Years of NASA's Physics of the Cosmos Program

Eric Burns, Ivan Agullo, Igor Andreoni et al. (+7 more)

Astrophysical observations of our universe have been key to our understanding of how the universe works. Shortly after the turn of the millennium, the National Research Council delivered Connecting Quarks with the Cosmos: Eleven Science Questions for the New Century. In the subsequent quarter-century, we have made substantial progress in answering each question. These advancements have, in part, arisen because of the success of major US facilities across several domains of physics, guided by long-term planning documents which still largely focus on these questions. This report seeks to provide a status update on each question, and to outline what space-based facilities are crucial for future progress, intended to guide NASA's preparatory work for the Astro2030 Decadal.
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All authors Eric Burns, Ivan Agullo, Igor Andreoni, Catherine M. Deibel, Christopher L. Fryer, Natasha Latouf, M. Coleman Miller, Jillian C. Rastinejad, Breann N. Sitarski, Zorawar Wadiasingh

Cosmology and Nongalactic Astrophysics

SPT-3G D1: Quadratic-Estimator CMB Lensing Reconstruction and Cosmology

Y. Omori, W. L. K. Wu, Y. Nakato et al. (+92 more)

We present a map of the cosmic microwave background (CMB) lensing potential reconstructed from observations taken during the 2019 and 2020 seasons with the third-generation camera on the South Pole Telescope (SPT), covering the $1500\,{\rm deg}^{2}$ SPT-3G Main field, referred to as the SPT-3G D1 dataset. From the multi-frequency temperature and polarization data, we reconstruct the CMB lensing field using a quadratic estimator that jointly accounts for the $T$, $E$, and $B$ fields and their covariance. The resulting lensing map is dominated by polarization information for $L \lesssim 600$ and provides the highest signal-to-noise measurement per mode reported to date. With nuisance parameters fixed to their best-fit values, we measure a lensing amplitude consistent with unity at $2\%$ precision relative to the $\Lambda$CDM model that best fits the combined Planck, ACT DR6, and SPT-3G D1 $TT/TE/EE$ likelihoods (${\rm CMB}_{\rm SPA}$). We further measure the structure-growth parameter $\sigma_{8}\Omega_{\rm m}^{0.25}$ to be $0.6046\pm0.0096$ from the SPT-3G D1 lensing spectrum alone and $0.6020\pm0.0084$ when combined with ACT DR6 and Planck PR4 CMB lensing. By further combining this with ${\rm CMB}_{\rm SPA}$ and the latest DESI DR2 BAO data, we obtain $\sum m_{\nu} < 0.072\,\mathrm{eV}$ (95% C.L.) when allowing the neutrino mass to vary within $\Lambda$CDM. Compared with previous work, the better agreement of our measurement with DESI DR2 BAO yields both this relaxed upper bound and reduced ($\mathord{\sim}2\sigma$) preferences for nonzero spatial curvature and for deviations of $(w_0,w_a)$ from the $\Lambda$CDM expectation. When we combine CMB lensing with the DES Y3 3$\times$2pt analysis, we obtain $S_{8}=0.811\pm0.011$, corresponding to a $1.4\%$ constraint on the late-time clustering amplitude. This precision is competitive with that obtained from the primary CMB within $\Lambda$CDM.
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All authors Y. Omori, W. L. K. Wu, Y. Nakato, F. Bianchini, L. Balkenhol, C. Daley, W. Quan, E. Anderes, A. J. Anderson, B. Ansarinejad, M. Archipley, D. R. Barron, P. S. Barry, K. Benabed, A. N. Bender, B. A. Benson, L. E. Bleem, S. Bocquet, F. R. Bouchet, E. Camphuis, M. G. Campitiello, J. E. Carlstrom, J. Carron, C. L. Chang, P. M. Chichura, A. Chokshi, T.-L. Chou, A. Coerver, T. M. Crawford, T. de Haan, K. R. Dibert, M. A. Dobbs, M. Doohan, D. Dutcher, C. Feng, K. R. Ferguson, N. C. Ferree, K. Fichman, A. Foster, S. Galli, A. E. Gambrel, A. K. Gao, F. Ge, F. Guidi, S. Guns, N. W. Halverson, E. Hivon, G. P. Holder, W. L. Holzapfel, J. C. Hood, A. Hryciuk, N. Huang, T. Jhaveri, F. Kéruzoré, A. R. Khalife, L. Knox, K. Kornoelje, C.-L. Kuo, K. Levy, Y. Li, A. E. Lowitz, C. Lu, G. P. Lynch, T. J. Maccarone, A. S. Maniyar, E. S. Martsen, F. Menanteau, M. Millea, J. Montgomery, T. Natoli, A. Ouellette, Z. Pan, P. Paschos, K. A. Phadke, A. W. Pollak, K. Prabhu, M. Rahimi, A. Rahlin, C. L. Reichardt, M. Rouble, J. E. Ruhl, A. C. Silva Oliveira, A. Simpson, J. A. Sobrin, A. A. Stark, J. Stephen, C. Tandoi, C. Trendafilova, J. D. Vieira, A. G. Vieregg, A. Vitrier, Y. Wan, N. Whitehorn, M. R. Young, J. A. Zebrowski

Cosmology and Nongalactic Astrophysics

Resonant Dynamics of Gravitational Wave and Chiral Alfvén wave in the Early Universe

Arun Kumar Pandey, Subalakshmi A and Sampurn Anand

In this work, we investigate the resonant interaction between stochastic gravitational waves (GWs) and chiral Alfvén waves in a magnetized chiral plasma in the early Universe. Starting from covariant chiral magnetohydrodynamics coupled to linearized gravity, we derive a closed system of equations for the coupled chiral-Alfvén velocity and magnetic-field perturbations. Both analytics and numerics show a parametric resonance at the sum frequency of the two CVE-split branches, with an instability band that widens as the GW strain grows. This CVE-to-Alfvén ratio is not a free parameter. In the early Universe, it is fixed by the Standard Model's relativistic degrees of freedom. Including the plasma's backreaction on the GW makes the energy exchange nonlinear, breaking the usual single-frequency Manley-Rowe picture. For a self-consistent choice of parameters, where backreaction is only a small correction, the unsuppressed resonance still drives the system to a finite-time blow-up within a few Hubble times. We then work out the resonant frequencies and growth rates involved, mapping out what current and future gravitational-wave detectors could observe.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.HE

The DSA/Chronoscope fast radio burst survey: forecasts and science overview

Liam Connor, Kaitlyn Shin, Vikram Ravi et al. (+14 more)

Fast radio bursts (FRBs) are bright extragalactic transients with several mysteries surrounding their origins. Large FRB samples enable accurate measurements of the cosmic matter distribution, in particular on scales $\lesssim 10$ Mpc. These measurements will impact cosmological inference and our understanding of astrophysical feedback, from the circumgalactic medium to cluster scales. Here we forecast the expected yields, redshifts, and host galaxies of FRBs as observed by the Deep Synoptic Array (DSA), and describe the key science cases enabled by the large FRB sample. The DSA will be an interferometer consisting of 1650$\times$6.15 m antennas, operating between 0.7–2 GHz, to be located in Nevada, USA. The Chronoscope backend on the DSA, hereafter DSA/Chronoscope, is designed to search for FRBs across the field of view in real time, enabling the storage of full-polarization voltage data. Extrapolating from existing FRB surveys, we expect roughly $10^4$ FRB detections per year in each of three search sub-bands. Combining across sub-bands, the survey could produce $\sim$ 10$^5$ FRBs over the nominal 5-year DSA survey, assuming Euclidean source counts and a baseline compute backend that can search $6\times10^6$ beams at 1 ms sampling. The well-characterized DSA synthesized beam and deep simultaneous reference images will enable localization precisions of $\lesssim$ 250 milliarcseconds. Key science cases include the use of FRB propagation effects in probing cosmic baryons, and studies of the FRB phenomenon using FRB host galaxies and their local environment, as well as multiwavelength counterparts.
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All authors Liam Connor, Kaitlyn Shin, Vikram Ravi, Stella Koch Ocker, Casey J. Law, Kritti Sharma, Samuel McCarty, Gregg Hallinan, Shami Chatterjee, James M. Cordes, Dean Howarth, Fabian Walter, Elisabeth Krause, Vishnu Balakrishnan, Alexa C. Gordon, Calvin Leung, Shion Andrew

Cosmology and Nongalactic Astrophysics

Measuring peculiar velocity and tomographic redshift dipole with DESI DR1 catalogs

Yi-Wen Wu and Jun-Qing Xia

The so-called “cosmic dipole tension” challenges the Cosmological Principle by positing a discrepancy between the Solar System's peculiar velocity inferred from the Cosmic Microwave Background (CMB) dipole and that derived from large-scale structure number-count dipoles. Here we provide a high-precision determination of the kinematic dipole using the redshift-dipole method applied to the first data release (DR1) of the Dark Energy Spectroscopic Instrument (DESI). By exploiting the Doppler-induced modulation of observed redshifts, this estimator is intrinsically less sensitive to imaging systematics and selection-function uncertainties that can bias traditional number-count measurements. We conduct a tomographic analysis of four tracer populations, Bright Galaxy Sample, Luminous Red Galaxies, Emission Line Galaxies, and quasars, spanning $0.1<z<2.1$. Survey geometry and statistical uncertainties are quantified using 1,000 EZmock realizations. We find that the high-redshift QSO sample implies a peculiar velocity of $v = 357.95_{-48.47}^{+55.05}\,\mathrm{km\,s^{-1}}$, in excellent agreement with the CMB-inferred value of $369.82 \pm 0.11\,\mathrm{km\,s^{-1}}$. By contrast, a complementary number-count analysis yields a significantly enhanced dipole amplitude, which we attribute to leakage of large-scale power and to incompleteness within the DESI DR1 footprint. These results indicate that the redshift dipole provides a cleaner and more reliable probe of the kinematic rest frame, offering strong support for the standard kinematic interpretation at high redshift and helping to resolve the apparent dipole anomaly.
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Cosmology and Nongalactic Astrophysics

Cosmic variance and ergodicity in finite systems with correlations

Dipayan Mukherjee and Syksy Rasanen

We consider the difference between ensemble and volume average in cosmology. It is known that for sufficiently weak long-range correlations the root mean square of the difference, which we call ergodicity bias, decays like $R^{-3/2}$ in the limit of large volume $R^3$. We calculate the condition this imposes on the power spectrum of a Gaussian random field. We quantify the bias for finite $R$, and show that the $R\to\infty$ limit is of little relevance for cosmological observations when the measured scales and correlations extend to the size of the observable universe. We consider curvature, density, and velocity perturbations. On large scales the bias is important in all three cases. For the density perturbations, which are observationally the most relevant, the relative bias first exceeds 100% at the separation $r=177$ Mpc, and is larger than 100% for all $r>560$ Mpc. It should be taken into account when comparing ensemble and volume averages for large-scale structure. The bias is also large for the cosmic microwave background temperature perturbations on large angular scales, but this is not relevant for observations, as their analysis does not involve volume averaging.
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Cosmology and Nongalactic Astrophysics

A consistent, physical, and analytical model for CMB observables of reionisation I. Derivation, constraining power, and detectability of the auto-spectra

Adélie Gorce

The Epoch of Reionisation imprints its history and morphology on the Cosmic Microwave Background temperature and polarisation anisotropies through two effects: The kinetic Sunyaev Zel'dovich (kSZ) effect and Thomson scattering. To perform joint analyses of these observables and put tight constraints on the reionisation history and morphology, a common reionisation model is necessary. We present a quick, physically-accurate analytical approach to derive consistently the angular power spectra of the three main resulting imprints that are the spatial fluctuations of the Thomson optical depth, the patchy kSZ effect, and the scattering and screening B-modes. The approach differs from existing analytical models, as it is calibrated on high-resolution hydrodynamical simulations and depends on physical parameters of reionisation. Our predicted power spectra are consistent with the ones derived from cosmological simulations, whilst including more physical information – such as the typical size of ionised bubbles and the duration of reionisation. We provide an updated detectability assessment and show that both $C_\ell^{\tau\tau}$ and $C_\ell^{BB}$ could be measured by experiments similar to CMB Stage 4 and CMB-HD, respectively. We show the complementarity of the three observables in constraining reionisation history and morphology, and illustrate the potential of their joint analysis to get a global picture of reionisation. This analytical model will be a powerful tool in the analysis of upcoming CMB data, either alone or in combination with independent datasets such as measurements of the high-redshift 21cm signal. The code to derive these spectra is publicly available online as the preion Python package.
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Cosmology and Nongalactic Astrophysics

Not all those missing are lost: leveraging galaxy clustering in incomplete catalogs to unleash dark sirens cosmology

Riccardo Barbieri, Marios Kalomenopoulos, Matteo Tagliazucchi et al. (+2 more)

Gravitational waves offer a unique opportunity to solve the Hubble tension. In order to do so, we have to extract as much information as possible from cross correlating gravitational wave events (used as "dark sirens") with incomplete galaxy catalogs. Traditional methods assume a uniform in comoving volume distribution for galaxies missing from the catalogs, which neglects the fact that galaxies tend to cluster, leading to less precise and possibly biased posteriors. In this paper, we introduce a new method for accounting for galaxy clustering when dealing with an incomplete galaxy catalog, by adding back galaxies to the incomplete catalog and distributing them in pixels according to the correlation function $\xi(r)$. We find that our method drastically improves on traditional ones when the galaxy catalog is only $1\%-10\%$ complete, leading to posteriors that are between 2 and 4 times as precise, depending on the completeness fraction, without introducing any biases. Our method produces results comparable to traditional methods at extremely low catalog completeness fractions (<0.5%) or for very high uncertainties in the recovered luminosity distance and sky localization of the gravitational wave events.
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All authors Riccardo Barbieri, Marios Kalomenopoulos, Matteo Tagliazucchi, Jonathan Gair, Sadegh Khochfar

Cosmology and Nongalactic Astrophysics

Thermodynamic reconstruction in observationally constrained dynamical dark energy models

Sonej Alam

We perform an observational and thermodynamic analysis of four cosmological models $\Lambda$CDM, CPL, MPL, and the three-parameter MmAH parametrization. All dynamical models improve the fit relative to $\Lambda$CDM, with $\Delta\chi^2 \sim 6$-$6.5$, with MPL providing the best fit, while MmAH remains viable. Although Bayesian evidence mildly favors $\Lambda$CDM due to its lower complexity, the dynamical dark energy models remain competitive alternatives given current observations. We then reconstruct thermodynamic quantities within observationally constrained cosmological models, extending previous theoretical studies. The bestfit heat capacity reconstruction indicates that the divergence associated with a second order thermodynamic phase transition coincides with the deceleration-acceleration transition only in $\Lambda$CDM, whereas for the dynamical dark energy models it occurs at distinct redshifts, suggesting that this coincidence is not universal. The generalized second law is satisfied for all models over $0 \le z \le 1$, while the Hessian analysis reveals a transient instability at the phase transition; however, the late time thermodynamic stability is model dependent, with CPL and MPL remaining stable and $\Lambda$CDM and MmAH failing to satisfy both stability conditions simultaneously. These results show that thermodynamic properties reconstructed within observationally constrained cosmological models provide a complementary probe of dark energy, with the thermodynamic phase transition emerging as an intrinsically model dependent phenomenon.
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