Cosmology and Nongalactic Astrophysics · Cross-listed from physics.flu-dyn
Probing magnetic correlations in anisotropic turbulence
Bijita Bose, Somdeep Dey and Soma Sanyal
The topological classes of coherent structures in magnetohydrodynamic
turbulence are studied using the irreducible representations of the SO(3) and SO(2) rotation groups. We probe the coherent structures around axisymmetric
magnetic fields in the universe. Such axisymmetric fields can be found around filamentary structures as well as
cosmic strings. We have considered a Gaussian and a non Gaussian
magnetic field. We find that the field distribution leads to different coherent structures for the two cases. Our results show that the scattering of particles from the Gaussian structure depends predominantly on two lengthscales. In the case of the non Gaussian distribution, we can define a third intermediate lengthscale, similar to the Taylor lengthscale. In both the cases, we find that there is a dominance of the polarization anisotropy which indicates that the field gradients are forced into rigid spatial configurations. In the early universe, this will change the mean free path of the baryons and leptons in the coherent structures. Trapping of charged particle as well as their acceleration will be more frequent in the case of a
magnetic field with a heavy tailed distribution. The lengthscale of density inhomogeneities close to these structures will thus be determined by the
magnetic field distribution of the fields.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
CHASE Spectral Survey I: Measuring Contamination in the Color-selected J-region Asymptotic Giant Branch Distance Indicator
Siyang Li, Alexei V. Filippenko, Arief Ahmad et al. (+11 more)
The J-region asymptotic giant branch (JAGB) method for distance measurements uses the near uniform luminosity of carbon-rich AGB
stars as a standard candle. Its application rests on an assumed but rarely examined premise: the
stars contained in the JAGB color-magnitude selection box are primarily carbon-rich AGB
stars. We investigate the purity of the photometric selection in the Milky Way with an optical spectroscopic survey (~3590-7150 $\mathring{A}$) called CHASE (Carbon
stars, Hubble tension, And Spectroscopic Exploration of JAGB populations) using the Shane 3 m
telescope at Lick Observatory. These
stars are classified using molecular bandhead step indices, which recover 100% of known classifications. We report the observations of 76
stars (54 within the standard JAGB selection box of 1.5 < J - K < 2.0 mag) and find only 13 of 54
stars are carbon-rich, a 76$\pm$6 oxygen-rich contamination under blind photometric selection. This contamination remains high (71%) even within $\pm$0.4 mag of the JAGB peak itself, showing it is not confined to the edges of the selection box. This inhomogeneity may explain why recent literature find field-to-field and methodological variations of 0.1-0.2 mag that now dominate its systematic error budget. These variations could be caused, in part, by inhomogeneous stellar populations that consist of differing spectral types, and hence differing mean magnitudes.
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All authors Siyang Li, Alexei V. Filippenko, Arief Ahmad, Adam G. Riess, Stefano Casertano, Thomas G. Brink, Richard Anderson, Caroline D. Huang, Louise Breuval, Noriyuki Matsunaga, Gracelynn Jost, Yash Mehta, Elaina Sadler, Julian Shapiro
Cosmology and Nongalactic Astrophysics
Cross-Bispectrum Constraints from HI Intensity Mapping and Galaxy Surveys
Warren Naidoo, Moumita Aich and Kavilan Moodley
Future neutral hydrogen (HI) intensity mapping (IM) and optical surveys probe large-scale structure over unprecedented volumes, offering powerful constraints on cosmological models. We study the cross-correlation between the HI IM field and the
galaxy density and
cosmic shear fields from optical surveys. By formulating the HI-HI-
galaxy and HI-HI-shear cross-bispectra, we recover sensitivity to long-wavelength radial modes otherwise removed by foreground subtraction in HI maps, evaluating their detectability for HIRAX and Rubin-LSST. Combining the probes breaks degeneracies in
redshift-dependent quantities, including the $f$-$\sigma_8$ degeneracy. Our constraints range from $0.74\%$ to $9.8\%$ on $f$ and $0.073\%$ to $3.5\%$ on $\sigma_8$ across the six
redshift bins that we consider. Our constraints on the first- and second-order HI bias parameters range from $0.42\%$ to $5.6\%$ on $b_{\rm HI}^{(1)}$ and from $2.0\%$ to $29\%$ on $b_{\rm HI}^{(2)}$, while the
galaxy bias constraints range from $2.6\%$ to $11\%$ on $b_{\rm gal}.$ The HI-HI-
galaxy density cross-bispectrum measurement allows us to constrain a linear scale-dependent model for the
stochastic cross-correlation coefficient between HI and
stars, $r_{{\rm HI \,HI\,}\delta_g} = r_0 + r_1 k,$ with a break scale of $0.14\,\mbox{Mpc}^{-1}.$ We obtain $r_0$ constraints that range from $3.8\%$ to $13.5\%$ and $r_1$ constraints that range from $7.5\%$ to $19.9\%$. For cosmology, adding cross-bispectra enhances Lambda CDM constraints, notably via the HI-HI-shear cross-bispectrum. For the $w_0\, w_a$CDM model, the power-spectrum-only constraints on $w_0$ and $w_a,$ including Planck priors, improve from $(\sigma_{w_0},\sigma_{w_a})=(0.036,0.15)$ and $(0.032,0.12)$ to $(\sigma_{w_0},\sigma_{w_a})=(0.014,0.057)$ and $(0.015,0.059)$ when adding the HI-HI-
galaxy and HI-HI-shear cross-bispectra, respectively.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Cosmology in sixth-order higher-derivative theories of gravity
Carlos Aguilar, Manuel Asorey, Diego Muñoz et al. (+1 more)
We analyze the cosmological implications of theories of
gravity with quadratic
curvature invariants $R^2$ and $C^{\mu\nu\rho\sigma}C_{\mu\nu\rho\sigma}$, and six-derivative operators $R\Box R$ and $C^{\mu\nu\rho\sigma}\Box C_{\mu\nu\rho\sigma}$. We first analyze homogeneous and isotropic cosmological solutions, showing that the theory admits expanding, recollapsing and non-singular bouncing solutions. We clarify in the Einstein-frame formulation the mechanism that circumvents the Hawking–Penrose singularity
theorems, and identify the role played by the additional higher-derivative degrees of freedom in that mechanism. We show that the complete set of linear equations governing tensor perturbations on standard backgrounds admit analytically stable solutions. The analysis reveals that the stability properties are determined by the pole structure of the propagator and by specific relations among the higher-derivative couplings, while the singularity-free backgrounds are found to be unstable against tensor perturbations. For scalar cosmological perturbations, the higher-derivative theories presents super-horizon scalar instabilities in de Sitter spacetimes for both quadratic and sixth-order
gravity. To extract inflationary observables, we adopt an EFT approach to the sixth-order theory, treating these terms as perturbative corrections around the Starobinsky background. Within this framework, we compute the modification of the primordial scalar and tensor power spectra, obtaining predictions for the scalar spectral index and tensor-to-scalar ratio. We find that sixth-order operators produce controlled deviations from the Starobinsky model while preserving the EFT expansion, thereby providing a consistent phenomenological framework to probe ultraviolet gravitational corrections through cosmological observables.
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All authors Carlos Aguilar, Manuel Asorey, Diego Muñoz, Miguel Pardina
Cosmology and Nongalactic Astrophysics
Basis function expansions of the two-point correlation function and reconstruction of the cosmological distance scale
Fatima Abd Alrahman, Farnik Nikakhtar, Marcello Musso et al. (+2 more)
The shape of the correlation function of
galaxy pairs can be used as a cosmological distance indicator. Most
estimators of this shape require that one bin the pair counts, and considerable effort is expended in finding the optimal bin size. Cosmological constraints are then derived, in a separate step, by fitting to the binned pair counts. By projecting the pair counts on a suitable basis set, it is possible to estimate the pair correlation function without binning. Recent work suggests that, in the context of estimating the cosmological distance scale from
galaxy clustering data,
polynomials and half-integer generalized Laguerre functions are particularly useful bases. We show how to use these bases to measure the correlation function and estimate the reconstructed distance scale in a single step. Our analysis includes the effects of shot-noise and
cosmic variance, and highlights the benefits of projecting pair counts onto orthogonal basis functions.
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All authors Fatima Abd Alrahman, Farnik Nikakhtar, Marcello Musso, Aseem Paranjape, Ravi K. Sheth
Cosmology and Nongalactic Astrophysics · Cross-listed from physics.hist-ph
Before WIMPs: Neutrinos and the origins of particle dark matter
Jaco de Swart
After four decades of null-results, the experimental quest to discover a dark matter particle ardently continues. While confidence in the leading candidate, the Weakly Interacting Massive Particle (WIMP), is waning, its explanatory success still shapes current experimental approaches and theoretical expectations - from underground detecting efforts in Europe, China, and the U.S. to modern theories of
cosmic structure. This paper traces the origins of this particle-based paradigm to a critical predecessor: the
neutrino-dominated universe. Proposed in the early 1970s as a solution to extra-galactic anomalies,
neutrinos became the leading explanation of 'missing matter' following experimental hints of
neutrino mass in 1980. Although short-lived, the model's coherent picture of
cosmic evolution and structure formation set strong conceptual and methodological standards - providing critical impetus to the field of particle cosmology. Examining this history invites renewed reflection on how such past aims and expectations continue to guide dark matter inquiry today.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Cosmological stasis and the coupled dark sector of the Dark Dimension
Alexander Stewart
We study cosmological stasis in coupled dark matter and dark energy models in which a scalar field drives the dark energy and sets the dark matter mass, with the Dark Dimension as the motivating realization. Treating dark matter, dark energy, baryons, and radiation as an autonomous dynamical system, we show that exact stasis requires exponential slopes along the trajectory, and that running slopes give exact stasis or a drifting quasi-stasis depending on whether the running is integrable. The constant abundance solutions are the stationary solutions of coupled quintessence, which we read as stasis epochs with computable lifetimes and exits. Anchoring the cosmology to the measured abundances at matter-radiation equality and today, we show that the stasis region for this model cannot accelerate for any initial conditions, and that the total equation of state is never phantom although the effective dark energy of a $\Lambda$CDM fit can appear so. For the Dark Dimension, capture into stasis in the future is excluded for
geometric sources of the potential once dark fifth-force bounds are imposed, and dark matter production from the Standard Model brane supports a further stasis which the standard scenario does not reach. The stasis solutions provide analytic exclusions of the parameter space which do not depend on initial conditions.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Gravitational wave signatures of subsolar neutron star formation in collapsar disks
Vishal Baibhav, Valerio De Luca, Loris Del Grosso et al. (+3 more)
Standard models for stellar core collapse predict the birth of
neutron stars with masses exceeding a solar mass. In the collapsar model, a rapidly rotating massive
star collapses to a black hole surrounded by a dense,
neutrino-cooled
accretion disk, whose outer regions may in some cases fragment into
neutron-rich clumps that collapse to form subsolar-mass
neutron stars. These disk-formed objects can then merge either with one another or, following possibly hierarchical
evolution, with the central black hole. In this work, we characterize the gravitational-wave signatures of these binaries, focusing on distinctive features of the collapsar environment: Doppler and other phase modulations from orbital motion about the central black hole, gas-driven migration in the disk, and tidal interactions during inspiral. We show that the combination of anomalously low component masses with these environmental imprints produces unique waveform signatures that can distinguish the collapsar channel from other subsolar merger scenarios. Current and next-generation detectors have good prospects for identifying the intrinsic properties of such objects and, if subsolar mergers are discovered, for testing and constraining the collapsar formation pathway.
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All authors Vishal Baibhav, Valerio De Luca, Loris Del Grosso, Emanuele Berti, Brian D. Metzger, Lam Hui
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
The KAGG survey: KCWI Analysis of Gas around Galaxies at z~3-5
Grecco A. Oyarzún, Marc Rafelski, J. Xavier Prochaska et al. (+5 more)
We present the KCWI Analysis of Gas around
Galaxies (KAGG) survey of Ly$\alpha$ emission around Damped Ly$\alpha$ Absorbers (DLAs) at z~3-5 with the Keck
Cosmic Web Imager (KCWI) integral-field spectrograph. The KAGG survey is characterized by the sample of 36 DLAs spanning a wide
metallicity range, the wide search area for associated Ly$\alpha$ emission (impact parameter b$~\lesssim 120~$kpc), and the high emission sensitivity, reaching Ly$\alpha$ luminosities $\lesssim10^{42}$ erg s$^{-1}$. We identify 7 DLA Ly$\alpha$ emitters that are likely DLA
galaxy candidates due to the good match between the Ly$\alpha$ emission and DLA
redshifts. Based on a composite sample of 11 DLA Ly$\alpha$ emitters from KAGG and MAGG (MUSE Analysis of Gas around
Galaxies), we find that the impact parameters of DLA Ly$\alpha$ emitters decrease with DLA
metallicity, from b$~>50~$kpc at [M/H]~-2 to b$~<50~$kpc at [M/H]~-1. Including Ly$\alpha$ emitters at larger velocity offsets and at larger impact parameters from the DLAs, we construct samples of 35 "Group" Ly$\alpha$ emitters and 17 "Large-scale" Ly$\alpha$ emitters. We find that their impact parameters and incidence rates also depend on DLA
metallicity. Based on simulations of our survey and comparisons with models of
galaxy formation, we conclude that higher DLA
metallicities are associated with higher
halo masses. The low Ly$\alpha$ emission detection rate at low impact parameters suggests that most DLA
galaxies either have low stellar masses (M$~\lesssim10^{8}M_{\odot}$) or have their Ly$\alpha$ emission suppressed due to HI resonant scattering and/or dust absorption.
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All authors Grecco A. Oyarzún, Marc Rafelski, J. Xavier Prochaska, Nissim Kanekar, Marcel Neeleman, Marie Wisz, Michele Fumagalli, Regina A. Jorgenson
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
Dark matter haloes from dwarf to massive galaxies: no systematic inner-density tension with {\Lambda}CDM hydrodynamical simulations
Pavel E. Mancera Piña, Justin I. Read, Jorge Sarrato-Alós et al. (+1 more)
Two of the most prominent small-scale challenges to the cold dark matter (CDM) paradigm are the cusp-core and diversity-of-rotation-curves problems. The former concerns the shallow inner DM density profiles inferred for many
galaxies compared with the cusps predicted by collisionless CDM, while the latter concerns the wider range of inner DM densities and rotation curve shapes inferred observationally than hydrodynamical simulations traditionally reproduce. Robust observational constraints on DM core sizes and
halo densities are therefore essential for testing both the nature of DM and the impact of
galaxy formation processes. We analyse the inner DM distribution of a curated sample of 48 gas-rich
galaxies and 8 Milky Way gas-poor satellites, spanning 6 orders of magnitude in $M_\ast$. We find substantial scatter in DM core sizes and degrees of coreness, with both cuspy and cored
haloes occurring over a broad $M_\ast$ range. The cores are energetically consistent with stellar feedback, requiring modest
supernova energy coupling efficiencies of order $0.1-1\%$. Comparisons with the NIHAO, FIRE-2, and EDGE simulations reveal broad agreement in the inner DM densities and logarithmic slopes of observed and simulated
galaxies. The main residual differences concern the steep slopes of some massive simulated
galaxies and differences in SHMRs. Using a rotation-curve diversity diagnostic from previous work, we find that extreme discrepancies with simulations are absent from our curated sample and largely attributable to uncertain kinematics or baryonic mass distributions. Within the scope of our analysis, we find no evidence of a systematic inner-density tension between our
galaxy sample and current $\Lambda$CDM hydrodynamical simulations. Together with the modest energetic requirements for core formation, this substantially alleviates the cusp-core and diversity-of-rotation-curves problems.
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All authors Pavel E. Mancera Piña, Justin I. Read, Jorge Sarrato-Alós, Claudia Muni
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Jinn-Ouk Gong, TaeHun Kim, Junghwan Lee et al. (+1 more)
We establish a direct
quantum Clausius relation for conformal fields inside the apparent horizon of a quasi-de Sitter spacetime. We compute the net heat flow across the horizon from the renormalized stress-energy tensor, and independently determine the time
evolution of the renormalized von Neumann
entropy using the replica method. At leading order in the Hubble-flow expansion, the two calculations agree exactly, without using the gravitational equations of motion. Beyond leading order, we find a scheme-independent
entropy balance that includes the corresponding Wald
entropy. Our results provide a
quantum field theoretic realization of dynamical horizon thermodynamics beyond exact de Sitter
equilibrium.
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All authors Jinn-Ouk Gong, TaeHun Kim, Junghwan Lee, Chang Sub Shin
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Cosmic Birefringence and Axiogenesis
Raymond T. Co, Lawrence J. Hall, Keisuke Harigaya et al. (+1 more)
Recent analyses of Planck and ACT CMB data report a $2\text{-}4\sigma$ hint of isotropic
cosmic birefringence ($\beta \approx 0.3^\circ$), corresponding to a parity-violating rotation of polarization planes that points to potential new physics. We show that both the hint of
cosmic birefringence and the observed baryon asymmetry can be simultaneously explained by the rotation of an
axion-like field. The minimal setup predicts a positive birefringence angle, consistent with the CMB hint, and matter and kination domination ending around a temperature of $\mathcal O(3\text{-}50)$ MeV, making the model falsifiable by astrophysical probes and potentially giving rise to characteristic gravitational-wave signals. We also introduce a mechanism that can exponentially enhance the angular momentum of the rotation generated by the Affleck-Dine mechanism.
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All authors Raymond T. Co, Lawrence J. Hall, Keisuke Harigaya, Taegyu Lee
Cosmology and Nongalactic Astrophysics
Statistical Fluctuations as Primordial Correlators in the CMB: Finite Chemical Potential Thermodynamics
Anish Ghoshal, Anupam Mazumdar and Bartłomiej Sikorski
Can primordial cosmological correlations originate from statistical fluctuations of an early-universe thermal system? We connect grand-canonical thermodynamics,
stochastic transport, and gauge-invariant cosmological perturbations for a charged fluid at finite chemical potential. Energy-charge susceptibilities determine
curvature, charge-isocurvature, and cross-correlation amplitudes, while transport sets when each mode leaves
equilibrium. For an isolated, adiabatic conformal
plasma with conserved charge-to-
entropy ratio and power-law
diffusion, diffusive freeze-out yields the universal spectrum $\mathcal P_S(k)\propto k^3$, with $n_{\rm iso}=4$, while equal-time local-
equilibrium curvature-isocurvature covariance vanishes in the conformal source basis. Thus neither finite chemical potential nor replacing Hubble crossing by
diffusion crossing alone yields approximate scale invariance. We evade this obstruction with an open subsystem of massless Dirac
fermions during a sourced quasi-de Sitter phase. There, grand-canonical energy cumulants generate a nearly scale-invariant red
curvature spectrum. A
benchmark gives $\mathcal P_{\zeta_X}(k_\star)=2.10\times10^{-9}$ and $n_s(k_\star)=0.9649$, stays within $0.30%$ of the fitted power law over $0.002\leq k/k_\star\leq4$, and predicts weak negative running and small positive intrinsic non-Gaussianity from higher-order cumulants, $f_{\rm NL}(k_\star)\simeq0.106$ and $g_{\rm NL}(k_\star)\simeq0.0158$. With a two-helicity
vacuum tensor spectrum, the tensor-to-scalar ratio is $r_{t/s}(k_\star)=1.82\times10^{-4}$. This isolates the limitation of isolated conformal thermal seeding and the open-system ingredient needed to overcome it. Thermal energy-charge fluctuations thus provide a calculable source of realistic scalar correlations, while reservoir dynamics, equilibration, and later
curvature-isocurvature transfer must come from a microscopic model.
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Cosmology and Nongalactic Astrophysics
Multi-Stage and Multi-Field Inflation in Random Inflationary Landscapes
Xingang Chen, Lucas Pinol, Zhong-Zhi Xianyu et al. (+1 more)
Generic potentials in an inflationary landscape are typically too steep to support a prolonged period of
cosmic inflation. Atypical flat regions of the landscape are required to support successful inflation. The occurrence of such regions leads broadly to two possibilities: a single prolonged period of slow-roll inflation (which we call single-stage inflation), or multiple shorter periods of inflation separated by transient departures from slow roll (which we call multi-stage inflation), giving rise to primordial features and other departures from the behavior of the simplest slow-roll model. The former is the possibility most commonly assumed when deriving the primordial density fluctuations for the Big Bang model. In this paper, using Gaussian random potentials as a simple model of the inflationary landscape, we study the relative occurrence of these two possibilities. We find a substantial fraction of multi-stage inflationary trajectories in landscapes with field-space dimensions one, two, and three, and this fraction increases with dimensionality at fixed typical landscape
curvature. In constructing the inflationary landscapes and identifying successful inflationary trajectories, we also define several relevant quantities and classify detailed properties of both multi-stage and multi-field inflationary trajectories.
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All authors Xingang Chen, Lucas Pinol, Zhong-Zhi Xianyu, Yisong Zhang
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Three-Flavoured Thermal Leptogenesis Without Tuning
Angus Spalding
We investigate thermal leptogenesis in an extension of the Type-I seesaw in which a real singlet scalar couples non-diagonally to the right-handed
neutrinos. The interactions $-y_{ij}\phi N_iN_j$, with $i\neq j$, introduce new sources of CP violation in heavy-
neutrino decays with a negligible enhancement of the standard leptonic washout. We derive an analytic upper bound on the scalar-induced CP asymmetry and present numerical results using fully flavoured Boltzmann equations and the density-
matrix formalism. We show that the observed baryon asymmetry can be generated with a hierarchical right-handed-
neutrino spectrum at the electroweak scale. In the minimal Type-I seesaw, lowering the scale of decay leptogenesis typically requires either a tuned quasi-degeneracy of the right-handed-
neutrino masses or cancellations between the tree-level and one-loop contributions to the light-
neutrino masses, while hierarchical leptogenesis instead requires a high scale that aggravates the
Higgs hierarchy problem. This singlet-scalar extension appears to avoid these tensions, allowing successful leptogenesis with a hierarchical right-handed-
neutrino spectrum down to the electroweak scale.
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Cosmology and Nongalactic Astrophysics
Tangled $\tau$: Planck CMB Constraints on Flash Reionization
Param Upadhyay, Elisa G. M. Ferreira and Evan McDonough
Recent cosmological tensions have renewed interest in the role of reionization in parameter inference, and flash reionization has been proposed as a transient high-
redshift ionization episode that can increase the Thomson optical depth while remaining compatible with CMB polarization data. In this work, we present the first Markov Chain Monte Carlo analysis of the flash reionization model fit to Planck
cosmic microwave background temperature, polarization, and
lensing data. We perform this analysis using Planck PR4 data in $\Lambda$CDM with flash reionization. We find that CMB data allow a wide range for the
redshift of the flash, $z_{\rm flash}$, but with constraints that are tightly correlated with the peak ionization fraction $x_{\rm flash}$. We find constraints $x_{\rm flash}=0.24 ^{+0.13} _{-0.07}$ and $x_{\rm flash}= 0.15 ^{+0.07} _{ - 0.05}$ for the
benchmark flash reionization scenarios with fixed $z_{\rm flash}=20$ and $25$ respectively. The standard $\Lambda$CDM parameters do not exhibit any significant shifts, and in particular, the total optical depth to reionization is not appreciably changed, with $\tau=0.061 \pm 0.007$ in flash reionization as compared to $\tau=0.059\pm 0.006$ in the standard tanh parametrization. We repeat this analysis for Planck PR3 data in place of PR4, and find that the mild preference for a flash is replaced by 95% CL upper bounds, given by $x_{\rm flash}<0.28$ and $x_{\rm flash}<0.18$ for $z_{\rm flash}=20$ and $25$, respectively, from Planck PR3 data.
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Cosmology and Nongalactic Astrophysics
Two-dimensional weak lensing shear for cluster mass, concentration, ellipticity and miscentering estimation
Calum Murray, Martin Kilbinger and Constantin Payerne
The effects of weak gravitational
lensing induced by clusters of
galaxies makes it possible to constrain their dark matter distribution. In general mass estimates from weak
lensing are made by compressing the two-dimensional shear-field into one-dimension. In this work we build a forward model of the two-dimensional reduced-shear field around a
galaxy cluster, including the non-Gaussian correlated large-scale structure from N-body simulations, the uncorrelated line-of-sight structure, cluster miscentering and ellipticity. We then use simulation-based inference to obtain posteriors on the cluster mass, concentration, miscentering and ellipticity from the full field. The two-dimensional approach leads to improvements on cluster mass constraints by up to 20%. We show that this is due to a better treatment of the spatially correlated noise across the shear field. There is also significant improvements on the cluster concentration and miscentering. Whilst improvements are also made to the estimation of cluster ellipticity, the constraints are still prior dependent for these individual cluster constraints. We also quantify the impact of the line-of-sight structure on the constraints. Neglecting it underestimates the mass uncertainty by up to a factor of $2$ for the most massive clusters.
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Cosmology and Nongalactic Astrophysics
Merlin: Fast and flexible 3x2pt cosmology with simulation-based inference
Alexandra Wernersson, Guillermo Franco-Abellán and Guadalupe Cañas-Herrera
We present Merlin, a simulation-based inference (SBI) pipeline to perform cosmological analyses of 3x2pt summary statistics:
cosmic shear,
galaxy clustering and the cross-correlation power spectra. Our approach combines Marginal Neural Ratio Estimation (MNRE) with 3x2pt angular power spectra predictions from the cloelib library, although the pipeline is readily extensible to other cosmology libraries. We demonstrate this pipeline on a realistic setting representative of a Stage-IV photometric survey, with a 50-dimensional parameter space describing cosmology and a wide range of systematic effects. We find posteriors that are in excellent agreement with the nested sampler Nautilus, while reducing the number of required CPU-hours by two orders of magnitude. Because the generation of training data and the training of inference networks are decoupled processes, a single simulation bank can be reused to perform inference under different analysis choices, further improving the simulator-efficiency. We illustrate this flexibility by applying scale cuts, varying the survey area, and removing
cosmic shear from the data vector (2x2pt), all at zero extra model evaluations, whereas sampling-based methods need costly re-runs for each case. The Merlin code is publicly available on GitHub.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Gauss–Bonnet running and the de Sitter saddle of quadratic gravity inflation
Ruolin Liu and Niayesh Afshordi
Inflation driven purely by the
quantum running of the
curvature-squared couplings of quadratic
gravity was shown to accommodate the high scalar tilt favored by recent
cosmic microwave background observations, starting from a Euclidean four-sphere at a maximum of the running $R^2$ coupling. That maximum exists only in one renormalization scheme, and is not stationary once the Euler trace anomaly is included. We show that the standard one-loop running, with the usually neglected Gauss–Bonnet coefficient retained, recovers the missing de Sitter state: the Euler running balances the scale dependence of the $R^2$ term at a unique coupling ratio, giving a de Sitter solution that is stationary for the gravitational constraint and for the compact Euclidean action alike, and whose scalaron potential is an extremely flat hilltop ($m^2/H^2\simeq-5\times10^{-10}$) joined to an inverse-linear inflationary plateau. The last $N_*\simeq50$–$60$ $e$-folds are scheme independent, with scalar tilt $n_s\simeq1-4/(3N_*)$, while the tensor-to-scalar ratio, $r$, is set by the number of matter fields that enhance the running. The current tensor bound excludes pure
gravity and sets a minimum matter content, some $4\times10^6$ conformally coupled scalars or $3\times10^5$ vectors—$2.6$ times fewer than the momentum-induced scheme requires—while one-loop control to the end of inflation sets a maximum about ten times higher. Across that window the model predicts $r\gtrsim0.008$ with $0.973\lesssim n_s\lesssim0.978$, within reach of upcoming CMB polarization surveys.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
LATED: JWST integral field spectroscopy of a galaxy caught in chemical infancy at $z=4.8$ behind Abell 2744
Mingyu Li, Roberto Maiolino, Zheng Cai et al. (+26 more)
When Population III (Pop III)
star formation ended remains an open question. LATED-1 is an intrinsically faint ($M_\mathrm{UV}=-16.15$) Ly$\alpha$ emitter at $z=4.80$ revealed by VLT/MUSE behind the
lensing cluster Abell 2744 ($z=0.308$). Before any spectroscopic
metallicity constraints, it was identified as an extremely metal-poor or metal-free
galaxy candidate from JWST imaging by LATED, our novel photometric selection framework. Here we present serendipitous JWST/NIRSpec PRISM integral-field spectroscopy of this target. The spectrum reveals Ly$\alpha$, H$\beta$, and H$\alpha$ at 7.0, 5.6, and 17.7$\sigma$, as well as tentative detections of [O III]$\lambda\lambda4959,5007$ at 2.9$\sigma$, and yields $R3=\mathrm{[O\,III]\lambda5007/H\beta}=0.59^{+0.27}_{-0.21}$, upholding the earlier LATED photometric prediction of $R3<1.54$ ($2\sigma$ limit). The canonical JWST-based strong-line calibration, extrapolated to low
metallicity, implies $\log (O/H)=6.45^{+0.17}_{-0.19}$, or $Z/Z_\odot=0.58_{-0.20}^{+0.28}\%$, placing LATED-1 among the most metal-poor
galaxies known. Its modest magnification ($\mu=2.80$) leaves the intrinsic properties insensitive to the lens model. LATED-1 is therefore a dwarf
galaxy caught in the earliest state of chemical enrichment, and a compelling target for testing whether Pop III
star formation can persist to $z<5$. The result demonstrates that photometric selection, especially through the LATED methodology, can reach below one per cent solar
metallicity to identify Pop III
galaxy candidates for spectroscopic follow-up.
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All authors Mingyu Li, Roberto Maiolino, Zheng Cai, Hannah Übler, Boyuan Liu, Qiao Duan, Fuyan Bian, Sijia Cai, Francesco D'Eugenio, Eiichi Egami, Bjorn H. C. Emonts, Xiaohui Fan, Yuki Isobe, Lucy R. Ivey, Xihan Ji, Gareth C. Jones, Maria Koller, Xiaojing Lin, Christopher C. Lovell, Kimihiko Nakajima, Masami Ouchi, Robert G. Pascalau, J. Xavier Prochaska, Jan Scholtz, Fengwu Sun, Sandro Tacchella, Yunjing Wu, Fujiang Yu, Zijian Zhang
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
LATED: Ly$\alpha$-anchored photometric selection of candidate metal-free and extremely metal-poor star formation from the end of reionisation to cosmic noon
Mingyu Li, Zheng Cai, Roberto Maiolino et al. (+24 more)
Cosmological simulations allow a low-level tail of Population III (Pop III)
star formation to persist to $z=2-6$. Spectroscopic confirmation is expensive, so an efficient photometric pre-selection is needed. We present LATED (Lyman-Alpha
Tomography of Extremely Metal-poor Domains), which selects metal-free and extremely metal-poor candidates from a Ly$\alpha$-emitter parent sample using strong-line diagnostics. The method requires three bands and two colours, $x=m_{\rm OIII}-m_{{\rm H}\alpha}$ and $y=m_{{\rm H}\alpha}-m_{\rm cont}$, which trace oxygen abundance and the H$\alpha$ equivalent width, respectively. Requiring that the filters simultaneously contain [O III]+H$\beta$ and H$\alpha$, together with a Ly$\alpha$ parent selection, defines five windows spanning $z=1.92-6.60$ (four JWST/NIRCam, one Roman/WFI). The criteria, $x\geq x_{\rm min}(z)$ and $y\leq y_{\rm max}(z)$, are set by the per-
redshift extrema of a forward-modelled Pop III template locus. Ordinary metal-enriched
star-forming and AGN templates fall outside the selection region, and possible contaminants such as little red dots are flagged by their multi-band colours. To check contamination empirically, we apply LATED to 1126 JADES spectroscopic
galaxies, and no source is selected in the four NIRCam windows. We release a Python package which converts the same photometry into R3=[O III]/H$\beta$ as a measurement or upper limit, reproducing JADES spectroscopy with small 0.12 dex scatter. Applied to 85 archival MUSE Ly$\alpha$ emitters in Abell 2744, LATED recovers the confirmed extremely metal-poor
galaxy AMORE6 and reveals three new candidates at $z=3-5$. Photometry alone cannot establish a metal-free nature. LATED delivers prioritised candidates for spectroscopic follow-up, providing a scalable route toward a systematic census of late-time Pop III
star formation.
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All authors Mingyu Li, Zheng Cai, Roberto Maiolino, Fuyan Bian, Sijia Cai, Francesco D'Eugenio, Qiao Duan, Eiichi Egami, Xiaohui Fan, Yuki Isobe, Xihan Ji, Gareth C. Jones, Maria Koller, Xiaojing Lin, Boyuan Liu, Christopher C. Lovell, Kimihiko Nakajima, Masami Ouchi, Robert G. Pascalau, Zijin Su, Jan Scholtz, Fengwu Sun, Sandro Tacchella, Hannah Übler, Yunjing Wu, Fujiang Yu, Zijian Zhang
Cosmology and Nongalactic Astrophysics
Biases from Astrophysical Environmental Effects in Standard-Siren Cosmology
Ioannis Liodis, Rodrigo Vicente, Soumen Roy et al. (+1 more)
Next-generation ground based gravitational wave detectors will enable precision standard-siren cosmology, making systematics increasingly important. We investigate how line-of-sight acceleration, as may arise for compact binaries in dense astrophysical environments, biases measurements of the Hubble constant $H_0$. We simulate a catalogue of 50 binary
neutron star bright sirens with known host
redshifts, assuming the signals have been impacted by line-of-sight acceleration and analysing them with
vacuum waveforms. Unmodelled line-of-sight acceleration biases the inferred luminosity distances and shifts the individual $H_0$ posteriors systematically towards lower values. Consequently, combining events narrows the posterior around a biased value rather than averaging away the systematic, even when the acceleration signs are assigned randomly. For our 50-event catalogues, affected fractions of approximately $10\%$ at $|a_\parallel|/c=10^{-6}\,\mathrm{s^{-1}}$, or $30\%$ at $|a_\parallel|/c=10^{-7}\,\mathrm{s^{-1}}$, produce offsets exceeding three posterior standard deviations in at least one quarter of the realisations. Considering larger catalogues further increases the significance of the effect. Our results indicate that environmental effects may constitute an important systematic for precision standard-siren cosmology and should be incorporated into future population analyses.
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All authors Ioannis Liodis, Rodrigo Vicente, Soumen Roy, Samaya Nissanke
Cosmology and Nongalactic Astrophysics
Probing modified gravity with galaxy-cluster-lensed gravitational-wave time delays: impact of systematic effects
Eleni Tsaprazi, Ettore Delpogetto, Federico Marulli et al. (+1 more)
Strongly lensed gravitational waves provide exceptionally precise measurements of relative macroimage arrival times, making their time delays a promising time-domain probe of
gravity on
galaxy-cluster scales. This precision places stringent demands on the control of
lensing systematic effects. We present a proof-of-concept pipeline for constraining a phenomenological modification, $D$, of the
galaxy cluster Weyl potential using the macroimage time-delay span of a simulated sample of binary
neutron star (BNS) sources and cluster lenses described by a Navarro–Frenk–White cluster
halo and a singular isothermal sphere for the brightest cluster
galaxy (BCG). Closure tests recover the injected general-relativistic (GR) limit. Adopting a fiducial 5 per cent precision on the reconstructed time-delay span, we assess controlled mis-specifications of the
halo mass and concentration, BCG contribution, source and lens positions,
redshifts, line-of-sight environment, projected ellipticity and secondary cluster-scale structure. Within the adopted
gravity model, neglecting
halo ellipticity, secondary cluster-scale structure, cluster mis-centring and line-of-sight perturbations can induce significant, strongly configuration-dependent biases in the inferred parameter $D$. Biased estimates of the cluster
halo mass and concentration, as well as systematic BNS source-position errors at the level considered here, produce significant coherent shifts. By contrast, uncertainties in the BCG contribution and in the lens and source
redshifts are comparatively subdominant. These results highlight the need for explicit treatment of the above uncertainties before cluster-lensed gravitational wave time delays can be used as precision tests of
gravity.
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All authors Eleni Tsaprazi, Ettore Delpogetto, Federico Marulli, Amandine M. C. Le Brun
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
StAGE: Stellar Archaeology-driven Galaxy Evolution II. Binary Black Hole Mergers in Quiescent Galaxies and their Star-forming Progenitors
Irene Iorio, Andrea Lapi, Lumen Boco et al. (+5 more)
We apply StAGE, a data-driven
galaxy-
evolution framework based on stellar archaeology, to study binary black hole (BBH) mergers in quiescent
galaxies (QGs) and their
star-forming progenitors. We combine StAGE
star-formation and chemical-enrichment histories with pre-computed SEVN binary population-synthesis catalogs to derive the BBH merger-rate density, its dependence on intrinsic binary and host-
galaxy properties, and the associated
stochastic gravitational-wave (GW) background. We assess uncertainties related to stellar-archaeology prescriptions, common-envelope
evolution, and $\alpha$-enhanced abundances. We find that QGs and their progenitors can contribute a sizeable fraction of the
cosmic BBH merger rate. For most of the binary-
evolution prescriptions explored here, we highlight a tension with the local LVK-inferred merger rates, underscoring the need to revisit some assumptions in the underlying modeling. Most BBHs form at moderately subsolar
metallicities, $Z\lesssim Z_\odot/3$, while their merger-time hosts typically have stellar masses $M_\star\lesssim10^{11}\,M_\odot$. At $z\gtrsim2$, hosts lie mainly on the
galaxy main sequence, whereas starbursting and quenching descendants contribute increasingly toward lower
redshift. Isolated binaries broadly reproduce the observed bulk of the primary- and chirp-mass distributions, but the predictions decline rapidly above $\sim 40-50\,M_\odot$, providing little support for the highest-mass systems inferred by LVK. Dynamical formation in young and globular clusters can populate this regime, but also increases the total merger-rate density, exacerbating the tension with LVK for the fiducial cluster normalizations adopted here. Finally, the predicted
stochastic background approaches the projected sensitivity of planned LVK upgrades and lies within reach of the Einstein
Telescope.
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All authors Irene Iorio, Andrea Lapi, Lumen Boco, Giovanni Antinozzi, Michele Bosi, Cecilia Sgalletta, Mario Spera, Luigi Danese
Cosmology and Nongalactic Astrophysics
Sound-Horizon-Independent Test of Cosmic Distance Duality Relation Using Artificial Neural Networks and Gaussian Processes
Bo-Hao Jiang, Guo-Jian Wang and Tao Yang
The
cosmic distance duality relation (CDDR), $D_L(z)(1+z)^{-2}/D_A(z) \equiv 1$, is a fundamental relation in modern cosmology linking luminosity distance $D_L$ and angular diameter distance $D_A$. We define $\eta(z) \equiv D_L(z)(1+z)^{-2}/D_A(z)$ and reconstruct the relevant quantities over $0 < z < 2.5$ using two independent non-parametric methods: Gaussian processes (GP) and artificial neural networks (ANN). Specifically, we reconstruct $D_L$ from three different Type Ia
supernovae (SNe$~$Ia) compilations (PantheonPlus, Union3, and DES-Dovekie), the baryon acoustic oscillation distance ratio $D_M/D_H$ from SDSS and DESI, and the Hubble function $H(z)$ from
cosmic chronometer (CC) data. Our CDDR test is independent of both the cosmological model and the sound horizon $r_d$ calibration, as $D_M/D_H$ naturally eliminates $r_d$. We render our GP reconstructions insensitive to mean-function and kernel choices via full
Bayesian marginalization over hyperparameters, with ANN as a cross-check$-$revealing the impact of data sparsity on the latter. Our results show no significant deviation from the CDDR exceeding $2\sigma$, and for the CC+BAO+DES-Dovekie combination it remains within $1\sigma$ over most of the
redshift range. With $r_d$ eliminated, varying the only remaining external parameter $M_B$ systematically shifts $\eta(z)$ through the $M_B$-$H_0$ degeneracy, indicating that the observed $\eta\neq1$ signal is closely tied to $H_0$ tension among
datasets and is likely driven by $M_B$ systematics rather than a true CDDR violation. Future high-quality CC, BAO, and SNe$~$Ia data$-$with either improved $M_B$ calibration or $M_B$-free distance measurements$-$will be essential for extending this calibration-free approach.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
A Sample of 459 Galaxy Groups Identified from the FAST All Sky HI Survey DR2
Z. S. Yuan and Z. L. Wen
Groups of HI-rich
galaxies are key laboratories for understanding
galaxy evolution and environmental effects, constructing samples of such groups is fundamental for relevant studies. Using the FAST All Sky HI Survey (FASHI) Data Release 2 (DR2), currently the largest and deepest HI catalog available, we identify
galaxy groups directly from HI signals, without relying on optical pre-selection. A group-finding
algorithm with a density contrast criterion and a minimum membership of five yields a catalog of 459
galaxy groups containing 3015 HI sources. Using archival spectroscopic data, we identify optical counterparts and derive total stellar masses of member
galaxies as a proxy for the group total mass. The group
redshift distribution peaks at z ~ 0.02, and the total HI mass peaks at ~ 10^{10} M_{\odot}. We find a significant positive correlation between total HI mass and total stellar mass, consistent with the increase in HI mass with
halo mass reported in previous stacking studies. The ratio of total HI mass to total stellar mass decreases significantly with increasing total stellar mass, indicating gradual HI depletion in groups. Our sample provides rich targets for future studies of
galaxy evolution and large-scale structure in the local Universe.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
The CAMELS-CROCODILE Simulation Suite: A New Cosmology–Astrophysics Playground for Machine Learning
Kentaro Nagamine, Yuri Oku, Atsushi J. Nishizawa et al. (+4 more)
We present CAMELS-CROCODILE, a suite of cosmological hydrodynamic simulations that extends the CAMELS framework with the \gadget{} smoothed particle hydrodynamics code and the Osaka feedback model. As a companion to the IllustrisTNG-based second-generation CAMELS suite, it provides an independent implementation of the baryonic physics that shapes
galaxies, the intergalactic medium, and large-scale structure, broadening the range of subgrid models over which machine-learning (ML) inference can be marginalized and tested. The suite comprises $25$ and $50Mpc/h$ boxes organized into one-parameter,
cosmic-variance, and Sobol-sequence sets that vary $26$ cosmological and astrophysical parameters around a fiducial Osaka model. We describe the simulation design and validate the suite against
benchmarks and other CAMELS suites. Compared with IllustrisTNG, the fiducial model suppresses the matter power spectrum by only a few per cent, against up to ${\sim}27\%$ at $z=0$, and forms
stars with similar efficiency below $10^{12.2} M_\odot/h$ but up to $2.5$ times more efficiently in group-scale
halos, both consistent with weaker AGN feedback. We also present the stellar and black hole bias and the Ly$\alpha$ absorption around
galaxies. As a first ML application, we apply a graph neural network trained on IllustrisTNG
galaxy catalogs, with frozen weights, to CAMELS-CROCODILE. It fails to recover $\Omega_{\rm m}$ and $\sigma_8$ and returns overconfident posteriors, mainly for simulations containing more
galaxies than any in its training set; within that range $\Omega_{\rm m}$ is recovered with an error only $1.5$ times the in-distribution value. These results underline the need to train and test ML inference across physically distinct
galaxy formation models.
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All authors Kentaro Nagamine, Yuri Oku, Atsushi J. Nishizawa, Jun-Young Lee, Francisco Villaescusa-Navarro, Shy Genel, Daniel Anglés-Alcázar