Cosmology and Nongalactic Astrophysics
Probing Baryons with the Kinematic Sunyae Zel'dovich Effect and Machine Learning Derived Peculiar Velocities using DESI DR2 and ACT DR6
Yulin Gong, Rachel Bean, Patricio A. Gallardo et al. (+54 more)
We present novel empirical constraints on average optical depths and gas density profiles from combining kinematic Sunyaev Zel'dovich effect (kSZ) measurements and nonlinear peculiar velocities, reconstructed using machine learning, for massive
halos traced by DESI DR2 luminous red
galaxies (LRG). The pairwise kSZ is measured using two ACT DR6
cosmic microwave background (CMB) temperature maps (ILC and 150 GHz maps) for seven luminosity-selected LRG samples. We find consistent results between the two maps and significant detections across the samples. We reconstruct LRG line-of-sight peculiar velocities in two
cosmic epochs, centered on $z=$ 0.55 and 0.8, using a simulation-trained
Transformer machine learning model to extend beyond the linear approximation. Average optical depths are inferred by comparing the kSZ pairwise correlation to the measured pairwise velocity correlation from the reconstructed velocity field and, separately, from a theoretical prediction using the best fit Planck cosmology, with the highest significance reaching SNR = 14.2 and 15.1 respectively. We also obtain velocity-weighted AP-filtered kSZ-stacked cluster density profiles, which show evidence of extended ionized gas around massive LRG groups and no strong
redshift evolution within current measurement uncertainties. These results demonstrate the power of combining spectroscopic
galaxy and CMB data, and employing machine learning methods, to probe diffuse baryons and coherent large-scale velocity fields. They open up new avenues to leverage upcoming
galaxy survey data from Euclid, Roman and Rubin LSST, in tandem with multi-frequency CMB/sub-mm data from CCAT and Simons Observatory.
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All authors Yulin Gong, Rachel Bean, Patricio A. Gallardo, Boryana Hadzhiyska, Yun-Hsin Hsu, Jenna Moore, Eve M. Vavagiakis, Nicholas Battaglia, J. Aguilar, S. Ahlen, A. Aviles, F. Beutler, D. Bianchi, D. Brooks, A. Carnero Rosell, T. Claybaugh, A. de la Macorra, Arjun Dey, Biprateep Dey, P. Doel, A. Font-Ribera, J. E. Forero-Romero, E. Gaztañaga, G. Gutierrez, K. Honscheid, S. Juneau, T. Karim, R. Kehoe, D. Kirkby, A. Kremin, O. Lahav, M. Landriau, L. Le Guillou, M. Manera, A. Meisner, R. Miquel, S. Nadathur, J. A. Newman, H. E. Noriega, E. Paillas, N. Palanque-Delabrouille, W. J. Percival, F. Prada, I. Pérez-Ràfols, C. Ravoux, G. Rossi, L. Samushia, E. Sanchez, C. Saulder, D. Schlegel, M. Schubnell, H. Seo, J. Silber, M. Siudek, G. Tarlé, B. A. Weaver, R. Zhou
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
How well do integral-of-motion distribution functions describe Milky Way-analogue halos?
Jason Kumar and Louis E. Strigari
We study the dark-matter phase space distribution of Milky Way-mass
halos in the Auriga simulations, considering both hydrodynamic and dark-matter-only runs. In a spherically averaged potential, we test whether the coarse-grained distribution function can be approximated as a function of the integrals of motion $E$ and $L$. We find that $f(E,L)$ provides a useful description of the simulated
halos: although the deviations from this form are formally statistically significant, the median fractional residuals between radial shells are typically $\lesssim 15\%$, with 90th-percentile residuals of order tens of percent. An energy-only approximation, $f(E)$, gives similar median residuals but is systematically disfavored by $\chi^2$ tests, indicating that angular momentum dependence is statistically preferred. Ultimately we find that neither $f(E)$ nor $f(E,L)$ fully describes the particle data at high precision. The remaining residuals likely reflect departures from spherical
equilibrium, including anisotropy, triaxiality, substructure, and baryonic effects.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
LMC-Perturbed LZ Dark Matter Landscape
Nassim Bozorgnia, Samantha Contreras, Graciela B. Gelmini et al. (+3 more)
The local dark matter (DM) velocity distribution is significantly altered by the gravitational impact of the Large Magellanic Cloud (LMC), which creates a high-velocity tail. We evaluate how the LMC reshapes the DM landscape for a wide variety of theoretical models in light of the recent putative LZ DM event. We show that the LMC-induced velocity shifts substantially modify the parameter space for inelastic endothermic DM models across a broad range of possible interactions, driving the viable regions towards larger mass splittings, which are more susceptible to
collider and indirect detection constraints. By contrast, models for elastically colliding DM are less impacted, and some remain viable candidates – for example, the simple light Singlet-Doublet Majorana DM candidate at the
Higgs blind spot. Our work confirms that accurately accounting for LMC effects is essential when high-velocity DM is probed, rather than relying on the simplified Standard
Halo Model.
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All authors Nassim Bozorgnia, Samantha Contreras, Graciela B. Gelmini, Alvine C. Kamaha, Javier Reynoso-Cordova, Yongheng Xu
Cosmology and Nongalactic Astrophysics
Constraining reionization with persistent homology: a novel summary statistic for wide-field Lyman-$\alpha$ emitter observations
Michael M. Wyatt, Nikolaos Triantafyllou, Steven R. Furlanetto et al. (+4 more)
The spatial clustering of Lyman-$\alpha$ emitters (LAEs) is one of the most promising observables for constraining reionization. In this work, we introduce persistent homology, a popular tool in topological data analysis, and specifically the Betti-0 curve as a summary statistic to characterize the clustering of LAEs. We compare the performance of the Betti-0 curve against the angular correlation function (ACF) and void probability function (VPF) by quantifying their ability to constrain the global neutral fraction $x_{\rm HI}$ during reionization using the Fisher information. We forward model observations of LAEs using 21cmFAST by including $\mathrm{Ly}\alpha$ emission as a post-processing step and account for
cosmic variance uncertainties. We focus our analysis within the framework of the SILVERRUSH. catalog at $z=5.7$ and 6.6, and find that the Betti-0 curve performs as well as or better than the ACF and VPF. We also find that the statistics are most sensitive to different physical scales and thus probe complementary information, and as a consequence that simultaneously constraining all three statistics improves constraints by a factor of $\sim 2$ compared with the ACF alone, with predicted minimum uncertainties of $\sigma_{\rm min} \sim$ 0.03 and 0.07 at $x_{\rm HI} = 0.05$ and $z=5.7$ and $x_{\rm HI} = 0.20$ and $z=6.6$, respectively. Our results show that the Betti-0 curve is a promising summary statistic to constrain reionization using LAE clustering and motivate further exploration of persistent homology for the same purpose in other wide-field surveys such as those made possible by the Nancy Grace Roman
Telescope.
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All authors Michael M. Wyatt, Nikolaos Triantafyllou, Steven R. Furlanetto, Hiroya Umeda, Samuel Gagnon-Hartman, Andrei Mesinger, Masami Ouchi
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Stochastic gravitational-wave background from subsolar neutron stars in collapsar disks
Valerio De Luca, Loris Del Grosso and Emanuele Berti
The fragmentation of the
neutrino-cooled
accretion disks that surround the black holes formed in collapsars has recently been proposed as an astrophysical channel for the production of
neutron stars with masses well below the standard core-collapse floor. These disk-born objects merge either with one another or with the central black hole, and the superposition of all such mergers across
cosmic history sources a
stochastic gravitational-wave background. In this work we compute the energy density of this background for both merger channels, adopting a formation history tied to the observed rate of long gamma-ray bursts. We find that the merger of a subsolar
neutron star with the central black hole is the loudest channel, already constrained by current data and within reach of next-generation observatories, while the binary
neutron-
star channel is at most two orders of magnitude fainter, with its widest binaries remaining accessible to next-generation detectors. Confronting these predictions with the fourth observing run of the LIGO–Virgo–KAGRA Collaboration, we derive two upper bounds on the fraction of collapsars whose disks produce such mergers: a robust one from the non-detection of an isotropic background, and a tighter one that could be achieved by a dedicated search for resolvable subsolar events in current data. Gravitational waves from non-axisymmetric deformations of the collapsar disk itself would provide an additional independent signature for the collapsar scenario, enabling cross-correlation studies with future deci-Hz detectors. Overall, the background computed here provides a population-level probe of disk-born subsolar
neutron stars, which next-generation detectors could bring firmly into view.
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Cosmology and Nongalactic Astrophysics
Connecting the Dots: Prospects for Detecting Multi-Source Inflation through Scale-Dependent and Stochastic Bias of Little Red Dots
Peter L. Taylor, Xinyi Chen, Christopher M. Hirata et al. (+1 more)
Recent work has proposed using the spatial clustering of Little Red Dots (LRDs) as a high-
redshift cosmological probe. In this paper, we investigate the feasibility of obtaining a LRD sample with a future space experiment, and forecast LRD constraints on primordial local-type non-Gaussianity, $f^{\rm loc}_{\rm NL}$, and the collapsed-limit trispectrum amplitude, $\tau^{\rm loc}_{\rm NL}$. LRDs are ideally suited to probe these inflationary parameters because they span a large cosmological volume, have high bias and are easily identifiable. We perform idealised joint $f_{\rm NL}^{\rm loc}$–$\tau_{\rm NL}^{\rm loc}$ Fisher forecasts assuming the universality relation, Gaussian covariance, Poisson shot-noise and a normalised
redshift dispersion, $\sigma(z) / \left( {1+z} \right)= 0.03$. We quantify the significance at which one would detect multi-source inflation under the Suyama–Yamaguchi relation, $\tau^{\rm loc}_{\rm NL} > \left( 6/5 f_{\rm NL}\right)^2$, across the $f_{\rm NL}^{\rm loc}$–$\tau_{\rm NL}^{\rm loc}$ plane. We find that a LRD analysis could robustly detect multi-source inflation at high-significance over a large region of parameter space, and would be more constraining than all other past or present experiments.
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All authors Peter L. Taylor, Xinyi Chen, Christopher M. Hirata, Charuhas Shiveshwarkar
Cosmology and Nongalactic Astrophysics
Cosmological-perturbation equations from the total-angular-momentum formalism
Marc Kamionkowski and Robert R. Caldwell
We derive the equations for the linear
evolution of cosmological perturbations using total-angular-momentum (TAM) waves. The
cosmic microwave background temperature and polarization transfer functions are first derived as integral equations and from these the usual Boltzmann hierarchy of differential equations are then obtained for both scalar and tensor perturbations. We include the effects of isotropic
cosmic birefringence and discuss anisotropic
cosmic birefringence. We note a subtle effect of
cosmic birefringence on temperature fluctuations. The TAM derivation of the equations provides physical insights to results obtained previously.
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Cosmology and Nongalactic Astrophysics
Enhanced density fluctuations: consequences for stellar dynamics and dark matter substructure
Wenzer Qin, David E. Kaplan and Neal Weiner
Enhanced density fluctuations form early dark matter
halos, which serve as early gravitational potential wells for baryons. These baryons can then condense to form
stars and black holes at high
redshifts, $1+z \gtrsim 100$. Larger density fluctuations result in denser
halos with higher virial temperatures; hence, a
halo at a mass that is below the threshold for forming
stars under standard astrophysical expectations may form astrophysical objects if its initial density is higher than expected, although the exact threshold for compact object formation is subject to large astrophysical uncertainties. We outline the conditions under which enhanced density fluctuations form dark (
star-less)
halos, early
galaxies, or even
star clusters. Using toy model enhancements to the primordial power spectrum that have been shown to explain the abundances of “little red dots", along with our fiducial set of astrophysical parameters, we show that the number of clusters initially captured by the Milky Way is highly sensitive to the shape of the enhancement, with the narrowly peaked enhancement resulting in $50$ clusters and the step-function enhancement resulting in $\sim 4.1 \times 10^5$. The initial stellar masses of the clusters is also $O (100) \,M_\odot$, although this range is also dependent on the shape of the enhancement. In addition, the abundance of dark matter subhalos with masses greater than $10^7 \, M_\odot$ can be enhanced by as much as a factor of $\sim 6.5$ and is denser than in $\Lambda$CDM, which will increase their detectability in future stellar stream surveys such as the Via Project.
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Cosmology and Nongalactic Astrophysics
Satellite stellar-to-halo mass relations in primordial black hole universes
Patricio Colazo, Nelson Padilla and Federico Stasyszyn
Primordial black holes (PBHs), in particular with a fixed-conformal-time (FCT) extended mass function, can modify small-scale structure through enhanced primordial power and discreteness-driven Poisson fluctuations, altering subhalo abundances and internal structure. We study their effects on satellite stellar-to-
halo mappings, bound-remnant compactness, and the link to compact dark perturbers. We compare two dark-matter-only simulations, a fiducial CDM run and an FCT/PBH run. As these runs form no
galaxies, we construct an approximate abundance-based stellar-to-
halo mapping using the progenitor virial mass at last isolation. The CDM mapping is anchored to a
redshift-dependent abundance-matching stellar-to-
halo relation, and the FCT mapping is derived from the relative cumulative subhalo abundances. We use resolved SOAP (V_max) and (R_max) to characterize present-day subhalo compactness, supplemented by a subgrid estimate of mass segregation in the unresolved PBH population. FCT enhances the subhalo abundance in a mass-dependent way, but abundance-based stellar-mass reassignment makes satellite stellar-mass functions weak discriminants. Internal structure is a stronger test: FCT subhaloes are more compact and have larger NFW-reconstructed enclosed masses at fixed radius, strengthening a Too-Big-To-Fail-like tension if all compact subhaloes host luminous satellites. FCT subhaloes also form earlier, accounting for much of the low-mass compactness difference, while PBH mass segregation adds a central perturbation with typical \mu ~ 0.4-0.5. Neither effect fully explains the resolved FCT compactness enhancement. Changes in the
galaxy–
halo mapping can partly hide the enhanced FCT subhalo abundance in satellite counts, whereas internal dynamics remain more discriminating. Satellite abundances, dynamics, and compact dark perturbers are complementary probes of PBH-induced small-scale structure.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
COSMOS-3D: Diverse Environments and Hot-dust Signatures among Dusty Star-forming Galaxies at $z$ = 4.9-7.2
Siwei Zou, Manuel Aravena, Shaoze Geng et al. (+20 more)
Dusty
star-forming
galaxies (DSFGs) are expected to trace early massive-
halo assembly, but the connection between dust-obscured
star formation, morphology, hot dust, and environment remains unclear at $z$>4. We combine JWST/NIRCam F444W grism spectroscopy from COSMOS-3D with MIRI F1000W/F2100W imaging and a mixed ALMA-selected and ALMA-followed dusty-
galaxy sample from CRISTAL, CHAMPS, REBELS, and A3COSMOS to study 18 DSFGs or DSFG candidates at z=4.9-7.2. We compare their environments with the parent spectroscopically confirmed emission-line sample and the COSMOS-Web photo-z
galaxy sample using separate and combined overdensity
estimators. The parent narrow-line H$\alpha$ sample has a median observed, dust-uncorrected ${\rm SFR}_{\rm H\alpha}=11.7 M_\odot~{\rm yr^{-1}}$. Within R=0.5 pMpc, DSFGs have a median $\delta_{\rm spec+phot}=0.92^{+0.06}_{-0.16}$, compared with $0.80^{+0.05}_{-0.04}$ for HAEs, with a stronger contrast on smaller scales. The strongest compact overdensities are associated with merger/interacting morphology: merging DSFGs reach $\delta_{\rm spec+phot}=4.70^{+1.61}_{-1.51}$ within R=0.5 pMpc. In contrast, MIRI-bright DSFGs do not show an enhanced number of nearby visible H$\alpha$-emitting companions, and their F2100W fluxes are difficult to explain with the 3.3 $\mu$m PAH feature alone, suggesting an additional hot-dust component. These results are consistent with a possible phase-dependent picture in which the compact line-emitter core, merger-driven dusty phase, and MIRI-bright hot-dust phase need not be spatially or temporally identical during early structure growth.
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All authors Siwei Zou, Manuel Aravena, Shaoze Geng, Romain A. Meyer, Jianwei Lyu, Jaclyn B. Champagne, Jia-Sheng Huang, Andreas L. Faisst, Shuqi Fu, Andrew J. Battisti, Hiddo Algera, Caitlin M. Casey, Xiaohui Fan, Maximilien Franco, Ghassem Gozaliasl, Linhua Jiang, Koki Kakiichi, Darshan Kakkad, Zihao Li, Lun-Jun Liu, Felix Martinez III, Jorge A. Zavala, Rasha M. Samir
Cosmology and Nongalactic Astrophysics
JWST lensed quasar dark matter survey V: Hints of self-interacting dark matter from 29 quadruply imaged quasars
D. Gilman, A. M. Nierenberg, J. Gurian et al. (+21 more)
Theories of self-interacting dark matter (SIDM) predict the eventual core collapse of dark matter
halos, a process that transforms these structures into extremely efficient gravitational lenses. We present a population-level inference on the abundance of core collapsed
halos and subhalos in the mass range $10^6 - 10^{10.7} M_{\odot}$ using 29 quadruply imaged
quasars, drawing on the collective
lensing signal of many low-mass perturbers. Our structure formation model predicts the abundance of collapsed (sub)
halos as a function of
halo mass and
redshift. We quantify how our results are affected by systematic uncertainties, including the abundance of globular clusters (GCs) and subhalos, and the internal structure of deeply collapsed
halos. Our data exhibits a strong preference for core collapsed
halos in the lens model, with Bayes factors disfavoring CDM relative to SIDM ranging from 8:1 to 24:1, depending on the assumed SIDM subhalo abundance and the internal structure of collapsed
halos. Explaining our data without core collapse requires both a GC abundance well above expectations and more subhalos than predicted by $N$-body simulations. These results pose a challenge to the CDM paradigm. We present a particle physics interpretation of these results in a companion paper.
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All authors D. Gilman, A. M. Nierenberg, J. Gurian, H. Paugnat, C. Gannon, M. N. Martinez, T. Treu, K. N. Abazajian, T. Anguita, V. N. Bennert, A. J. Benson, S. Birrer, S. G. Djorgovski, S. F. Hoenig, R. E. Keeley, A. Kusenko, M. Millon, T. Morishita, L. A. Moustakas, P. Mozumdar, D. Paris, W. Sheu, D. Sluse, K. C. Wong
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Constraining dark matter using 20-year INTEGRAL/IBIS observations II: Sub-GeV dark matter
Jordan Koechler and Pedro De la Torre Luque
We present new constraints on sub-GeV dark matter (DM) annihilation and decay using twenty years of diffuse hard X-ray observations from the INTEGRAL/IBIS
telescope. By performing a joint analysis of the spectral and morphological information contained in the IBIS
dataset, we simultaneously fit Galactic longitudinal profiles and energy spectra, exploiting their complementary signatures to disentangle potential DM signals from the dominant astrophysical backgrounds. We use physically motivated background models combining inverse-Compton (IC) emission from Galactic
cosmic-ray electrons with thermal emission from unresolved accreting white dwarfs, and consistently include the secondary IC emission generated by DM-induced electron and positron populations propagated through the
Galaxy. We conservatively derive 95% upper limits on the annihilation cross section $\langle\sigma v\rangle$ and decay half-life $\tau$ for the $e^+e^-$, $\mu^+\mu^-$, and $\pi^+\pi^-$ final states across the mass range 1 MeV to 5 GeV. Our constraints are in the range $10^{-28}$ cm$^3$/s $\lesssim \langle\sigma v\rangle \lesssim 10^{-26}$ cm$^3$/s for annihilation and $\tau \gtrsim 10^{25}$ s for decay at DM masses of a few MeV, improving upon existing X-ray limits by up to two orders of magnitude over much of the mass range. Our bounds are translated into constraints on the kinetic mixing parameter $\epsilon$ of a dark
photon and the scalar-
Higgs mixing angle $\sin\theta$, and compared with existing indirect, direct and accelerator limits available, providing a comprehensive picture of the allowed parameter space for light portal DM.
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Cosmology and Nongalactic Astrophysics
Current and Future Constraints on the Primordial Power Spectrum
Zachary Cheslog, Emily Finson, Amanda MacInnis et al. (+4 more)
The primordial scalar power spectrum provides a powerful window onto early-universe physics, including a broad class of inflationary scenarios. These models often predict a characteristic scalar spectral index $(n_s)$, nonzero running $(\alpha_s)$, or more general deviations from a pure power-law form. We find that freeing the number of light relic species $(N_{\rm eff})$ and the sum of the
neutrino masses $(\sum m_\nu)$ broadens the $n_s$ error contours enough that key early-Universe models are no longer excluded. In particular, while both Starobinsky inflation and the Bi-thermal Big Bang model are ruled out at about the 95% confidence level in the six-parameter $\Lambda$CDM model, we find that in the nine-parameter $\Lambda{\rm CDM} + \alpha_s + N_{\rm eff} + \sum m_\nu$ model, CMB data from Planck, ACT, and SPT (CMB-PAS) combined with DESI DR2 give $n_s = 0.9758 \pm 0.0064$ and $\alpha_s = 0.0080 \pm 0.0064$, consistent with both models. Future CMB facilities will sharply improve constraints on $n_s$, $\alpha_s$, and, more generally, the binned primordial power spectrum $\mathcal{P}(k)$. For example, CMB-PAS constrains $e^{-2\tau}\mathcal{P}(k = 0.2\,{\rm Mpc}^{-1})$ to 0.5%, while SO-like and CMB-HD-like surveys would tighten this to 0.1%; CMB-HD would also extend this measurement to smaller, previously unprobed scales, constraining $e^{-2\tau}\mathcal{P}(k = 30\,{\rm Mpc}^{-1})$ to within a factor of ten. We release our forecast code and update the public CMB-HD likelihood and Fisher codes to support CLASS in addition to CAMB.
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All authors Zachary Cheslog, Emily Finson, Amanda MacInnis, Neelima Sehgal, Niayesh Afshordi, Simran K. Nerval, Renée Hložek
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Low Frequency Gravitational Wave Detection with Gravito-Magnetism
Reza Ebadi and Surjeet Rajendran
The detection of gravitational waves in the low-frequency band (10 nHz to 1 micro-Hz) using inner solar system proof masses is severely limited by Newtonian
gravity gradient noise (GGN) sourced by the asteroid belt. In this paper, we propose a novel detection concept that exploits the relativistic nature of gravitational waves to break the degeneracy between the signal and the asteroid GGN background. The non-relativistic motion of asteroids dominantly sources gravito-electric fields, with velocity suppressed gravito-
magnetic components. Relativistic gravitational waves produce gravito-electric and gravito-
magnetic components of equal magnitude. We propose detecting the gravito-
magnetic component of low frequency gravitational waves using the Lorentz acceleration of test bodies. The measurement of this Lorentz acceleration is metrologically possible due to the fact that expected astrophysical sources of low frequency gravitational waves have considerably higher characteristic strains than the strains typically expected at higher frequencies. We show that this measurement allows for unambiguous extraction of the gravitational wave signal from the
gravity gradient noise in a three satellite constellation. The gravito-
magnetic measurement still requires a proof mass that is well isolated from non-gravitational noise. We propose the use of atom interferometers to serve as such a pristine inertial reference.
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Cosmology and Nongalactic Astrophysics
LIMFAST. V. Probing Reionization with the Synergy Between 21 cm and Photometric Galaxy Surveys
Guochao Sun, Adam Lidz, Tzu-Ching Chang et al. (+4 more)
Cross-correlating the 21\,cm signal from intergalactic neutral hydrogen with the
galaxy distribution is a powerful probe of the Epoch of Reionization and the physical mechanisms driving it. While upcoming surveys with the SKA-Low
radio telescope and the Roman Space
Telescope offer ideal synergies for this measurement, foreground mitigation of 21\,cm data requires exquisite
redshift precision of
galaxies, effectively excluding the rich photometrically selected samples of Lyman-break
galaxies (LBGs) with typical
redshift uncertainties $\sigma_z \gtrsim 0.1$. We overcome this challenge using a squared statistic of the foreground-cleaned 21\,cm signal. Squaring the filtered 21\,cm signal couples surviving high $k_\parallel$ modes into low $k_\parallel$ fluctuations accessible to photometric LBG surveys. This higher-order cross-correlation statistic remains measurable even when direct cross-correlations are strongly suppressed. Applying Fisher
matrix analysis to this LBG–21\,cm$^2$ cross-correlation signal simulated by the LIMFAST code over $6 \lesssim z \lesssim 10$, we investigate the prospects for constraining EoR physics combining SKA-Low 21\,cm measurements and Roman photometric
galaxy samples. For an overlapping survey area covering 10\,deg$^2$, we find that the LBG–21\,cm$^2$ cross-correlation is detectable at high significance across much of the EoR through 1000\,hours of SKA-Low integration with 15\,MHz bandwidth and a Roman photometric
galaxy sample from the High-Latitude Wide-Area Survey (HLWAS) reaching $m_\mathrm{AB,lim}=27$ and photo-$z$ uncertainties of $\sigma_z \sim 0.1$–0.3. The characteristic sign
evolution of the large-scale cross-power spectrum—driven primarily, though not exclusively, by the evolving neutral fraction—provides strong constraints on the physical parameters governing the ionization and thermal history of the IGM.
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All authors Guochao Sun, Adam Lidz, Tzu-Ching Chang, Claude-André Faucher-Giguère, Steven R. Furlanetto, Aritra Kundu, Jordan Mirocha
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
Massive Population III Galaxies Near a GN-z11 Analog: The Role of the Baryon-Dark Matter Streaming Velocity
Eli Visbal, Greg L. Bryan and Ryan Hazlett
Recently the James Webb Space
Telescope (JWST) detected Hebe, a Population III (Pop III) candidate located ${\sim}3$ kpc in projection from the massive $z=10.6$
galaxy GN-z11. This raises the question of whether Pop III
star formation is expected in the vicinity of massive high-
redshift galaxies or whether it would be prevented by early metal enrichment. We address this with a semi-analytic model of Pop III and metal-enriched
star formation applied to a zoom-in N-body simulation of a highly overdense region surrounding a GN-z11 analog. The zoom-in region resolves the minihalos where the first
stars form. We find that Pop III and metal-enriched
star formation both occur earlier, and with a higher
star formation rate density, than in a typical mean-density environment. The majority of Pop III
star formation in minihalos ends by $z\sim15$; however, we identify a distinct population of late-forming Pop III
galaxies that form near the central
galaxy. These systems have their
star formation delayed due to ionizing feedback from the central GN-z11 analog and experience a Lyman-Werner (LW) intensity of ${\sim}10$ - $100~J_{21}$, potentially leading to massive Pop III starbursts similar to Hebe. Interestingly, the abundance of these Pop III
galaxies depends strongly on the baryon-dark matter streaming velocity, $v_{\rm bc}$, because a higher streaming velocity allows
halos to remain chemically pristine for longer. None of these late-forming Pop III sources occur for $v_{\rm bc}=0$, while many form at high $v_{\rm bc}$. Averaging over the expected distribution of streaming velocities, we predict that of order four GN-z11-like
galaxies would need to be surveyed at $z\sim11$ to expect to find one such source. We also note these environments may provide a natural formation site for heavy black hole seeds.
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Cosmology and Nongalactic Astrophysics
Can Fingers of God be Resummed?
Shi-Fan Chen and Alejandro Aviles
Fingers of God (FoGs), Doppler shifts due to the small-scale virial motions of
galaxies, are one of the most significant challenges for analytic models of
galaxy clustering in
redshift surveys. In the effective field theory approach, the characteristic scale of these shifts introduces a new, large length scale, limiting the reach of the theory. This has motivated many phenomenological models of FoGs in the literature where their effect is approximated by a single damping function of the line-of-sight wavenumber $\lambda=k\mu$, effectively resumming powers of $\lambda$ due to single-point contractions of small-scale velocities. The goal of this work is to investigate whether such a resummation can be rigorously constructed. We show that common damping models can be understood as the mean-field limit of the single-particle characteristic function (SPCF) of FoG velocities, but that the environmental dependence of the SPCF generates equally large corrections that break the simple damping form. We develop the long-wavelength theory of the SPCF, showing that it admits an expansion in anisotropic bias operators closely related to those derived for selection effects, but with $\lambda$-dependent coefficients satisfying selection rules. We estimate these coefficients using the
halo model for DESI-like
galaxies, showing that they make significant contributions at the level of the 2- and 3-point functions of
galaxies. To answer the titular question: potentially, but at the cost of significantly expanding the operator basis and promoting free coefficients to free functions.
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Cosmology and Nongalactic Astrophysics
Gauge Backreaction in Standard Model Warm Inflation
Rafid H. Dejrah and Anish Ghoshal
Standard-Model warm inflation (SMWI) makes QCD the microscopic origin of inflationary dissipation, so the real-time response of the gauge
plasma enters the cosmological prediction. We show that a slowly relaxing gauge-helicity response cannot, in general, be absorbed into an effective friction coefficient and must instead remain dynamical. We therefore evolve the
quark axial densities and a matched hard-helicity mode, with QCD sphalerons and an effective $2\leftrightarrow3$ channel generating both charge transfer and correlated
stochastic sources in the full perturbation covariance system. The resulting backreaction is substantial but mainly indirect: gauge-helicity screening can reduce the warm dissipation ratio by an order-one fraction on the strong branch, while the $2\leftrightarrow3$ channel contributes only $0.2\%-0.7\%$ of the zero-density sphaleron friction directly, shifting the amplitude-normalized trajectory in both $n_s$ and $r_{\rm vac}$. The relevant trajectories, however, lack a parametrically broad hard-soft hierarchy and extend beyond strict linear response. The predictions should therefore be understood within the stated local Gaussian transport closure; a parameter-free Standard-Model (SM) result requires finite-affinity real-time $SU(3)$ drift, susceptibility, and noise kernels.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
GAIA meets LZ: a high velocity tail-tale sign for dark matter
Anirban Das, Subhabrata Majumdar, Manibrata Sen et al. (+1 more)
The interpretation of high-energy nuclear recoils in direct-detection experiments can depend sensitively on the high-velocity tail of the galactic dark matter (DM) distribution. The LUX-ZEPLIN (LZ) experiment has recently reported an event, LZ230616, with nuclear recoil energy 248 $\pm$ 23 (stat) $\pm$ 23 (sys) keV, while the Gaia mission has provided an unprecedented view of the kinematics and mass distribution of the Milky Way. We bring these two probes together to investigate the inelastic DM interpretation of LZ230616, using a velocity distribution inferred from Gaia-informed galactic model. Compared to the Standard
Halo Model, the resulting distribution has a lower escape speed and a significantly suppressed high-velocity tail, with a higher local density. We find that while the exothermic interpretation is largely insensitive to this change, the endothermic interpretation requires substantially larger scattering cross sections and smaller mass splittings. Furthermore, using simulation-based study of the gravitational effects of the Large Magellanic Cloud, we show that the high-velocity tail can extend the allowed endothermic parameter space towards lower DM masses and larger splittings. Our results demonstrate how combining direct searches for DM detection with precision measurements of galactic dynamics can qualitatively affect the particle-physics interpretation of high-energy nuclear recoils.
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All authors Anirban Das, Subhabrata Majumdar, Manibrata Sen, Amogh Srivastav
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.HE
Empirical determination of the Galactic neutron star–black hole merger rate using StarTrack models
Terrence Pierre Jacques, D. R. Lorimer, Nihan Pol et al. (+2 more)
The discovery of a
pulsar in a binary system with a black hole would provide a unique laboratory for testing general relativity in the strong-field regime and offer vital constraints on massive
star evolution. We assess prospects for the detectability of such systems by utilizing the
radio pulsar population and survey models within the modeling package PsrPopPy and, as a proof of principle, two evolutionary models with different treatments of common-envelope phases from the stellar population synthesis code StarTrack. For these two models, assuming the
radio pulsar beaming model proposed by Tauris and Manchester and accounting for the effects of orbital motion on
pulsar detectability, we calculate upper limits on the number of
neutron star–black hole systems in the
Galaxy and the corresponding merger rate given the lack of any
radio-detected
pulsar–black hole binary systems in current
radio surveys. For the most constraining model, we find a Galactic merger rate $< 4.3~\text{Myr}^{-1}$ (at 95% confidence). These results are extrapolated to the expected horizon distance for the fifth LIGO observing run, leading to LIGO detection rate estimates that are consistent with the latest values reported by the LIGO-Virgo-KAGRA collaboration. Our results indicate that the increased sensitivity of FAST, MeerKAT, and DSA offers the best prospects yet for uncovering this elusive population.
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All authors Terrence Pierre Jacques, D. R. Lorimer, Nihan Pol, M. A. McLaughlin, K. Belczynski
Cosmology and Nongalactic Astrophysics
Tide-and-Seek: Anisotropic scale-dependent bias in the Lyman-alpha forest and designer samples
Yong Sheng Yap, William R. Coulton and Vid Iršič
Searches for primordial non-Gaussianity are powerful ways of learning new information about the early Universe. Observing primordial signals in the late Universe is challenging as, in general, it is difficult to disentangle the small, primordial signatures from the complex physics that describes the distribution of
galaxies and large-scale
cosmic structures. We demonstrate that scale-dependent bias from primordial non-Gaussianity with non-trivial directional dependence in the squeezed limit (also known as anisotropic primordial non-Gaussianity) can arise in a much larger class of tracers than previously considered. This is a smoking gun signature of primordial Universe physics that cannot be mimicked by late-Universe processes. We demonstrate this explicitly with simulations of the Lyman-$\alpha$ forest and
halos selected through their projected shape. The former is a standard cosmological probe and standard analyses could be simply extended to constrain this. The latter provides an interesting new approach: design samples with strong selection effects to provide new sensitivity to primordial physics. As a demonstration of these concepts, we apply this method to BOSS DR12 data, finding no evidence of anisotropic non-Gaussianity.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.IM
Accelerating massive ensembles of ordinary differential equations
Lawrence Berry, Will Handley, Oliver Hahn et al. (+1 more)
Solving large ensembles of small, independent ordinary differential equations (ODEs) is a common task in computational science and engineering, arising for example in
Bayesian parameter estimation, Monte Carlo uncertainty quantification, and the integration of uncoupled physical systems such as the linearised Einstein-Boltzmann equations of cosmology. Modern graphics processing units (GPUs) with thousands of cores are well suited to such parallel workloads, but realising this potential requires careful
attention to GPU-specific architectural constraints. We present modax, a Python library of GPU-accelerated ODE solvers specifically optimised for solving large ensembles of low-dimensional, independent problems. Our solvers are compatible with the JAX ecosystem but are written in a low-level, thread-based programming paradigm better suited to ensembles of highly divergent trajectories than their pure-JAX counterparts.
Benchmarks on the Lorenz, Robertson and van der Pol
lattice systems compare modax against diffrax, DiffEqGPU$.$jl and torchdiffeq across ensemble size, dimensionality, and trajectory divergence. Our explicit Tsit5 solver achieves 30x speed-up over diffrax on Lorenz systems, and our implicit Rodas5P solver achieves over 700x speed-up on Robertson systems, demonstrating the superiority of linearly implicit Rosenbrock-Wanner methods on GPUs. Our implicit solver scales well to higher dimensions thanks to the use of sparsity-exploiting techniques and data structures. We conclude by applying modax to three examples from the field of cosmology -
Bayesian parameter estimation from primordial abundances, Monte Carlo uncertainty quantification of the global 21cm signal, and the computation of uncoupled
Fourier modes in the primordial power spectrum - and demonstrate significant efficiency improvements in our ability to model physical phenomena described by low-dimensional (<200D) ODEs.
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All authors Lawrence Berry, Will Handley, Oliver Hahn, Nils Schöneberg
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
The abundance and emission of PAHs from the local to early Universe
Massimiliano Parente, Desika Narayanan, Paul Torrey et al. (+8 more)
We present the first large-volume cosmological simulation of
galaxy evolution with a model for the abundance and luminous emission of Polycyclic Aromatic Hydrocarbons (PAHs) across a wide range of
cosmic time ($0 < z \lesssim 6$). The simulation is built on a semi-analytic model (SAM) that includes a treatment of dust size distribution, with PAHs being identified with the smallest carbonaceous grains ($< 15$ A) residing in the diffuse ISM of
galaxies. PAH emission is computed by post-processing the simulation output with the radiative transfer code GRASIL. In our model, where
stars only inject large grains, the PAH abundance emerges from the growth and shattering of dust grains in the ISM, naturally reproducing the observed correlation between the PAH mass fraction ($q_{\rm PAH}$) and both
metallicity and specific
star formation rate (sSFR). We derive a relation to infer $q_{\rm PAH}$ from $L_{\rm PAH}$, $L_{\rm IR}$, and sSFR, with a relatively small scatter (a factor of $\approx 1.3$). Simulated PAH emission correlates well with key
galaxy properties such as SFR and molecular gas content, and reproduces observational constraints. Taken together, these results support the viability of a top-down formation scenario for PAHs. We extend our model predictions to higher
redshifts, which can be exploited for future missions such as PRIMA. This work is a significant step toward leveraging PAH observations as a tool for studying
galaxy evolution.
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All authors Massimiliano Parente, Desika Narayanan, Paul Torrey, Gian Luigi Granato, Brandon S. Hensley, Jed McKinney, Alexandra Pope, Gergö Popping, Irene Shivaei, Laura Silva, J.D.T. Smith
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.IM
Source–Line Associations in JWST/NIRSpec Dense-Shutter Spectroscopy
Zihao Wu, Daniel J. Eisenstein, Francesco D'Eugenio et al. (+9 more)
We demonstrate the feasibility of source–line association in JWST/NIRSpec dense-shutter spectroscopy, with $\sim$2000 sources observed simultaneously per pointing regardless of spectral overlap. While JWST wide-field slitless spectroscopy (WFSS) can disentangle overlapping spectra using two grisms with perpendicular dispersion directions, NIRSpec can achieve this using gratings with different dispersions. Compared with WFSS, NIRSpec dense-shutter spectroscopy offers substantially higher sensitivity and broader wavelength coverage. We develop a
Bayesian framework that combines cross-dispersion offsets, wavelength consistency, and changes in relative line positions between gratings to jointly determine source associations and
redshifts. We test the method using mock observations based on the observed source distribution and emission-line fluxes from the JWST Advanced Deep Extragalactic Survey (JADES), accounting for the NIRSpec optical model, MSA operability, measurement noise, false-positive detections, and bad pixels. Although the spectral traces overlap extensively, fewer than 0.5% of the simulated emission lines are blended with another line on the detectors in NIRSpec grating spectroscopy. Applying our method to these simulations, we obtain
redshifts, at an accuracy of 98%, for the $\sim$1800 sources that have detectable emission lines, of which $\sim$1500 are classified as confident and are 99.9% accurate. We further investigate how the association accuracy depends on the number of grating configurations. By combining high multiplexing, high sensitivity, and broad wavelength coverage, NIRSpec dense-shutter spectroscopy enables efficient, highly complete spectroscopic surveys for the high-
redshift Universe.
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All authors Zihao Wu, Daniel J. Eisenstein, Francesco D'Eugenio, Erica Nelson, Benjamin D. Johnson, Andrew J. Bunker, Zhiyuan Ji, Pierluigi Rinaldi, Brant Robertson, Sandro Tacchella, Christopher N. A. Willmer, Joris Witstok
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
ViCTORIA project: A pilot study of the M49 region in the Virgo cluster in polarisation
A. Spasic, A. Benati, M. Brüggen et al. (+7 more)
Large-scale
magnetic fields permeate the Intracluster Medium (ICM) of
galaxy clusters. Understanding these fields gives an insight into the origin of
cosmic magnetic fields and the interaction of cluster
galaxies with the ICM. Using MeerKAT observations of the Virgo cluster as part of the ViCTORIA project, we probe
magnetic fields via Rotation Measure (RM) synthesis. The aim of this work is to characterise the
magnetic fields in and around the infalling group M49 in the Virgo cluster. We will probe the interaction of M49 with its surrounding medium through its imprint on the polarised emission and Faraday rotation. We use L-band MeerKAT data in full polarisation calibrated with the ViCTORIA MeerKAT Survey (ViMS) pipeline, which is designed for the calibration, imaging, mosaicking and RM Synthesis of the fields in the Virgo cluster, to achieve high-fidelity reconstruction of, both, total intensity and polarised emission. We analyse the background sources of the cluster for potential local changes in the
magnetic field, by calculating the RM distribution. In the final polarised image, consisting of four pointings of 45 min, we reach a noise level of $23.3 \mu \textrm{Jy/beam}$. We detect 101 background sources in the $\sim 2.5\, \textrm{deg}^2$ region around M49, corresponding to a source density of 40 sources/$ \textrm{deg}^2$. Across the $112\, \textrm{deg}^2$ observations of the Virgo cluster, this implies a total number of 4000 polarised sources. In M49 we find structured, diffuse polarised emission extending in the direction of the total intensity
radio tails. A higher polarisation fraction across the upper edge of the source indicates the effect of
magnetic field draping. Around M49 we find a larger RM scatter (at $3.8\sigma$) in the wake of M49 compared to the region in front of it. This can inform the modelling of the
turbulence created by galactic motions.
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All authors A. Spasic, A. Benati, M. Brüggen, H. W. Edler, F. De Gasperin, V. Gustafsson, P. Serra, A. Bonafede, A. Boselli, H. McCall
Cosmology and Nongalactic Astrophysics
LISA bright sirens as a tiebreaker among cosmologies in tension
M. F. A. Medeiros, F. C. Carvalho and L. L. Sales
Gravitational waves from massive black hole binaries detected by LISA will deliver luminosity distances without any astrophysical calibration, offering a probe of the expansion history independent of the
cosmic distance ladder. Rather than asking how tightly LISA will constrain a single fiducial cosmology, we ask which of several mutually discrepant present-day cosmologies a future LISA
dataset would render most self-consistent. We build mock catalogues of LISA bright sirens under three fiducial cosmologies drawn from
datasets that participate in the current $H_0$ discrepancy (Planck 2018, Union3 and Pantheon+SH0ES), with a self-consistent error budget from instrumental noise, weak
lensing and host peculiar velocities. We compare the posterior from the simulated LISA data alone with that of a real-data combination of Type Ia
supernovae, DESI baryon acoustic oscillations,
cosmic chronometers and the compressed Planck 2018 CMB, and quantify their internal tension in the $(H_0,\Omega_m)$ plane, crossing each fiducial with three SN Ia compilations. The fiducial drives the tension, from $2.08\sigma$ to well beyond $5\sigma$, while the
supernova compilation changes it by at most $1.2\sigma$. The discriminating power is strongly asymmetric: a Pantheon+SH0ES universe is inconsistent with every background we test, at a significance far in excess of $5\sigma$ and still at $3$-$5\sigma$ for the $10$-$20$ events expected from recent population models, whereas the Planck 2018 and Union3 fiducials, which differ by only $0.24$ km/s/Mpc in $H_0$, cannot be separated by any catalogue size. LISA bright sirens are therefore a sharp arbiter of the Cepheid-calibrated scenario and, on this error budget, silent between the other two.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
A Cuscuton Representation of the Loop Quantum Cosmology Bounce
Niayesh Afshordi and Kristina Giesel
Loop
Quantum Cosmology (LQC) replaces the big bang singularity of the homogeneous universe by a bounce, usually described by the modified Friedmann equation $H^2=\rho(1-\rho/\rho_c)/(3M_p^2)$. We show that this background dynamics follows from a local cuscuton effective theory, whose scalar equation is a constraint rather than a wave equation. One way to establish this is to write the cuscuton in terms of an angular coordinate $\theta$, identified with the LQC polymerization angle $2\lambda b$. Its constraint gives $H\propto\sin\theta$, while the Einstein constraint gives $\rho=\rho_c\sin^2(\theta/2)$, exactly reproducing the LQC bounce. To our knowledge, this is the first closed-form, local, generally covariant realization of the exact standard flat-FLRW LQC background dynamics for minimally coupled matter satisfying null energy condition, without introducing additional local dynamical degrees of freedom. A branchwise Legendre transformation establishes a canonical equivalence between the clock-gauge-fixed homogeneous mimetic system in the case of vanishing mimetic dust energy density and the cuscuton systems. It selects the constant-tension cuscuton coordinate $\Theta=\sin\theta-\theta$, while $\theta$ retains its interpretation as the LQC polymerization angle. This equivalence does not establish agreement of the inhomogeneous theories or their perturbations. The angular action also admits an explicit branched $f(K)$ representation, where $K$ is the mean extrinsic
curvature of spatial hypersurfaces. The construction is therefore an effective covariant representation of the LQC holonomy correction, not a derivation from full loop
quantum gravity.
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Cosmology and Nongalactic Astrophysics
MATISSE in the era of GRAVITY+
Florentin Millour, Anthony Soulain, Stéphane Lagarde et al. (+28 more)
MATISSE, the mid-infrared spectro-interferometric imager of the Very Large
Telescope Interferometer (VLTI), has been feeding on the light corrected by the
GRAVITY+ Adaptive Optics (GPAO) systems since the retirement of MACAO on the four Unit
Telescopes in 2024. We report the assessment of the new MATISSE performance with GPAO, based on commissioning observations obtained in 2024 and 2025 and compared with archival MACAO observations of the same stellar sources. The instrumental visibility transfer function is more stable in the L band, while its typical value in the L and N bands is unchanged; the visibility signal-to-noise ratio is consistent with, or better than, the values reported at the initial MATISSE commissioning. The correlated flux increases by 20–30% in GRA4MAT mode thanks to a better fringe tracking performance, and the total flux injected into the instrument increases by a factor of 1.3 to 1.4 (up to 1.7) in the L band at low spectral resolution, with no measurable loss in the N band. Combined with the new K-band fringe-tracking limits enabled by GPAO, this translates into a sensitivity gain of a factor 2 to 6 in the L and M bands, a confirmation of the N-band limits similar to the MACAO era. We then report the performances of MATISSE with the GPAO's
laser guide
stars in November and December 2025. The updated noise figures follow the exposure time calculator predictions in LM LOW and MED and come out better than them in N LOW, the L-band transfer function is stable at the few percent level between observing blocks an hour apart, and correlated fluxes, differential phases and closure phases are recovered down to a 10\,mJy target. Embedded young stellar objects and AGN are now within reach, thanks to the better performances on red targets brought by the
lasers. We finally discuss the science cases opened by this gain and the case for a future upgrade of the instrument.
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All authors Florentin Millour, Anthony Soulain, Stéphane Lagarde, Alexis Matter, Valentin Fleury, Farin Drewes, Mathis Houllé, Jules Scigliuto, Bruno Lopez, Anthony Meilland, G. Petrov Romain, Philippe Berio, Anthony Berdeu, Guillaume Bourdarot, Sylvestre Lacour, Mathias Nowak, Jean-Baptiste Le Bouquin, Antoine Mérand, Frank Eisenhauer, Julien Woillez, Miguel Montargès, Diogo Ribeiro, Taro Shimizu, Jens Kammerer, Xavier Haubois, Stefan Gillessen, Pierre Cruzalèbes, Frédéric Gonté, Walter Jaffe, James Leftley, Nicole Nesvadba
Cosmology and Nongalactic Astrophysics
Localized Enhancements of the Primordial Power Spectrum and the Abundance of Early Bright Galaxies
Shaghayegh Yavari, Hamed Kameli and Shant Baghram
Recent observations of bright
galaxies at high
redshifts by the James Webb Space
Telescope have motivated renewed interest in cosmological mechanisms that can enhance the abundance of early massive dark matter
halos. We study a phenomenological modification of the primordial
curvature power spectrum in the form of a localized Gaussian enhancement. The modified spectrum is propagated to the linear matter power spectrum, the smoothed density variance, and the Sheth-Tormen
halo mass function. We show that a bump centered at small scales can selectively enhance the abundance of rare high-
redshift halos and, through a fixed semi-analytic mapping between
halo mass and ultraviolet luminosity, shift the bright end of the UV luminosity function toward JWST measurements. The enhancement becomes more pronounced at higher
redshift due to the exponential sensitivity of the rare-
halo tail to the variance. We emphasize that the effect is limited by small-scale power-spectrum constraints, particularly Lyman-$\alpha$ forest data, and should be interpreted as a partial cosmological contribution rather than a complete solution to the JWST
galaxy tension.
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Cosmology and Nongalactic Astrophysics
The separate universe approach with non minimal coupling to gravity
Hugo Holland and Julien Grain
In this paper we extend a study of the validity conditions of the separate universe approach of cosmological perturbations to models of inflation with multiple fields that are non minimally coupled to
gravity. The separate universe approach effectively describes the universe as a collection of homogeneous and isotropic patches, leading to an effective description of cosmological perturbations at large scales. This approximation is a necessary step in
stochastic inflation and in the $\delta \N$ formalism. We study and compare the dynamics of cosmological perturbation theory at large scales to the dynamics derived in the separate universe picture for non linear sigma models where we have allowed a non minimal coupling between the fields and
gravity. We found that the separate universe approach adequately reproduces the dynamics of the large scale perturbations, provided the wavelength of the modes considered is greater than a list of lower bounds derived from the background
evolution of the model we consider. These lower bounds are then compared to those derived in the classically equivalent Einstein frame description of the Jordan frame model at hand. In particular these conditions are derived and compared for a
Higgs-like toy model of inflation in the large field limit.
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