astro-ph.CO updates on arXiv.org

First Search for Kaluza-Klein Gravitons and Radion Using Planck Data

Alexander P. Cassem, Soubhik Kumar — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.02651v1 Announce Type: new Abstract: Heavy moduli and Kaluza-Klein (KK) gravitons from extra dimensions may evade terrestrial probes but can be produced during inflation, generating primordial non-Gaussianity (NG) through unavoidable couplings to density perturbations. In a warped five-dimensional (5D) model, we compute the full radion- and KK-graviton-mediated bispectra and perform the first search for these signals using Planck 2018 temperature and polarization data. We find no significant evidence for NG, with the maximum significance being $1.8\sigma$ for $m_{\rm KK}\approx 1.6H$. We also identify a 5D setup which naturally generates NG with $f_{\rm NL}\sim 1-50$, within the reach of future surveys.

The youth of the intracluster medium. I. A non-parametric characterisation of the gas and electron number density profiles of $z \simeq 2$ protoclusters

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.02654v1 Announce Type: new Abstract: Context. Protoclusters of galaxies are the earliest phase in the assembly of galaxy clusters and can provide invaluable information about plasma physics, cosmic magnetism, and cosmology. However, due to small angular sizes and cosmological dimming, observing the proto-intracluster medium (proto-ICM) associated with protocluster cores is far from trivial. Aims. We aim to provide a non-parametric description of the gas mass and electron number density profiles of the proto-ICM at $z = 2$, and to study their dependence on mass, dynamical state and central activity. Methods. We extract and analyse over $3800$ regions around protocluster cores with spherical-overdensity masses above $M_\mathrm{500c} > 10^{13} \, M_\odot$ out of a large simulated volume within the Magneticum suite. We study their density profiles, temperature structure, ionisation degree and electron number density as a function of mass and other secondary properties characterising dynamical state and central activity, extending from the central halo to the surrounding protocluster environment. Results. Protoclusters present moderate deviations from self-similarity in their density profiles and temperature structure, with a strong double-$\beta$ structure especially relevant at high masses and intense AGN accretion. Hot, ionised gas is only dominant at intermediate radii ($r \gtrsim [0.1-0.5] R_\mathrm{500c}$), where its density also correlates with mass and dynamical disturbance. Conclusions. These results constitute the basis for a forthcoming parametric calibration of proto-ICM density profiles, which could be useful for interpreting observables sensitive to the density and ionisation of the diffuse gas.

Limits on global cosmic birefringence using radio sources

Richard A. Battye, Neal Jackson, Ian Browne — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.02664v1 Announce Type: new Abstract: We have made measurements of the difference between the position angle (PA) on the sky and the polarization position angle (PPA) of radio sources using data from a combination of the Radio Fundamental Catalogue (RFC) across a range of frequencies between 2.7 and 15~GHz and Cosmic Lens All Sky Survey (CLASS) which observes polarization at 8.4~GHz (X-band). For the 2111 sources with jet PAs measured in the X-band and a known redshift, the distribution is peaked at $\approx 0^{\circ}$ as expected for no birefringence and it can be modelled by two populations: one which is a Gaussian with mean $\mu_{\beta}=(0.2\pm 1.0)^{\circ}$ and standard deviation $\sigma_{\beta}=(14.7\pm 1.1)^{\circ}$ and the other a uniform distribution of sources which are a fraction $f_\beta=0.72\pm 0.02$ of the total. Uncertainties in $\mu_\beta$ can be reduced to $\approx 0.6^{\circ}$ by stacking measurements of the PA from other wavebands. We find that limits of $\approx 0.1^{\circ}$ might be possible with a sample of $\sim 10^5$ similarly selected sources and that this could provide a confirmation of recent claims of global birefringence made using the Cosmic Microwave Background observations from the {\it Planck} satellite.

S-PLUS Clusters And Large-scale Environments (SCALE): I. A catalog of known clusters and groups in DR5 and a pilot study of Abell 4038

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.02704v1 Announce Type: new Abstract: Within the framework of the Southern Photometric Local Universe Survey (S-PLUS), we introduce ${\bf S}$-PLUS ${\bf C}$lusters ${\bf A}$nd ${\bf L}$arge-scale ${\bf E}$nvironments (SCALE), a project dedicated to the study of galaxy clusters, groups, and their environments using 12-band photometry of S-PLUS combined with spectroscopic and photometric data from the literature. In this first paper, we present a catalog of 83 previously known systems in the redshift range $0.008 \leq z_{\rm spec} \leq 0.1$, for which we derive $R_{200}$, $M_{200}$, and velocity dispersions. Spectroscopic members are selected and matched with S-PLUS photometric redshifts (photo-$z$s). We find very good agreement between literature spectroscopic redshifts (spec-$z$s) and S-PLUS photometric redshifts (photo-$z$s), demonstrating the potential of the latter for cluster and group membership determination. As a proof of concept, we obtain photometric memberships for Abell 4038 using the Reliable Photometric Membership technique. A two- and three-dimensional analysis of the region within $10 h^{-1}$ Mpc ($10\times R_{200}$) from the center of Abell 4038 reveals about a dozen substructures including two additional clusters within $1.3\times R_{200}$ (Abell 4038B and Abell 4049). A color-luminosity segregation analysis shows that more luminous (less luminous) galaxies are redder (bluer), as expected. Low-concentration galaxies ($C \leq 2.5$) exhibit a weaker color-luminosity dependence, compared to higher-concentration ones, indicating mass-dependent evolutionary pathways that challenge a simple morphology-color dichotomy, with low-luminosity galaxies presenting bluer colors largely independent of concentration. The SCALE catalog provides a valuable basis for future studies of large-scale structures and their connection to galaxy evolution.

S-PLUS Clusters And Large-scale Environments (SCALE): II. PZWav versus redMaPPer identification of eRosita groups

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.02706v1 Announce Type: new Abstract: We present the construction and characterization of a multi-wavelength catalog of galaxy groups and clusters by matching optical detections from the Southern Photometric Local Universe Survey (S-PLUS) with extended X-ray emission from the first eROSITA all-sky survey data release (eRASS1). We employ a probabilistic matching framework, based on the modified Hausdorff distance, to associate galaxy systems identified by the PZWav cluster finder and characterized by the AME membership estimator with X-ray surface brightness contours. This method explicitly accounts for the photometric redshift probability distribution of galaxies and allows us to explore the critical trade-off between catalog completeness and purity. We investigate how the matched sample changes with different optical selection depths, defined by absolute magnitude cuts of $M_r$ < -18.5, -19, -19.5, and -20 sampling redshifts within 0.08 < z < 0.25, and across purity levels of 80%, 90%, and 95%. We find that fainter optical cuts enhance the recovery of low-mass, low-luminosity groups, while brighter cuts favor more massive clusters and increase the effective survey volume at higher redshifts. Stricter purity requirements reduce contamination but systematically lower completeness, particularly for low-luminosity systems. The derived X-ray luminosity functions agree well with previous determinations, and the logN-logS distributions confirm the high recovery rate of luminous clusters. Comparisons with the redMaPPer cluster catalog validate our approach, showing consistent trends and significant overlap, while our method offers improved completeness at the group scale. This work demonstrates a robust, flexible methodology for creating reliable multi-wavelength cluster catalogs, essential for cosmological studies and investigations of galaxy evolution in dense environments.

Evading the CMB $\mu$-distortion bound on Supermassive Primordial Black Hole seeds with Non-Gaussian tails

Sanket Dave, Sheng-Feng Yan, Amara Ilyas, Yi-Fu Cai — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03138v1 Announce Type: new Abstract: Supermassive black holes (SMBHs) powering quasars at $z \gtrsim 6$ are difficult to grow from stellar mass remnants, motivating seeds from primordial black holes (PBHs) with masses $10^5-10^7 M_{\odot}$. This range is constrained by the COBE/FIRAS bound on the CMB $\mu$-distortion, which limits the small-scale curvature variance to $\sigma_\zeta^2 \lesssim 10^{-4}$. For Gaussian perturbations, the variance fixes the far tail of the one-point probability distribution function (PDF), making the PBH abundance negligible. We call this the Gaussian barrier. The barrier can be evaded only if the variance probed by the distortion is decoupled from the tail probability controlling collapse. We implement this idea in the non-perturbative $\delta N$ formalism and relate asymptotic PDF tails to the global shape of the $\delta N$ map. Four Gaussian-cored families are analyzed: generalized-normal, stretched-exponential, power-law, and log-normal tails. After standardizing each family to unit variance, we impose the FIRAS cap and compute the distortion-limited PBH abundance in the tail-shape parameter space. The ordinary exponential tail produced by standard single-field non-attractor dynamics is still too light to reopen the seed window. Algebraic tails from fractional-potential dynamics, and sufficiently heavy log-normal tails treated as a phenomenological proxy for multiplicative dynamics, can supply seed-relevant abundances while respecting the distortion bound.

Neutrino mass constraints in the Schwarzschild-de Sitter black-hole dark energy model with ACT DR6 and DESI DR2 data

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03183v1 Announce Type: new Abstract: Recent DESI observations have posed new challenges to $\Lambda$CDM, showing a preference for dynamical dark energy and yielding neutrino mass constraints within $\Lambda$CDM that approach the lower bound allowed by neutrino oscillation experiments. In this work, we investigate cosmological constraints on the key neutrino parameters, $\sum m_\nu$ and $N_{\rm eff}$, within the Schwarzschild-de Sitter black-hole dark energy (SdSDE) framework. We use cosmic microwave background (CMB) data from Planck and ACT DR6, baryon acoustic oscillation data from DESI DR2, and type Ia supernova data from DES-Dovekie and PantheonPlus. We find that SdSDE scenarios prefer a positive neutrino mass whenever $\sum m_\nu$ is allowed to vary. Using CMB+DESI+DES-Dovekie data, we obtain $\sum m_\nu=0.207^{+0.047}_{-0.052}~{\rm eV}$ for SdSDE+$\sum m_\nu$, reduced to $\sum m_\nu=0.162^{+0.055}_{-0.056}~{\rm eV}$ when $N_{\rm eff}$ is also varied. This arises from the positive correlation between $N_{\rm eff}$ and $\sum m_\nu$, together with the systematic preference of SdSDE for values of $N_{\rm eff}$ below the standard value. Furthermore, the best-fit $\chi^2$ comparison shows that $\Lambda$CDM with extended neutrino parameters is strongly preferred over the corresponding SdSDE extension. Overall, the positive neutrino mass preference induced by SdSDE may reflect parameter compensation rather than an improved global fit, a possibility that should be further tested with future high-precision observational data.

Cosmology with HI Intensity Mapping

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03259v1 Announce Type: new Abstract: The redshifted spectral emission from neutral hydrogen (HI) at rest wavelength 21 cm can be used as a tracer of large-scale structure and its evolution. Within the HI intensity mapping method, sufficient signal-to-noise is achieved by integrating the line emission within large voxels over a wide sky area and line of sight depth which allows access to the largest scales of the matter distribution. The resulting tomographic maps usually feature low angular and high redshift resolution. The SKAO will be able to conduct HI intensity mapping experiments observing up to 20,000 square degrees over a wide range of redshifts. For SKA-Mid, we will employ the array in a fast-scanning single-dish mode using Band 1 and 2 to access 0

Euclid: Measuring the intrinsic alignment of galaxies around cosmic voids in the \Euclid Flagship simulation\

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03312v1 Announce Type: new Abstract: We present a methodology to measure the intrinsic alignment (IA) signal of galaxies in the vicinity of cosmic voids using the \Euclid-like Flagship cosmological simulation from the Euclid Consortium. The IA signal is quantified and compared with the predictions of the linear alignment (LA) model, providing one of the first detailed investigations of this effect in underdense large-scale environments. While the IA signal around cosmic voids has received little attention to date, it may constitute a non-negligible systematic in forthcoming cosmological analyses that exploit void-lensing measurements. Our analysis examines red and blue galaxy populations separately, enabling a comparison of their alignment behaviour in void environments with the corresponding trends measured in galaxy-galaxy correlations. We find that the redshift evolution of the IA amplitude in cosmic voids is broadly consistent with that measured in the general galaxy population for both colour-selected samples. Additionally, our modelling allows us to estimate the linear bias of voids, $b_{\rm V}(z)$ which characterises how cosmic voids trace the underlying dark-matter density field, for voids with radii in the range $10 < R_{\rm V}/(h^{-1} {\rm Mpc}) < 15$. The measured bias exhibits a positive trend with redshift, consistent with theoretical predictions for the clustering of underdense regions. These results highlight the importance of accurately modelling IA in void studies, both to mitigate systematic effects in void-lensing cosmology and to further improve our understanding of galaxy-environment interactions in low-density regions of the Universe.

Strong-lensing effects in high-redshift massive black-hole binary population inference

Yan-Heng Jin, Wen-Biao Han — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03345v1 Announce Type: new Abstract: High-redshift massive black-hole binary (MBHB) mergers provide a probe of black-hole seed formation and early galaxy assembly, but the population detected by LISA can be modified by galaxy-scale strong lensing. We quantify this effect for MBHB mergers at $10\leq z\leq20$ and assess its impact on the inference of intrinsic formation-channel fractions. We use four channels, corresponding to light- and heavy-seed scenarios with delayed and non-delayed mergers, and compute 4-year LISA-detectable event numbers with and without strong lensing. To bracket the uncertain lens population, we compare a conservative velocity-dispersion-function (VDF) prescription with an optimistic halo-mass-function (HMF)-based prescription. We consider a reference mixture with equal seed-channel weights and additional mixtures in which the intrinsic seed population is weighted toward selected formation channels, and jointly infer the formation fractions and the strength of the lensing contribution. Strong lensing does not affect all channels equally: it can change the detected channel mixture as well as the total number of detections. This effect is weak for the conservative VDF prescription, but becomes significant in the high-lensing-rate HMF case, where neglecting strong lensing can bias the recovered formation fractions. The inference precision depends on the underlying intrinsic channel composition, while the lensing contribution is more accurately recovered in the high-lensing-rate case. These results indicate that galaxy-scale strong-lensing effects and event-count information should be included when using high-redshift MBHB detections to infer intrinsic formation-channel fractions.

The giant radio source 0917+75: Origin and properties

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03368v1 Announce Type: new Abstract: Context. Several author have studied the giant radio source GRS0917 + 75 , but its origin remains unclear. Aims. This source is unusual, because of its large size and its location outside a rich cluster of galaxies. We aim to understand and discuss the properties and nature of this source and its connection to the environment. Methods. We conducted optical observations to obtain new spectroscopic data. We also acquired a LOFAR image at 144 MHz to derive information at low radio frequency. Moreover, we performed a new analysis of archival VLA data in the L and C bands for a multifrequency study of the source properties in the radio band. Results. From the observational data, we classify GRS0917 + 75 as a giant radio galaxy with a size of 1.5 Mpc and an estimated age of about 100 Myr. The optical parent galaxy is a bright low-excitation radio galaxy, the brightest member of a very poor group belonging to a large supercluster. GRS0917 + 75 is a peculiar low-power Fanaroff-Riley Class I giant radio galaxy with a bright central emission but no jet-like features. Conclusions. The existence of giant radio galaxies such as GRS0917 + 75 could explain the origin of relativistic particles and magnetic fields in low-density environments.

The heating rate of the Intergalactic Medium by Lyman-$\alpha$ photon scattering

Avery Meiksin (Institute for Astronomy, University of Edinburgh) — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03400v1 Announce Type: new Abstract: The strength of the 21-cm Cosmic Dawn radio absorption signature against the Cosmic Microwave Background or against a bright background radio source depends on the temperature of the neutral hydrogen in the intergalactic medium. While x-rays from forming galaxies will likely dominate the heating rate, recent models suggest scenarios in which heating by the scattering of Lyman-$\alpha$ photons sourced by the galaxies contributes non-negligibly as well, and may even dominate. The efficiency of Lyman-$\alpha$ photon heating for a point source at high redshift using a numerical solution to the exact radiative transfer equation is provided here. It is found to be a factor of several smaller than the rate computed in the commonly used diffusion approximation to the radiative transfer equation.

Disentangling modified gravity and galaxy bias with field-level inference

Sophie Hoyland, Daniela Saadeh, Kazuya Koyama, Harry Desmond — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03514v1 Announce Type: new Abstract: We present a field-level inference framework for testing gravity with the large-scale structure that exploits the full information content of the galaxy distribution. Traditional analyses based on the power spectrum discard non-Gaussian and Fourier phase information, resulting in strong degeneracies between modified gravity (MG) and galaxy bias. Our approach overcomes this limitation by performing a Bayesian likelihood analysis directly on the three-dimensional galaxy number counts field, jointly constraining MG and bias parameters using both amplitudes and phases. As an illustrative application, we analyse mock data in the context of the $f(R)$ theory of gravity and a non-linear galaxy bias model. Non-linear structure formation is modelled using the COmoving Lagrangian Acceleration (COLA) method under different gravity strengths, parameterised by $f_{R0}$. The resulting dark matter fields are then mapped to mock galaxy catalogues via a non-linear bias prescription. We demonstrate that, with fixed and known initial phases, including non-Gaussian and phase information yields tighter constraints on both $f_{R0}$ and the primary bias parameter, $\beta$, relative to the power-spectrum-only analyses. Notably, the field-level approach breaks the degeneracies between MG and galaxy bias inherent to two-point statistics. Through a cosmic web classification into voids, walls, filaments and clusters, we find that under-dense regions are the primary drivers in distinguishing gravity models at the field level. Finally, we establish the robustness of our pipeline against variations in initial conditions, Poisson noise, and galaxy field thresholding, providing a powerful path forward for field-level tests of gravity with next-generation surveys.

Pulsar Timing Sensitivity to Dark Matter Substructure in the Presence of a Stochastic Gravitational-Wave Background

Abhiram Cherukupalli, Vincent S. H. Lee, Kim Berghaus, Kathryn M. Zurek — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03533v1 Announce Type: new Abstract: Pulsar timing arrays (PTAs) can detect dark matter (DM) substructure through the small shifts a transiting DM subhalo imprints on pulse arrival times. Recently found evidence for a stochastic gravitational-wave background (GWB) acts as red noise and competes with the substructure signal. Here we provide an analytic understanding of how this background degrades PTA sensitivity to DM substructure. We derive the full gauge-invariant proper-time observable induced by a transiting DM subhalo and develop a framework for the expected signal-to-noise ratio in the presence of red noise, accounting for the degeneracy with the pulsar timing model. From this we obtain simple scaling relations for the reach across the static, dynamic, and stochastic regimes, and numerically compute the reach for a Square Kilometre Array benchmark at three representative points of the NANOGrav 15-year posterior. The GWB background suppresses the sensitivity to DM substructure by one to three orders of magnitude compared to forecasts in the presence of only white noise, and the suppression depends on the amplitude and spectral index of the background within a factor of three. The dynamic Shapiro signal suffers the smallest suppression and gives the best sensitivity to DM substructure near $10^{-2}\, M_\odot$. Probing the regime where subhalos make up all or part of the DM remains a challenge even for surveys with more pulsars and longer observing time. Despite this, PTA measurements remain a competitive probe of DM substructure, and future surveys will increase in sensitivity by up to two orders of magnitude from existing NANOGrav limits.

Inflation with nondynamic distortion to leading order in slow roll

Ali Hassan — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03566v1 Announce Type: new Abstract: We study inflation in metric-affine gravity. We write an action that contains all the second order algebraic distortion terms, and all first order distortion terms with a single covariant derivative, coupled to a scalar field. We include the Einstein--Hilbert term with nonminimal coupling, a scalar field potential, and impose projective invariance. The distortion equation of motion is algebraic by construction, and the distortion is integrated out analytically. This yields a kinetic term sourced entirely by distortion, with a kinetic coupling function determined by the 13 free coupling constants of the starting action. We compute inflationary observables for three model classes with a monomial distortion coupling. For a monomial potential, the spectral index and tensor-to-scalar ratio depend only on the ratio of the exponents, with the starting coupling constants dropping out entirely; however, this model lies outside the Planck + BK18 $2\sigma$ contours. For a potential of the $\alpha$-attractor form, the observables are governed by a single parameter and approach the Starobinsky predictions as a limit. Including a nonminimal coupling to the Ricci scalar with a monomial potential can also yield an asymptotically flat effective potential with the same modified Starobinsky observables.

Hubble tension in k-essence: Evidence for robust tension alleviation

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03569v1 Announce Type: new Abstract: The Hubble tension has come to stay as a major problem in modern cosmology as it continues to plague the standard cosmological model ($\Lambda$CDM). As one of the viable, self-consistent dark energy theories, k-essence involves nontrivial self-interactions that can modify the background expansion beyond recombination; thereby impacting the sound horizon to last scattering, and hence, the inferred value of the Hubble constant. We examine this tension in two physically motivated k-essence models, dilaton and tachyon, using datasets from Planck and late-Universe probes including Pantheon+SH0ES, cosmic chronometer (CC), Supernova Cosmology Project Union compilation (Union3), Dark Energy Survey Year~5 (DESY5), and Dark Energy Spectroscopic Instrument (DESI) measurements. While $\Lambda$CDM exhibits inconsistent tension inferences, both k-essence models exhibit a substantial tension alleviation that is robust against the inclusion of the independent late-Universe cosmological datasets, giving consistent tension reduction irrespective of whether the observations are supernovae (Pantheon+SH0ES, Union3, DESY5) alone or in combination with cosmic chronometers (CC) and baryon acoustic oscillation measurements (DESI). The combined late-Universe dataset leads to only $0.14\sigma$ and $0.69\sigma$ offsets from the Planck prediction in the dilaton and tachyon models, respectively, compared to $5.89\sigma$ tension in $\Lambda$CDM. Both models demonstrate that the inferred tension alleviation is a stable, intrinsic consequence of the underlying k-essence dynamics rather than of model fine tuning: model parameters remain unchanged across datasets. The results establish that the apparent Hubble tension is not an unavoidable feature of late-Universe cosmology but depends critically on the description of dark energy.

Hubble constant measurement with 13 bright standard sirens from binary black hole mergers inside active galactic nuclei

Dhruv Kumar, Alejandro Torres-Orjuela — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03672v1 Announce Type: new Abstract: We measure the Hubble constant $H_0$ using 13 gravitational-wave binary black hole mergers associated with active galactic nucleus hosts. We find $H_0=70.50^{+3.37}_{-2.89}\,({\rm stat})\pm1.56\,({\rm cal})$\,km\,s$^{-1}$\,Mpc$^{-1}$ ($4.4\%$ precision), consistent with both Planck\,2018 ($0.98\sigma$) and SH0ES\,2024 ($0.76\sigma$), with no significant preference between the two. Combining with the bright siren GW170817 sharpens the constraint to $H_0=70.31^{+3.00}_{-2.85}\,({\rm stat})\pm1.55\,({\rm cal})$\,km\,s$^{-1}$\,Mpc$^{-1}$ ($4.2\%$ precision), and further combining with an independent dark-and-bright-siren sample tightens it to $H_0=69.71^{+2.55}_{-2.40}\,({\rm stat})\pm1.54\,({\rm cal})$\,km\,s$^{-1}$\,Mpc$^{-1}$ ($3.5\%$ precision). Assuming a luminosity-distance prior centered around the value related to a fixed cosmology in turn, recovers $H_0=67.62\pm0.72$ (Planck-anchored) and $H_0=72.91\pm0.72$\,km\,s$^{-1}$\,Mpc$^{-1}$ (SH0ES-anchored). We show that under such an assumption, a rejection of $\gtrsim4\sigma$ to the opposing anchor is obtained.

Baryonic assembly bias in X-ray-selected galaxy groups and clusters: insights from the Magneticum simulation

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03746v1 Announce Type: new Abstract: Galaxy groups and clusters trace the large-scale matter distribution, with their clustering usually interpreted mainly as a function of halo mass. Yet, at fixed mass, their baryonic properties retain information about halo growth, gas accretion, and feedback. The intrinsic scatter in X-ray luminosity and gas fraction suggests that X-ray-selected systems may not be a random subset of the halo population. If these observables correlate with halo assembly, they may trace secondary variations in halo bias. We test this using the Magneticum hydrodynamical simulation, measuring the clustering of systems selected by X-ray luminosity and gas fraction at fixed halo mass. We construct mass-matched subsamples by ranking halos in percentiles of X-ray luminosity and derive the linear halo-matter bias from the halo-matter cross-power spectrum. X-ray-bright halos are more strongly clustered than X-ray-faint halos at fixed mass. For the 84th-16th percentile split, we find $\Delta b_{\rm lin}=0.17\pm0.03$, corresponding to a $\sim17\%$ enhancement relative to the X-ray-faint sample. A 67th-33rd split gives a consistent signal, with $\Delta b_{\rm lin}=0.12\pm0.02$ and a $\sim12\%$ enhancement. The effect is strongest at group scales and negligible for cluster-size halos. Gas fraction shows an even stronger clustering dependence, with relative enhancements of $\sim39\%$ and $\sim26\%$ for the two percentile splits. This signal is present from $z\simeq2$, whereas X-ray luminosity becomes significant only at $z\simeq0.3$, once the gas thermodynamic state is more closely coupled to baryon retention. Matching halos by both mass and formation time reduces the large-scale bias difference to below $2\sigma$, indicating that formation time captures much of the signal. These results show that, in Magneticum, X-ray luminosity traces a baryonic manifestation of halo assembly bias beyond mass.

KiDS-Legacy: The consistency test of the large-scale structure with Bernardeau-Nishimichi-Taruya transform

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.04384v1 Announce Type: new Abstract: We perform the first $k$-cut cosmic shear analysis of the KiDS-Legacy survey. This method uses the Bernardeau-Nishimichi-Taruya (BNT) transform to construct weak-lensing kernels that are more localised than conventional ones, and remove information from selected physical scales while retaining the constraining power of the targeted range. Removing the scale of $k \geq 0.33~\mathrm{Mpc}^{-1}$ from the KiDS-Legacy pseudo-$C_\ell$ data vector, and using a covariance matrix whose Gaussian component is computed from the theoretical data vector, we find $S_8 = 0.798 \pm 0.045$. This agrees with both the fiducial KiDS-Legacy bandpower result and our no-$k$-cut pseudo-$C_\ell$ posterior to within $0.1\sigma$, indicating no significant bias from nonlinear astrophysical feedback at the precision of KiDS-Legacy. We also study the case in which the Gaussian covariance is computed from the observed data vector. In this setup, the same scale cut of $k < 0.33~\mathrm{Mpc}^{-1}$ gives a much lower $S_8=0.717_{-0.046}^{+0.047}$. Further $k$-cut tests reveal a mild scale-dependent trend, with larger physical scales preferring lower $S_8$ values and a maximum low- versus high-$k$ deviation of $1.80\sigma$. Mock tests show that this behaviour is not produced by the covariance prescription or data vector alone, but may arise from their interplay. These results show that BNT $k$-cuts provide both a mitigation strategy for nonlinear systematics and a diagnostic of weak-lensing inference pipelines.

Strong gravitational lensing constraints on interacting dark energy models

F. Villalobos, T. Verdugo, P. Troncoso-Iribarren, N. Pi\~na, J. Maga\~na — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.04460v1 Announce Type: new Abstract: The possible interaction between dark matter and dark energy has been proposed as a mechanism to alleviate the coincidence problem and the Hubble tension. Strong gravitational lensing observations provide valuable constraints to test the properties of the dark components of the Universe. We present estimates of cosmological parameters employing strong lensing data for an interaction model Q, proportional to the dark matter density and dependent on the deceleration parameter q. The obtained results are consistent with an accelerating Universe. Furthermore, these results agree with previous studies suggesting that an interaction in the dark sector may help alleviate existing tensions in the expansion history of the Universe and highlight the potential of strong gravitational lensing as an independent cosmological probe.

Reflection polarization of close binaries as a probe of axion dark matter birefringence

Tomoki Matsuoka, Kimihiro Nomura, Hidetoshi Omiya — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.04550v1 Announce Type: new Abstract: We propose close binary polarimetry as a probe of birefringence induced by ultralight axion dark matter. In a close binary, reflection or scattering can generate a small linear polarization whose time dependence is locked to the orbital phase. This phase-locked polarization provides a template against which an oscillatory rotation of the polarization angle induced by the axion can be searched for. We show that axion birefringence appears as sidebands around the orbital harmonics. For a single bright binary, with parameters motivated by observed systems and current high-precision optical polarimetry, we estimate the sensitivity to the axion-photon coupling under white noise assumption to be the level of $10^{-12}$ GeV$^{-1}$ at an axion mass of $10^{-20}$ eV. A future array of suitable binaries could further improve the sensitivity to $10^{-13}$ GeV$^{-1}$ in an optimistic scenario. This method could provide a complementary high-cadence optical probe of axion birefringence, compared to existing astrophysical searches.

Collisionless damping of the gravitational instability in fuzzy dark matter: spectral shape and quantum-to-thermal crossover

Yosuke Matsumoto, Kohji Yoshikawa, Naoki Yoshida — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.04893v1 Announce Type: new Abstract: We present a quantum-kinetic linear theory of the gravitational instability in the context of fuzzy dark matter universe. Starting from the Wigner transport equation, we apply Landau's approach to the linearized Wigner--Poisson system and derive a kinetic dispersion relation that incorporates quantum effects exactly by introducing the plasma dispersion function. The growth rate as a function of wavenumber is characterized by a dimensionless quantum-to-thermal ratio $\alpha = k_{\mathrm{qJ}}/k_{\mathrm J}$, where $k_{\mathrm{qJ}}$ and $k_{\mathrm J}$ represent the quantum and thermal Jeans wavenumbers, respectively. We derive an analytic expression for the spectral slope at the cutoff wavenumber, revealing that the spectral shape undergoes a sharp transition across $\alpha \sim 0.5$. This implies a crossover from a thermally dominated kinetic regime, in which collisionless damping occurs via phase mixing and Landau resonance, to a regime dominated by quantum pressure. By applying these results to fuzzy dark matter, we show that the cutoff scale and its spectral shape depend sensitively on both the particle mass and the initial velocity dispersion, suggesting a method for simultaneously constraining these parameters through observations of the matter power spectrum. This framework provides a theoretical basis for future studies on the transition from early-phase thermal states to the formation of Bose-Einstein condensates in galactic structures.

Inverse-k Primordial Oscillations from a Symbolic Regression Search

Ze-Yu Peng, Qing-Yu Lan, Yun-Song Piao — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.04925v1 Announce Type: new Abstract: Oscillatory features in the primordial power spectrum, potential signatures of new physics in the early universe, are usually searched for using fixed templates. In this work, we perform a template-free search for primordial features using symbolic regression. We find that both Planck and the combined Planck+ACT+SPT-3G datasets independently select an inverse-$k$ oscillation, $\cos(B/k)$ with $B\simeq4\,\mathrm{Mpc}^{-1}$, as the leading low-complexity feature. Comparing this inverse-$k$ template with standard linear and logarithmic oscillating templates, we find that it fits the data best, showing a weak preference for a non-zero amplitude. Our results show that symbolic regression as a powerful machine learning technique can provide an interpretable, model-independent approach to cosmological discovery.

Spectroscopic redshifts of selected flat-spectrum radio sources I

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.04959v1 Announce Type: new Abstract: We present the first results of a spectroscopic campaign carried out as part of the Search for Milli-Lenses (SMILE) program, which aims to constrain the prevalence of gravitational lens systems on milli-arcsecond angular scales (milli-lenses) using high-resolution Very Long Baseline Interferometry (VLBI) imaging. The SMILE parent sample contains ~ 5000 radio-loud active galaxies, selected as a flux-limited, complete subsample of CLASS (The Cosmic Lens All-Sky Survey) sources. We compiled redshift information for the full sample from multiple literature and catalog sources and found that 491 sources have no available redshift estimate, either spectroscopic or photometric. A further 948 sources have only photometric redshifts, many of which show substantial discrepancies between catalogs. Reliable redshifts are essential for VLBI radio-source studies because they convert angular measurements into physical linear scales, enable estimates of intrinsic luminosities and jet kinematics, and allow robust cosmological and population studies. To address this key limitation for lensing and population studies, we initiated a dedicated spectroscopic campaign to secure reliable redshifts for as many targets as possible. This paper focuses on the brightest sources in the SMILE sample. We report newly determined spectroscopic redshifts for 6 targets out of 15 observed with the Skinakas 1.3 m telescope.

Alleviating the Hubble Tension with Smooth Sign-Switching Dark Energy: Full CMB Constraints with DESI and PantheonPlus

Mariam Bouhmadi-L\'opez, Hsu-Wen Chiang, Be\~nat Ibarra-Uriondo — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.05044v1 Announce Type: new Abstract: Sign-switching dark energy has recently been proposed as a minimal modification of the late-time expansion history aimed at alleviating tensions within the standard cosmological model. In this work, we investigate ECDM, a smooth realisation of this scenario, with the dark energy density gradually transitioning from a negative to a positive value. We develop a consistent formulation of the perturbation equations that remains well behaved even when the dark energy equation-of-state parameter diverges during the transition. We confront the model with a comprehensive set of cosmological observations, including cosmic microwave background measurements from Planck 2018, ACT DR6 and SPT-3G, baryon acoustic oscillation measurements from DESI DR2, Type Ia supernova distances from Pantheon+, and local Hubble constant measurement of SH0ES. The inclusion of perturbations allows us to assess the impact of the model on structure growth and CMB anisotropies, providing a more thorough test of sign-switching dark energy. Our results show that this class of models is fully compatible with current precision cosmological observations while alleviating the Hubble tension and providing a compelling modification of the late-time dynamics of the Universe.

Modeling Uncertainties in Modified Gravity Predictions for the Stochastic Gravitational-Wave Background

Rodrigo Fraga, Rafael C. Nunes — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.05331v1 Announce Type: new Abstract: We investigate the impact of modified gravity on the stochastic gravitational-wave background (SGWB) generated by a cosmological population of unresolved binary black hole mergers. We consider two complementary classes of beyond-General Relativity (GR) effects: waveform-generation modifications described within the parametrized post-Einsteinian (ppE) framework and cosmological propagation effects associated with a modified gravitational-wave luminosity distance. Astrophysical uncertainties in the binary black hole population are consistently incorporated using a Power-Law plus Peak mass model combined with a Madau--Dickinson merger-rate evolution. Using SGWB forecasts for Advanced LIGO, the Einstein Telescope (ET), and Cosmic Explorer (CE), we perform injection-recovery analyses jointly varying modified-gravity and astrophysical population parameters. We show that frequency-dependent ppE corrections produce characteristic distortions in the SGWB spectral shape and can be meaningfully constrained by third-generation detectors, particularly CE. In contrast, modified propagation effects mainly induce smooth amplitude rescalings and exhibit stronger degeneracies with astrophysical uncertainties. Our results demonstrate that future SGWB observations will provide a complementary probe of gravitational physics across cosmic history and may open new avenues for testing deviations from GR beyond individually resolved compact-binary events.

Investigating a Possible Variation of the Gravitational Constant Through Gas Mass Fraction Measurements and Type Ia Supernovae Observations

L. R. Cola\c{c}o, R. F. L. Holanda, Marcelo Ferreira — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.05367v1 Announce Type: new Abstract: In this paper, we investigate a possible time variation of the gravitational constant (G) using a non-parametric approach. Our main cosmological probe is the gas mass fraction of galaxy clusters measured from X-ray observations. We also account for the effect of a varying $G$ on the intrinsic luminosity of type Ia supernovae (SNe Ia) through the Chandrasekhar mass-luminosity relation. We consider a specific phenomenological scenario, motivated by some scalar-tensor and screened modified-gravity frameworks, in which the standardized luminosity of SNe Ia decreases with increasing Chandrasekhar mass. Using gas mass fraction measurements jointly with luminosity distances from the Pantheon+ compilation, we reconstruct the evolution of G through Gaussian Processes. Our results indicate that a constant gravitational coupling remains broadly consistent with the data, although mild low-redshift departures are allowed.

Effects of Solar Wind Plasma Noise on Stochastic Gravitational Wave Background Searches with the LISA-Taiji Network

Mengfei Sun, Borui Wang, Jie Wu, Jin Li, Shengyi Ye — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.05368v1 Announce Type: new Abstract: The LISA-Taiji dual detector network improves millihertz SGWB sensitivity through cross correlation measurements. Solar wind plasma, however, can generate plasma noise correlated between detectors and bias SGWB cross correlation estimates. We use high time resolution electron density data from Wind/SWE, estimate the solar wind electron density fluctuation spectrum with the Lomb-Scargle method, and propagate the resulting plasma noise to the TDI A/E channels of the LISA-Taiji network. By including finite arm propagation, Taylor frozen flow spatial correlations, and the network overlap reduction response, we compute the SGWB parameter bias induced by interdetector plasma noise. Although the single detector plasma residual is below the reference noise, the component correlated between detectors can enter the SGWB cross correlation estimator directly. Under dual detector scale coverage, the plasma induced parameter bias for a power law SGWB can reach 12.73% of the corresponding Fisher parameter uncertainty. For M2/M3 cosmic string spectra, the bias in ln Gmu can reach 19.26% of the corresponding Fisher parameter uncertainty for the network configurations, observing times, and frequency bands considered here. These results show that the impact of solar wind plasma noise cannot be assessed from the single detector residual noise level alone. In LISA-Taiji SGWB searches, the interdetector correlated component of this noise can directly affect parameter estimation.

Polar coordinate transformations for machine learning based dark matter subhalo detection in strong gravitational lenses

Jacob M Campbell, Simon Dye, Emma Chapman, Adam Moss — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.02663v1 Announce Type: cross Abstract: Strong gravitational lensing provides a powerful probe of dark matter, particularly on small scales where the gravitational effects of dark matter subhalos within galaxies can manifest as perturbations within the extended arcs of gravitationally lensed sources. We investigate whether transforming lensed images into polar coordinates improves the ability of convolutional neural networks to infer subhalo mass. We introduce a machine learning architecture that outputs a prediction uncertainty alongside a mass prediction to enable assessment of network reliability. Using simulated Hubble Space Telescope observations, we compare our models trained on Cartesian and polar representations under different initialisation schemes, noise levels, and subhalo concentrations ($c=60$, $c=30$). We find that polar-transformed inputs consistently yield higher subhalo detection fractions than standard Cartesian images across all tested masses. For subhalos with mass $10^9M_\odot \leq M \leq 10^{9.5}M_\odot$, the fraction of subhalos the network is able to detect increases by $\sim 15$ per cent. Pretrained networks outperform randomly initialized networks, and the polar transform consistently improves network performance in both low signal-to-noise data and for lower-concentration subhalos. The relative improvement is highest in regimes where subhalo perturbations are most difficult to detect, such as low signal-to-noise data or systems containing low concentration subhalos. These results demonstrate that presenting strong lensing images in a polar representaion provides a computationally inexpensive way of improving CNN-based subhalo detection.

nmma: An extended Bayesian framework for Nuclear Multimessenger Astronomy in the Era of Next-Generation Detectors

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03045v1 Announce Type: cross Abstract: Context. The joint analysis of different (astro-)physical messengers, in particular gravitational-wave data and electromagnetic follow-up observations, allows us to establish, explore and deepen links between different physical fields. As new survey capacities and improved detection methods will lead to a significant increase in the number of multimessenger detections in the upcoming decades, efficient and versatile software frameworks are essential to maximise the scientific outcome of such multimessenger studies. Aims. We present a major upgrade to the Nuclear Multimessenger Astronomy (nmma) framework, incorporating various recent developments in theoretical modelling and machine learning in a modularised and easily extendable Bayesian framework. For the first time, this allows direct sampling on nuclear parameters alongside gravitational-wave, kilonova and afterglow parameters. Methods. We combine fast surrogate models for electromagnetic transients with speed-ups from emulators that map nuclear parameters to macroscopic neutron-star properties. Additional acceleration methods for the evaluation of state-of-the-art waveform approximants enable full Bayesian analyses of multimessenger events at the speed required in the era of next-generation detectors. Results. We demonstrate the capabilities of the upgraded nmma framework through a series of representative applications. Reanalysing the 2017 multi-messenger detection of a neutron-star merger, we achieve 20- to 60-fold speed-ups while using more detailed physical models compared to previous studies. Moreover, we demonstrate for a hypothetical future detection how we can simultaneously constrain nuclear parameters and the Hubble parameter with robustly quantified uncertainties.

The SKAO Pulsar Timing Array

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03059v1 Announce Type: cross Abstract: Pulsar timing arrays (PTAs) are ensembles of millisecond pulsars observed for years to decades. The primary goal of PTAs is to study gravitational-wave astronomy at nanohertz frequencies, with secondary goals of undertaking other fundamental tests of physics and astronomy. Recently, compelling evidence has emerged in established PTA experiments for the presence of a gravitational-wave background. To accelerate a confident detection of such a signal and then study gravitational-wave emitting sources, it is necessary to observe a larger number of millisecond pulsars to greater timing precision. The SKAO telescopes, which will be a factor of three to four greater in sensitivity compared to any other southern hemisphere facility, are poised to make such an impact. In this chapter, we motivate an SKAO pulsar timing array (SKAO PTA) experiment. We discuss the classes of gravitational waves present in PTA observations and how an SKAO PTA can detect and study them. We then describe the sources that can produce these signals. We discuss the astrophysical noise sources that must be mitigated to undertake the most sensitive searches. We then describe a realistic PTA experiment implemented with the SKA and place it in context alongside other PTA experiments likely ongoing in the 2030s. We describe the techniques necessary to search for gravitational waves in the SKAO PTA and motivate how very long baseline interferometry can improve the sensitivity of an SKAO PTA. The SKAO PTA will provide a view of the Universe complementary to those of the other large facilities of the 2030s.

Majoron Dark Energy via Freezing Induced by Quantum Coherence

Keunsu Cheon, Sin Kyu Kang, Jungjai Lee — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03070v1 Announce Type: cross Abstract: We propose a nonequilibrium mechanism for Majoron dark energy in which the late-time freezing of a physical Majoron is induced by quantum coherence in a hidden pseudo-Dirac sterile fermion reservoir. The evolving Majoron background derivatively couples to the hidden pseudo-Dirac number current and drives a lagged reservoir response with a finite memory time. In the short-memory regime, the causal response kernel reduces to $\dot X+\Gamma_{\rm PD}X=\beta\ddot\phi$. The leading linear-response matching $Q=\alpha X$ then yields an effective scalar equation containing the exchange structure $q_{\rm exch}\ddot\phi/\dot\phi$. We show that this term can dynamically suppress the Majoron velocity and sustain a response-dominated freezing branch even when the intrinsic Majoron mass is larger than the present Hubble scale. The microscopic origin of the lag variable is identified with the phase-lagged off-diagonal coherence of the hidden pseudo-Dirac ensemble, while the response strength is controlled by a response-weighted hidden density rather than by an independent gravitating component. The resulting state is a metastable nonequilibrium frozen phase with $w_\phi\simeq -1$, rather than an exactly static cosmological constant.

Flipped rotating axion: Baryogenesis and Dark Matter

Konstantinos Dimopoulos — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03085v1 Announce Type: cross Abstract: It is shown that the co-genesis of baryon asymmetry and dark matter can be achieved through the rotation of a spectator axion-like particle, because of a flip in the vacuum manifold's orientation at the end of inflation. This can occur if the axion has a periodic non-minimal coupling to gravity (while preserving the discrete shift symmetry) in non-oscillating inflation models, where the inflaton field is characterised by a runaway potential. Our rotating axion can generate the baryon asymmetry of the Universe through spontaneous baryogenesis, while at a later epoch it can oscillate as dark matter. We show that in order to avoid fragmentation of the axion condensate during the rotation, we require the non-minimal coupling $\xi\sim(f/m_P)^2$, where $f$ is the axion decay constant.

George, I and the curvaton

Konstantinos Dimopoulos — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03101v1 Announce Type: cross Abstract: George Lazarides was a pivotal collaborator and friend to me. We worked together on several projects, developing and exploiting the curvaton hypothesis, which was new at the time. This is a brief overview of our joint research.

Advancing extragalactic spectral line studies with the Square Kilometre Array Observatory

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03271v1 Announce Type: cross Abstract: We present an overview of the Square Kilometre Array Observatory (SKAO) science potential in the area of extragalactic spectral lines besides 21-cm neutral hydrogen. It highlights the main points from the SKAO Science Book chapters on individual topics, but is augmented by additional prospects. The SKAO will push studies and use of masers, kilomasers, megamasers, molecular and radio-recombination-line emission and absorption to a wider variety of environments, including to very high redshift where it may detect the first molecule (HeH$^+$). It will open the door to measurements of hydrogen and helium isotopes, probing the conditions for star formation and Big Bang nucleosynthesis. While the planned SKAO of the 2030s (AA*) is destined to forge major progress, an SKAO as initially envisaged (AA4) will truly transform the landscape, and an extension towards higher frequencies (up to 24 GHz) would enable water maser and ammonia surveys in nearby galaxies and systematic molecular gas inventories at redshift 5.

Dark energy genesis: modeling dissipative effects in primordial cosmology

Pietro Pellecchia, Alejandro Perez, Salvatore Ribisi — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03272v1 Announce Type: cross Abstract: In various approaches to quantum gravity, spacetime geometry is understood to emerge from more fundamental discrete structures at the Planck scale. As sometimes posited, their presence could lead to dissipative effects in the smooth effective sector. In this paper, we develop the idea of non-conservation in gravity, by introducing an effective cosmological model within unimodular gravity, in which a varying cosmological constant arises as a consequence of dissipation. We show that this requires to incorporate hidden degrees of freedom -- termed quantum gravity defects -- that act as an effective bath for the matter fields. To illustrate the viability of the framework, we study the case of an Ohmic bath inspired by the Caldeira-Leggett model for Brownian motion, leading to a diffusion equation for the matter energy density. The results show that, starting from a primordial universe with no dark energy, dissipation can account for the generation of a small positive cosmological constant.

Euclid: A UV-faint quasar in a highly luminous star-forming host galaxy at $z \approx 7.7$

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03430v1 Announce Type: cross Abstract: Constraining the co-evolution of supermassive black holes and their host galaxies in the first billion years after the Big Bang is essential for understanding the formation of the earliest cosmic structures. Here, we present IRAM/NOrthern Extended Millimeter Array (NOEMA) observations of the $z \approx 7.7$ quasar EUCL\,J125308.55+705432.3, recently discovered in the first data release of the Euclid Wide Survey. We report the most distant detections of [CII] 158$\mu\mathrm{m}$ and cold dust emission in a quasar host to date. The [CII] emission line sets the systemic redshift at $z=7.6980\pm0.0004$. The source exhibits luminosities of $L_{\rm FIR}=3.6\times10^{12}\,L_{\odot}$ and $L_{[CII]}=2\times10^9\,L_{\odot}$, respectively, a dust mass of 1.4$\times 10^{8}\,M_{\odot}$, and a dynamical mass in the range 0.33-1.3$\times10^{10}\,M_{\odot}$. Remarkably, despite being nearly two magnitudes fainter in the rest-frame UV ($M_{1450}=-24.06$) than previously known $z\approx7.5$ quasars ( $\sim-$26.5), EUCL\,J125308.55+705432.3 exhibits the brightest [CII] emission among them. This indicates that the host galaxy is actively star-forming, with a star-formation rate $>250\,M_{\odot}\,\mathrm{yr}^{-1}$, consistent with recent findings that UV-faint quasars at $z>6$ preferentially reside in [CII]-luminous galaxies. The UV-faintness likely reflects dust obscuration or sub-Eddington accretion, rather than lower host mass, suggesting these systems are at a different stage in their evolution compared to UV-bright quasars. These IRAM/NOEMA observations highlight the power of combining Euclid's wide-area quasar discovery potential with submillimetre follow-up observations to characterise the host galaxies of early supermassive black holes across a broader redshift and luminosity range than previously accessible.

Pebbles to Gems: Intermediate-mass black holes in the first star clusters

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03536v1 Announce Type: cross Abstract: The rapid assembly of supermassive black holes (SMBHs) observed at $z\gtrsim7$ requires efficient seeding mechanisms in the early Universe. Population III (Pop. III) star clusters have recently emerged as a promising pathway that may bridge the gap between traditional light- and heavy-seed scenarios by producing intermediate-mass black holes (IMBHs) with masses up to $\sim10^4\,\rm M_{\odot}$. We investigate the properties and number densities of IMBHs forming in Pop. III star clusters with masses $M_{\rm cl}\sim10^3-4\times10^5\,\rm M_{\odot}$, and hosted in isolated dark matter minihalos, using a suite of direct $N$-body simulations. We adopt cosmologically motivated initial conditions and explore different stellar evolution prescriptions, binary orbital parameter distributions, and cluster dynamical configurations. By $z\sim19$, the IMBH mass function consistently peaks at $m_{\rm IMBH}\sim200\,\rm M_{\odot}$, with number densities of $n_{\rm IMBH}\sim0.2-5\,\rm cMpc^{-3}$. In sufficiently dense and massive clusters, IMBHs with masses $>10^3\,\rm M_{\odot}$ can already form by $z\sim19$, reaching number densities of $n_{\rm IMBH}\sim10^{-4}-10^{-2}\,\rm cMpc^{-3}$. The most massive IMBHs in our models reach $\sim6200\,\rm M_{\odot}$ through the collapse of very massive stars assembled by repeated stellar collisions, a process enhanced in fractal clusters. Lower-mass IMBHs form instead predominantly through single and binary stellar evolution and binary stellar mergers. We find that models combining large stellar radii and tight binaries produce the highest IMBH abundances relative to isolated Pop. III evolution. Owing to the high retention fraction of IMBHs ($\gtrsim88\%$), massive dense Pop. III star clusters can act as efficient incubators of both light and heavy SMBH seeds, even if only a fraction of Pop. III stars formed in such environments.

Gravitational Wave Signatures of Cosmological Stasis: A Unified Spectral Template

Gabriela Barenboim, Anne-Katherine Burns — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03537v1 Announce Type: cross Abstract: Proposed in 2022 by Dienes et al., stasis is a dynamical fixed point in the early universe in which the equation of state, $w_s$, is fixed at a constant value. In this study we show that the inflationary gravitational wave imprint of any stasis epoch is captured by a closed-form spectral template controlled by two physical inputs, the equation of state $w_s$ and the stasis duration $\Delta N_\mathrm{stasis}$, that applies uniformly across every microphysical realization. The template presented here yields two independently measurable observables, the spectral tilt of the spectra in the stasis band, $\alpha(w_s)$ and the amplitude step $C^2(w_s)$ at the beginning and end of the stasis band. Eliminating $w_s$ gives a one-parameter consistency curve $C^2 = C^2(\alpha)$ on which the data must lie if the underlying cosmology is any constant-$w$ era. This makes the spectrum falsifiable without knowing $w_s$ in advance: a measured $(\alpha, C^2)$ pair either lands on the curve or rules out the constant-$w$ class. We show that BBO and DECIGO can resolve the perpendicular displacement from the consistency curve to $\sigma_\perp \simeq 1.5\times10^{-5}$ at a tensor-to-scalar ratio, $r = 0.01$, four orders of magnitude below the curve's range in $C^2$ meaning that any off-curve deviation is detectable across a broad range of allowed $r$ values.

Black Hole Memory Burden and its Signatures in Gravitational Waves from Mergers

Gia Dvali, Michael Zantedeschi, Sebastian Zell — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03560v1 Announce Type: cross Abstract: Swift memory burden (MB) implies that the information stored in a black hole (BH) can modify its classical dynamics when the BH is perturbed. This influences the gravitational waves (GWs) emitted during BH mergers. In this paper, we investigate how the BH memory load is determined by the features of the collapsing source. We show that the memory load can vastly exceed the information content of its progenitor. An extreme example is a BH formed in a two-particle collision, which exhibits maximal MB. We then derive bounds for BHs formed through stellar collapse and examine the impact of swift MB on BH quasinormal modes, quantifying the MB-induced frequency shift of GWs. These findings imply that GW observations probe the fundamental mechanisms of BH information storage as well as their formation history.

Machine Learning and the SKA for Cosmic Dawn and the Epoch of Reionization

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03606v1 Announce Type: cross Abstract: When operational, the SKA will generate unprecedented amounts of data and provide exquisite sensitivity for 21 cm tomography of Cosmic Dawn (CD) and the Epoch of Reionization (EoR). With this comes opportunities for new data-driven algorithms that unlock new methods for instrument modelling, data analysis, theoretical simulation, and inference for understanding the high-redshift universe. In this chapter, we provide an overview of some machine learning algorithms that have been proposed for CD and EoR science with the SKA

Identifying lensed gravitational waves with physics-informed posterior learning

Tian-Yang Sun, Xiao Guo, Jing-Fei Zhang, Xin Zhang — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.03885v1 Announce Type: cross Abstract: Gravitational lensing of gravitational waves can probe compact lenses, dark matter substructure, and cosmological distances, but identifying lensed events is difficult when unrelated binary mergers overlap in the same analysis window. We develop physics-informed posterior learning for ranking lensed multi-image signals against unrelated multiple-merger events. The method exploits the geometric-optics consistency that lensing can change amplitudes, arrival times, and Morse phase offsets while preserving the intrinsic phase evolution of the source. We infer a simulation-trained approximate posterior for the common detector-frame chirp mass and symmetric mass ratio, and fuse posterior samples with direct waveform features. Training uses generic multi-image simulations, while point-mass, singular-isothermal-sphere, singular-isothermal-ellipsoid, and shear-perturbed lenses are reserved for held-out lens-family evaluation. For the observationally motivated binary-black-hole population, the fusion ranking raises the detection efficiency from $20.8\%$ to $35.2\%$ at a $1\%$ reference false-positive-rate threshold calibrated on the corresponding unrelated multiple-merger sample. It lowers the network signal-to-noise ratio needed for $50\%$ detection efficiency from 45.3 to 33.5, which corresponds to a 1.35 times larger signal-to-noise-ratio-equivalent distance scale. The gain is limited by loud unrelated multiple-merger events that are partly source consistent, and by the need to calibrate the unrelated multiple-merger population. These results suggest that physical consistency can become a guiding principle for machine learning searches in dense gravitational-wave catalogs.

Assembly bias from nuisance to probe I: the relation between galactic conformity and the linear matter clustering

Nelson Padilla, Ivan Lacerna, Dante Paz — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.04022v1 Announce Type: cross Abstract: Two-halo galactic conformity is commonly interpreted as a manifestation of galaxy assembly bias, but its statistical structure and physical origin remain unclear. We aim to write the quenched-neighbour statistic in correlation-function form, test whether its scale dependence follows the linear matter correlation function $\xi_{\rm mm}^{\rm lin}(r)$, and separate the contributions of halo-mass bias and assembly bias to its amplitude. Using galaxies in IllustrisTNG300-1 at $z=0$, we measure the two-halo galactic conformity statistic of quenched neighbours at distance $r$, $\Delta f_Q(r)$, and related quantities in real space, compute the required correlations, perform shuffling tests at fixed halo mass, compare several $\Delta f$ observables, and explore the transformed family $G_n$. We show explicitly that $\Delta f_Q(r)$ can be written directly in terms of correlation functions and that, over $\sim 2$-$40\,h^{-1}\,\mathrm{Mpc}$, it is well described by $A_{\rm fit}\,\xi_{\rm mm}^{\rm lin}(r)$. Thus nonlinear and baryonic terms do not dominate the residual scale dependence isolated by this statistic. Halo-mass bias alone predicts lower amplitudes than measured, while fixed-mass shuffling strongly suppresses the signal; in TNG300 the amplitude is therefore dominated by %fixed-mass assembly-dependent occupancy. galaxy assembly bias at fixed halo mass. Quenching, colour, and concentration share a common rescaled shape, whereas stellar-mass and halo-mass splits do not. These results suggest that galaxy assembly bias sets the amplitude of two-halo conformity, while the double-difference structure of the statistic suppresses nonlinear residuals when the compared populations have similar halo-mass and transition-scale structure.

Measuring the Angular Auto-power Spectrum of Fast Radio Burst Dispersion Measures as a Robust Cosmological Probe and Baryon Tracer

Bao Wang, Zhiyu Lu, Yang Liu, Jun-Jie Wei, Xue-Feng Wu — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.04106v1 Announce Type: cross Abstract: Fluctuations in the cosmic electron density are imprinted on the dispersion measures (DMs) of fast radio bursts (FRBs), making DMs a promising probe of cosmology and the spatial distribution of ionized baryons. In this work, we present the first measurement of the angular auto-power spectrum of FRB DMs, using 3455 apparently non-repeating bursts from the CHIME/FRB Catalog 2. We detect an angular correlation signal at $>3\sigma$ significance, associated with large-scale electron-density fluctuations. By fitting the measured spectrum to theoretical models, we constrain two key parameter combinations: $\Omega_{\rm b}h^2$-$H_0$, which probes the cosmic baryon density and expansion rate, and $\Omega_{\rm b}h^2$-$f_{\rm d}$, which traces the baryon fraction in cosmic large-scale structure (LSS). We further assess the robustness of the power-spectrum method against systematic uncertainties arising from the assumed FRB redshift distribution and from the DM contributions of host galaxies (${\rm DM}_{\rm host}$), the Galactic halo (${\rm DM}^{\rm MW}_{\rm halo}$), and the Milky Way interstellar medium (${\rm DM}^{\rm MW}_{\rm ISM}$), using mock samples. Our results demonstrate that the angular power spectrum is largely insensitive to uncorrelated DM components such as ${\rm DM}_{\rm host}$, thereby effectively mitigating the impact of poorly constrained host-galaxy systematics. In contrast to the traditional ${\rm DM}_{\rm LSS}$-$z$ relation, this method does not require individual redshift measurements--it relies only on the overall redshift distribution--and it partially breaks the parameter degeneracies in the $\Omega_{\rm b}h^2$-$H_0$ and $\Omega_{\rm b}h^2$-$f_{\rm d}$ planes. These findings establish the DM angular power spectrum as a robust cosmological probe and a powerful baryon tracer.

Turbulent Magnetogenesis and Large-scale Magnetic Dynamo Amplification in Ion--electron Plasmas

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.04437v1 Announce Type: cross Abstract: Using fully kinetic simulations that capture unprecedentedly large (from electron to ion) scales, we study magnetogenesis driven by continuous large-scale forcing until nonlinear dynamo saturation. We uncover a two-stage mechanism in collisionless ion-electron plasmas whose dynamics diverge dramatically from the pair-plasma case. In the first phase, electron pressure anisotropy triggers electron-Weibel modes, seeding small-scale magnetic fields. Then, a second growth phase emerges when the more massive ions develop their own strong anisotropy and drive ion-Weibel-type modes; concurrently, a Biermann-battery mechanism contributes to amplifying the magnetic field. This combined dynamics provides a tenfold amplification of the magnetic field in comparison to the pair-plasma case. Over long times, dynamo action continues until the system reaches a statistical steady state. This self-consistent kinetic mechanism provides a plausible explanation for robust magnetogenesis wherever an external forcing continuously stirs the plasma.

Shifted Hybrid Realization of Non-Minimal Higgs Inflation in Light of ACT DR6 and Planck Data

Nadir Ijaz, Pirzada, Mansoor Ur Rehman — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.04504v1 Announce Type: cross Abstract: We investigate non-minimal Higgs inflation in a no-scale-inspired supergravity framework and confront its predictions with the latest CMB constraints from ACT DR6 and \emph{Planck}. Working within a shifted hybrid inflation scenario, we construct an effective single-field description in which the GUT Higgs direction serves as the inflaton after stabilization of the orthogonal scalar fields. We show that the inclusion of the leading nonrenormalizable operator in the superpotential induces a controlled deformation of the Starobinsky attractor, allowing the scalar spectral index to be shifted into the range favored by recent ACT and related CMB datasets while maintaining a small tensor-to-scalar ratio, $r \sim 10^{-3}-10^{-2}$. The resulting inflationary dynamics remain theoretically consistent, with controlled supergravity corrections and sub-Planckian inflaton field values. We perform a detailed numerical analysis of the model parameter space, including reheating and nonthermal leptogenesis, and identify regions that simultaneously satisfy current observational constraints and yield a viable post-inflationary cosmological history.

Constraining inflationary models via de-Sitterization of Bianchi Cosmologies

Apurba Samanta (IIT Mandi), Rahul Kothari (IIT Mandi) — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.04701v1 Announce Type: cross Abstract: Our Universe is isotropic and homogeneous when we observe it on $\gtrsim$ Mpc length scales. It is desirable that present state of the Universe has no dependence on its initial geometry. In case of Bianchi Universes, i.e., anisotropic but homogeneous Universe, this has already been demonstrated via cosmological constant in a process that we call \textit{de Sitterization}. In this letter, we show that for Bianchi Universe, the same state can be achieved by a homogeneous inflaton field with a general potential and satisfying a criterion without the need of a cosmological constant. More importantly, we show that the same condition can constrain models of inflation and explain our idea with examples.

In-Band Scattering and Absorption of Infrared Blocking Foam Filters for Millimeter-wave Cameras

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.05003v1 Announce Type: cross Abstract: Expanded closed-cell polymer foams are widely used as thermal infrared (IR) blocking filters in millimeter-wave cameras, particularly for Cosmic Microwave Background observations. Precise knowledge of their millimeter-wave properties is essential for optimizing sensitivity. We present broadband (150 GHz - 2 THz) transmittance spectroscopy of Styroace-II and several Zotefoam filters, fitting their spectra with a radiative transfer model incorporating dielectric absorption and Rayleigh, Mie, and higher-order scattering. For a typical 5~cm thick filter stack at 280~GHz, Styroace-II exhibits ${\sim}10\%$ scattering with absorption estimated as ${\lesssim}5\%$ by effective-medium theory, while Zotefoam HD30 offers superior performance at ${\sim}3\%$ scattering and absorption likewise bounded to ${{\lesssim}0.3\%}$. Each model component is constrained at the ${\sim}0.1\%$ transmittance level for millimeter wavelengths. We observe batch-to-batch scattering variability of up to 2 percentage points in foams with multiple tested batches. Less commonly used Zotefoam formulations (LD15 and LD24) can further reduce in-band scattering to ${<}1\%$ while maintaining negligible in-band absorption and likely comparable IR blocking due to shared polyethylene absorption features and similar cell sizes. Based on this work, a filter constructed from the best measured LD24 batch has replaced the Styroace-II filter in a Simons Observatory 220/280 GHz Small Aperture Telescope.

Pathways and impediments towards a detection of the relic neutrino wind

Andrew J. Long, Michiru Uwabo-Niibo, Masahide Yamaguchi — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.05221v1 Announce Type: cross Abstract: A direct detection of the cosmic neutrino background (CNB) in laboratories on Earth has been called the ``holy grail'' of experimental neutrino physics, but a still more glorious prize awaits. Beyond simply detecting the presence of relic neutrinos and measuring their flux, one may aspire to measure their energy distribution, polarization, anisotropies, temporal variation, and other properties. In this work we focus on the CNB wind, which is the approximately dipolar anisotropy in the CNB flux resulting from the relative velocity of the CNB rest frame and the lab frame. We consider a CNB detection strategy based on measuring the angular distribution of recoiling electrons at the tritium $\beta$-decay endpoint. In order to quantify the difficulty of detecting the CNB wind, we calculate the required exposure (detector mass times observation duration) for a $3\sigma$ discovery. We find that detecting the CNB wind would require an exposure that is at least $10^{5}$ times larger than what's required for detecting the CNB flux alone. Additionally if the experimental energy resolution were to exceed the neutrino mass scale, then an exceptionally good control of systematic uncertainties would also be required. For nonrelativistic neutrinos, the Majorana wind signal is suppressed relative to the Dirac case by the cancellation of the leading helicity-odd angular-correlation term, leading parametrically to an exposure penalty of order $(m_\nu/T_\nu)^2$.

Weak Evolution of Cosmic Atomic Hydrogen over the Past 4.5 Billion Years

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.05326v1 Announce Type: cross Abstract: The cosmic star formation rate density (CSFRD) has declined sharply toward the present day, but the roles of the atomic and molecular gas reservoirs remain uncertain. We measure the cosmic HI density, $\Omega_{\mathrm{HI}}$, over $0

Cosmological Correlators in KLF and the Double-Exchange

Nathan Belrhali, Arthur Poisson, S\'ebastien Renaux-Petel — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.05327v1 Announce Type: cross Abstract: In this work, we present the procedure to find series representations of tree-level cosmological correlators using the Kontorovich-Lebedev-Fourier (KLF) space formalism. This framework allows us to trade the in-in nested time integrals for frequency integrals over rational propagators and vertex functions, which encode interactions among quantum fields on a de Sitter background. Because these functions are the key objects to understand in order to perform a diagrammatic computation, we derive their relevant analytic properties by using both their integral representation and series representation in terms of Lauricella functions. For a vertex involving any number of fields, we obtain the location of singularities, the corresponding residues and the large-frequency asymptotic behaviour. Gathering these properties at each frequency integration allows us to compute a tree-level correlator directly, without relying on the differential equations it satisfies. To illustrate this procedure, we provide a complete treatment of the double-exchange diagram. The computation naturally distinguishes the different physical contributions, whether to the background or to the cosmological collider signal. The newly derived result is expressed at most in terms of a double series over hypergeometric functions, which simplifies the analytical expression of the correlator.

Five parameters are all you need (in $\Lambda$CDM)

Paulo Montero-Camacho, Yin Li, Miles Cranmer — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2405.13680v3 Announce Type: replace Abstract: The standard cosmological model, with its six independent parameters, successfully describes our observable Universe. One of these parameters, the optical depth to reionization $\tau_\mathrm{reio}$, represents the scatterings that Cosmic Microwave Background (CMB) photons will experience after decoupling from the primordial plasma as the intergalactic medium transitions from neutral to ionized. $\tau_\mathrm{reio}$ depends on the neutral hydrogen fraction $x_\mathrm{HI}$, which, in turn, should theoretically depend on cosmology. We present a novel method to establish the missing link between cosmology and reionization timeline using symbolic regression. We discover the timeline has a universal shape well described by the Gompertz mortality law, applicable to any cosmology within our simulated data. Unlike the conventional tanh prescription, our model is asymmetric in time and a good fit to astrophysical constraints on $x_\mathrm{HI}$. By combining CMB with astrophysical data and marginalizing over astrophysics, we treat $\tau_\mathrm{reio}$ as a derived parameter, tightening its constraint to $<3\%$. This approach reduces the error on the amplitude of the primordial fluctuations by a factor of 2.3 compared to Planck's PR3 constraint and provides a commanding constraint on the ionization efficiency $\zeta_\mathrm{UV} = 26.9^{+2.1}_{-2.5}$. We expect further improvements in the near term as reionization constraints increase and our understanding of reionization advances.

RG-Flow Renormalized One-Loop Corrections to the Power Spectrum in USR Inflation

Haidar Sheikhahmadi, Amin Nassiri-Rad — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2411.18525v3 Announce Type: replace Abstract: The nature of one-loop corrections to long-wavelength CMB-scale modes in single-field inflation models with an intermediate ultra-slow-roll (USR) phase remains a subject of active debate. In this work, we perform a detailed investigation into the regularization and renormalization of these one-loop corrections to the curvature perturbation power spectrum. Employing a combined UV-IR regularization scheme within the renormalization group (RG) flow formalism, we compute the renormalized one-loop contributions, including those from the tadpole diagram, arising from both the cubic and quartic interaction Hamiltonians. This allows us to study meaningfully the running of the coupling constant aiming at removing the divergences appear in our study. We demonstrate that the fully regularized and renormalized fractional loop correction to the power spectrum is controlled by its peak value at the end of the USR phase, scaling as $\mathcal{P}_\mathrm{peak} \sim e^{6 \Delta N}$, where $\Delta N$ is the duration of the USR phase. This result confirms the original conclusion that loop corrections can become non-perturbatively large if the transition from the USR phase to the final slow-roll phase is instantaneous and sharp, potentially challenging the perturbative framework of such inflationary scenarios for primordial black hole formation.

BBN-simple: How to Bake a Universe-Sized Cake

Aidan Meador-Woodruff, Dragan Huterer — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2412.07893v2 Announce Type: replace Abstract: Big Bang Nucleosynthesis (BBN), the process of creation of lightest elements in the early universe, is a highly robust, precise, and ultimately successful theory that forms one of the three pillars of the standard hot-Big-Bang cosmological model. Existing theoretical treatments of BBN and the associated computer codes are accurate and flexible, but are typically highly technical and opaque, and not suitable for pedagogical understanding of the BBN. Here we present BBN-simple -- a from-scratch numerical calculation of the lightest element abundances pitched at an advanced undergraduate or beginning graduate level. We review the physics of the early universe relevant for BBN, provide information about the reaction rates, and discuss computational-mathematics background that is essential in setting up a BBN calculation. We calculate the abundances of the principal nuclear species in a standard cosmological model, and find a reasonably good agreement with public precision-level BBN codes.

Beyond the Power Spectrum: A New Framework for Non-Stationary Fields with Applications to Light-Cone Effects in Line Intensity Mapping

Matt\'eo Blamart, Adrian Liu — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2505.09674v3 Announce Type: replace Abstract: Modern cosmological surveys cover extremely large volumes and map fluctuations on scales reaching gigaparsecs. As a result, it is no longer a valid assumption to ignore cosmological evolution along the line of sight from one end of the survey to the other. When extracting cosmological information, the power spectrum becomes suboptimal because it relies on the assumption of translational invariance of the observed field. For example, during the Epoch of Reionization (EoR), the 21cm brightness temperature field on the nearby (low-redshift) end of a large survey volume exhibits statistical properties that differ significantly from those at the far (high-redshift) end. To overcome these limitations, we have developed a eigen decomposition-inspired non-Fourier basis that captures evolution effects. Our work demonstrates that using this new basis integrated in a new summary statistic yields tighter constraints on astrophysical parameters compared to the traditional power spectrum. Additionally, we provide an illustrative example and a practical guide for applying this basis in the context of a realistic forecast for interferometers such as the Hydrogen Epoch of Reionization Array (HERA).

The DESI DR1 Peculiar Velocity Survey: growth rate measurements from galaxy and momentum correlation functions

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2512.03230v2 Announce Type: replace Abstract: Joint analysis of the local peculiar velocity and galaxy density fields offers a promising route to testing cosmological models of gravity. We present a measurement of the normalised growth rate of structure, $f\sigma_8$, from the two-point correlations of velocity and density tracers from the DESI DR1 Peculiar Velocity and Bright Galaxy Surveys, the largest catalogues of their kind assembled to date. We fit the two-point correlation measurements with non-linear correlation function models, constructed from density and momentum power spectra generated using 1-loop Eulerian perturbation theory, and validate our methodology using representative mock catalogues. We find $f\sigma_8 = 0.391^{+0.080}_{-0.081}$, consistent to within $1\sigma$ with accompanying analyses of the same datasets using power spectrum and maximum-likelihood fields methods. Combining these growth rate results from different methods including appropriate correlations, we find a consensus determination $f\sigma_8(z = 0.07) = 0.4497 \pm 0.0548$, consistent with predictions from \textit{Planck}$+\Lambda$CDM cosmology. Jointly fitting to this consensus low-redshift growth rate and the DESI DR1 full-shape clustering dataset, we measure gravitational growth index $\gamma_{\rm L} = 0.580^{+0.110}_{-0.110}$, consistent with the prediction of general relativity.

UV Luminosity Functions from HST and JWST: A Possible Resolution to the High-Redshift Galaxy Abundance Puzzle and Implications for Cosmic Strings

Matt\'eo Blamart, Adrian Liu, Robert Brandenberger, Julian B. Mu\~noz, Bryce Cyr — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2512.09980v2 Announce Type: replace Abstract: Recent observations of high redshift galaxies by the James Webb Space Telescope suggest the presence of a bright population of galaxies that is more abundant than predicted by most galaxy formation models. These observations have led to a rethinking of these models, and numerous astrophysical and cosmological solutions have been proposed, including cosmic strings, topological defects that may be remnants of a specific phase transition in the very early moments of the Universe. In this paper, we integrate cosmic strings, a source of nonlinear and non-Gaussian perturbations, into the semi analytical code Zeus21, allowing us to efficiently predict the ultraviolet luminosity function (UVLF). We conduct a precise study of parameter degeneracies between star-formation astrophysics and cosmic-string phenomenology. Our results suggest that cosmic strings can boost the early-galaxy abundance enough to explain the measured UVLFs from the James Webb and Hubble Space Telescopes from redshift z = 4 to z = 17 without modifying the star-formation physics. In addition, we set a new upper bound on the string tension of $G\mu \lessapprox 10^{-8}$ ($95\%$ credibility), improving upon previous limits from the cosmic microwave background. Although with current data there is some level of model and prior dependence to this limit, it suggests that UVLFs are a promising avenue for future observational constraints on cosmic-string physics.

Low-Frequency Stochastic Gravitational-Wave Background in Gaia DR3 catalog

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2603.23028v3 Announce Type: replace Abstract: We investigate the potential to detect low-frequency gravitational waves (GWs) through their imprints on the proper motions of distant quasars observed by the Gaia mission. Using astrometric data from Gaia DR3, we simulate the effect of GWs on the proper motions of quasars, incorporating their actual sky positions and measurement uncertainties. We investigate two closely related data analysis techniques for the extraction and characterization of GW signals from quasar proper motions: Vector Spherical Harmonics (VSH) and angular correlation functions, commonly referred to as Hellings-Downs curves (HDC). Using realistic simulated data, we forecast their sensitivity and accuracy to GWs, and evaluate the impact of systematic errors. From these simulations, we derive an upper limit on the amplitude of a stochastic GW background, constrained by the observational timespan, astrometric precision, and the sky distribution of quasars. VSH decomposition appears less sensitive to uneven sky sampling and anisotropic noise. The HDC approach retains a larger fraction of the pairwise correlation information and therefore exhibits higher raw statistical sensitivity under idealized conditions. We find that, with Gaia DR3 proper motion errors, the lower limit for a detectable GW strain is of 10^{-11}, with possible improvements to about 3 x 10^{-12} for the next Gaia Data Release 4 (for the same number of quasars). This limit holds for a stochastic GW spectrum integrated over all frequencies less than half the inverse of the 34-month observational timespan of Gaia DR3, corresponding to approximately 5.6 nHz. We also investigate how different data-restriction and weighting schemes influence the final estimate of the gravitational wave strain.

Consistency relations of amplitude and phase fluctuations of gravitational waves magnified by strong gravitational lensing

Yuta Nakazono, Teruaki Suyama — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2604.02216v2 Announce Type: replace Abstract: We discuss the amplitude and phase fluctuations of gravitational waves due to wave optics lensing in the presence of both a strong lens and cosmological weak lenses. By applying the geometric optics approximation to the strong lens and treating the weak lensing potential perturbatively, we obtain the amplification factor up to the second order in the weak lensing potential. Additionally, we establish a methodology to systematically evaluate the weak lensing effects based on diagrammatic rules. Based on the derived amplification factor, we evaluate the statistics of the fluctuations and demonstrate that the consistency relations originally established in the absence of a strong lens still hold in exactly the same form when a strong lens is present. The physical origin of these relations is also discussed. Furthermore, we demonstrate that for the mean of the weak lensing signal, both the magnification of the signal and the shift of the Fresnel scale to larger scales occur, consistent with the behavior observed in the variance.

Breaking Free from the Swampland of Impossible Universes through the DESI Portal

Luis A. Anchordoqui, Dieter Lust — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2605.10476v3 Announce Type: replace Abstract: The persistent challenge of creating stable de Sitter vacua within string theory undermines the observational validity of the $\Lambda$ cold dark matter (CDM) model. This difficulty suggests that the concordance model of cosmology, characterized by a constant dark energy $\Lambda$, may reside in the swampland of inconsistent quantum gravity theories rather than the string landscape of consistent ones. Recent observational data, particularly from the Dark Energy Spectroscopic Instrument (DESI), have significantly challenged $\Lambda$CDM cosmology. Specifically, the combination of DESI baryon acoustic oscillation measurements with cosmological surveys seem to indicate a preference for a dynamic, time-evolving dark energy rather than a constant, with roughly 10\% reduction in density over the last several billion years. This review summarizes significant advancements made over the past two years in linking DESI findings to string-inspired scenarios.

Learning the Universe with cosmological rescaling of merger trees and semi-analytic galaxy formation models

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2606.10024v2 Announce Type: replace Abstract: Learning cosmology from galaxy surveys requires large suites of simulations spanning the cosmological and astrophysical parameter space, yet hydrodynamical simulations of galaxy formation remain prohibitively expensive. Semi-analytic models offer an inexpensive, physically grounded alternative, but still require halo merger trees from $N$-body simulations, and densely sampling cosmological parameters in sufficient volume remains expensive. We address this by extending cosmological rescaling to operate directly on merger trees and applying it in the $\Omega_{\rm m}$-$\sigma_8$ plane, running the Santa Cruz semi-analytic model for galaxy formation on the rescaled trees to produce galaxy populations across new cosmological and astrophysical parameters at negligible additional cost. A novel halo-profile-based correction, controlled by a single free parameter, suppresses systematic bias in rescaled halo masses to below the per cent level. We apply the method to parameter estimation of $\Omega_{\rm m}$ and $\sigma_8$ given either the stellar mass function or the two-point correlation function, finding that as few as 64, and potentially fewer, base $N$-body simulations, rescaled to $\sim1000$ training samples, match the accuracy of 750 dedicated $N$-body simulations; rescaling to 3200 realisations improves the prediction of $\Omega_{\rm m}$ by $\sim25\%$. Rescaling all merger trees from a single CAMELS-SAM $N$-body simulation costs $\sim0.1$ CPUh, compared to several thousand CPUh to run the simulation itself. We demonstrate a practical route to obtaining predictions of galaxy summary statistics across cosmological and astrophysical parameters, even with a relatively small number of base $N$-body simulations.

Does DESI prefer Damped Oscillating Dark Energy over Cosmological constant?

Saddam Hussain, Simran Arora, Qiang Wu, Tao Zhu — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2606.17550v2 Announce Type: replace Abstract: We investigate a dark-energy equation of state governed by a damped harmonic oscillator equation, admitting underdamped, critically damped, and overdamped solutions. Confronting the model against Planck CMB, DESI BAO, BBN, Cosmic Chronometers, and three Type~Ia supernova compilations, we find that the underdamped solution yields $H_0 = 70.9 \pm 1.1$ km/s/Mpc, with DESY5 and $H_0 = 72.0^{+1.4}_{-2.1}$ km/s/Mpc with Union3, reducing the tension with SH0ES to $\sim\!1.5\sigma$, while Pantheon+ strongly favors a near-critically damped solution with positive $w_0$ and $H_0 = 66.23 \pm 0.85$ km/s/Mpc, revealing a significant systematic tension among supernova datasets. Bayesian evidence relative to $\Lambda$CDM is inconclusive for DES and Union3 data, demonstrating that $H_0$ tension alleviation is achievable at no statistical cost relative to the standard model.

Rapid Hubble constant inference from GW170817 using GPU-accelerated nested sampling: prior sensitivity and the limits of post-hoc reweighting

Ming Han Yang, Metha Prathaban, David Yallup, Will Handley — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2606.30504v2 Announce Type: replace Abstract: The bright-siren measurement of the Hubble constant from GW170817 (Abbott et al. 2017) assumes that switching from a volumetric to a uniform-in-$d_L$ luminosity-distance prior can be implemented by post-hoc reweighting of the baseline samples, rather than by re-running the inference under the target prior. Using a GPU-native heterodyned nested sampling pipeline that completes the full $n_{\rm live}=5000$ analysis in about 13 min on a single A100, we recompute the GW170817 $H_0$ posterior under four prior variants for the modern aligned-spin tidal waveform IMRPhenomXAS_NRTidalv3. Switching from the volumetric to a uniform-in-$d_L$ distance prior raises the high-tail probability $P(H_0>120\,\mathrm{km/s/Mpc})$ from 0.017 to 0.159 when imposed during sampling and shifts the weighted-median $H_0$ from 77.6 to 87.6 km/s/Mpc, while the binned MAP stays at 70.5 km/s/Mpc: both the tail and the bulk move under a change of prior that leaves the mode in place. Post-hoc reweighting of the baseline samples to the same target prior recovers only $P=0.041$ in the tail, approximately 17% of the directly sampled shift. The three prior variants that carry an independent nested sampling evidence agree to $\Delta\ln Z\lesssim 1.8$, so the data show at most a weak preference among the distance priors; the tail and bulk shifts are therefore properties of the prior, not a data update. Targeted mode-isolated runs reveal a $(d_L,\iota)$ bimodality whose high-$H_0$, low-$d_L$ branch (Mode B; $|\ln\mathcal{B}_{\rm B/A}|<1$) the volumetric prior assigns negligible mass: this is the mechanism behind the reweighting deficit. The reweighted posterior has a lower effective sample size than the baseline, independently flagging the coverage failure. The runtime budget makes full-sample prior-sensitivity reruns the default robustness tool for bright-siren cosmology, replacing post-hoc reweighting.

Synchrotron and free-free mapping with simulated REACH observations between 50-170 MHz

Daniel Robins, Dominic Anstey, Harry Bevins, Eloy de Lera Acedo, Melis O. Irfan — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.00299v2 Announce Type: replace Abstract: Global 21cm experiments aim to detect the hydrogen 21cm signal by separating it from foreground emission that can be orders of magnitude brighter than the signal. REACH (the Radio Experiment for the Analysis of Cosmic Hydrogen) forward-models the sky by jointly fitting signal and foreground spectral parameters to an existing sky map. The fitted parameters yield spectrally constrained, absolutely calibrated maps of the radio sky across the full 50-170 MHz observing band, among the lowest continuous frequencies yet mapped. We assess REACH's ability to fit the 21cm signal and recover accurate foreground maps, using physically motivated foreground models of increasing complexity (starting from a pure synchrotron power law model, then introducing variable amplitudes, curvature, and a free-free component). We evaluate these models against simulated REACH observations of correspondingly complex foregrounds, based on the Global Sky Model and the Python Sky Model. To recover the 21cm signal, more complex datasets require correspondingly complex models, but this introduces degeneracies which limit accurate recovery of foreground parameters. Fitting a foreground with independent synchrotron and free-free emission enables component-separated sky mapping, which has applications beyond radio cosmology; synchrotron is well-recovered across the sky, but free-free recovery is limited. REACH is therefore capable of probing Galactic physics at uniquely low frequencies, alongside its primary goal of detecting the 21cm signal.

Foreground Characterization and Mitigation in the Observations of the CD/EoR with the SKA

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2607.01048v2 Announce Type: replace Abstract: The Square Kilometre Array (SKA), with its unprecedented sensitivity, frequency coverage, and large collecting area, is poised to revolutionize our understanding of the Cosmic Dawn (CD) and Epoch of Reionization (EoR) epochs marking the formation of the first luminous sources and the subsequent reionization of the intergalactic medium (IGM). However, detecting the faint redshifted 21-cm signal from neutral hydrogen remains one of the foremost challenges in observational cosmology, as it is buried beneath bright foregrounds from Galactic synchrotron radiation, free-free emission, and extragalactic point sources that are 4-5 orders of magnitude stronger than the cosmological signal. In this chapter, we highlight the key components and characteristics of these foregrounds and review ongoing efforts to model, characterize, and mitigate them. We emphasize how the SKA-Low AA* configuration, through its optimized array design, wide field of view, and improved calibration accuracy, enhances our capacity to suppress foreground contamination and recover the cosmological signal. The SKA Observatory Foreground Challenge plays a pivotal role in this effort by bringing together the global EoR/CD community to develop, compare, and validate foreground removal pipelines using realistic simulated datasets. Building on the experience of existing pathfinders such as LOFAR, MWA, and HERA, these collaborative initiatives are helping refine statistical and machine learning-based approaches for signal recovery. Together, these advancements are laying the groundwork for the SKA to probe the thermal and ionization history of the early Universe with unprecedented precision.

Gravitational waves from first-order cosmological phase transitions: lifetime of the sound wave source

John Ellis, Marek Lewicki, Jos\'e Miguel No — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2003.07360v4 Announce Type: replace-cross Abstract: We survey systematically the general parametrisations of particle-physics models for a first-order phase transition in the early universe, including models with polynomial potentials both with and without barriers at zero temperature, and Coleman-Weinberg-like models with potentials that are classically scale-invariant. We distinguish three possibilities for the transition - detonations, deflagrations and hybrids - and consider sound waves and turbulent mechanisms for generating gravitational waves during the transitions in these models, checking in each case the requirement for successful percolation. We argue that in models without a zero-temperature barrier and in scale-invariant models the period during which sound waves generate gravitational waves lasts only for a fraction of a Hubble time after a generic first-order cosmological phase transition, whereas it may last longer in some models with a zero-temperature barrier that feature severe supercooling. We illustrate the implications of these results for future gravitational-wave experiments.

Gravitational Wave from Graviton Bremsstrahlung during Reheating

Basabendu Barman, Nicol\'as Bernal, Yong Xu, \'Oscar Zapata — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2301.11345v4 Announce Type: replace-cross Abstract: We revisit graviton production via Bremsstrahlung from the decay of the inflaton during inflationary reheating. Using two complementary computational techniques, we first show that such 3-body differential decay rates differ from previously reported results in the literature. We then compute the stochastic gravitational wave (GW) background that forms during the period of reheating, when the inflaton perturbatively decays with the radiative emission of gravitons. By computing the number of relativistic degrees of freedom in terms of $\Delta N_\text{eff}$, we constrain the resulting GW energy density from BBN and CMB. Finally, we project current and future GW detector sensitivities in probing such a stochastic GW background, which typically peaks in the GHz to THz ballpark, opening up the opportunity to be detected with microwave cavities and space-based GW detectors.

Gravitational Waves in Chern-Simons-Gauss-Bonnet Gravity

Tatsuya Daniel, Leah Jenks, Stephon Alexander — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2403.09373v2 Announce Type: replace-cross Abstract: It is known that the four-dimensional effective field theory arising from heterotic string theory is general relativity with both a Chern-Simons and Gauss-Bonnet term. We study the propagation of gravitational waves in this combination of Chern-Simons and Gauss-Bonnet gravity, both of which have an associated scalar field, the axion and the dilaton respectively, that are kinetically coupled. We review how the combination of dynamical Chern-Simons and Gauss-Bonnet gravities can arise from string theory as corrections to general relativity and show how the gravitational wave waveform is modified in such a theory. We compare our results to a novel framework recently introduced for parametrizing the parity-violating sector (Chern-Simons), and use that to guide our construction of a similar parametrization for the parity-conserving (Gauss-Bonnet) sector. In general, we find that the contributions from the parity-violating and parity-conserving sectors are similar. Moreover, the kinetic coupling between the axion and dilaton introduces an extra contribution to the parity-violating sector of the gravitational waves. Using our parametrization, we are able to comment on initial constraints for the theory parameters, including the time variations of the axion and dilaton.

The effective speed of sound in cosmological perturbation theory

Sanil Unnikrishnan — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2411.07045v2 Announce Type: replace-cross Abstract: In a multi-field/fluid cosmological system consisting of minimally coupled canonical scalar fields, non-canonical scalar fields, and barotropic perfect fluids, we introduce a new definition for the effective speed of sound of the entire system to describe the evolution of cosmological perturbations. This effective speed of sound is not only gauge-invariant but also a background-dependent quantity; it can, therefore, be treated as a parameter to quantify perturbations in such multi-field/fluid systems. It is with this effective speed that the gauge-invariant Bardeen potential and the curvature perturbation propagate at scales much smaller than the sound horizon. Furthermore, the effective speed of sound defined in this paper generalizes the one provided by Garriga and Mukhanov for a single non-canonical scalar field to a system consisting of multiple minimally coupled barotropic perfect fluids, canonical scalar fields, and non-canonical scalar fields. Moreover, as in the single pure-kinetic non-canonical scalar field case, this effective speed of sound for the total system equals the total adiabatic speed of sound when the dynamics are driven by multiple pure-kinetic non-canonical scalar fields. This makes such a system tantamount to a system of equivalent multi-barotropic perfect fluids. We also derive a set of equations governing the evolution of perturbations in a general multi-field/fluid universe. Using these equations, we demonstrate that in the large-scale limit ($k \to 0$), initially adiabatic perturbations remain adiabatic at those scales throughout the evolution, extending this well-known result to a general multi-field/fluid system containing non-canonical scalar fields. Consequently, at those scales, such a multi-field/fluid universe dynamically behaves as if it contains only a single barotropic perfect fluid.

Schwinger Current in de Sitter Space

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2503.01981v2 Announce Type: replace-cross Abstract: We study classical background electric fields and the Schwinger effect in de Sitter space. We show that having a constant electric field in de Sitter requires the photon to have a tachyonic mass proportional to the Hubble scale. This has physical implications for the induced Schwinger current which affect its IR behaviour. To study this we recompute the Schwinger current in de Sitter space for charged fermions and minimally coupled scalars imposing a physically consistent renormalization condition. We find a finite and positive Schwinger current even in the massless limit. This is in contrast to previous calculations in the literature which found a negative IR divergence. We also obtain the first result of the Schwinger current for a non-minimally coupled scalar, including for a conformally coupled scalar which we find has very similar behaviour to the fermion current. Our results may have physical implications for both magnetogenesis and inflationary dark matter production.

From particles to precision. Simulating subsonic turbulence with Smoothed Particle Hydrodynamics

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2503.10273v3 Announce Type: replace-cross Abstract: The numerical simulation of subsonic turbulence with smoothed particle hydrodynamics (SPH) has traditionally been hampered by zeroth-order (E0) errors, inaccurate gradient evaluations, and excessive numerical dissipation. We aim to investigate whether a modern SPH formulation can overcome these challenges by comparing its results to those obtained using moving-mesh and meshless finite-volume methods such as AREPO and GIZMO. For this purpose, we used SPH-EXA, a highly scalable, natively GPU-accelerated, state-of-the-art SPH code. Our results show that SPH-EXA accurately reproduces the Kolmogorov inertial range scaling in the subsonic regime with increasing resolution, closely matching the results of the reference methods. We also identify accurate grad-h terms as critical: a noisy standard implementation can imprint spurious granulation in the density field once dissipation is sufficiently reduced. These results demonstrate that, with appropriate methodological advances, SPH can achieve a level of fidelity in modeling subsonic turbulence comparable to the most advanced Eulerian and moving-mesh approaches.

Geometric formulation of $k$-essence and late-time acceleration

Lehel Csillag, Erik Jensko — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2505.15975v2 Announce Type: replace-cross Abstract: We study a class of geometries in which nonmetricity is fully determined by a vectorial degree of freedom and three independent coefficients. Formulating the simplest linear action in this geometry, implemented through Lagrange multipliers, naturally leads to an equivalence with the purely kinetic $k$-essence models with quadratic kinetic terms. A detailed dynamical systems analysis reveals that the $\Lambda$CDM phenomenology is embedded within the model. Crucially, we find that if stability conditions such as a positive sound speed squared and energy density are not enforced, the model generically exhibits instabilities and divergent behaviour in the phase space. These physical viability criteria allow us to isolate stable regions of the parameter space and derive well-motivated priors for parameter inference. Using Markov Chain Monte Carlo methods and late-time observational data, including cosmic chronometers, Pantheon$^{+}$ Type Ia supernovae, and DESI baryon acoustic oscillations, we constrain the degrees of freedom associated with nonmetricity and demonstrate the viability of the model. We discuss the implications of these results in light of the recent cosmic tensions, and give a possible explanation as to why the equivalent $k$-essence models have been missed as serious competitors to $\Lambda$CDM in the past. Finally, we review the geometric foundations of the theory and show that the integrable Weyl, Schr\"{o}dinger and completely symmetric geometries are embedded within our framework as special cases.

Distinguishing Monochromatic Signals in LISA and Taiji: Ultralight Dark Matter versus Gravitational Waves

Heng-Tao Xu, Yue-Hui Yao, Yong Tang, Yue-Liang Wu — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2506.09744v2 Announce Type: replace-cross Abstract: Ultralight dark matter (ULDM) is an attractive candidate for cold dark matter, one of the main mysterious components of the Universe. Recent studies suggest that gravitational-wave (GW) laser interferometers can also detect bosonic ULDM fields, which would produce monochromatic signals resembling those from gravitational waves (GWs). Distinguishing between these potential origins therefore would be essential. In this work, we develop a method to address this challenge for space-based GW interferometers (such as LISA and Taiji) by utilizing the null-response channel (NRC) in interferometric combinations, a channel constructed to have zero response to a specific type of source from a given direction. We find that while the GW NRC remains blind to GWs from a specific direction, it still responds to ULDM, particularly at frequencies above the interferometer's critical frequency. The ULDM NRC exhibits similar behavior. Based on these observations, we outline a test procedure to discriminate between signal origins. Our method provides a new diagnostic tool for analyzing monochromatic signals in space-based GW interferometers, potentially expanding the scientific scope of future missions.

Field theory vacuum and entropic dark energy models

Michael Maziashvili — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2507.22093v2 Announce Type: replace-cross Abstract: While in the standard quantization the energy spectrum of oscillator does not depend on its mass - for Planck length deformed quantization the energy spectrum becomes mass dependent. That means that the field oscillator masses will source a gravitational field through the Nullpunktsenergie as long as we follow this scheme of quantization. Admitting these masses are tangible, their gravitational effect will manifest itself even within the framework of standard field theory. We shall consider the possible gravitational implications based on this approach. If the mass scale for field oscillators is set by the inverse size of the box containing the field and three-momentum cutoff dictated by the black hole energy bound is exploited, one finds that the number of Fourier modes saturates the black hole entropy bound. Following certain "holographic" reasoning, one can derive various kinds of dark energy models that maybe interesting for further study.

Cogenesis of baryon and lepton number asymmetries matching the EMPRESS Data

Kyu Jung Bae, Arghyajit Datta, Rinku Maji, Wan-Il Park — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2509.13098v2 Announce Type: replace-cross Abstract: We show that a simple supersymmetric $U(1)_{B-L}$ extension of the standard model can explain simultaneously the large electron neutrino asymmetry hinted by the recent EMPRESS data as well as the observed tiny baryon asymmetry via the resonant leptogenesis mechanism. The condensation of $B-L$ Higgs dominating the universe at its decay is the sole source for these generation processes. Here, the infrequent decays of the $B-L$ Higgs to heavy right-handed neutrinos and successive prompt decays of these right-handed neutrinos around the electroweak phase transition produce the observed baryon asymmetry while the complete decay of the same $B-L$ Higgs at a later epoch leads to a large lepton number asymmetry. The right amounts of both asymmetries are found to be obtained for the symmetry breaking scale $v_\phi \sim 10^{10}~{\rm GeV}$. Moreover, in a close connection to the positivity of both asymmetries, seemingly only the normal mass hierarchy of light neutrino species works. Finally, the gravitational wave background from the topologically stable strong type-I cosmic strings, generated from the breaking of $U(1)_{B-L}$ symmetry, can be within the reach of future experiments such as ultimate DECIGO.

Dynamically generated tilt of isocurvature fluctuations

Saarik Kalia — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2510.11803v2 Announce Type: replace-cross Abstract: Light scalar fields acquire isocurvature fluctuations during inflation. While these fluctuations could lead to interesting observable signatures at small scales, they are strongly constrained on large scales by cosmic microwave background observations. When the mass of the scalar is much lighter than the inflationary Hubble scale, $m\ll H_I$, the spectrum of these fluctuations is flat. Meanwhile, if $m\gg H_I$, the fluctuations are suppressed. A blue-tilted isocurvature spectrum which exhibits enhanced structure on small scales but avoids observational constraints on large scales therefore requires a coincidence of scales $m\sim H_I$ for a free massive scalar. In this work, we show that if a scalar field possesses a nontrivial potential, its inflationary dynamics naturally cause this condition to be satisfied, and so a blue-tilted spectrum is generically expected for a large class of potentials. Specifically, if its potential $V$ exhibits a region which satisfies the slow-roll condition $V''<3H_I^2$, the scalar condensate will spend most of inflation close to the boundary of this region, so that its effective mass is typically close to $H_I$. The resulting blue tilt is inversely proportional to the number of $e$-folds of inflation prior to horizon crossing. If the scalar is long-lived, this mechanism leads to an attractor prediction for its relic abundance, which is insensitive to initial conditions of the scalar. In particular, a scalar field with quartic self-interactions can achieve the correct abundance to constitute all of the dark matter for a wide range of masses. We compute the relationship between the mass and self-coupling of quartic dark matter predicted by this mechanism.

Beyond general relativity: gravitational waves in non-minimally coupled theories

Stephon Alexander, Tatsuya Daniel, Tucker Manton — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2510.25895v2 Announce Type: replace-cross Abstract: Non-minimal couplings between matter and curvature tensors arise in many different contexts. Such couplings modify solutions of general relativity (GR) and therefore can be probed in various astrophysical systems. A particularly interesting scenario arises if dark matter experiences non-minimal couplings, as dark matter densities are expected to spike in the vicinity of binary black hole mergers. This gives a novel setting for simultaneously studying dark matter and (beyond) GR physics via observations of gravitational waves (GWs). In this work, we explore effects of various non-minimal couplings on GWs by working with a model-independent parameterization for left- and right-handed GW strains. We extend the parameterization proposed in \cite{Jenks:2023pmk,Daniel:2024lev} to include early-universe effects, and we write down the generic solution assuming slowly-varying matter fields. We then systematically apply our results to three models: Kalb-Ramond dark matter with dimension-four operators, axion-dilaton-Chern-Simons-Gauss-Bonnet dimension-five operators, and dimension-six couplings to a (dark) vector field.

From metallicity distributions to mutual information: A new perspective on stellar halo assembly

Amit Mondal, Biswajit Pandey — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2511.23452v2 Announce Type: replace-cross Abstract: The metallicity structure of stellar halos encodes the fossil record of galaxy assembly, tracing the chemical evolution and dynamical imprint of past mergers. Using five Milky Way-mass halos from the Aquarius simulations, we introduce an information-theoretic framework to quantify spatial-chemical correlations through the mutual information (MI) between angular position and metallicity. We divide stars in each halo into high- and low-metallicity populations based on their median metallicity and examine their metallicity distribution functions (MDFs), spatial anisotropies, and angular-metallicity couplings as a function of galactocentric radius. The MDFs exhibit remarkable diversity, ranging from single-peaked distributions dominated by one or two massive progenitors to broad or bimodal forms shaped by multiple accretion events, revealing the stochastic nature of halo assembly. The low-metallicity stars, primarily contributed by disrupted satellites, display higher spatial anisotropy and stronger angular clustering than their metal-rich counterparts. After removing bound satellites, anisotropy decreases significantly, yet high-metallicity stars remain marginally more anisotropic, reflecting the lingering debris of massive, centrally deposited progenitors. The mutual information between angular position and metallicity increases with radius before saturating in the outskirts, with the difference between the data and randomized controls confined mainly to the inner halo signifying residual spatial-chemical coupling driven by incomplete phase mixing. Our results demonstrate that information-theoretic diagnostics provide a powerful and intuitive way to quantify the chemical complexity of stellar halos and offer a promising route to compare simulations with forthcoming high-dimensional Galactic survey data.

Inflationary Particle Production and the Swampland

Dieter L\"ust, Joaquin Masias, Mauro Pieroni, Marco Scalisi — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2512.07930v2 Announce Type: replace-cross Abstract: We investigate the impact of particle production during inflation in scenarios where an infinite tower of states features a mass scale that decreases exponentially along the inflationary trajectory. Such couplings naturally arise in string effective field theories and are in fact motivated by the Swampland Distance Conjecture (SDC). We show that the corrections to inflationary observables sourced by the tower scale as $(H/\Lambda_{\text{sp}})^{2+p}$, with $H$ being the Hubble scale, $\Lambda_{\text{sp}}$ being the species scale, that is the quantum gravity cut-off, and $p\geq 1$ characterizes the density of states in the tower. As a result, in gravitationally weakly coupled cosmological effective theories, the tower-induced contributions are suppressed relative to the standard single-field predictions, leaving the inflationary phenomenology essentially unchanged. We demonstrate this explicitly across a set of well-motivated inflationary potentials, and we compare the resulting predictions with the most recent observational constraints, including those from the Atacama Cosmology Telescope.

Constraining Gravitational Dark Matter with LHAASO and Fermi-LAT

Basabendu Barman, Arindam Das, Prantik Sarmah, Rakesh Kumar SivaKumar — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2512.09997v2 Announce Type: replace-cross Abstract: We use diffuse Galactic high energy gamma ray data from LHAASO and Fermi-LAT to constrain gravitationally produced decaying dark matter (DM). Focusing on four benchmark candidates: a dark photon, a heavy right-handed neutrino (RHN), a pseudo-Nambu-Goldstone boson (pNGB), and a non-minimally coupled scalar we derive bounds on the DM mass and its couplings to the visible sector. For dark photons, RHNs, and pNGBs, the combined data constrain the relevant interaction strength to $\lesssim\mathcal{O}(10^{-30})$ for DM masses $\gtrsim\mathcal{O}$(TeV), while the non-minimally coupled scalar is limited to $\lesssim\mathcal{O}(10^{-10})$. Moreover, photon-dark photon oscillations yield strong constraints for massive dark photon beyond 10 GeV, closing a region of parameter space previously left unconstrained.

Parametric-Resonance Production of QCD Axions

Pirzada, Yu Gao, Qiaoli Yang — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2602.06922v2 Announce Type: replace-cross Abstract: Dark matter axion production can be significantly enhanced through a generic cosmological mechanism: primordial temperature fluctuations periodically modulate the axion mass during the QCD phase transition, thereby triggering parametric resonance in axion field evolution. This interplay between the resonance and the misalignment mechanism moves the predicted axion mass window for the observed dark matter abundance to $10^{-4}-10^{-3} \, \text{eV}$, shifting the preferred mass to previously unexplored higher ranges.

Evolution of Linear Perturbations under Time-Dependent Hubble Friction I: SR-USR-SR Inflation

Wen Li, Chao Chen — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2602.13074v2 Announce Type: replace-cross Abstract: The origin of the finite dip in the curvature power spectrum of instantaneous Slow-Roll (SR)-Ulta-Slow-Roll (USR)-SR inflation remains controversial at linear order, and its full spectral features still lack a complete asymptotic analytical description. We revisit linear perturbation dynamics in this framework. Using the junction method and asymptotic expansions of Hankel functions, we for the first time derive accurate and simple asymptotic expressions for mode evolution and the resulting power spectrum, based on three systematic rules for dominant-term identification across transitions. We find the finite dip arises from cancellation between two growing modes within linear perturbation theory, rather than between constant and growing terms as previously suggested. We also provide analytical descriptions of the amplitude enhancement and the two oscillatory patterns observed in the spectrum. All asypmtotic analytical results are validated by numerical calculations with the reconstructed SR-USR-SR inflationary potential.

Non-Minimal Dilaton Inflation from the Effective Gluodynamics

Pirzada, Imtiaz Khan, Mussawair Khan, Tianjun Li, Ali Muhammad — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2603.00818v2 Announce Type: replace-cross Abstract: We develop a nonminimal dilaton-inflation model in which the inflaton is the lightest scalar excitation of a hidden confining gauge theory. The Migdal--Shifman anomaly-matching action fixes a logarithmic contribution to the scalar potential, $V_{\rm MS}=A\varphi^4[\ln(\varphi/\mu)-1/4]$, with $(A,\mu)$ mapped to the scalar mass and vacuum condensate. Embedding this sector in the leading curved-space EFT introduces the independent Wilson coefficients $\lambda$ and $\xi$, and the resulting Einstein-frame dynamics yields a plateau with a calculable anomaly-induced deformation. We analyze the pure MS limit as a baseline, derive the $\mu$--$\lambda$ reparametrization, state finite-window RG-control conditions, and impose both the nonminimal-gravity cutoff and the intrinsic confining-sector gap. Exact slow-roll scans show that the viable regime combines the usual large-$\xi$ attractor behavior with a logarithmic imprint tied directly to nonperturbative trace-anomaly matching.

Particle-antiparticle perturbation superhorizon crossing: baryogenesis, leptogenesis, magnetogenesis and darkogenesis

She-Sheng Xue — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2603.27257v2 Announce Type: replace-cross Abstract: During the reheating epoch, gravitationally produced superheavy particle-antiparticle pairs undergo quantum oscillations. Perturbations in their relative densities cross out the horizon, leading to an asymmetry of particles and antiparticles inside the horizon. Massive particles decay into light baryons and leptons, thereby explaining baryogenesis and leptogenesis, whose charged components must generate a nontrivial electric current, thereby producing a primordial magnetic field (magnetogenesis). As a result, the baryon (lepton) number-to-entropy ratio and the primordial magnetic field bound are consistent with observational data. We also discuss darkogenesis, the origin of dark matter and anti-dark matter asymmetry.

Boltzmann Equation Solver for Thermalization

Jong-Hyun Yoon — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2603.28848v2 Announce Type: replace-cross Abstract: We present BEST (Boltzmann Equation Solver for Thermalization), a Python framework for solving the momentum-resolved Boltzmann equation for arbitrary $n_{\rm in} \to n_{\rm out}$ scattering processes. The collision integral is evaluated directly in $3(n_{\rm total}-2)$ dimensions using the VEGAS adaptive Monte Carlo algorithm with vectorized batch evaluation. Momentum conservation is enforced exactly by expressing one particle's momentum through the constraint, while energy conservation is imposed via a narrow Gaussian representation of the delta function. We identify a subtlety in the construction of the collision integral for processes with unequal initial and final multiplicities ($n_{\rm in} \neq n_{\rm out}$) involving identical particles: the full collision rate requires separate evaluation with the observed momentum pinned to each side of the reaction, weighted by the respective particle multiplicities. Failure to account for this leads to systematic violation of energy conservation. The code supports massive particles with time-dependent masses, Bose-Einstein and Fermi-Dirac quantum statistics, multiple coupled species, cosmological expansion with comoving momenta, and both Euler and Heun time integration. Parallelization is achieved by distributing independent momentum grid points across MPI ranks, yielding near-linear scaling to hundreds of cores. We validate the Monte Carlo results against a semi-analytical $2 \to 2$ collision integral with exact energy conservation, following the phase-space reduction of Ala-Mattinen et al. As a demonstration, we study thermalization of a massive scalar field through a $2 \leftrightarrow 3$ number-changing process and show that energy conservation is restored only when all identical-particle contributions are correctly summed. The code is publicly available at https://github.com/best-hep/best.

Big Bang revisited

Frans R. Klinkhamer — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2604.00077v4 Announce Type: replace-cross Abstract: The Friedmann cosmological solution of the standard Einstein gravitational field equation has a curvature singularity at a moment in time known as the Big Bang. It has been suggested that this Big Bang curvature singularity can be eliminated by use of a degenerate spacetime metric. This proposal was the main topic of our talk at the Workshop, but, here, we also discuss the possible appearance of CPT-conjugated worlds and the conjectured relevance of an extended version of Einstein's field equation.

ACT Data and Positive Running of the Spectral Index for Scalar Theory and Modified Gravity

S. D. Odintsov, V. K. Oikonomou — Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2605.17813v2 Announce Type: replace-cross Abstract: In this work we address the possibility of having a positive running of the spectral index in inflationary theories. The recent ACT data indicate mildly that the running of the spectral index might be positive, and several other physical indications point out this possibility. If the running of the spectral index is confirmed to be positive by future cosmic microwave background experiments, this can rule out quite popular inflationary scenarios. We investigate how it is possible to obtain a positive running of the spectral index in the context of minimally coupled scalar field gravity and modified gravity. For the modified gravity we choose two mainstream and of string origin candidate theories, $F(R)$ gravity and Einstein-Gauss-Bonnet gravity. In the case of scalar field inflation and $F(R)$ gravity inflation, we demonstrate the difficulties for obtaining a positive running of the spectral index for a viable inflationary regime, so scalar theories and $F(R)$ gravity are mostly compatible with the Planck data. But nuanced scalar field scenarios can be compatible with the ACT data and produce a positive running of the spectral index. In the context of Einstein-Gauss-Bonnet theories which are compatible with the GW170817 event, the running of the spectral index can easily be positive while in parallel having a viable inflationary era.

Baryonic mass budgets in the central regions of the Bullet Cluster and their consistency with strong lensing in MOND

Tue, 07 Jul 2026 00:00:00 -0400

arXiv:2606.19454v3 Announce Type: replace-cross Abstract: Strong lensing observations of the Bullet Cluster have traditionally been regarded as strong evidence for dark matter and a major challenge to Milgromian dynamics (MOND). The offset between the lensing mass and the X-ray gas centroids implies a substantial amount of unseen mass near the brightest cluster galaxies (BCGs). However, the high metallicities observed in both the intracluster gas and the massive early-type member galaxies suggest a past stellar population dominated by massive stars, whose evolved remnants contribute additional baryonic mass. This effect is naturally incorporated in the integrated galaxy-wide initial mass function (IGIMF) theory, which predicts substantially larger baryonic masses than a canonical IMF. In this work, we re-estimate the baryonic masses of the three BCG-centred core regions of the Bullet Cluster using recent JWST photometry and compare them with MOND strong-lensing masses. We derive IGIMF masses using stellar population synthesis models with constant and (self-) enriched metallicities, representing lower and upper mass limits, respectively. We find that the MOND strong-lensing masses of all three cores lie within the range predicted by the IGIMF models. These results suggest that the baryonic mass budget is consistent with MOND requirements from strong-lensing observations in the core regions of the Bullet Cluster. However, the physical viability of this scenario also depends on the spatial distribution and dynamical behavior of the remnant population, which remain to be established. More generally, regardless of the validity of MOND, the results imply that less dark matter may be required than previously inferred.