Astrophysics Papers

ALT The dispersion measures (DMs) of fast radio bursts (FRBs) trace ionised baryons along the line of sight, probing baryonic feedback. Two complementary observables can be constructed from an FRB catalogue: the DM-redshift (Macquart) relation of host-identified FRBs, and the angular power spectrum of the DM field of the full catalogue. Their joint analysis requires their cross-covariance. We derive it within the halo model and show it is a super-sample effect: only the monopole of an individual DM correlates with the angular power spectrum, yielding an exact, model-independent bound on the correlation coefficient. We validate the calculation against log-normal forward simulations of 10⁴ FRBs. For individual DMs, the correlation with the bandpowers is at the per cent level. Neglecting the cross-covariance changes the width of the χ² distribution by only 0.8 per cent, so the two observables can be treated as effectively independent for wide-area surveys. In a joint forecast with an LSST-lik

ALT The vast majority of cosmological simulations employ periodic boundary conditions to achieve statistical homogeneity and to mimic the infinite spatial extent of our Universe. In a cubic periodic domain the Green function breaks full rotational invariance and introduces a geometry-induced anisotropy in the gravitational interaction. We quantify how this intrinsic anisotropy affects cosmic structure growth and investigate the extent to which it biases the commonly used large-scale structure and halo-based observables in dark-matter-only simulations. We analyse an ensemble of 498 cosmological dark-matter-only N-body simulations in cubic T³ topological manifolds, evolved to z=0, spanning box sizes from L=6.25 Mpc to L=100 Mpc at fixed mass and force resolution. We compare anisotropy-sensitive statistics across the suite, including the matter power spectrum, halo abundance, merger histories, shapes and alignments, and filament orientations. Finite periodic boundaries imprint orientation-dep

ALT We present a multi-probe observational analysis of a clustering tachyonic Dirac-Born-Infeld (DBI) dark energy model. Its noncanonical kinetic term gives a subluminal sound speed, so dark energy perturbations can grow on subhorizon scales. Working in a multifluid framework that tracks both the background expansion and linear perturbations, we constrain the model with nested sampling, using Planck 2018 compressed CMB distance priors, DESI DR2 BAO, cosmic chronometers, fσ₈ growth data, and three Type Ia supernova compilations: Pantheon+, DES-SN5YR, and Union3. The standard cosmological parameters agree with ΛCDM within 2σ, with DBI preferring a slightly lower H₀ and higher Ωₘ₀, with the largest shift being ≃1.8σ in H₀ for Pantheon+. The Bayesian evidence favours DBI in every compilation, moderately for Pantheon+ (ΔlnZ≃3.4) and inconclusively for DES-SN5YR and Union3 (ΔlnZ≃0.6-0.7). The field thaws naturally. Dark energy perturbations stay several orders of magnitude below matter perturbat

ALT Flexion, the second-order gravitational lensing distortion, probes small-scale mass distribution and complement the cosmic shear measurement. However, its detection is highly challenging due to the faint signal and the contamination arising from the intrinsic galaxy morphology. In this Letter, we present GradFlex, a new method that extracts flexion from the gradient field of galaxy surface brightness distributions without assuming a specific point-spread function model or galaxy morphology. Using surface-brightness conservation, we relate the pre- and post-lensing gradient fields and derive flexion estimators from ensemble-averaged statistics of the corresponding spins. Tests on numerical simulations across diverse galaxy morphologies and multiple noise realizations demonstrate its reliability under realistic observing conditions. Combined with shear measurements, it could tighten constraints on cluster density profiles and enable more detailed studies of substructure than shear alone.

ALT Karchev et al. (2026) derived a value of H0 by combining the ZTF SN Ia DR2 sample with SH0ES calibrator Type Ia supernovae (SNe Ia; Riess et al. 2022), used to anchor the SN Ia absolute luminosity. The ZTF SN Ia DR2 dataset (Rigault et al., 2025) is the largest (O(3000)) SN Ia sample to date obtained with a single telescope. However, as emphasized in the data release, the absolute photometric calibration of the survey has not yet been established to the precision required for cosmological inference. The relative photometric zeropoint offset between the SH0ES and ZTF SN Ia DR2 samples, which is fully degenerate with H0, is therefore unknown and cannot be determined from publicly available data. The photometric corrections introduced in Karchev et al. (2026) do not address this global calibration offset. Consequently, their reported H0 determination is not supported by the available calibration information. We nonetheless share the excitement of pursuing state-of-the-art cosmology with Z

ALT We investigate the cosmological implications of supermassive primordial black holes (PBHs) as a component of dark matter (DM), focusing on their seed effect on large-scale structure formation. In contrast to the Poisson effect associated with the discrete distribution of PBHs, the seed effect arises because PBHs act as early gravitational seeds, accreting surrounding DM and developing dense DM spikes to form dressed PBHs. These structures enhance the matter power spectrum, particularly on small scales. We model their contribution within the halo-model framework under two prescriptions for DM accretion: an optimistic scenario (Case 1) and a conservative scenario (Case 2), which predict different modifications to the 1-halo term. We constrain the PBH abundance using weak-lensing measurements from the Dark Energy Survey Year 3 (DES Y3), performing a Markov Chain Monte Carlo analysis to derive upper limits on the PBH fraction f_PBH, as a function of the PBH mass M_PBH. We find that weak le

ALT The total mass distribution of galaxies provides a sensitive probe of the fundamental physical processes governing galaxy evolution, including gas inflow/star formation, AGN/SN feedback, galaxy merging, and the nature of dark matter. State-of-the-art cosmological simulations have therefore made extensive predictions for the evolution of the total-mass density slope. Interestingly, their predictions diverge significantly at high redshift, primarily due to differences in how these key physical mechanisms are implemented. However, measurements of the total-mass structure evolution have been largely confined to low and intermediate redshifts, leaving the regime where model predictions differ most significantly (z>0.8) largely unexplored. In the first paper of this series, we reported the discovery of 84 candidate strong-lens systems with lens redshifts above 0.8. In this work, we perform lens modeling of the 80 galaxy-scale systems to assess their lensing nature. Of these, 71 systems (appr

ALT We develop an algebraic classification of canonical single-field inflationary dynamics using an exact depressed cubic equation for the inflaton velocity. Its root structure identifies a branch-swap boundary distinct from the limiting boundary of downhill motion, where ultra-slow-roll inflation naturally emerges. Independently, the conservation of momentum conjugate to the comoving curvature perturbation in the long-wavelength limit provides a criterion for the growth or decay of the gauge-invariant difference between comoving and uniform-density curvature perturbations. Combining these criteria, we construct a unified dynamical chart in terms of the Hubble and potential slow-roll parameters, illustrating its applicability to constant-roll inflation and simple toy models. Our classification shifts the emphasis from assigning models to fixed categories toward understanding the dynamical regimes traversed by inflationary trajectories and their implications for primordial perturbations.

ALT We demonstrate a viable fit to current cosmological data from a simple Horndeski modified gravity theory that softly breaks shift symmetry. This SBSS model crosses the phantom divide w=-1 at z≈0.5 and fits observational data (baryon acoustic oscillations and supernova distances, and cosmic microwave background power spectra) better than w₀wₐCDM, by Δχ²≈-3 for the same number of effective parameters, while providing a physical foundation for cosmic acceleration. The theory is healthy, has no cosmological constant or potential, and has substantial protection against high energy quantum loop corrections.

ALT Dynamical dark energy models are often difficult to constrain with background observations alone due to parameter degeneracies. This is especially true when the dark energy sector evolves through an effective pressureless matter phase, leading to degeneracies between the model parameters and the matter density parameter. In this work, we show that redshift-space distortion (RSD) measurements help break this degeneracy when combined with expansion history probes including Pantheon⁺ supernovae and DESI DR2 BAO measurements. We demonstrate this in the ghost and dilatonic ghost condensate k-essence models, restricting the observational analysis to physically admissible solutions by imposing the absence of ghosts and gradient instabilities. Given the small scalar sound speeds in these models, we also explicitly check the validity of the quasi-static approximation used in the growth analysis. Our results show that combining growth-rate data with stability requirements and standard background

ALT Our Universe serves as a complementary laboratory for particle physics interactions. One intriguing possibility is that neutrinos may have beyond-the-Standard-Model (BSM) self-interactions, which can delay their free streaming and have an observable effect across different redshifts. Such interactions can induce scale-dependent changes in the matter power spectrum. The James Webb Space Telescope (JWST) has opened up a new window onto the early Universe by discovering a large population of high-redshift galaxies up to z ∼ 15 and various probable galaxy candidates at even higher redshifts, between z ∼ 15-30. Such high-redshift observations can probe the matter power spectrum on small scales, since structure formation is hierarchical and the structures hosting these high-redshift galaxies are therefore expected to be small. We, for the first time, use the UV luminosity function data from JWST and combine them with the Planck CMB data to probe neutrino self-interactions (νSI). If only one

ALT Reheating is a crucial phase that connects inflation with the hot Big Bang Universe. During this phase, the nonlinear interactions among the inflaton, the radiation plasma, and the primordial magnetic fields can influence the subsequent evolution of cosmic structures we observe today. In this paper, we develop a multifluid framework to investigate the evolution of three dimensional nonlinear magnetohydrodynamics (MHD) during the non instantaneous reheating phase driven by the perturbative decay of the inflaton into the radiation plasma. For the present paper, we consider the simplest scenario where the inflaton field homogeneously injects energy into the radiation sector. We study the MHD evolution of the coupled inflaton radiation system during the reheating phase, including the evolution of their individual kinetic energies, the velocity perturbations, vorticity, magnetic fields, and gravitational waves. We find that homogeneous energy transfer from the inflaton to the radiation sect

ALT We provide a description of general Newtonian cosmologies for collisionless matter in terms of an exact and dynamical volume partitioning of global realizations of Newtonian models. Employing the formalism for the description of cosmological backreaction, an interaction between the inhomogeneities of the formation of structures in the Universe and their average properties can be analyzed. Our results can be regarded as a tool for many potential applications in the context of Newtonian simulations, but they also provide an exact way to assume analytical properties of the universe models on regional scales in conformity with global integral constraints on their average properties. We discuss approaches in relation to `separate Universe conjectures' in the literature and examine their consistency with the exact partitioning framework. In particular, using the Average Expansion Rate Approximation (AvERA) as an example, we show that identifying locally assigned Friedmannian rates with physi

ALT The age of the cosmic neutrino is upon us. Aside from their fundamental importance to particle physics and the recent tensions in their mass scale Mν = ∑ mν, neutrinos' degeneracies with other cosmological parameters in analyses of scale-dependent cosmic clustering will significantly affect the estimates of these parameters, making accurate, inexpensive, easily-implemented approximations essential tools for theoretical cosmology. We present a new linear approximation, SE-EdS, applicable to non-relativistic neutrinos and other hot dark matter, which is exact in the linear Einstein-de Sitter case, and < 3% accurate for a broad range of flat and non-flat cosmologies characterized by parameters 0.2 ≤ Ωₘ,₀ ≤ 1, 0 ≤ Ων,₀ ≤ 0.018, -0.1 ≤ ΩK,0 ≤ 0.1, and w₀ ≤ -0.6, at all length scales. This broad coverage in Ωₘ,₀ makes SE-EdS ideal for N-body simulations, whose redshift range z ≲ 100 demands accuracy for time-dependent Ωₘ between unity and the preferred late-time values ∼ 0.3. SE-EdS may be u

ALT Unraveling the nature of the cosmic expansion, driven by Dark Energy (DE), remains one of the key challenges in modern cosmology. Modified Gravity (MG) models provide an alternative to the standard cosmological constant paradigm. These models predict distinct signatures in the growth of structure, yet analytical predictions are challenging due to the highly non–linear equations involved. To overcome this problem, we study MG as an effective DE fluid. To this end, we have incorporated linear DE perturbations into the N–body code CONCEPT, which relies on the Einstein–Boltzmann solver CLASS. We replaced the CLASS version used by CONCEPT with mochi_CLASS, a patched version that includes Horndeski family models. By writing linear DE perturbations (δρ_DE, δ P_DE, θ_DE, and σ_DE) in terms of metric perturbations in the synchronous gauge, the N–body code is able to evolve the effective fluid using the Boltzmann equation. Our current simulations encompass a range of cosmological scenarios —w₀wₐ

ALT We study inflation with an exponential factor multiplying the scalar Lagrangian and depending on the accumulated expansion history through a field-dependent coupling. Variation of the complete action on a finite interval yields an adjoint response with a final-time boundary condition. We derive the background and coupled scalar perturbation equations and examine five benchmarks for an exponential plateau potential and a smooth single-window coupling. The kinetic, direct-coupling and adjoint contributions nearly cancel, producing transient positive minima of the first Hubble slow-roll parameter, ∊₁, without a comparable reduction in field velocity. The scalar spectra, normalized to the cosmic microwave background (CMB) pivot amplitude, develop localized peaks with amplitudes 0.033–0.098. Under Gaussian statistics and the adopted radiation-era collapse prescription, the the primordial black hole (PBH) abundance peaks span masses from 4.52×10⁻¹³ to 34.05 M⊙. The lightest-mass benchmark re

ALT Wide-area cluster catalogues from Stage-IV surveys will substantially improve the precision of cluster clustering measurements, making the control of observational systematic effects essential for cosmological inference. In preparation for the first Euclid data release (DR1), we assess the impact of the survey mask and non-homogeneous sky coverage on the two-point correlation function of galaxy clusters and its covariance. Using DR1-like lightcone mocks, we confirm that the irregular footprint does not introduce appreciable changes in the two-point correlation function when the same mask is applied to the random catalogue. We also find that spatial inhomogeneities, implemented as variations of the cluster selection function in different patches of the sky, do not significantly bias the clustering amplitude, up to levels of variation well above those expected for DR1. When the degree of inhomogeneity is increased to the regime where the effect becomes significant, we show that its ampli

ALT The abundance of compact objects ranging from stellar to intermediate masses (∼ 1 - 10⁵M⊙) remains poorly constrained, particularly for populations such as primordial black holes and dark matter subhalos that emit little or no electromagnetic radiation. Gravitational-wave (GW) microlensing provides a complementary way to probe these populations through wave-optics effects imprinted on the GW signals, with implications for astrophysical and cosmological inference. We develop a hierarchical Bayesian framework to infer the population properties of microlenses from an ensemble of microlensed GW events, constraining the slope of the power-law lens mass function (αₘₗ), the lens number density (n₀), and the fraction of dark matter in compact lenses (f_DM). Using simulated microlensed GW signals drawn from a realistic binary black hole population, we find that ∼ 100 detected microlensed events are able to constrain both αₘₗ and n₀, although a degeneracy between the two remains. For a low-mass-

ALT The remnants of binary black-hole (BBH) mergers are accurately described by numerical relativity, but the physical principle governing the selection of the final states remains unclear. A recently proposed maximum-entropy conjecture suggests that a BBH merger produces the Kerr BH that maximizes the Bekenstein-Hawking entropy, subject to the post-Newtonian formalism or balance laws for energy and angular momentum. In this work, we test this conjecture with the event GW250114, inferring the progenitor and remnant properties from the observed pre-merge and post-merge signals, separately. We construct the surrogate Kerr entropy associated with candidate remnant states along the inferred energy-angular-momentum trajectory. We then compare the maximum-entropy state with the independently inferred mass and dimensionless spin of the final BH. We find that the conjecture predicts a remnant mass of Mf=70.0⁺⁰.³⁵₋₀.₂₁ M⊙ and spin of χf=0.70⁺⁰.⁰⁰₋₀.₀₁, compared with the ringdown estimates Mf=72.3⁺³

ALT We present PrimordialPy, an open-source Python library designed to compute the cosmological predictions of arbitrary canonical single-field inflationary models. By numerically solving the background dynamics and the curvature perturbation equation, the package evaluates the primordial power spectrum of scalar and tensor perturbations at all relevant scales. Furthermore, it automatically computes the resulting mass fraction and abundance of Primordial Black Holes (PBHs), as well as the associated spectrum of scalar-induced gravitational waves (SIGWs). Users can seamlessly implement any canonical single-field model by simply specifying the inflaton potential V(φ) and its parameters. Designed to be modular, efficient, and highly accessible, PrimordialPy comes with comprehensive documentation, validation benchmarks, and practical examples, making it a versatile tool for both research and education in early-universe cosmology.