New Isocurvature Constraints from JWST UV Luminosity Function

TL;DR

This paper uses JWST UV luminosity function data combined with other cosmological observations to place new, model-agnostic constraints on primordial isocurvature perturbations across a broad range of scales.

Contribution

It provides the first UVLF-based, model-agnostic constraints on various types of primordial isocurvature perturbations, extending the understanding of structure formation.

Findings

Constructed 68% and 95% credible envelopes for isocurvature power in k-space.

Found constraints are largely insensitive to the assumed power-law form of the isocurvature spectrum.

Combined large- and small-scale data to improve isocurvature constraints.

Abstract

We constrain uncorrelated primordial isocurvature perturbations using a combination of large- and small-scale cosmological probes, with the small-scale data provided by the ultraviolet luminosity function (UVLF) -- a measure of number density of galaxies as a function of UV brightness. We consider several isocurvature modes, including cold dark matter, baryon, neutrino density, neutrino velocity, and dark radiation perturbations. The isocurvature power spectrum is modeled using two independent parameterizations: a broken power law and a running power law, without fixing the spectral index a priori. Our analysis combines large-scale data from the Cosmic Microwave Background (CMB), baryon acoustic oscillations, and Type Ia supernovae with small-scale constraints from UVLF measurements obtained by \textit{HST} and \textit{JWST}. The UVLF probes matter fluctuations over a continuous range of intermediate scales, $k \sim 0.5$--$10~\mathrm{Mpc}^{-1}$ over a wide range of redshift $4\lesssim z \lesssim 13$, providing a direct handle on structure formation in a regime where constraints on the scale dependence of isocurvature perturbations remain comparatively limited. Our result represents the first UVLF-based constraint on model-agnostic isocurvature perturbations carried by various components. We construct $68\%$ and $95\%$ credible envelopes in $k$-space for the allowed isocurvature power and find good agreement between the envelopes for the $95\%$ envelope across a wide range of scales, indicating that our constraints are mostly insensitive to the assumed power-law form.