Probing Compensated Isocurvature with the 21-cm Signal during Cosmic Dawn

TL;DR

This paper explores how upcoming 21-cm hydrogen line observations during cosmic dawn can detect or constrain compensated isocurvature perturbations, offering a new way to probe early universe cosmology.

Contribution

It evaluates the potential of HERA and SKA1-low experiments to detect CIPs, showing they can achieve sensitivities comparable or superior to other cosmological probes.

Findings

HERA and SKA1-low can constrain uncorrelated CIPs at levels of 10^{-3} to 10^{-4}.

Constraints are comparable to future CMB experiments.

Potential to surpass cosmic-variance limited BAO survey sensitivities.

Abstract

Upcoming measurements of the 21-cm line of neutral hydrogen will open a new observational window into the early stages of structure growth, providing a unique opportunity for probing large-scale cosmological signatures using the small-scale signals from the first stars. In this paper we evaluate the detection significance of compensated isocurvature perturbations (CIPs) from observations of the 21-cm hydrogen-line during the cosmic-dawn era. CIPs are modulations of the relative baryon and dark-matter density that leave the total matter density unchanged. We find that, under different assumptions for feedback and foregrounds, the ongoing HERA and upcoming SKA1-low experiments will provide constraints on uncorrelated CIPs at the level of $\sigma(A_{\rm CIP})= 10^{-3}-10^{-4}$, comparable to the sensitivity of upcoming CMB experiments, and potentially exceeding the constraints from cosmic-variance limited BAO surveys.