Predictions for the sky-averaged depth of the 21cm absorption signal at high redshift in cosmologies with and without non-baryonic cold dark matter

TL;DR

This paper predicts the sky-averaged 21cm absorption signal at high redshift, showing it could be twice as strong without dark matter, which could influence theories of gravity.

Contribution

It provides a comparative analysis of the 21cm absorption signal in cosmologies with and without non-baryonic cold dark matter, highlighting potential observational differences.

Findings

Absence of dark matter leads to approximately double the absorption signal.

Different universe expansion histories affect the expected 21cm signal.

Observation of the signal could challenge standard dark matter models.

Abstract

We consider the 21cm absorption signal expected at high redshift in cosmologies with and without non-baryonic cold dark matter. The expansion of the early universe decelerates strongly with dark matter, but approximately coasts without it. This results in a different path length across the epochs when absorption is expected, with the consequence that the absorption is predicted to be a factor of $\sim 2$ greater without dark matter than with it. Observation of such a signal would motivate consideration of extended theories of gravity in lieu of dark matter.