Axion dark matter and the 21-cm signal

TL;DR

This paper discusses how axion dark matter could cool baryons at cosmic dawn, potentially explaining the EDGES 21-cm signal anomaly, and explores the consistency of this hypothesis with other cosmological observations.

Contribution

It proposes that axion dark matter can cool baryons via thermal contact, providing a novel explanation for the EDGES 21-cm signal anomaly.

Findings

Axion dark matter can cool baryons at cosmic dawn.

Baryon cooling by axions is consistent with baryon acoustic oscillations.

Supports axions as a partial component of dark matter.

Abstract

It was shown in ref. [1] that cold dark matter axions reach thermal contact with baryons, and therefore cool them, shortly after the axions thermalize among themselves and form a Bose-Einstein condensate. The recent observation by the EDGES collaboration of a baryon temperature at cosmic dawn lower than expected under "standard" assumptions is interpreted as new evidence that the dark matter is axions, at least in part. Baryon cooling by dark matter axions is found to be consistent with the observation of baryon acoustic oscillations.