# A detailed exploration of the EDGES 21 cm absorption anomaly and axion-induced cooling

## TL;DR

This paper investigates how axion-like particles could explain the EDGES 21 cm absorption anomaly through cooling of cosmic hydrogen, proposing a testable dark matter scenario involving Bose-Einstein condensates.

## Contribution

It provides a detailed analysis of axion-induced cooling mechanisms and computational insights supporting axions as a solution to the EDGES anomaly within standard models.

## Key findings

- Axion-like particles in the (6, 400) meV range can explain the EDGES signal.
- Axions can form Bose-Einstein condensates that produce observable cosmological effects.
- Future experiments like IAXO and EUCLID can test this axion-based explanation.

## Abstract

The EDGES collaboration's observation of an anomalously strong 21 cm absorption feature around the cosmic dawn era has energised the cosmological community by suggesting a novel signature of dark matter in the cooling of cosmic hydrogen. In a recent letter we have argued that by virtue of the ability to mediate cooling processes whilst in the condensed phase, a small amount of axion dark matter can explain these observations within the context of standard models of axions and axion-like particles. These axions and axion-like particles (ALPs) can thermalize through gravitational self-interactions and so eventually form a Bose-Einstein condensate (BEC), whereupon large-scale long-range correlation can produce experimentally observable signals such as these. In this context the EDGES best-fit result favours an axion-like-particle mass in the (6, 400) meV range. Future experiments and galaxy surveys, particularly the International Axion Observatory (IAXO) and EUCLID, should have the capability to directly test this scenario. In this paper, we will explore this mechanism in detail and give more thorough computational details of certain key points.