# Ruling out 3 keV warm dark matter using 21 cm-EDGES data

## TL;DR

This study constrains warm dark matter particles using 21 cm observations from cosmic dawn, ruling out particles with masses below 3 keV based on their inability to match the EDGES signal.

## Contribution

It provides new constraints on warm dark matter particle masses using high-redshift 21 cm data, extending limits beyond previous low-redshift methods.

## Key findings

- WDM models with mass ≤ 3 keV are ruled out by EDGES data.
- CDM and 5 keV WDM can fit observations with an excess radio background.
- Constraints extend the understanding of dark matter properties to earlier cosmic times.

## Abstract

Weakly interacting cold dark matter (CDM) particles, which are otherwise extremely successful in explaining various cosmological observations, exhibit a number of problems on small scales. One possible way of solving these problems is to invoke (so-called) warm dark matter (WDM) particles with masses $m_x \sim$ keV. Since the formation of structure is delayed in such WDM models, it is natural to expect that they can be constrained using observations related to the first stars, e.g., the 21 cm signal from cosmic dawn. In this work, we use a detailed galaxy formation model, Delphi, to calculate the 21 cm signal at high-redshifts and compare this to the recent EDGES observations. We find that while CDM and 5 keV WDM models can obtain a 21 cm signal within the observed redshift range, reproducing the amplitude of the observations requires the introduction of an excess radio background. On the other hand, WDM models with $m_x \leq 3$ keV can be ruled out since they are unable to match either the redshift range or the amplitude of the EDGES signal, irrespective of the parameters used. Comparable to values obtained from the low-redshift Lyman Alpha forest, our results extend constraints on the WDM particle to an era inaccessible by any other means; additional forthcoming 21 cm data from the era of cosmic dawn will be crucial in refining such constraints.