Constraints on ALPs and excited dark matter from the EDGES 21-cm absorption signal

TL;DR

This paper uses the EDGES 21-cm absorption data to set new constraints on axion-like particles and excited dark matter, surpassing previous limits in certain energy ranges and challenging some dark matter explanations for the 3.5 keV line.

Contribution

It provides novel bounds on ALPs and excited dark matter properties based on 21-cm observations, improving upon existing constraints in specific energy ranges.

Findings

New bounds on ALPs and excited dark matter from 21-cm data

Excludes dark matter explanations for the 3.5 keV line at 95% confidence

Constraints outperform previous limits for energy injections between 10.2 eV and 50 keV

Abstract

The recent observation of the 21-cm absorption signal by the EDGES experiment provides a new observational window into the dynamics of the young Universe. Based on this result, we constrain the properties of ALPs and excited dark matter via the energy injections into the gaseous medium that these models produce. In particular, we derive bounds that outperform the present constraints for energy injections in the 10.2 eV to 50 keV range by analysing the intensity of Lyman-$\alpha$ photons and the electron emissivity produced by ionising radiation. Our results also show that once the standard temperature of the soft radiation background is assumed, the explanations of the observed 3.5 keV photon signal within the considered dark matter model are excluded at 95\% confidence level.