Two-component millicharged dark matter and the EDGES 21cm signal

TL;DR

This paper proposes a two-component dark matter model with a long-lived heavier component decaying into a millicharged lighter component, explaining the EDGES 21cm signal while evading multiple experimental constraints.

Contribution

It introduces a novel two-component dark matter framework with specific decay properties to account for the EDGES 21cm anomaly, overcoming limitations of minimal models.

Findings

The model can explain the EDGES 21cm signal.

It remains consistent with CMB, underground detection, and XQC constraints.

The heavier dark matter's lifetime exceeds 0.1 times the age of the universe.

Abstract

We propose a two-component dark matter explanation to the EDGES 21 cm anomalous signal. The heavier dark matter component is long-lived whose decay is primarily responsible for the relic abundance of the lighter dark matter which is millicharged. To evade the constraints from CMB, underground dark matter direct detection, and XQC experiments, the lifetime of the heavier dark matter has to be larger than $0.1\, \tau_U$, where $\tau_U$ is the age of the universe. Our model provides a viable realization of the millicharged dark matter model to explain the EDGES 21 cm, since the minimal model in which the relic density is generated via thermal freeze-out is ruled out by various constraints.