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