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