Contributions of dark matter annihilation to the global 21cm spectrum
  observed by the EDGES experiment
  The EDGES experiment has observed an absorption feature in the global 21 cm
spectrum with a surprisingly large amplitude. These results can be explained by
decreasing the kinetic temperature of baryons, which could be achieved through
the scattering between the baryons and cold dark matter particles. It seems
that the most researched dark matter annihilation model is not able to explain
such a large amplitude, since the interactions between the particles produced
by the dark matter annihilation and the particles that have been present in the
Universe could increase the baryonic temperature. Recently, C. Feng and G.
Holder have suggested that the large amplitude in the global 21 cm spectrum
could be produced by considering the possible excess of the early radio
radiation. In this paper, we propose that the dark matter annihilation still
works to explain the large amplitude observed by the EDGES experiment. Even
including the dark matter annihilation, the large absorption amplitude in the
global 21 cm spectrum can be produced by considering the possible excess of the
early radio radiation.
