Constraining Baryon--Dark Matter Scattering with the Cosmic Dawn 21-cm
  Signal
  The recent detection of an anomalously strong 21-cm signal of neutral
hydrogen from Cosmic Dawn by the EDGES Low-Band radio experiment can be
explained if cold dark matter particles scattered off the baryons draining
excess energy from the gas. In this Letter we explore the expanded range of the
21-cm signal that is opened up by this interaction, varying the astrophysical
parameters as well as the properties of dark matter particles in the widest
possible range. We identify models consistent with current data by comparing to
both the detection in the Low-Band and the upper limits from the EDGES
High-Band antenna. We find that consistent models predict a 21-cm fluctuation
during Cosmic Dawn that is between 3 and 30 times larger than the largest
previously expected without dark matter scattering. The expected power spectrum
exhibits strong Baryon Acoustic Oscillations imprinted by the
velocity-dependent cross-section. The latter signature is a smoking gun of the
velocity-dependent scattering and could be used by interferometers to verify
the dark matter explanation of the EDGES detection.
