Axion dark matter and the 21-cm signal
  It was shown in ref. [1] that cold dark matter axions reach thermal contact
with baryons, and therefore cool them, shortly after the axions thermalize
among themselves and form a Bose-Einstein condensate. The recent observation by
the EDGES collaboration of a baryon temperature at cosmic dawn lower than
expected under "standard" assumptions is interpreted as new evidence that the
dark matter is axions, at least in part. Baryon cooling by dark matter axions
is found to be consistent with the observation of baryon acoustic oscillations.
