Axion dark matter and the 21-cm signal

Understand

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.