Evaporating Axion Dark Matter and the Hubble Constant

Abstract

Axion-like particles are a well-motivated dark matter candidate that can form a condensate with low momentum and high occupation number. In the presence of dark radiation, this condensate loses energy, naturally increasing the energy density of the universe around matter-radiation equality without requiring additional inputs. This general mechanism may offer a solution to the Hubble tension.

Comments: 11 pages, 8 figures