Evaporating Axion Dark Matter and the Hubble Constant

TL;DR

This paper explores how evaporating axion-like particle dark matter, interacting with dark radiation, can increase early universe energy density and potentially resolve the Hubble tension.

Contribution

It introduces a mechanism where axion condensates lose energy via dark radiation, providing a novel approach to addressing the Hubble tension.

Findings

Axion condensates can transfer energy to dark radiation.

This process increases early universe energy density.

Potential to resolve the Hubble tension.

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.