Cosmic Axion Bose-Einstein Condensation

TL;DR

This paper demonstrates that cold axions, a candidate for dark matter, thermalize through gravity and form a Bose-Einstein condensate, leading to observable differences from other dark matter models.

Contribution

It reveals that gravitational self-interactions cause axions to thermalize and condense, a novel insight into axion dark matter behavior.

Findings

Axions thermalize via gravitational interactions.

Axions form a Bose-Einstein condensate.

Dark matter behavior differs from other models.

Abstract

QCD axions are a well-motivated candidate for cold dark matter. Cold axions are produced in the early universe by vacuum realignment, axion string decay and axion domain wall decay. We show that cold axions thermalize via their gravitational self-interactions, and form a Bose-Einstein condensate. As a result, axion dark matter behaves differently from the other proposed forms of dark matter. The differences are observable.