Axion Kinetic Misalignment Mechanism

TL;DR

This paper introduces a novel axion dark matter production mechanism where a nonzero initial velocity of the axion field, generated by early universe symmetry breaking, allows for a lower decay constant than traditional models.

Contribution

It proposes the kinetic misalignment mechanism, expanding axion dark matter models by incorporating initial velocity, thus relaxing the decay constant constraints.

Findings

Enables axion decay constant below conventional limits.

Links axion velocity to early universe symmetry breaking.

Provides an alternative to the standard misalignment scenario.

Abstract

In the conventional misalignment mechanism, the axion field has a constant initial field value in the early universe and later begins to oscillate. We present an alternative scenario where the axion field has a nonzero initial velocity, allowing an axion decay constant much below the conventional prediction from axion dark matter. This axion velocity can be generated from explicit breaking of the axion shift symmetry in the early universe, which may occur as this symmetry is approximate.