Altered Axion Abundance from a Dynamical Peccei-Quinn Scale

TL;DR

This paper proposes a model where a new light scalar modifies the axion relic abundance by making the PQ scale dynamical, allowing for a wider range of axion dark matter masses and impacting search strategies.

Contribution

The authors introduce a dynamical PQ scale via a light scalar, altering axion abundance predictions beyond the standard misalignment mechanism.

Findings

Can accommodate lighter axion dark matter

Can also produce heavier axion dark matter

Impacts axion search strategies and fundamental physics

Abstract

We build a model in which the relic abundance of axions is altered from the standard misalignment mechanism, either increased or decreased, due to the presence of a new light scalar that couples to the radial part of the Peccei-Quinn (PQ) field. The light scalar makes the effective PQ symmetry-breaking scale dynamical, altering the early-time dynamics for the axion and affecting its late-time dark matter abundance. We analyze this new mechanism semianalytically and numerically, showing that we can accommodate both lighter or heavier axion dark matter, compared to the standard treatments. We discuss implications of the model for axion searches and fundamental physics.