QCD axions and axionlike particles in a two-inflation scenario

TL;DR

This paper explores how a two-inflation scenario affects the behavior and density of QCD axions and axionlike particles, revealing potential for increased axion energy density and expanded parameter space.

Contribution

It provides a detailed analysis of axion field evolution after two inflationary periods, including numerical and analytical methods for dilution effects.

Findings

Dilution of axion energy density is possible in a two-inflation scenario.

Small increases in QCD axion energy density are feasible.

The parameter space for axion decay constant $f_A$ can be expanded.

Abstract

We investigate the phenomenology of QCD axions and axionlike particles in a scenario with two eras of inflation. In particular, we describe the possible solutions for the QCD axion field equation after the second inflation and reheating. We calculate the dilution numerically for QCD axions and give an analytic approximation for axionlike particles. While it has been realised before that such a scenario can dilute the axion energy density and open up the parameter space for the axion decay constant $f_A$, we find that even a small increase in the relative QCD axion energy density is possible.