Axion global fits with Peccei-Quinn symmetry breaking before inflation using GAMBIT

TL;DR

This paper performs comprehensive global fits of axion models considering cosmological and astrophysical data, focusing on the pre-inflationary Peccei-Quinn symmetry breaking scenario, to constrain axion properties and their role in dark matter.

Contribution

It provides the first detailed Bayesian and frequentist analysis of axion models with pre-inflationary symmetry breaking, incorporating diverse experimental and observational constraints.

Findings

Identifies credible parameter regions for QCD axions consistent with dark matter and cooling hints.

Sets bounds on axion mass based on combined likelihood analyses.

Suggests QCD axions are likely a sub-dominant component of dark matter.

Abstract

We present global fits of cosmologically stable axion-like particle and QCD axion models in the mass range 0.1 neV to 10 eV. We focus on the case where the Peccei-Quinn symmetry is broken before the end of inflation, such that the initial value of the axion field can be considered to be homogeneous throughout the visible Universe. We include detailed likelihood functions from light-shining-through-wall experiments, haloscopes, helioscopes, the axion relic density, horizontal branch stars, supernova 1987A, white dwarf cooling, and gamma-ray observations. We carry out both frequentist and Bayesian analyses, with and without the inclusion of white dwarf cooling. We explore the degree of fine-tuning present in different models and identify parameter regions where it is possible for QCD axion models to account for both the dark matter in the Universe and the cooling hints, comparing them to specific DFSZ- and KSVZ-type models. We find the most credible parameter regions, allowing us to set (prior-dependent) upper and lower bounds on the axion mass. Our analysis also suggests that QCD axions in this scenario most probably make up a non-negligible but sub-dominant component of the dark matter in the Universe.