Axion Dark Matter and Planck favor non-minimal couplings to gravity

TL;DR

This paper explores how non-minimal kinetic couplings of axions to gravity can reconcile QCD axion dark matter models with observational constraints, proposing a minimal early universe cosmology framework.

Contribution

It introduces non-minimal kinetic couplings as a novel approach to revive QCD axion dark matter models compatible with Planck data.

Findings

Non-minimal couplings prevent overproduction of isocurvature fluctuations.

Axions can account for observed dark matter density with these couplings.

A minimal cosmological model links axion and Higgs couplings.

Abstract

Constraints on inflationary scenarios and isocurvature perturbations have excluded the simplest and most generic models of dark matter based on QCD axions. Considering non-minimal kinetic couplings of scalar fields to gravity substantially changes this picture. The axion can account for the observed dark matter density avoiding the overproduction of isocurvature fluctuations. Finally, we show that assuming the same non-minimal kinetic coupling to the axion (dark matter) and to the standard model Higgs boson (inflaton) provides a minimal picture of early time cosmology.