QCD axion from broken scale symmetry

TL;DR

This paper proposes that the dilaton, arising from broken scale symmetry, can serve as a QCD axion candidate, satisfying cosmological and theoretical conditions for a consistent axion model.

Contribution

It introduces a novel axion model where the dilaton acts as the axion, addressing key cosmological and theoretical constraints.

Findings

Dilaton can function as a QCD axion candidate.

The model satisfies conditions for domain-wall collapse.

Effective field theory remains valid above inflationary scales.

Abstract

A consistent non-compact axion cosmology requires a non-periodic field, an effective field theory valid sufficiently above the inflationary scale, and a small non-QCD contribution to the potential that tilts the axionic vacuum landscape in order to trigger a timely domain-wall collapse. All conditions can be met by the dilaton -- the pseudo-Nambu-Goldstone boson of spontaneously broken approximate scale invariance.