A Lighter QCD Axion from Anarchy

TL;DR

The paper proposes the Anarchic Axion, a lighter QCD axion model that addresses the Strong CP problem, predicts a residual neutron EDM, and opens new experimental parameter space.

Contribution

It introduces a novel axion model with soft symmetry breaking, providing a new framework for axion searches and effective field theory targets.

Findings

Lighter axion consistent with nEDM constraints

Residual neutron electric dipole moment predicted

New parameter space for axion experiments

Abstract

We introduce the Anarchic Axion, a class of axion models which solves the Strong CP problem within current nEDM constraints with a lighter than usual QCD axion, thus populating new parameter space that ongoing and future experiments target. The Anarchic Axion is driven light by a soft breaking of the Peccei-Quinn symmetry, which also predicts a residual neutron electric dipole moment. We introduce a novel measure to quantify the tuning required for large deviations from the usual QCD axion band. In addition to motivating searches for unusually light axions, this work establishes a new target for axion effective field theory.