Axion Window on New Macroscopic Forces

TL;DR

This paper explores how certain CP-violating mechanisms can relax EDM constraints, expanding the viable parameter space for axion-mediated forces and guiding future experimental searches for scalar axion couplings.

Contribution

It identifies mechanisms that relax EDM constraints, significantly enlarging the QCD axion window for axion-mediated force experiments.

Findings

Relaxation of EDM constraints broadens axion parameter space.

Enhanced prospects for detecting axion-mediated forces.

Guidance for future experimental searches.

Abstract

Axion-mediated forces are enhanced by the presence of CP-violating axion couplings, which are however tightly constrained by electric dipole moment (EDM) searches. We discuss the underlying hypotheses behind different sources of CP violation at high energies and the interplay between axion-mediated force experiments and EDM observables. Specifically, we identify various mechanisms, based on new sources of CP violation or Peccei-Quinn symmetry breaking, that can significantly relax EDM constraints, leading to a substantial redefinition of the QCD axion window for axion-mediated forces. By considerably enlarging the QCD axion parameter space, our results provide a well-motivated target for experiments probing scalar axion couplings to matter fields. These include fifth-force tests of gravity, as well as searches for spin-dependent forces via precision magnetometry, proton storage rings and ultracold molecules.