Light axions with large hadronic couplings

TL;DR

This paper introduces models where axions have large hadronic couplings without gaining mass, enabling new experimental searches and revealing potential flavor violations.

Contribution

It proposes a novel mechanism for large hadronic axion couplings with no associated mass increase, expanding the scope of axion phenomenology.

Findings

Models achieve large hadronic couplings with light axions.

Flavor violations are predicted and could be experimentally tested.

Coupling strength can be independent of axion mass.

Abstract

We present models in which axions have large couplings to hadrons while remaining naturally light. By assigning $U(1)_{PQ}$ charges to Standard Model quarks such that $U(1)_{PQ}$ is not anomalous under QCD, the derivative couplings naturally arise while no potential is generated for the axion upon QCD confinement. We present simple models that implement this idea both for an axion-like particle and for the QCD axion. We show that both models lead to sizable flavor violations that could be probed by future experiments. Our construction shows that the axion coupling to hadrons can be essentially independent from its mass and thus motivates experimental searches in a wide range of axion parameter space.