Light axions with large hadronic couplings

Understand

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.