Flavored Axions

Precision flavor experiments can look for the QCD axion complementarily to usual searches with axion helio- and haloscopes, allowing to test PQ breaking scales as high as ${10}^{12}\mathrm{G}\mathrm{e}\mathrm{V}$. Such searches are sensitive to flavor-violating axion couplings, which are generic and potentially sizable whenever SM fermions carry flavor non-universal PQ charges. A particularly predictive scenario is obtained when PQ is identified with the simplest FN flavor symmetry, so that all flavor-violating axion couplings are related to Yukawa hierarchies, up to $\mathcal{O}(1)$ coefficients.