The axion flavour connection

A local flavour symmetry acting on the quarks of the Standard Model can automatically give rise to an accidental global U(1) which remains preserved from sources of explicit breaking up to a large operator dimension, while it gets spontaneously broken together with the flavour symmetry. Such non-fundamental symmetries are often endowed with a mixed QCD anomaly, so that the strong CP problem is automatically solved via the axion mechanism. We illustrate the general features required to realise this scenario, and we discuss a simple construction based on the flavour group SU(3) × SU(2) × U(1)F to illustrate how mass hierarchies can arise while ensuring at the same time a high quality Peccei-Quinn symmetry.