  Non-universal axion models, with the Peccei-Quinn (PQ) symmetry acting on
Standard Model (SM) fermions in a generation-dependent way, are typically
accompanied by two different sources of flavour violation, dubbed here as
infrared (IR) and ultraviolet (UV). The former is due to the flavour violating
axion couplings to SM fermions, while the latter arises from the heavy degrees
of freedom that UV complete the axion effective field theory. We point out that
these two sources of flavour violation are directly related and exemplify this
connection in a general class of non-universal axion model, based on a
renormalizable DFSZ-like setup with two Higgs doublets (PQ-2HDM). We next
discuss the interplay of axion flavour phenomenology with the signatures
stemming from the heavy radial modes of the PQ-2HDM, including meson
oscillation observables and charged lepton flavour violating decays. We
emphasize the strong complementarity between flavour observables, LHC direct
searches and standard axion physics.
