On the IR/UV flavour connection in non-universal axion models

Abstract

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.

Light dark matter and flavour

“…For instance, for a vector FIP, kinetic mixing typically arises back with a loop factor from SM fermions loop, and plays a critical role in experimental searches [41,[45][46][47][48][49]. Similarly for an axion-like particle, most couplings reappear radiatively in the RGE, including possible flavour-violating interactions [50][51][52][53][54][55][56][57]. Altogether, one must therefore be particularly careful when dealing with large FIP couplings to second and third generations as they will probably re-introduce couplings to first-generation fermions or to photons, both of which can be easily constrained in precision frontier experiments.…”

The quark flavor-violating ALPs in light of B mesons and hadron colliders

“…The couplings are determined by the generation textures of PQ charge matrices in flavor basis [32][33][34][35][36][37][38]. If one loosens the assumption of the universality of the PQ current and allows non-universal PQ charges in a flavor symmetry, the flavor-violating ALP couplings to SM quarks or leptons arise at tree-level [39][40][41][42][43][44]. The mass mixing between the heavy vectorlike quark in the Kim-Shifman-Vainshtein-Zakharov (KSVZ) type models [20,21] and the SM quarks can also lead to flavor-violating interactions [45].…”