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

TL;DR

This paper explores the connection between IR and UV sources of flavour violation in non-universal axion models, highlighting their relationship and implications for phenomenology and experimental searches.

Contribution

It establishes a direct link between IR and UV flavour violation sources in non-universal axion models within a DFSZ-like framework, and analyzes their phenomenological implications.

Findings

IR and UV flavour violations are directly related.

Heavy radial modes impact meson oscillations and lepton decays.

Complementarity of flavour, collider, and axion searches is emphasized.

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.