Linking LFV Higgs decays $h\to \ell_i \ell_j$ with CP violation in multi-scalar models

Abstract

The study of LFV decays of the Higgs boson, $h\to \ell_i \ell_j$, has become an active research subject both from the experimental and theoretical points of view. Such decays vanish within the SM and are highly suppressed in several theoretical extensions. Due to its relevance and relative simplicity to reconstruct the signal at future colliders, it is an important tool to probe SM extensions where it could reach detectable levels. Here we identify a mechanism that induces LFV Higgs interactions, by linking it with the appearance of CP violation in the scalar sector, within the context of general multi-Higgs models. We then focus on the simplest model of this type to study its phenomenology. The scalar sector of this minimal model consisting of a Higgs doublet and a Froggatt--Nielsen (FN) (complex) singlet is studied thoroughly, including the scalar spectrum and the Yukawa interactions. Constraints on the parameters of the model are derived from low-energy observables and LHC Higgs data, which is then applied to study the resulting predicted rates for the decay $h\rightarrow \tau \mu$. Overall, branching ratios for $h \rightarrow \tau \mu$ of the order $10^{-3}$ are obtained within this approach consistent with all known constraints.