The General One-loop Structure for the LFV Higgs Decays $H_r \to l_a l_b$ in multi-Higgs Models with Neutrino Masses

TL;DR

This paper derives general one-loop formulas for lepton flavor violating Higgs decays in multi-Higgs models with neutrino masses, providing a unified framework applicable to various models and calculating branching ratios consistent with experimental bounds.

Contribution

It introduces a comprehensive method to compute LFV Higgs decay amplitudes at one-loop in multi-Higgs models with neutrino masses, unifying different particle contributions and applying to specific models.

Findings

Largest SM-like Higgs LFV decay branching ratio is about 10^{-12}

Scotogenic model predicts LFV Higgs decay branching ratios up to 10^{-9}

Results are consistent with current LHC experimental constraints

Abstract

In this paper we present general formulae for the calculation of LFV Higgs decays $H_r \to l_a l_b$ at one-loop, with $H_r$ being part of the Higgs spectrum of a generic multi-scalar extension of the Standard Model (SM) with neutrino masses. We develop a method based on a classification of the particles appearing in the loop diagrams (scalars, fermions and vectors), and by identifying the corresponding couplings, we are able to present compact expressions for the form factors involved in the amplitudes. Our results are applicable to models where Flavor Changing Neutral Currents (FCNC) are forbidden at tree-level, but change of flavor is induced by charged currents. Then, as applications of our formalism, we evaluate the branching ratio for the mode $h \to l_a l_b$, for two specific models: the See-Saw Type I-$\nu$SM and the Scotogenic model (here $h = H_1$ corresponds to the SM-like Higgs boson); we find that the largest branching ratio for SM-like Higgs $h$ boson within the $\nu$SM is of the order $\mathcal{BR}(h\to \mu \tau)\simeq 10^{-12}$, while for the Scotogenic model we find $\mathcal{BR}(h\to l_a l_b)\lesssim 10^{-9}$, which satisfy the latest experimental LHC results.