Lepton flavour violating Higgs and tau to mu gamma

TL;DR

This paper explores constraints on a Two Higgs Doublet Model with lepton flavor violation, analyzing collider signals and rare decay limits to identify potential signatures of new physics involving tau and muon interactions.

Contribution

It provides a detailed phenomenological analysis of lepton flavor violating Higgs interactions in a Type III 2HDM, including collider prospects and decay constraints.

Findings

Neutral scalars could be detected via $ au ar{ au}$ and $ au ar{}$ channels.

Collider cross-sections can match Standard Model expectations with some tuning.

Current bounds from $ au o   $ decay constrain the model parameters.

Abstract

We update phenomenological constraints on a Two Higgs Doublet Model with lepton flavour non-conserving Yukawa couplings. We review that $\tan \beta$ is ambiguous in such "Type III" models, and define it from the $\tau$ Yukawa coupling. The neutral scalars $\phi$ could be searched for at hadron colliders in $ \phi \to \tau \bar{\mu}$, and are constrained by the rare decay $\tau \to \mu \gamma$. The Feynman diagrams for the collider process, with Higgs production via gluon fusion, are similar to the two-loop "Barr-Zee" diagrams which contribute to $\tau \to \mu \gamma$. Some "tuning" is required to obtain a collider cross-section of order the Standard Model expectation for $\sigma (gg \to h_{SM} \to \tau^+ \tau^-)$, while agreeing with the current bound from $\tau \to \mu \gamma$.