Flavor-phenomenology of two-Higgs-doublet models with generic Yukawa structure

TL;DR

This paper investigates flavor physics in a two-Higgs-doublet model with generic Yukawa couplings, constraining parameters through various flavor observables and exploring potential deviations from the Standard Model in B meson decays.

Contribution

It provides a comprehensive analysis of flavor constraints on the 2HDM with generic Yukawa structure, identifying which Yukawa couplings are tightly constrained and how they affect flavor observables.

Findings

Most off-diagonal Yukawa couplings are tightly constrained by flavor data.

Unconstrained couplings ^u_{32,31} can significantly affect B decay processes.

Deviations from SM predictions in B, B, and B decays can be explained by certain Yukawa couplings.

Abstract

We perform an extensive study of flavor observables in a 2HDM with generic Yukawa structure (the decoupling limit of the MSSM). We examine the effects in flavor physics and constrain the model both from tree-level processes and loop-observables. The free parameters of the model are the heavy Higgs mass, tan(\beta) and the "non-holomorphic" Yukawa couplings \epsilon^f_ij (f=u,d,\ell). In our analysis we constrain the elements \epsilon^f_ij in various ways: In a first step we give order of magnitude constraints on \epsilon^f_ij from 't Hooft's naturalness criterion. Then we constrain the Yukawa structure of the type-III 2HDM from tree-level FCNC processes (B_s,d->\mu^+\mu^-, \tau^-->\mu^-\mu^+\mu^-, etc.) and observe that all flavor off-diagonal elements except \epsilon^u_32,31 and \epsilon^u_23,13 must be very small in order to satisfy the experimental bounds. In a third step, we consider Higgs mediated loop contributions to FCNC processes (b->s,d\gamma, \mu->e\gamma, etc.) finding that also \epsilon^u_13 and \epsilon^u_23 must be very small, while the bounds on \epsilon^u_31 and \epsilon^u_32 are especially weak. Taking into account the constraints from FCNC processes we study the possible size of contributions from tree-level charged Higgs exchange. Interestingly, the unconstrained elements \epsilon^u_{32,31} enter directly the branching ratios for B->\tau\nu, B->D\tau\nu and B->D*\tau\nu and we show that the deviations from the SM predictions in these processes can be explained simultaneously. We give upper limits on the branching ratios of the lepton flavor-violating neutral B meson decays and correlate the radiative lepton decays to the corresponding neutral current lepton decays (\tau^- ->\mu^-\mu^+\mu^-, \tau^- ->e^-\mu^+\mu^- and \mu^- ->e^-e^+e^-). A detailed appendix contains all relevant information for the considered processes for general scalar-fermion-fermion couplings.