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

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(β) and the "non-holomorphic" Yukawa couplings ε^f_ij (f=u,d,\ell). In our analysis we constrain the elements ε^f_ij in various ways: In a first step we give order of magnitude constraints on ε^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->μ^+μ^-, τ^-->μ^-μ^+μ^-, etc.) and observe that all flavor off-diagonal elements except ε^u_32,31 and ε^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,dγ, μ->eγ, etc.) finding that also ε^u_13 and ε^u_23 must be very small, while the bounds on ε^u_31 and ε^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 ε^u_{32,31} enter directly the branching ratios for B->τν, B->Dτνand B->D*τνand 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 (τ^- ->μ^-μ^+μ^-, τ^- ->e^-μ^+μ^- and μ^- ->e^-e^+e^-). A detailed appendix contains all relevant information for the considered processes for general scalar-fermion-fermion couplings.