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

In this article, we perform an extensive study of flavor observables in a two-Higgs-doublet model with generic Yukawa structure (of type III). This model is interesting not only because it is the decoupling limit of the minimal supersymmetric standard model but also because of its rich flavor phenomenology which also allows for sizable effects not only in flavor-changing neutral-current (FCNC) processes but also in tauonic B decays. We examine the possible effects in flavor physics and constrain the model both from tree-level processes and from loop observables. The free parameters of the model are the heavy Higgs mass, tan beta (the ratio of vacuum expectation values) and the nonholomorphic Yukawa couplings epsilon(f)(ij)(f = u, d, l). 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, finding that all epsilon(f)(ij) must be rather small unless the third generation is involved. In a second step, we constrain the Yukawa structure of the type-III two-Higgs-doublet model from tree-level FCNC processes (B-s,B-d -> mu(+)mu(-), K-L -> mu(+)mu(-), (D) over bar (0) -> mu(+)mu(-), Delta F = 2 processes, tau(-) -> mu(-)mu(+)mu(-), tau(-) -> e(-)mu(+)mu(-) and mu(-) -> e(-)e(+)e(-)) and observe that all flavor off-diagonal elements of these couplings, except epsilon(u)(32,31) and epsilon(u)(23,13), must be very small in order to satisfy the current experimental bounds. In a third step, we consider Higgs mediated loop contributions to FCNC processes [b -> s(d)gamma, B-s,B-d mixing, K - (K) over bar mixing and mu -> e gamma] 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. Furthermore, considering the constraints from electric dipole moments we obtain constrains on some parameters epsilon(u,l)(ij). Taking into account the constraints from FCNC processes we study the size of possible effects in the tauonic B decays (B -> tau v, B -> D tau v and B -> D*tau v) as well as in D-(s) -> tau v, D-(s) -> mu v, K(pi) -> ev, K(pi) -> mu v and tau -> K(pi)v which are all sensitive to tree-level charged Higgs exchange. Interestingly, the unconstrained epsilon(u)(32,31) are just the elements which directly enter the branching ratios for B -> tau v, B -> D tau v and B -> D*tau v. We show that they can explain the deviations from the SM predictions in these processes without fine-tuning. Furthermore, B -> tau v, B -> D tau v and B -> D*tau v can even be explained simultaneously. Finally, we give upper limits on the branching ratios of the lepton flavor-violating neutral B meson decays (B-s,B-d -> mu e, B-s,B-d -> tau e and B-s,B-d -> tau mu) and correlate the radiative lepton decays (tau -> mu gamma, tau -> e gamma and mu -> e gamma) 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.