Flavor constraints on the two-Higgs-doublet model with general Yukawa couplings

We consider the general, CP-conserving, two-Higgs-doublet model (2HDM). For a natural coupling hierarchy with negligible FCNCs at tree-level, constraints on the free Yukawa couplings (one for each fermion) and the charged Higgs mass m H + are obtained from flavor physics. We find that the coupling λ tt of the top quark is restricted by b → sγ transitions and ∆M B d to |λ tt | < 1 for m H + 600 GeV. Stringent constraints from B decays are also obtained on the other third generation couplings λ bb and λ τ τ , but with stronger dependence on m H +. For the second generation, we obtain constraints on combinations of λ ss , λ cc , and λ µµ from leptonic K and D s decays. The results from the individual observables are combined and presented on the (m H + , tan β) plane of 2HDM types I – IV with a Z 2 symmetry. Of these, the flavor constraints are most excluding in the type II model which lacks a decoupling limit in tan β. A lower limit of m H + 300 GeV is obtained in models type II and III, while no lower bound is found for types I and IV. For the type II model, a χ 2 fit is performed to the flavor data. The resulting best fit point is m H + ≃ 600 GeV, tan β ≃ 6.