Flavor constraints on two-Higgs-doublet models with general diagonal Yukawa couplings

We consider constraints from flavor physics on two-Higgs-doublet models (2HDM) with general, flavor-diagonal, Yukawa couplings. Analyzing the charged Higgs contribution to different observables, we find that b→sγ transitions and ΔM_Bd restrict the coupling λₜₜ of the top quark (corresponding to cotβ in models with a Z₂ symmetry) to |λₜₜ|<1 for m_H⁺500 GeV. Stringent constraints from B meson decays are obtained also on the other third generation couplings λbb and λ_ττ, but with stronger dependence on m_H⁺. For the second generation, we obtain constraints on combinations of λₛₛ, λcc, and λ_μμ from leptonic K and Dₛ decays. The limits on the general couplings are translated to the common 2HDM types I--IV with a Z₂ symmetry, and presented on the (m_H⁺,tanβ) plane. The flavor constraints are most excluding in the type II model which lacks a decoupling limit in tanβ. We obtain a lower limit m_H⁺300 GeV in models of type II and III, while no lower bound on m_H⁺ is found for types I and IV.