Charged-Higgs-boson effect inBd0-B¯d0mixing,K→πνν¯decay, and rare decays ofBmesons

Extensions of the standard model containing two Higgs-boson doublets leads to the existence of charged Higgs bosons which can be important in rare meson decays, such as K→πνν¯, $B_d$→$X_s$νν¯, and $B_d$→$X_s$γ. We analyze these in the minimal two Higgs-boson doublets with the constraint placed on the charged-Higgs-boson mass, the t-quark mass, and the ratio of the vacuum expectation values of the two doublets by $B_d^0$-B${¯}_d^0$ mixing. An enhancement factor of ∼1.5 over the prediction of the standard model is obtained for the branching ratio of K→πνν¯.