$B_s\to l^{+}{l}^{-}$ in a type-II two-Higgs-doublet model and the minimal supersymmetric standard model

In this paper we analyze the process $B_s\to l^{+}{l}^{-}$ in a type-II two-Higgs-doublet model (2HDM) and the minimal supersymmetric standard model (MSSM). All the leading terms of Wilson coefficients relevant to the process are given in the large $\tan \beta$ limit. It is shown that the decay width for $B_s\to l^{+}{l}^{-}$ depends on all parameters except $m_{A^0}$ in the 2HDM. The branching ratio of $B_s\to {\mu }^{+}{\mu }^{-}$ can reach its experimental bound in some large $\tan \beta$ regions of the parameter space in the MSSM because the amplitude increases as ${\tan }^3\beta$ in the regions. For $l=\tau ,$ the branching ratio can even reach ${10}^{-4}$ in the regions. Therefore, the experimental measurements of leptonic decays of $B_s$ could put a constraint on the contributions of neutral Higgs bosons and consequently the parameter space in the MSSM.