B_s \to \ell^+ \ell^- in a model II 2HDM and MSSM

In this paper we analyze the process $B_s \to \ell^+ \ell^-$ in a model II 2HDM and 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 $B_s \to \ell^+ \ell^-$ 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 MSSM because the amplitude increases like 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 MSSM.