Search for rare flavor-changing and penguin decays of the $B^0_s$ meson

Using data collected with the D\O\ detector in Run II of the Tevatron, limits are presented for searches for the rare flavour changing neutral current decay $B^0_s \rightarrow \mu^+ \mu^-$, as well as $B^0_s \rightarrow \mu^+ \mu^- \phi$. The former decay mode is particularly sensitive to supersymmetric extensions of the Standard Model. For the latter mode, a measurement of the branching ratio could validate the prediction of the Standard Model.