Implications of the non-universal Z boson in FCNC mediated rare decays

Abstract

We analyze the effect of the non-universal $Z$ boson in the rare decays $B_s \to l^+ l^- $, $B_s \to l^+ l^- \gamma $ and $Z \to b \bar s$ decays. These decays involve the FCNC mediated $ b \to s $ transitions, and are found to be very small in the standard model. The smallness of these decays in the standard model makes them sensitive probe for new physics. We find an enhancement of at least an order in these branching ratios because of the non-universal $Zbs$ coupling.