Constraints on flavor-changing Z' models by B_s mixing, Z' production,   and B_s -> \mu^+ \mu^-
  Certain string-inspired Z' models have non-universal interactions to three families of fermions and induced tree-level flavor-changing couplings. We use recent results on B_s-anti-B_s mixing to constrain the size of the flavor-changing couplings in the b-s sector. In some highly predictive Z' models, such a constraint on b-s coupling can be translated into the flavor-diagonal couplings. Based on the Z' production limits at the Tevatron, we obtain the limit on the leptonic couplings of Z' and then make predictions for B_s -> \mu^+ \mu^- branching ratios. We conclude that with the present constraints from B_s mixing and Z' production, the muonic decay of $B_s$ may not be observed at the Tevatron if the projected integrated luminosity is less than O(5-10) fb. 
Kingman Cheung, Cheng-Wei Chiang, N.G. Deshpande, and J. Jiang