New physics upper bound on the branching ratio of B_s --> l+ l- gamma

Abstract

We consider the effect of new physics on the branching ratio of B_s--> l+ l- gamma where l=e,mu. If the new physics is of the form scalar/pseudoscalar, then it makes no contribution to B_s--> l+ l- gamma, unlike in the case of B_s--> l+ l-, where it can potentially make a very large contribution. If the new physics is in the form of vector/axial-vector operators, then present data on B-->(K,K^*)l+ l-, does not allow a large enhancement for B_s--> l+ l- gamma. If the new physics is in the form of tensor/pseudotensor operators, then the data on B-->(K,K^*)l+ l- gives no useful constraint but the data on B-->K^* gamma does. Here again, a large enhancement of B(B_s--> l+ l- gamma), much beyond the Standard Model expectation, is not possible. Hence, we conclude that the present data on b-->s transitions allow a large boost in B_s--> l+ l- but not in B_s--> l+ l- gamma.