Tension between scalar/pseudoscalar new physics contribution to B_s → μ⁺μ^- and B → Kμ⁺μ^-

Abstract

New physics in the form of scalar/pseudoscalar operators cannot lower the semileptonic branching ratio Br(B → K μ⁺μ^-) below its standard model value. In addition, we show that the upper bound on the leptonic branching ratio Br(B_s → μ⁺μ^-) sets a strong constraint on the maximum value of Br(B → K μ⁺μ^-) in models with multiple Higgs doublets: with the current bound, Br(B → K μ⁺μ^-) cannot exceed the standard model prediction by more than 2.5%. The conclusions hold true even if the new physics couplings are complex. However, these constraints can be used to restrict new physics couplings only if the theoretical and experimental errors in Br(B → K μ⁺μ^-) are reduced to a few per cent. The constraints become relaxed in a general class of models with scalar/pesudoscalar operators.