New physics in [B.sub.d,s]-[[bar.B].sub.d,s] mixings and [B.sub.d,s] [right arrow] [[mu].sup.+][[mu].sup.-] decays

A new way of probing new physics in the B meson system is provided. We define double ratios for the observables of [B.sub.d,s]-[[bar.B].sub.d,s] mixings and [B.sub.d,s] [right arrow] [[mu].sup.+][[mu].sup.-] decays, and find simple relations between the observables. By using the relations we predict the yet-to-be-measured branching ratio of [B.sub.d] [right arrow] [[mu].sup.+][[mu].sup.-] to be (0.809-1.03) x [10.sup.-10], up to the new physics models.