Higgs-mediated B0 → μ+ μ- in minimal supersymmetry

We demonstrate a new source for flavor-changing neutral currents within the minimal supersymmetric standard model. At moderate to large tan beta, it is no longer possible to diagonalize the masses of the quarks in the same basis as their Yukawa couplings. This generates flavor-violating couplings of the form (b) over bar(R)d(L)phi and (b) over bar(R)S(L)phi where phi is any of the three neutral, physical Higgs bosons. These new couplings lead to rare processes in the B system such as B-0 --> mu(+) mu(-) and B-0 - (B) over bar(0) mixing. We show that the tatter are anomalously suppressed, while the former is in the experimentally interesting range, with an observable signal possible at Run II of the Tevatron if m(A) less than or similar to 400-700 GeV.