Scalar flavour-changing neutral currents in the large-tan β limit

Abstract

We analyse scalar flavour-changing neutral currents of down-type quarks in models with two Higgs doublets, coupled separately to up-and down-type quarks, in the limit where the ratio of the two expectation values (tan β = vu /vd ) is large. We clarify the origin of this phenomenon, both in ∆F = 1 and ∆F = 2 processes, analysing differences and analogies between supersymmetric and non-supersymmetric models. We confirm previous findings of a sizeable enhancement at large tan β of specific ∆F = 1 and ∆F = 2 amplitudes in the MSSM and, in these cases, we discuss how large-tan β corrections can be controlled beyond lowest order. Finally, we emphasize the unique role of the rare processes Bs,d → τ+ τ− and Bs,d → µ+ µ− in probing this scenario.