Scalar flavour-changing neutral currents in the large-tan(beta) 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 ($\tan \beta =v_u/v_d$) is large. We clarify the origin of this phenomenon, both in $\Delta F=1$ and $\Delta F=2$ processes, analysing differences and analogies between supersymmetric and non-supersymmetric models. We confirm previous findings of a sizeable enhancement at large $\tan \beta$ of specific $\Delta F=1$ and $\Delta F=2$ amplitudes in the MSSM and, in these cases, we discuss how large-$\tan \beta$ corrections can be controlled beyond lowest order. Finally, we emphasize the unique role of the rare processes $B_{s,d}\to {\tau }^{+}{\tau }^{-}$ and $B_{s,d}\to {\mu }^{+}{\mu }^{-}$ in probing this scenario.

Comments: 22 pages, Latex, 6 figures; v3: minor misprints corrected with respect to the published version