Bs,d → l+l- and KL → l+l- in SUSY models with non-minimal sources of flavour mixing -: art. no. 063

We present a general analysis of B-s,B-d --> l(+)l(-) and K-L --> l(+)l(-) decays in supersymmetric models with non-minimal sources of flavour mixing. In spite of the existing constraints on off-diagonal squark mass terms, these modes could still receive sizeable corrections, mainly because of Higgs-mediated FCNCs arising at large tan beta. The severe limits on scenarios with large tan beta and non-negligible (d) over tilde (i)(R(L))-(d) over tilde (j)(R(L)) mixing imposed by the present experimental bounds on these modes and DeltaB = 2 observables are discussed in detail. In particular, we show that scalar-current contributions to K-L --> l(+)l(-) and B-(B) over bar mixing set non-trivial constraints on the possibility that B-s --> l(+)l(-) and B-d --> l(+)l(-) receive large corrections.