2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/40293Rare flavour-changing neutral-current transitions of the type $s \to d \ell^+\ell^-(ν\barν)$ and $b \to s \ell^+\ell^-(ν\barν)$ are analysed in supersymmetric extensions of the Standard Model with generic flavour couplings. It is shown that these processes are particularly sensitive to the left--right mixing of the squarks and that, in the presence of non-universal $A$ terms, they could lead to unambiguous signatures of new physics in exclusive $K$ and $B$ meson decays.15 pages, Latex, invited talk at RADCOR 2000 (Carmel CA, USA, Sept. 2000)High Energy Physics - Phenomenologytext