Supersymmetric contributions to rare kaon decays

We analyze the contributions to rare kaon decays mediated by flavor-changingZ-penguin diagrams in a generic low-energy supersymmetric extension of theStandard Model. In order to perform a model-independent analysis we expand thesquark mass matrices around the diagonal, following the so calledmass-insertion approximation. We argue that in the present case it is necessaryto go up to the second order in this expansion to take into account allpossible large effects. The current bounds on such second-order term, which wasneglected in previous analyses, are discussed in detail and the correspondingupper bounds for the rare kaon decay rates are derived. As a result, we showthat supersymmetric effects could lead to large enhancements of K -> pi nu{\barnu} and K_L -> pi^0 e^+ e^- branching ratios.Comment: Latex, JHEP style, 21 pages, 2 figure