  We analyze the contributions to rare kaon decays mediated by flavor-changing
Z-penguin diagrams in a generic low-energy supersymmetric extension of the
Standard Model. In order to perform a model-independent analysis we expand the
squark mass matrices around the diagonal, following the so called
mass-insertion approximation. We argue that in the present case it is necessary
to go up to the second order in this expansion to take into account all
possible large effects. The current bounds on such second-order term, which was
neglected in previous analyses, are discussed in detail and the corresponding
upper bounds for the rare kaon decay rates are derived. As a result, we show
that supersymmetric effects could lead to large enhancements of K -> pi nu{\bar
nu} and K_L -> pi^0 e^+ e^- branching ratios.

High Energy Physics - Phenomenology