SUPERSYMMETRIC CONTRIBUTIONS TO B(0)-(B)OVER-BAR(0) AND K(0)-(K)OVER-BAR(0) MIXINGS

We show that in the supersymmetric standard model (SSM) box diagrams m ediated by charginos and up-type squarks may give large contributions to B0-BBAR0 and K0-KBAR0 mixings. This is due to the fact that a heavy top quark mass allows large mass differences among the up-type squark s, which leads to a less efficient cancellation among the different sq uark diagrams. If the ratio of the vacuum expectation values of the Hi ggs bosons is of order of unity, box diagrams mediated by charged Higg s bosons also contribute appreciably. For sizable regions of the SSM p arameter space, the SSM contributions could be sufficiently large to a ffect significantly the evaluation of the CKM matrix from the experime ntal values of the mixing parameter x(d) and the CP violation paramete r epsilon.