SUPERSYMMETRIC FLAVOR-CHANGING NEUTRAL CURRENTS - EXACT AMPLITUDES AND PHENOMENOLOGICAL ANALYSIS

We present an exact calculation of the most general supersymmetric amp litudes for K0-K0BAR and B0-B0BAR mixing resulting from gluino box dia grams. We use these amplitudes to place general constraints on the mag nitude of off-generational, flavor-changing mass mixings in the squark mass matrices (with arbitrary chirality structures) that can arise bo th in and beyond the minimal supersymmetric Standard Model (MSSM). We use the renormalization-group equations to estimate these mass mixings in the MSSM and in nonminimal supersymmetric models in terms of a gen eral parameterization of universal soft supersymmetry breaking. We sho w that while these mass mixings are too small in the MSSM to yield any observable effects, the converse is true in most nontrivial extension s of the MSSM, including supersymmetric GUTs. In nonminimal supersymme try, the K(L)-K(S) mass difference is sensitive to such contributions from supersymmetric particles with masses up to 100 TeV (10 TeV for th e B(L)-B(S) mass difference), and the CP impurity parameter epsilon(K) is sensitive to sparticle masses up to 1000 TeV. We show that supersy mmetric CP violation can be predominantly ''superweak'' (i.e., contrib ute mainly to epsilon(K)) or ''milliweak'' (epsilon') depending on the chirality of the off-generational squark mass mixings. The rare decay b --> sgamma is less sensitive than the aforementioned constraints, b ut probes somewhat different squark mass mixings. The lepton-number vi olating decay mu --> egamma is very sensitive to off-generational slep ton mixing for sleptons up to a TeV. All these processes provide valua ble information regarding the structure of physics beyond the MSSM per taining to arbitrarily high mass scales, including the nature of super symmetry breaking.