Constraint on the scale-unifying supersymmetric preon model from - mixing

Abstract

We study the flavour changing neutral current process in - mixing in the supersymmetric preon model (SPM). Compared to the minimal supersymmetric standard model (MSSM), one distinguishing feature of - mixing in the SPM is that there are new contributions from box diagrams involving two vector-like families of quarks and their supersymmetric (SUSY) partners with masses of order 1 TeV. Another special feature of the process in the SPM, in contrast to the MSSM, is that left - right squark - mixing is highly suppressed owing to symmetries of the underlying model. We calculate the SUSY box diagrams for - mixing for the case of the SPM, using observed - mass splitting, and obtain the constraint of on the squark mass degeneracy in the model. This upper limit is smaller by about a factor of 3.6 than the corresponding limit for the MSSM. The difference arises because of the absence of - mixing in the the preon model.