PROTON DECAY AND REALISTIC MODELS OF QUARK AND LEPTON MASSES

It is shown that in realistic SUSY GUT models of quark and lepton mass es both the proton decay rate and branching ratios differ in general f rom those predicted in the minimal SU(5) supersymmetric model. The obs ervation of proton decay, and in particular the branching ratio B[(p - -> pi(+)<(nu)over bar>)/(p --> K+<(nu)over bar>)], would thus allow de cisive tests of these fermion mass schemes. It is shown that the charg ed lepton decay mode p --> K-0 mu(+) arising through gluino dressing d iagrams is significant and comparable to the neutrino modes in large t an beta models. Moreover, it is found that in certain classes of model s the higgsino-mediated proton decay amplitudes are proportional to a model-dependent group-theoretical factor which in some cases can be qu ite small. There is thus a natural suppression mechanism which can exp lain without adjustment of parameters why in the context of SUSY GUTs proton decay has not yet been seen. The most interesting such class co nsists of SO(10) models in which the dominant flavor-symmetric contrib ution to the up-quark mass matrix comes from an effective operator of the form 16(i)16(j)10(H)45(H), where [45(H)] points approximately in t he I-3R direction. This class includes a recent model of quark and lep ton masses proposed by the authors.