Weak-Symmetry Breaking in Locally Supersymmetric Grand Unified Theories

Abstract

A possibility of the radiative breaking of the weak gauge symmetry is studied in the framework of grand unified theories coupled to the N = 1 supergravity. Some supersymmetry breaking mass parameters in the effective low energy theory, which do not emerge at the tree level from the spontaneous breakdown of the N = 1 supergravity, are found to become sizable when the loop effect of heavy particles is taken into account at the grand unification mass scale. These mass parameters, as well as those produced at the tree level, are considered as boundary values at the unification mass scale for the renormalization group equations. It is remarkably found that there isa possibility that the top quark can be as light as the present experimental lower bound in order for the radiative weak symmetry breaking to occur. It is further shown that gluinos acquire phenomenologically allowable masses even if the canonical kinetic term is assumed for the Yang-Mills supergravity coupling. Wiggsinos (i.e., mixed states of gauge and Higgs fermions) also obtain sizable masses.