THE EFFECT OF YUKAWA COUPLINGS ON UNIFICATION PREDICTIONS AND THE NONPERTURBATIVE LIMIT

We investigate the effects of Yukawa couplings on the phenomenological predictions for a class of supersymmetric models which allows for the presence of complete SU(5) multiplets in addition to the minimal supe rsymmetric standard model spectrum. We develop a two-loop analytical a pproach to quantify the predictions for gauge unification including Yu kawa couplings. The effects of the heavy thresholds of the model are a lso included. In some cases accurate predictions can be made for the u nification scale, irrespective of the initial (unknown) Yukawa couplin gs, so long as perturbation theory remains valid. We also consider the limit of a large number of extra states and compute the predictions i n a resummed perturbation series approach to show that the results are stable in this limit. Finally we consider the possibility of making p redictions for the case the gauge and Yukawa couplings enter the non-p erturbative domain below the unification scale and estimate the errors which affect these predictions. (C) 1998 Elsevier Science B.V.