String Gauge Unification and Infra-Red Fixed Points in MSSM+X Models

摘要

We perform a detailed analysis of large class of MSSM+X models and find that thenumber of (3,1) representations added must be greater than the total of the number of (3,2) and (1,2) representations. Predictions of M(sub I), M(sub X) and alpha(M(sub X)) are obtained for models with up to 5 extra vector representations than the MSSM. We also study the infra-red fixed point behavior of the top quark Yukawa coupling in a large class of MSSM+X models and find that the low energy MSSM quasi-fixed point prediction of the top quark mass is more likely to be realized in these theories than in the MSSM. In other words, the top quark tends to be heavier in MSSM+X models than in the MSSM. The implementation of a U(1)X family symmetry into MSSM+X models to account for the Standard Model fermion masses is discussed and a particular viable model is presented.