Light Fermion Masses in Superstring Derived Standard--like Models

Abstract

I discuss the suppression of the lightest generation fermion mass terms in realistic superstring standard--like models in the free fermionic formulation. The suppression of the mass terms is a consequence of horizontal symmetries that arise due to the $Z_2\times Z_2$ orbifold compactification. In a specific model I investigate the possibility of resolving the strong CP puzzle by a highly suppressed up quark mass. In some scenarios the up quark mass may be as small as $10^{-8}MeV$. I show that in the specific model the suppression of the up quark mass is incompatible with the requirement of a nonvanishing electron mass. I discuss how this situation may be remedied.