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×Z 2 orbifold compactification. In a specific toy 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.