Phenomenologically consistent discrete symmetries in superstring theories

Abstract

The light matter supermultiplets are specified uniquely in most superstring theories when compactified on Calabi-Yau manifolds. It is pointed out that the discrete symmetries considered earlier in these models cannot give rise to a phenomenologically consistent fermion mass spectrum and suppress fast proton decay. We propose here a simple model which demonstrates the type of discrete symmetries one has to look for to make the superstring theories phenomenologically acceptable. Some interesting consequences of the model are pointed out.