DISCRETE GAUGE SYMMETRIES IN SUPERSYMMETRIC GRAND UNIFIED MODELS

We investigate the presence of discrete gauge symmetries in grand unif ication models based on SO(10) and E6. These models include flipped an d unflipped SU(5), SU(4) X SU(2)L X SU(2)R, SU(3)C X SU(3)L X SU(3)R, and SU(6) X SU(2). Using the Dynkin formalism we find the U(1) subalge bras contained in the unified groups, give an expression for the Higgs fields that preserves each discrete symmetry, and determine the low-e nergy matter content implied by chirality. We discuss two Z2 and three Z3 non-equivalent cases. Among the possibilities found, only the usua l Z2 matter parity (R parity) of supersymmetric extensions is consiste nt with a minimal matter content with no right-handed neutrinos, extra Higgs doublets, or nonstandard down-type quarks.