Masses and Mixing of Neutral Leptons in a Grand Unified E_6 Model with Intermediate Pati-Salam Symmetry

A brief review of the assignment of elementary fermions and bosons to irreducible multiplets in grand unified $E_6$ models is followed by a discussion of different, hierarchical symmetry breaking chains from $E_6$ down to $SU(3{)}_C\times U(1{)}_{EM}$. We concentrate here on a model with an intermediate Pati-Salam symmetry for which $(B-L)$ is conserved. In particular, the mass/mixing matrix of electrically neutral fermions (i.e.neutrinos) that would be derived from Yukawa couplings is constructed. The pattern of neutrino masses and some bounds on mixing parameters are discussed.