Fermion masses in E_6 grand unification with family permutation   symmetries
  Neutrino masses have been extensively studied in the context of discrete symmetries. A family permutation symmetry easily explains all neutrino oscillations and their mixing angles. However it is not obvious the embedding of such symmetry in a grand unified theory where all fermions live in the same representation. We show that it is possible to embed such a horizontal discrete symmetry in a grand unified theory. We discuss an E_6   GUT model as in [1], but differently from [1], we take the SM Higgs doublet in the 351' to have (+3,+5) charges with respect the additional U(1)_r X U(1)_t. This choice makes possible two different horizontal symmetry breaking patterns and a distinction between neutrinos and the rest of matter fermions. 
Francesco Caravaglios and Stefano Morisi