An SO(10) model with adjoint fermions for double seesaw neutrino masses

Abstract

An SO(10) model where the 10_H and 120_H representations are used for generating fermion masses is quite predictive, though due to the absence of SU(2)_L,R triplet/singlet fields it cannot give rise to neutrino masses through the usual type-I or type-II seesaw mechanisms. In this paper for neutrino masses we propose an extension of such an SO(10) model by adding fermions in the adjoint representation (45_F) and a symmetry breaking scalar 16̅_H. The 16̅_H couples the adjoint fermions to the standard fermions in 16_F and induces neutrino masses through the 'double seesaw' mechanism. In order to enhance the predictivity of the model we impose μ-τ flavour symmetry on the Yukawa matrices for 10_H and 16̅_H whereas for the 120_H it is assumed to be antisymmetric. We discuss the conditions that the mass matrices must obey so that the model can reproduce the tri-bimaximal mixing pattern.