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

TL;DR

This paper extends an $SO(10)$ grand unified theory by adding adjoint fermions and a scalar to generate neutrino masses via a double seesaw mechanism, aiming for predictive neutrino mixing patterns.

Contribution

It introduces a novel $SO(10)$ model extension with adjoint fermions and a scalar, enabling neutrino mass generation through double seesaw, with flavor symmetry constraints for predictive mixing.

Findings

Successfully reproduces tri-bimaximal mixing pattern.

Provides conditions for mass matrices to fit neutrino oscillation data.

Enhances model predictivity with flavor symmetry assumptions.

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 $\bar{16}_H$. The $\bar{16}_H$ 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 $\mu-\tau$ flavour symmetry on the Yukawa matrices for $10_H$ and $\bar{16}_H$ 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.