Fermion masses and mixings in a renormalizable SO(10) x Z_2 GUT

Abstract

We investigate a scenario in a supersymmetric SO(10) Grand Unified Theory in which the fermion mass matrices are generated by renormalizable Yukawa couplings of the $\mathbf{10} \oplus \mathbf{120} \oplus \bar{\mathbf{126}}$ representation of scalars. We reduce the number of parameters by assuming spontaneous CP violation and a $\mathbbm{Z}_2$ family symmetry, leading to nine real Yukawa coupling constants for three families. Since in the ``minimal SUSY SO(10) GUT'' an intermediate seesaw scale is ruled out and our scenario lives in the natural extension of this theory by the $\mathbf{120}$, we identify the vacuum expectation value (VEV) $w_R$ of $(\mathbf{10}, \mathbf{1}, \mathbf{3}) \in \bar{\mathbf{126}}$ with the GUT scale of $2 \times 10^{16}$ GeV. In order to obtain sufficiently large neutrino masses, the coupling matrix of the scalar $\bar{\mathbf{126}}$ is necessarily small and we neglect type II seesaw contributions to the light-neutrino mass matrix. We perform a numerical analysis of this 21-parameter scenario and find an excellent fit to experimentally known fermion masses and mixings. We discuss the properties of our numerical solution, including a consistency check for the VEVs of the Higgs-doublet components in the SO(10) scalar multiplets.