Quasi-degenerate neutrinos in SO(10)

TL;DR

This paper proposes a novel Yukawa matrix structure in SO(10) grand unified theories that results in quasi-degenerate neutrino masses, supported by detailed fermion mass and mixing angle fits, differing from the typical hierarchical expectations.

Contribution

It introduces a specific ansatz for Yukawa matrices in SO(10) models that produce quasi-degenerate neutrinos, supported by detailed fits and an extended model with vector-like fermions and flavor symmetry.

Findings

The ansatz successfully explains fermion masses and mixing angles.

Quasi-degenerate neutrinos naturally emerge from the proposed structure.

Large neutrino mixing angles are linked to neutrino mass degeneracy.

Abstract

Quark lepton universality inherent in grand unified theories based on $SO(10)$ gauge group generically leads to hierarchical neutrino masses. We propose a specific ansatz for the structure of Yukawa matrices in $SO(10)$ models which differ from this generic expectations and lead to quasi degenerate neutrinos through the type-I seesaw mechanism. Consistency of this ansatz is demonstrated through a detailed fits to fermion masses and mixing angles all of which can be explained with reasonable accuracy in a model which uses the Higgs fields transforming as $10,120$ and $\overline{126}$ representations of $SO(10)$. The proposed ansatz is shown to follow from an extended model based on the three generations of the vector like fermions and an $O(3)$ flavour symmetry. Successful numerical fits are also discussed in earlier proposed models which used combination of the type-I and type-II seesaw mechanisms for obtaining quasi degenerate neutrinos. Large neutrino mixing angles emerge as a consequence of neutrino mass degeneracy in both these cases.