Quasidegenerate neutrinos in SO(10)

Abstract

We propose a specific ansatz for the structure of Yukawa matrices in SO(10) models that lead to quasidegenerate neutrinos through the type-I seesaw mechanism. Consistency of this ansatz is demonstrated through detailed fits to fermion masses and mixing angles, all of which can be explained with reasonable accuracy in a model that uses the Higgs fields transforming as 10, 120, and 126^̅ representations of SO(10). The proposed ansatz is shown to follow from an extended model based on the three generations of the vectorlike fermions and an O(3) flavor symmetry. Successful numerical fits are also discussed in earlier proposed models, which used a combination of the type-I and type-II seesaw mechanisms for obtaining quasidegenerate neutrinos. Large neutrino mixing angles emerge as a consequence of neutrino mass degeneracy in both these cases.