Fermion masses in SO(10) models

We examine many SO(10) models for their viability or otherwise in explaining all the fermion masses and mixing angles. This study is carried out for both supersymmetric and nonsupersymmetric models and with minimal (10 +(126) over bar) and nonminimal (10 + (126) over bar + 120) Higgs content. Extensive numerical fits to fermion masses and mixing are carried out in each case, assuming dominance of type-II or type-I seesaw mechanism. Required scale of the B-L breaking is identified in each case. In supersymmetric case, several sets of data at the GUT scale with or without inclusion of finite supersymmetric corrections are used. All the cases studied provide quite good fits if the type-I seesaw mechanism dominates. This is not the case in the minimal model based on several data sets and type-II seesaw mechanism. This can be traced to the absence of the b-tau unification at the GUT scale in these cases. In contrast, the type-II seesaw mechanism works uniformly well in all the supersymmetric cases when 120 Higgs is also included. The minimal nonsupersymmetric model with type-I seesaw dominance gives excellent fits. In the presence of a 45(H) and an intermediate scale, the model can also account for the gauge coupling unification making it potentially interesting model for the complete unification. Structure of the Yukawa coupling matrices obtained numerically in this specific case is shown to follow from a very simple U(1) symmetry and a Froggatt-Nielsen singlet.