Model for neutrino mixing based on SO(10)

Assuming grand unified theory (GUT) and supersymmetry, we propose a simple model which can consistently accommodate the masses and mixings for quarks and leptons. The grand unified group is SO(10), and $\bf 10$, $\bf 120$, and $\bar {\bf 126}$ representations are introduced for the Higgs superfields which give masses to the quarks and leptons. The differences of masses and mixings between the quarks and the leptons are attributed to the Higgs boson structure. Below the GUT energy scale, the model is the same as the minimal supersymmetric standard model except its inclusion of dimension-5 operators for the small neutrino masses. The renormalization group equations of the independent parameters for the Higgs couplings with the quarks and leptons are given explicitly to connect the two energy scales of GUT and electroweak theory.