Neutrino mass in nonsupersymmetric SO(10) GUT

We study a prediction on neutrino observables in a nonsupersymmetric renormalizable SO(10) grand unified theory model that contains a 10 complex scalar field and a 126 scalar field whose Yukawa couplings with 16 matter fields provide the quark and charged lepton Yukawa couplings, neutrino Dirac Yukawa coupling and Majorana mass for the singlet neutrinos. The SO(10) breaking is achieved in two steps by a O(10(15)) GeV vacuum expectation value (VEV) of a 54 real scalar field and a O(10(14)) GeV VEV of the 126 field. First, we analyze the gauge coupling unification conditions and determine the VEV of the 126 field. Next, we constrain the Yukawa couplings of the 10 and 126 fields at the scale of the 126 field's VEV from experimental data on quark and charged lepton masses and quark flavor mixings. Then we express the active neutrino mass with the above Yukawa couplings and the 126 field's VEV based on the Type-1 seesaw mechanism, and fit neutrino oscillation data, thereby deriving a prediction on poorly or not measured neutrino observables. What distinguishes our work from previous studies is that we do not assign Peccei-Quinn charges on visible sector fields so that the 10 scalar field and its complex conjugate both have Yukawa couplings with 16 matter fields. From the fitting of neutrino oscillation data, we find that not only the normal neutrino mass hierarchy, but also the inverted hierarchy can be realized. We also reveal that in the normal hierarchy case, the Dirac CP phase of the neutrino mixing matrix delta(CP) is likely in the ranges of -2.4 < delta(CP) < -1.2 and 1.2 < delta(CP )< 2.4, and not in the region with delta(CP)similar to pi, and that in the normal hierarchy case, theta(23) is likely in the upper octant and in the range of 0.50 less than or similar to sin(2)theta(23 )less than or similar to 0.55.

Automated summary

In this study, we make predictions on neutrino observables in a nonsupersymmetric renormalizable SO(10) grand unified theory model. We analyze gauge coupling unification conditions, constrain Yukawa couplings, and fit neutrino oscillation data to derive predictions on poorly or not measured neutrino observables. Our work distinguishes itself by not assigning Peccei-Quinn charges on visible sector fields and considering both normal and inverted neutrino mass hierarchies. We find estimates for the Dirac CP phase and sin(2)theta(23) in the neutrino mixing matrix.