Predictions for the neutrino parameters in the minimal gauged hbox {U}(1)_{L_mu -L_tau } model

Abstract

We study the structure of the neutrino-mass matrix in the minimal gauged hbox {U}(1)_{L_mu -L_tau } model, where three right-handed neutrinos are added to the Standard Model in order to obtain non-zero masses for the active neutrinos. Because of the hbox {U}(1)_{L_mu -L_tau } gauge symmetry, the structure of both Dirac and Majorana mass terms of neutrinos is tightly restricted. In particular, the inverse of the neutrino-mass matrix has zeros in the (mu ,mu ) and (tau ,tau ) components, namely, this model offers a symmetric realization of the so-called two-zero-minor structure in the neutrino-mass matrix. Due to these constraints, all the CP phases – the Dirac CP phase delta and the Majorana CP phases alpha _2 and alpha _3 – as well as the mass eigenvalues of the light neutrinos m_i are uniquely determined as functions of the neutrino mixing angles theta _{12}, theta _{23}, and theta _{13}, and the squared mass differences Delta m_{21}^2 and Delta m_{31}^2. We find that this model predicts the Dirac CP phase delta to be delta simeq 1.59pi –1.70pi (1.54pi –1.78pi ), the sum of the neutrino masses to be sum _{i}m_i simeq 0.14–0.22 eV (0.12–0.40 eV), and the effective mass for the neutrinoless double-beta decay to be langle m_{beta beta }rangle simeq 0.024–0.055 eV (0.017–0.12 eV) at 1sigma (2sigma ) level, which are totally consistent with the current experimental limits. These predictions can soon be tested in future neutrino experiments. Implications for leptogenesis are also discussed.