Quantum effects for the neutrino mixing matrix in the democratic-type model

Abstract

We investigate the quantum effects for the democratic-type neutrino mass matrix given at the right-handed neutrino mass scale $m_R$ in order to see (i) whether $\theta_{23}=-\pi/4$ predicted by the model is stable to explain the atmospheric neutrino anomaly, (ii) how $\theta_{12}$ and $\theta_{13}$ behave, and (iii) whether the predicted Dirac CP phase $\delta$ keeps maximal size, at the weak scale $m_Z$. We find that, for the (inversely) hierarchical mass spectrum with $m_1\sim m_2$, $\theta_{23}$ and $\theta_{13}$ are stable, while $\theta_{12}$ is not so, which leads to the possibility that the solar neutrino mixing angle can become large at $m_Z$ even if it is taken small at $m_R$. We also show that $\delta$ keeps almost maximal for the above mass spectrum, and our model can give the large CP violation effect in the future neutrino oscillation experiments if the solar neutrino puzzle is explained by the large mixing angle MSW solution.