Breaking Tri-Bimaximal Mixing and Large θ_<13>(Particles and Fields)

概要

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The long baseline neutrino experiment, T2K, and the reactor experiment, Double Chooz will soon present new data. If we expect sinθ_<13> to be 0.1-0.2, which is close to the present experimental upper bound, we should not persist in the paradigm of the tri-bimaximal mixing. We discuss breaking the tri-bimaximal mixing by adding a simple mass matrix, which could be derived from some non-Abelian discrete symmetries. It is found that sinθ_<13>=0.1-0.2 is expected in our model independent analysis of the generalized mass matrix for the normal or inverted hierarchical neutrino mass spectrum. On the other hand, sin^2θ_<23> and sin^2θ_<12> are expected to be not far from 1/2 and 1/3, respectively. As a typical example, we also discuss the A_4 flavor model with the 1 and 1' flavons, which break the tri-bimaximal mixing considerably. In this modified version of the Altarelli and Feruglio model, sinθ_<13> is predicted to be around 0.15 in the case of the normal hierarchical neutrino masses m_3≫m_2, m_1, and 0.2 in the case of the inverted hierarchy m_3≪m_2, m_1. The form of the neutrino mass matrix looks rather interesting-it is suggestive of other discrete symmetries as well.
2011-07-25