Structure of neutrino mass matrix and CP violation
Abstract
We reconstruct the neutrino mass matrix in the flavor basis, using all available experimental data on neutrino oscillations. Majorana nature of neutrinos, normal mass hierarchy (ordering) and validity of the LMA MSW solution of the solar neutrino problem are assumed. We study dependences of the mass matrix elements, $m_{\alpha\beta}$, on the CP violating Dirac, $\delta$, and Majorana, $\rho$, $\sigma$, phases, for different values of the mixing angle $\theta_{13}$ and of the absolute mass scale, $m_1$. The contours of constant mass in the $\rho-\sigma$ plane have been constructed for all $m_{\alpha\beta}$. Possible structures of the mass matrix have been analyzed. We identify regions of parameters in which the matrix has (i) a structure with the dominant $\mu\tau$-block, (ii) various hierarchical structures, (iii) structures with special ordering or equalities of elements, (iv) the democratic form. In certain cases the matrix can be parameterized by powers of a unique expansion (ordering) parameter $\lambda \approx 0.2-0.3$ ($\lambda_{ord}\approx 0.6 - 0.7$). Perspectives to further restrict the structure of mass matrix in future experiments, in particular in the $\beta\beta_{0\nu}$-decay searches, are discussed.
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