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}. These rho-sigma plots allow to systematically scan all possible structures of the mass matrix. We identify regions of parameters in which the matrix has (i) a structure with the dominant mu tau-block, (ii) various hierarchical structures, (iii) flavor alignment, (iv) structures with special ordering or equalities of elements, (v) the democratic form. In certain cases the matrix can be parameterized by powers of a unique expansion (ordering) parameter lambda approximately 0.2 - 0.3 (lambda_{ord} approximately 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.