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 αβ , on the CP-violating Dirac, δ, and Majorana, ρ, σ, phases, for different values of the mixing angle θ 13 and of the absolute mass scale, m 1. The contours of constant mass in the ρ– σ plane have been constructed for all m αβ . These ρ– σ 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 μτ-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 λ≈0.2–0.3 ( λ ord≈0.6–0.7). Perspectives to further restrict the structure of mass matrix in future experiments, in particular in the ββ 0 ν -decay searches, are discussed.