Extended scaling and residual flavor symmetry in the neutrino Majorana mass matrix

TL;DR

This paper introduces a complex extension of the real scaling ansatz for the neutrino Majorana mass matrix, allowing for nonzero neutrino masses, nonzero θ13, and maximal leptonic CP violation, with testable predictions for upcoming experiments.

Contribution

It proposes a novel complex extension of the real scaling ansatz that accommodates realistic neutrino masses, mixing angles, and CP violation, expanding the theoretical framework of neutrino flavor symmetry.

Findings

Leptonic Dirac CP-violation must be maximal.

Allowed normal mass ordering not favored by previous models.

Predictions testable in T2K, NOvA, and DUNE experiments.

Abstract

The residual symmetry approach, along with a complex extension for some flavor invariance, is a powerful tool to uncover the flavor structure of the $3\times3$ neutrino Majorana mass matrix $M_\nu$ towards gaining insights into neutrino mixing. We utilize this to propose a complex extension of the real scaling ansatz for $M_\nu$ which was introduced some years ago. Unlike the latter, our proposal allows a nonzero mass for each of the three light neutrinos as well as a nonvanishing $\theta_{13}$. A major result of this scheme is that leptonic Dirac CP-violation must be maximal while atmospheric neutrino mixing need not be exactly maximal. Moreover, each of the two allowed Majorana phases, to be probed by the search for nuclear $0\nu \beta\beta$ decay, has to be at one of its two CP-conserving values. There are other interesting consequences such as the allowed occurrence of a normal mass ordering which is not favored by the real scaling ansatz. Our predictions will be tested in ongoing and future neutrino oscillation experiments at T2K, NO$\nu$A and DUNE.