Weak complementarity from discrete symmetries

TL;DR

This paper reviews discrete symmetry models, especially S4, to explain lepton mixing patterns like bimaximal mixing, and presents a model that aligns with experimental data and cosmological constraints.

Contribution

It introduces an explicit S4-based flavor model that produces bimaximal mixing corrected to match observations and explores its implications for neutrino hierarchy and leptogenesis.

Findings

Bimaximal mixing can be a good starting point for lepton mixing models.

The proposed S4 model yields a neutrino spectrum with a moderate normal hierarchy.

The model's predictions are compatible with leptogenesis constraints.

Abstract

The neutrino oscillation data find a good approximation in the so-called tri-bimaximal pattern. Recently a paper appeared showing that also the bimaximal pattern, which is already ruled out by the measurements, could be a very good starting point in order to describe the lepton mixing. In this paper I review both the flavour structures and then I present an explicit flavour model based on the discrete group S4, in which the PMNS mixing matrix is of the bimaximal form in first approximation and after it receives corrections which bring it in agreement with the data. The resulting spectrum of light neutrinos shows a moderate normal hierarchy and is compatible, within large ambiguities, with the constraints from leptogenesis as an explanation of the baryon asymmetry in the Universe.