Theory of neutrino masses and mixing

TL;DR

This paper reviews the current theoretical landscape of neutrino masses and mixing, discussing models, symmetries, and the role of right-handed neutrinos in explaining experimental observations.

Contribution

It provides a comprehensive overview of theoretical approaches, emphasizing the importance of symmetries, right-handed neutrinos, and UV completions in understanding neutrino properties.

Findings

Right-handed neutrinos are crucial for understanding neutrino mass mechanisms.

Symmetry considerations are key to explaining mixing patterns.

Minimal models like $ u$MSM are plausible in light of LHC results.

Abstract

In spite of enormous experimental progress in determination of the neutrino parameters, theory of neutrino mass and mixing is still on the cross-roads. Guidelines could be (i) the connection between zero neutrino charges (and therefore a possibility to be Majorana particle), smallness of the neutrino mass and large lepton mixing, (ii) joint description of leptons and quarks, (iii) existence of the right handed (RH) neutrinos without special quantum numbers. Properties of the RH neutrinos and the UV completion of the seesaw may turn out to be the key to understand the neutrino mass and mixing. In view of the LHC results minimalistic scenarios like $\nu$MSM look rather plausible. Still the GUT's with additional hidden sector, QLC, high scale flavor symmetries are appealing. Concerning mixing, the main issue is "symmetry or no symmetry" behind the observed pattern. The symmetry group condition is useful tool to study consequences of symmetries and to perform "symmetry building". Sterile neutrinos are challenge but also opportunity for the present theoretical constructions.