Seesaw mechanism and structure of neutrino mass matrix

TL;DR

This paper investigates the seesaw mechanism for neutrino mass generation, showing how certain assumptions lead to a natural explanation of large lepton mixing, favoring a normal mass hierarchy and specific neutrino mass scales.

Contribution

It introduces a constrained minimal seesaw model with hierarchical Dirac masses and large lepton mixing, providing insights into neutrino mass hierarchy and mixing parameters.

Findings

Large atmospheric mixing can be naturally obtained.

Favors the normal neutrino mass hierarchy.

Predicts a small $V_{e3}$ and a right-handed neutrino mass scale of 10^{10}-10^{11} GeV.

Abstract

We consider the seesaw mechanism of neutrino mass generation in the light of our present knowledge of the neutrino masses and mixing. We analyse the seesaw mechanism constrained by the following assumptions: (1) minimal seesaw with no Higgs triplets, (2) hierarchical Dirac masses of neutrinos, (3) large lepton mixing primarily or solely due to the mixing in the right-handed neutrino sector, and (4) unrelated Dirac and Majorana sectors of neutrino masses. We show that large mixing governing the dominant channel of the atmospheric neutrino oscillations can be naturally obtained and point out that this constrained seesaw mechanism favours the normal mass hierarchy for the light neutrinos leading to a small $V_{e3}$ entry of the lepton mixing matrix and a mass scale of the lightest right handed neutrino $M\simeq 10^{10} - 10^{11}$ GeV. Any of the three main neutrino oscillation solutions to the solar neutrino problem can be accommodated. The inverted mass hierarchy and quasi-degeneracy of neutrinos are disfavoured in our scheme.