Tri-Bimaximal Lepton Mixing and Leptogenesis

TL;DR

This paper investigates the relationship between Tri-Bimaximal lepton mixing and leptogenesis, showing that exact mixing leads to zero CP asymmetry in certain scenarios, but deviations can restore this asymmetry.

Contribution

It provides a model-independent analysis confirming that exact Tri-Bimaximal mixing results in vanishing leptogenesis asymmetry in unflavoured type I see-saw models, and explores how deviations affect this.

Findings

Exact Tri-Bimaximal mixing yields zero CP asymmetry in unflavoured leptogenesis.

Deviations from Tri-Bimaximal mixing can generate non-zero leptogenesis asymmetry.

The link between low-energy mixing parameters and high-energy leptogenesis is clarified.

Abstract

In models with flavour symmetries added to the gauge group of the Standard Model the CP-violating asymmetry necessary for leptogenesis may be related with low-energy parameters. A particular case of interest is when the flavour symmetry produces exact Tri-Bimaximal lepton mixing leading to a vanishing CP-violating asymmetry. In this paper we present a model-independent discussion that confirms this always occurs for unflavoured leptogenesis in type I see-saw scenarios, noting however that Tri-Bimaximal mixing does not imply a vanishing asymmetry in general scenarios where there is interplay between type I and other see-saws. We also consider a specific model where the exact Tri-Bimaximal mixing is lifted by corrections that can be parametrised by a small number of degrees of freedom and analyse in detail the existing link between low and high-energy parameters - focusing on how the deviations from Tri-Bimaximal are connected to the parameters governing leptogenesis.