A Case of Subdominant/Suppressed "High Energy" Contribution to the Baryon Asymmetry of the Universe in Flavoured Leptogenesis

TL;DR

This paper investigates the role of high-energy CP-violation in flavoured leptogenesis within a type I see-saw model, revealing scenarios where low-energy phases dominate despite large high-energy CP-violating parameters.

Contribution

It demonstrates that in certain parameter regions, high-energy CP-violation is subdominant, and successful leptogenesis relies primarily on low-energy Majorana phases.

Findings

High-energy CP-violation can be large but subdominant in baryon asymmetry production.

Successful leptogenesis can occur with suppressed high-energy contributions if low-energy phases provide CP-violation.

Inverted hierarchy neutrino spectrum favors scenarios with dominant low-energy CP-violation.

Abstract

The CP-violation necessary for the generation of the baryon asymmetry of the Universe $Y_B$ in the "flavoured" leptogenesis scenario can arise from the "low energy" PMNS neutrino mixing matrix $U$ and/or from the "high energy" part of neutrino Yukawa couplings, which can mediate CP-violating phenomena only at some high energy scale. The possible interplay between these two types of CP-violation is analysed. The type I see-saw model with three heavy right-handed Majorana neutrinos having hierarchical spectrum is considered. We show that in the case of inverted hierarchical light neutrino mass spectrum, there exist regions in the corresponding leptogenesis parameter space where the relevant "high energy" phases have large CP-violating values, but the purely "high energy" contribution in $Y_B$ plays a subdominant role in the production of baryon asymmetry compatible with the observations. In some of these regions the purely "high energy" contribution in $Y_B$ is so strongly suppressed that one can have successful leptogenesis only if the requisite CP-violation is provided by the Majorana phase(s) in the neutrino mixing matrix.