Leptogenesis from Low Energy $CP$ Violation

TL;DR

This paper investigates whether the observed matter-antimatter asymmetry can be explained by low-energy $CP$ violation in neutrino physics through thermal leptogenesis, highlighting conditions for its viability across a wide temperature range.

Contribution

It demonstrates the viability of thermal flavoured leptogenesis driven solely by low-energy neutrino phases over a broad temperature spectrum, clarifying the role of different $CP$ phases.

Findings

Thermal flavoured leptogenesis is viable from $10^{6}$ to $10^{13}$ GeV.

Low-energy $CP$ phases can generate the baryon asymmetry at high scales.

Majorana phases can lead to successful leptogenesis without fine-tuning.

Abstract

We revisit the possibility of producing the observed baryon asymmetry of the Universe via thermal leptogenesis, where $CP$ violation comes exclusively from the low-energy phases of the neutrino mixing matrix. We demonstrate the viability of thermal flavoured leptogenesis across seven orders of magnitude $\left(10^{6}<T \text{ (GeV)}< 10^{13}\right)$, using modern numerical machinery, where the lower bound can be reached only if flavour effects are taken into account and its value depends on the allowed degree of cancellation between the tree-level and radiative contributions to the light neutrino masses. At very high scales $\left( T \gg 10^{12} \text{ GeV} \right)$, we clarify that thermal leptogenesis is sensitive to the low-energy phases, in contradiction with what is usually claimed in the literature. In particular we demonstrate that Majorana-phase leptogenesis is in general viable while Dirac-phase leptogenesis requires some level of fine-tuning.