Bounds on right-handed neutrino parameters from observable leptogenesis

TL;DR

This paper derives bounds on right-handed neutrino parameters within a minimal extension of the Standard Model, linking leptogenesis, neutrino masses, and observable CP-violating phases, providing analytical tools and constraints.

Contribution

It introduces an analytical approximation to kinetic equations in leptogenesis, revealing parameter dependencies and deriving bounds on heavy neutral lepton properties and CP phases.

Findings

Bounds on HNL mixings depending on their masses

Constraints on CP-violating phases and neutrinoless double-beta decay

Good agreement with numerical results

Abstract

We revisit the generation of a matter-antimatter asymmetry in the minimal extension of the Standard Model with two singlet heavy neutral leptons (HNL) that can explain neutrino masses. We derive an accurate analytical approximation to the solution of the complete linearized set of kinetic equations, which exposes the non-trivial parameter dependencies in the form of parameterization-independent CP invariants. The identification of various washout regimes relevant in different regions of parameter space sheds light on the relevance of the mass corrections in the interaction rates and clarifies the correlations of baryogenesis with other observables. In particular, by requiring that the measured baryon asymmetry is reproduced, we derive robust upper or lower bounds on the HNL mixings depending on their masses, and constraints on their flavour structure, as well as on the CP-violating phases of the PMNS mixing matrix, and the amplitude of neutrinoless double-beta decay. We also find certain correlations between low and high scale CP phases. Especially emphasizing the testable part of the parameter space we demonstrate that our findings are in very good agreement with numerical results. The methods developed in this work can help in exploring more complex scenarios.