Insights on the Scale of Leptogenesis from Neutrino Masses and Neutrinoless Double-Beta Decay

TL;DR

This paper investigates how low-energy neutrino observables, like the lightest neutrino mass and neutrinoless double-beta decay parameters, constrain the minimal scale of heavy neutrinos needed for successful leptogenesis.

Contribution

It provides a numerical analysis of the minimum heavy neutrino mass for leptogenesis, considering flavor effects and the interplay with neutrino mass orderings and cancellations.

Findings

Minimum heavy neutrino mass depends on lightest neutrino mass and decay parameters.

Flavor effects significantly influence leptogenesis scale.

Results inform experimental searches for neutrinoless double-beta decay and neutrino mass measurements.

Abstract

We revisit the thermal leptogenesis scenario in the type-I seesaw framework featuring three heavy Majorana neutrinos with a hierarchical mass spectrum. We focus on low energy observables, specifically the lightest neutrino mass $m_{\nu}^{\rm lightest}$ and the neutrinoless double-beta decay effective mass parameter $m^{\rm eff}_{\beta\beta}$. In particular, we numerically calculate the minimum mass of the lightest heavy Majorana neutrino, $M_1^{\rm min}$, required for successful leptogenesis as a function of $m_{\nu}^{\rm lightest}$ and $m_{\beta\beta}^{\rm eff}$, considering both normal and inverted light neutrino mass orderings. Flavour effects are taken into account within the flavoured density matrix formalism. We also examine the interplay between fine-tuned cancellations in the seesaw relation and $M_1^{\rm min}$. Recent and forthcoming searches for neutrinoless double-beta decay, along with cosmological probes of the sum of neutrino masses, motivate this analysis, as they can provide key insights into the minimal scale of thermal leptogenesis and its broader implications.