A split seesaw model with hidden neutrinoless double beta decay but successful leptogenesis

TL;DR

This paper proposes a split seesaw model that hides neutrinoless double beta decay while still allowing successful leptogenesis, by employing specific neutrino mass structures and symmetries.

Contribution

It introduces a split seesaw framework with one light and two heavy right-handed neutrinos that achieves the AIT ansatz and successful leptogenesis simultaneously.

Findings

The AIT ansatz can be realized with specific Yukawa coupling conditions.

Abelian flavor symmetry can implement the AIT ansatz.

Leptogenesis is viable with triangular or μ-τ reflection symmetric mass matrices.

Abstract

In a paper by Asaka, Ishida and Tanaka \cite{hiding}, they proposed a novel possibility (which will be referred to as the AIT ansatz) that, in spite of the Majorana nature of neutrinos, the neutrinoless double beta ($0\nu \beta\beta$) decay can be hidden. In the original AIT model, the AIT ansatz is realized in the minimal seesaw model with two right-handed neutrinos which have a hierarchical mass structure: the lighter and heavier right-handed neutrinos are respectively much lighter and heavier than the typical Fermi-momentum scale of nuclei. However, the original AIT model does not accommodate a successful leptogenesis. For this problem, in this paper we study a split seesaw model with one lighter right-handed neutrino but two heavier right-handed neutrinos which can realize the AIT ansatz and accommodate a successful leptogenesis simultaneously. We first give the condition on the neutrino Yukawa couplings for realizing the AIT ansatz, discuss its realization by employing an Abelian flavor symmetry, and study its implications for the mixing of the lighter right-handed neutrino with three left-handed neutrinos. We then successively study the implications for leptogenesis of the interesting scenarios where $M^{}_{\rm D}$ is a triangular matrix (which has maximally-restricted texture zeros, in line with the simplicity principle) or respects the $\mu$-$\tau$ reflection symmetry (which is well motivated by the experimental results), on top of the AIT ansatz.