Neutrino masses from new generations

TL;DR

This paper explores how adding extra generations and right-handed neutrinos can generate neutrino masses radiatively, analyzing the resulting phenomenology and experimental prospects for detection.

Contribution

It proposes a minimal extension with five generations and two right-handed neutrinos to explain neutrino masses and explores observable consequences.

Findings

Standard three-generation model is incompatible with observed neutrino hierarchy under minimal assumptions.

Five generations and two right-handed neutrinos can accommodate all current data.

Potential observable signals in neutrinoless double beta decay, muon-electron conversion, and LHC experiments.

Abstract

We reconsider the possibility that Majorana masses for the three known neutrinos are generated radiatively by the presence of a fourth generation and one right-handed neutrino with Yukawa couplings and a Majorana mass term. We find that the observed light neutrino mass hierarchy is not compatible with low energy universality bounds in this minimal scenario, but all present data can be accommodated with five generations and two right-handed neutrinos. Within this framework, we explore the parameter space regions which are currently allowed and could lead to observable effects in neutrinoless double beta decay, $\mu - e$ conversion in nuclei and $\mu \rightarrow e \gamma$ experiments. We also discuss the detection prospects at LHC.