Direct Search for Right-handed Neutrinos and Neutrinoless Double Beta Decay

TL;DR

This paper explores an extension of the Standard Model with two light right-handed neutrinos, analyzing their mass constraints, implications for neutrinoless double beta decay, and potential for baryogenesis via flavor oscillations.

Contribution

It provides new constraints on the mass range of right-handed neutrinos and links these to neutrinoless double beta decay rates within a minimal extension of the Standard Model.

Findings

Right-handed neutrino masses are constrained to specific ranges depending on neutrino hierarchy.

The Majorana phase is restricted for certain mass ranges, affecting decay rates.

Neutrinoless double beta decay rates are limited by the model's parameters.

Abstract

We consider an extension of the Standard Model by two right-handed neutrinos, especially with masses lighter than charged $K$ meson. This simple model can realize the seesaw mechanism for neutrino masses and also the baryogenesis by flavor oscillations of right-handed neutrinos. We summarize the constraints on right-handed neutrinos from direct searches as well as the big bang nucleosynthesis. It is then found that the possible range for the quasi-degenerate mass of right-handed neutrinos is $M_N \geq 163 \MeV$ for normal hierarchy of neutrino masses, while $M_N = 188 \text{--} 269 \MeV$ and $M_N \geq 285 \MeV$ for inverted hierarchy case. Furthermore, we find in the latter case that the possible value of the Majorana phase is restricted for $M_N = 188 \text{--} 350 \MeV$, which leads to the fact that the rate of neutrinoless double beta decay is also limited.