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

Original · EN

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 Mₙ ≥ 163 for normal hierarchy of neutrino masses, while Mₙ = 188 -- 269 and Mₙ ≥ 285 for inverted hierarchy case. Furthermore, we find in the latter case that the possible value of the Majorana phase is restricted for Mₙ = 188 -- 350, which leads to the fact that the rate of neutrinoless double beta decay is also limited.