Majorana neutrino. Is double neutrinoless beta decay possible in the framework of the weak interactions? How to prove that neutrino is Majorana particle

Abstract

Usually it is supposed that Majorana neutrino produced in the superposition state $\chi_L = \nu_L + (\nu_L)^c$ and then follows the neutrinoless double beta decay. But since weak interactions are chiral invariant then the neutrino at production has definite helicity (i.e., $\nu_L$ and $(\nu_L)^c$ neutrinos are separately produced and then neutrino is not in the superposition state). This helicity cannot change after production without any external interactions. Thus we see that for unsuitable helicity the neutrinoless double $\beta$ decay is not possible even if neutrino is a Majorana particle. Also transition of Majorana neutrino into antineutrino at their oscillations is forbidden since helicity in vacuum holds. Then only possibility to prove that neutrino is a Dirac but not Majorana particle is detection transition of $\nu_L$ neutrino into (sterile) antineutrino $\bar\nu_R$ (i.e., $\nu_L \to \bar\nu_R$) at neutrino oscillations. Transition Majora neutrino $\nu_L$ into $(\nu_R)^c$ (i.e., $\nu_L \to (\nu_R)^c$) at oscillations is unobserved since it is supposed that mass of $(\nu_R)^c$ is very big.