The e ective neutrino mass of neutrinoless double-beta decays:how possible to fall into a well

摘要: The neutrinoless double-beta (0ν2β) decay is currently the only feasible process in particle and nuclear physics to probe whether massive neutrinos are the Majorana fermions. If they are of the Majorana nature and have a normal mass ordering, the effective neutrino mass term mee of a 0ν2β decay may suffer significant cancellations among its three components and thus sink into a decline,resulting in a “well” in the three-dimensional graph of |mee| against the smallest neutrino mass m1 and the relevant Majorana phase ρ. We present a new and complete analytical understanding of the fine issues inside such a well, and identify a novel threshold of |mee| in terms ofthe neutrino masses and flavor mixing angles: |mee|∗ = m3 sin2 θ13 in connection with tan θ12 = m1/m2 and ρ = π. This threshold point, which links the local minimum and maximum of |mee|, can be used to signify observability or sensitivity of the future 0ν2β-decay experiments. Given current neutrino oscillation data, the possibility of |mee| < |mee|∗ is found to be very small.