Lepton family numbers and non-relativistic Majorana neutrinos
  In this talk, we have reviewed the recent development on the time evolution
of lepton family number carried by Majorana neutrinos \cite{Adam:2021qiq}. This
article focuses on the subtle points of the derivation of the lepton family
numbers and their time evolution. We also show how the time evolution is
sensitive to $m_{ee}$ and $m_{e\mu}$ components of the effective Majorana mass
matrix by applying the formula to the two family case. The dependence on the
Majorana phase is clarified and the implication on CNB (cosmic neutrino
background) is also discussed.
