1. M. Kobayashi and T. Maskawa, Prog, Theor. Exp. Phys. 49, 652 (1973).
2. M. Tanabashi et al. (Particle Data Group), Phys. Rev. D 98, 030001 (2018) and 2019 update.
3. Carlo Giunti and Chung W. Kim, Fundamentals of Neutrino Physics and Astrophysics (Oxford University Press, 2007).
4. C. Jarlskog, Phys. Rev. Lett. 55, 1039 (1985).
5. V. A. Rubakov and M. E. Shaposhnikov, Phys. Usp. 39, 461 (1996).