1. Particle Data Group collaboration, J. Beringer et al., Review of particle physics, Phys. Rev. D 86 (2012) 010001 [ INSPIRE ].
2. C.W. Chiang, T. Nomura and J. Tandean, Dark matter and Higgs boson in a model with discrete gauge symmetry, Phys. Rev. D 87 (2013) 073004 [ arXiv:1205.6416 ] [ INSPIRE ].
3. L.M. Krauss and F. Wilczek, Discrete gauge symmetry in continuum theories, Phys. Rev. Lett. 62 (1989) 1221 [ INSPIRE ].
4. P. Minkowski, μ → eγ at a rate of one out of 1-billion muon decays?, Phys. Lett. B 67 (1977) 421 [ INSPIRE ].
5. T. Yanagida, Horizontal symmetry and masses of neutrinos, in the proceedings of the Workshop on unified theory and baryon number in the universe, O. Sawada and A. Sugamoto eds., KEK, Tsukuba, Japan (1979).