1. A. Strumia, F. Vissani, (2006). hep-ph/0606054
2. μ→eγ at a rate of one out of 109 muon decays?
3. T. Yanagida, Proceedings of the Workshop on the Baryon Number of the Universe and Unified Theories, Tsukuba, Japan, 13–14 Feb 1979 (1979), in: Proceedings of the Workshop on the Baryon Number of the Universe and Unified Theories, Tsukuba, Japan, 13–14 Feb 1979
4. M. Gell-Mann, P. Ramond, R. Slansky, (1980), Print-80-0576 (CERN)