Symmetry of Leptonic Weak Interactions and Lepton Mass Spectrum
J. P. Hsu · Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D. Particles and fields · 1972
The invariance principle that excludes the neutral leptonic currents and uniquely determines the leptonic weak interactions is discussed. Based on symmetry considerations and the existence of two different neutrinos, we suggest that the neutrino masses are not strictly zero and there are new heavy charged leptons and their neutrinos. A possible lepton mass spectrum is obtained.