Lepton flavor nonconservation

Interest in lepton flavor nonconservation has grown in the past three years because it provides a signal for the existence of hitherto unobserved heavy particles, and for the grand unification of strong and electro-weak interactions. Heavy particles which may be associated with the violation of lepton flavor include: heavy leptons, especially neutral ones; new multiplets of Higgs scalars in addition to the one needed for the minimal Glashow-Weinberg-Salam model of electro-weak interactions; or new kinds of gauge vector bosons which transmit the horizontal symmetries between the various families of leptons and quarks. This something new aspect of the subject applies particularly to charged lepton processes like μ → eν