General lepton structure with naturalness assumptions

Two classes of lepton models which have natural $\mu e$ universality and $\mu e$-flavor-diagonal neutral currents are studied within the SU(2) x U(1) gauge-theory framework. One of them has both $V+A$ and $V-A$ decaying negatively charged heavy leptons, vanishing $\mu \to e\gamma$ and $\mu \to \mathrm{ee}\overline{e}$ decay rates, and Weinberg-Salam-type neutral currents for known leptons. The other, which is vectorlike, has $V-A$ decaying (and probably $V$ decaying) charged heavy leptons and nonvanishing $\mu \to \mathrm{ee}\overline{e}$ decay rates at higher orders. Also an updated analysis of neutrino-electron scattering is presented.