If a fourth generation of leptons exists, both the neutrino and its charged partner must be heavier than 45 GeV. We suppose that the neutrino is the heavier of the two, and that a global or discrete symmetry prohibits intergenerational mixing. In that case, nonrenormalizable Planck scale interactions will induce a very small mixing; dimension-five interactions will lead to a lifetime for the heavy charged lepton ∼(1–100) yr. Production of such particles is discussed, and it is shown that a few thousand can be produced and collected at a linear collider. The possible uses of these heavy leptons are also briefly discussed.

• Received 10 May 1993

DOI:https://doi.org/10.1103/PhysRevD.48.5437