Single Neutral Heavy Lepton Production at e^+e^- and \mu^+ \mu^- Colliders

Many extensions of the Standard Model include extra fermions. We here consider a model containing Dirac neutral heavy leptons in addition to massless neutrinos. These neutral heavy leptons can be produced singly along with a massless neutrino in $e^+ e^-$ and $\mu^+ \mu^-$ collisions. The production rates depend on the neutral heavy lepton masses and mixing parameters. We here consider the rates for this process and potential signatures for the machine energies and luminosities suggested for the Snowmass study.