Heavy-neutral-lepton production in electron-positron colliding-beam experiments

We present possible mechanisms for single and pair heavy-neutral-lepton production in electron-positron colliding-beam experiments for the general class of gauge models involving these leptons. We have calculated the cross sections for the processes e⁺e⁻→E⁰Ē⁰, e⁺e⁻→M⁰M̄⁰, $e^{+}{e}^{-}\to {\bar{M}}^0{\nu }_{\mu }$, e⁺e⁻→Ē⁰νₑ, and e⁺e⁻→μ⁺μ⁻ in all such models. Specific results that obtain in the Georgi-Glashow model and the B\'eg-Zee version of the SU(2)⊗U(1) model are also presented. The process e⁺e⁻→E⁰Ē⁰ turns out to be a dominant mode in the e⁺e⁻-annihilation experiments, in the Georgi-Glashow model, if the W boson is not very heavy.