Heavy neutrinos production and decay in future $e^+e^-$ colliders

The production of heavy and light neutrinos in $e^+e^-$ future colliders is considered. The cross section for the process $e^+e^- \rightarrow \nu N$ and then the heavy neutrino decay $N \rightarrow W^{\pm} e^{\mp}$ is determined for experimentally possible values of mixing matrix elements. The bound on the heavy neutrino-electron mixing is estimated in models without right-handed currents. The role of neutrino CP eigenvalues and the mass of the lightest Higgs particle are investigated. The angular distribution of charged leptons in the total CM frame resulting from the heavy neutrino decay and from the main $W^+W^-$ production background process are briefly compared.