Extending limits on neutral heavy leptons

Neutral leptons corresponding to "right-handed neutrinos" are expected in many grand unified theories of the electroweak strong interactions. At present, the experimental limits on the masses and mixings with ordinary neutrinos of these leptons are very poor for masses above about 1 GeV. Suggestions are made for extending these limits, in experiments involving the production of $b$ quarks, $W$ and $Z$ bosons, and any heavier gauge bosons that might exist, and via high-statistics studies of neutral-current neutrino interactions.