  Sterile neutrinos are an attractive extension of the Standard Model of
elementary particles towards including a mechanism for generating the observed
light neutrino masses. We discuss that when an approximate protective "lepton
number"-like symmetry is present, the sterile neutrinos can have masses around
the electroweak scale and potentially large neutrino Yukawa couplings, which
makes them well testable at planned future particle colliders. We
systematically discuss the production and decay channels for sterile neutrinos
at electron-proton colliders and give a complete list of the leading order
signatures for sterile neutrino searches. We highlight several novel search
channels and present a first look at the possible sensitivities for the
active-sterile mixing parameters and the heavy neutrino masses. We also compare
the performance of electron-proton colliders with the ones of proton-proton and
electron-positron colliders, and discuss the complementarity of the different
collider types.
