Prospects for testing electroweak scale sterile neutrinos at future colliders

The extension of the Standard Model of particle physics by sterile neutrinos can naturally explain the smallness of neutrino masses as observed by neutrino oscillation and nuclear beta decay experiments. These hypothetical particles, also referred to as heavy neutrinos in the mass eigenbasis, can give rise to a testable phenomenology when they have masses around the electroweak scale. Hence they are actively searched for at, for instance, colliders such as the Large Hadron Collider. The proposed future colliders, which are currently in the design phase, will be more powerful than the operated colliders to date. The new possibilities which they provide to search for sterile neutrinos and to test the neutrino mass mechanism in the not too far future have therefore to be assessed.
In this thesis, various aspects of the sterile neutrino phenomenology as well as various searches for sterile neutrinos at colliders are investigated. In particular, we study the contributions from sterile neutrinos to the Higgs boson production mechanism at colliders, the implications of long-lived heavy neutrinos that lead to displaced vertex events, lepton-number violation as the manifestation of heavy neutrino-antineutrino oscillations, lepton-flavour violation as the consequence of leptonic mixing, the possibilities to resolve heavy neutrino-antineutrino oscillations, how to test the viable leptogenesis parameter space, and their implications to collider searches. These collider studies are investigated in the context of low scale seesaw scenarios featuring ns = 2 sterile neutrinos with masses in the range of O(1 GeV) and O(1 TeV), which constitutes the benchmark scenario. Within the benchmark scenario, analytical calculations, and analyses of Monte Carlo generated event samples are performed.
The investigated collider studies demonstrate promising avenues to test sterile neutrinos at future colliders. This contains novel possible search strategies by the search for Higgs bosons produced from heavy neutrinos and by probing the effects from heavy neutrino-antineutrino oscillations via the displaced vertex search. The assessed capabilities of the future colliders with respect to the sterile neutrino searches contribute to the physics case of the future colliders.