Muonium-Antimuonium Oscillations in an Extended Minimal Supersymmetric Standard Model : Springer : 9781441983299 : 1441983295 : 09 Feb 2011 : This innovative work investigated two models where the muonium-antimuonium oscillation process was mediated by massive Majorana neutrinos and sneutrinos. First, we modified the Standard Model only by the inclusion of singlet right-handed neutrinos and allowing for general renormalizable interactions producing neutrino masses and mixing. The see-saw mechanism was employed to explain the smallness of the observed neutrino masses. A lower bound on the righthanded neutrino mass was constructed using the experimental limits set by the nonobservation of the muonium-antimuonium oscillation process. Second, we modified the Minimal Supersymmetric Standard Model by the inclusion of three right-handed neutrino superfields. The experimental result of the muonium-antimuonium oscillation process generated a lower bound on the ratio of the two Higgs field VEVs.