GAUGE INVARIANCE OF THE MUONIUM-ANTIMUONIUM OSCILLATION TIME SCALE AND LIMITS ON RIGHT-HANDED NEUTRINO MASSES

The guage invariance of the muonium-antimuonium (M (M) over bar) oscillation time scale is explicitly demonstrated in the Standard Model modified only by the inclusion of singlet right-handed neutrinos and allowing for general renormalizable interactions. The see-saw mechanism is exploited resulting in three light Majorana neutrinos and three heavy Majorana neutrinos with mass scale M-R >> M-W. The leading order matrix element contribution to the M (M) over bar oscillation process is computed in R-xi guage and shown to be xi-independent thereby establishing the guage invariance to this order. Present experimental limits resulting from the non-observation of the oscillation process sets a lower limit on M-R roughly of order 600 GeV.