Neutrinoless Double Beta Decay and Its “inverse”

Recent considerations by these authors pointed out the attractive features which a search for the exchange of heavy Majorana neutrinos could have for solving the mass and the lepton number puzzles for all neutrinos, in TeV-level electron-electron scattering. In the present note, we show that, contrary to subsequently published arguments, non-observation of neutrinoless double beta decay has, to date, no bearing on the promise of this important task for future linear electron colliders. Recent developments in the planning for electron colliders in the TeV energy region have renewed interest in the possibility to investigate the reaction e−e− → W−W−, (1) which can proceed by means of the exchange of a Majorana neutrino. While previous work on this reaction (Refs. [1,2,3,4]) had not led to promising experimental prospects, we showed that the new generation of presently projected linear colliders can in fact deliver luminosities compatible with the production of convincing signals for reaction (1), or, failing that, important new limits on the masses and couplings of heavy Majorana neutrinos. This is predicated on the availability of highly polarized electron beams at center-of-mass energies upward of 500 GeV, where left-handed electrons will be able to interact via the exchange of heavy lefthanded Majorana singlet neutrino states with masses ≥ 1 TeV. For the case of