ABSTRACT
This process is only possible if the neutrino is a massive Majorana particle, and thus it is impossible within the SM. Experiments that search for such rare decay have since long being performed but always with negative results [5). Currently the Heidelberg-Moscow !3!3 experiment at the GranSasso laboratory in Italy provides the best experimental lower bound on the half-life of the process [6]:
The proposed GENIUS double beta experiment (see section VI), now under development, will either increase the lower bound on the half-life by two or three orders of magnitude or observe the decay. From the theoretical point of view, the strong bound on the half-life in Eq. (2) has been turned into a powerful tool to impose constraints on models of new physics which predict a non zero amplitude for the !3i30v decay [7). Studies in this direction include: an investigation of new super-symmetric contributions from Rparity violating MSSM [8] which shows how constraints on parameters of the model from non-observation of !3!3ov are stronger than those available from accelerator experiments; a detailed analysis of the contribution to !3!3ov from left-right symmetric models[9]; a study of the effective low energy charged current lepton-quark interactions due to the exchange of heavy leptoquarks [10].
