The Nuclear Double Beta Decay and its Implications

The nuclear double beta decay is a process of second order in the perturbative expansion of the weak-interaction lagrangian. It can be detected only in nuclear environment in few very special cases where the nuclear-structure conditions do not allow the first-order processes (beta decays) to take place. The neutrinoless form of the double beta decay can only proceed via massive majorana neutrinos and its detection would thus imply existence of physics going beyond the standard model of electroweak and strong interactions. In this article special cases of these decays, namely the ones feeding 0⁺ states of the final nucleus, are discussed in more detail. These decays are of present interest due to their implications conserning future underground experiments using huge active-mass detectors.