Double beta decay

We review the recent developments in the field of nuclear double beta decay , which is presently an important topic in both nuclear and particle physic s. The mechanism of lepton number violation within the neutrinoless double beta decay (Ov beta beta-decay) is discussed in the context of the problem of neutrino mixing and the R-parity violating supersymmetric extensions of the standard model. The problem of reliable determination of the nuclear ma trix elements governing both two-neutrino and neutrinoless modes of the dou ble beta decay is addressed. The validity of different approximation scheme s in the considered nuclear structure studies is analysed and the role of t he Pauli exclusion principle for a correct treatment of nuclear matrix elem ents is emphasized. The constraints on different lepton-number violating pa rameters such as effective electron neutrino mass, effective right-handed w eak interaction parameters, effective Majoron coupling constant and R-parit y violating SUSY parameters are derived from the best presently available e xperimental limits on the half-life of Ov beta beta-decay.