Study of the nuclear double beta decay is a subject of the current intensive
activity, both experimental and theoretical. The neutrinoless mode of this
process of the double beta decay with emission of two
electrons only is
related to physics beyond the Standard Model. It requires the existence of the
lepton number violating massive Majorana neutrinos and/or right-handed current
admixture to the standard V-A weak interaction. The other possibility is to
extend the SM to the Minimal Supersymmetric Standard Model (MSSM).
From the explicit dependence of the neutrinoless double beta decay transition probability one can deduce immediately that the transition depends on different nuclear matrix elements, which have to be calculated reliably if we expect reliable limits on the nonstandard physics parameters like the electron neutrino mass, the mixing angle between the vector bosons mediating left- and right-handed weak interactions and the mass ratio of these bosons.