The recent progress in theoretical description of the neutrinoless double beta decay (0νββ−decay) is briefly reviewed. A possible effect of nuclear medium on exchange of three light neutrinos is addressed. It is shown that non-standard neutrino interaction generates in-medium Majorana neutrino masses, which influences the 0νββ-decay rate.
Nuclear physics is important for extracting useful information from the 0νββ-decay data. Interpreting existing results as a measurement of effective Majorana neutrino mass depends crucially on the knowledge of the corresponding nuclear matrix elements (NMEs) that govern the decay rate and must be evaluated using tools of nuclear structure theory. To this end, the results of NMEs calculation within sophisticated nuclear structure approaches are presented. Subject of interest are the accuracy and reliability of calculated NMEs. An impact of the quenching of the axial-vector coupling constant on double-beta decay processes is discussed.
Further, the 0νββ-decay with the inclusion of the right-handed leptonic and hadronic currents and by assuming small neutrino masses is revisited. Differential characteristics and phase-space integrals are calculated by using exact Dirac wave function with finite nuclear size and electron screening. The effective lepton number violating parameters are discussed in light of recent progress achieved by the GERDA, EXO and Kamland-Zen experiments.
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