Double Beta Decay, Nuclear Structure and Physics beyond the Standard Model

Abstract

The Neutrinoless Double Beta Decay (0νββ) allows to determine the absolute scale of the neutrino masses. For this one must assume, that the light Majorana neutrino exchange is the leading mechanism for 0νββ and that the matrix element of this transition can ba calculated reliably. The different methods: Quasi-particle Random Phase Approximation (QRPA), Shell Model (SM), Projected Hartree-Fock-Bogoliubov (PHFB) and Interacting Boson Model (IBM2) to calculate these matrix elements are reviewed. The question, how one can determine the leading mechanism or mechanisms from the data of the 0νββ decay in different nuclei is studied in the later part of this article. Possible interference terms allow to test CP (Charge and Parity conjugation) violation.