Two-neutrino double beta decay of 76Ge within deformed QRPA: A new suppression mechanism

The effect of deformation on the two-neutrino double decay (2nbb-decay) for ground state transition 76Ge -> 76Se is studied in the framework of the deformed QRPA with separable Gamow-Teller residual interaction. A new suppression mechanism of the 2nbb-decay matrix element based on the difference in deformations of the initial and final nuclei is included. An advantage of this suppression mechanism in comparison with that associated with ground state correlations is that it allows a simultaneous description of the single beta and the 2nbb-decay. By performing a detail calculation of the 2nbb-decay of 76Ge, it is found that the states of intermediate nucleus lying in the region of the Gamow-Teller resonance contribute significantly to the matrix element of this process