Abstract
It is shown that the nondynamical violation of the isospin and Wigner SU(4) symmetries, induced by the Hartree-Fock-BCS approximation, can be circumvented by using the quasiparticle random-phase approximation. The suppression mechanism for the ββ-decay transition rates, proposed by Vogel and Zirnbauer, is found to be closely related to the restoration of SU(4) symmetry. It is suggested that the extreme sensitivity of the ββ-decay amplitude on the proton-neutron coupling is a consequence of the explicit violation of the SU(4) symmetry and therefore an artifact of the model. A prescription is given for fixing this interaction strength within the quasiparticle random-phase approximation itself, which in this way acquires predicting power on both single and double β-decay lifetimes.

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