The qrpa and beyond

3 Conclusions

In the opinion of this moderator the talks presented by the speakers do show the variety of views about the physics governing double beta decay transitions. Therefore, these conclusions can also show a strong bias and they should be taken as such.

The predictive power of the QRPA approximation, in its conventional form, seems to be more firmly established. The physical meaning of the collapse of the QRPA, as induced by a change in the two-body correlations mostly of isoscalar nature, was discussed. Other approximations which aimed at the removal of the “phase-instability” (like the RQRPA) apparently do not pay-off since they violate the Ikeda Sum Rule as much as the consistency of the interactions. More realistic treatments based on the simultaneous description of fermionic and bosonic couplings are, for the moment, at some embrionary level of development and more theoretical work has to be done in order to see which kind of self-consistency can be achieved and how the question of the QRPA “phase-transition” can be overcome. The inclusion of proton-neutron pairing correlations for nuclei with large neutron excess is not justified, as seen by the results obtained in the calculations of the structure of pairing effects in light mass nuclei. The use of spectroscopic information and single-beta decay data, as experimental tools to test the validity of the models, is strongly recommended.