Influence of 2p-2h configurations on β-decay rates

The effects of the phonon-phonon coupling on the beta-decay rates of neutron-rich nuclei are studied in a microscopic model based on Skyrme-type interactions. The approach uses a finite-rank separable approximation (FRSA) of the Skyrme-type particle-hole (p-h) residual interaction. Very large two-quasiparticle spaces can thus be treated. A redistribution of the Gamow-Teller (G-T) strength is found due to the tensor correlations and the 2p-2h fragmentation of G-T states. As a result, the beta(-)-decay half-lives are decreased significantly. By using the Skyrme interaction SGII together with a volume-type pairing interaction, we illustrate this reduction effect by comparing with available experimental data for Ni isotopes and neutron-rich N = 50 isotones. We give predictions for Fe-76 and Ni-80 in comparison with the case of the doubly magic nucleus Ni-78 which is an important waiting point in the r process.