Nuclear Β -Decay Half-Lives Within the Subtracted Second Random-Phase Approximation

We employ, within the framework of Skyrme energy-density functional theory, the subtracted second random-phase approximation, recently developed for charge-exchange excitations, to compute β -decay half-lives in four nuclei, ^24 O, ^34 Si, ^78 Ni, and ^132 Sn. Following our recent results on the description of the Gamow–Teller strength, we proceed coherently in the present work by computing β -decay half-lives using the bare value of the axial-vector coupling constant g_A . Half-lives are thus obtained, within the allowed Gamow–Teller approximation, without the use of any ad hoc quenching factors. A genuine quenching is indeed microscopically introduced in our model owing to the correlations induced by the coupling of one-particle one-hole configurations with two-particle two-hole ones. The role of the so-called J^2 terms is also studied. By comparing our results with experimental data, we show a general improvement of β -decay half-lives with respect to results obtained within the commonly used Random Phase Approximation (RPA). The inclusion of the two-particle two-hole configurations produces a more fragmented and richer spectrum within the β -window, resulting in lower β half-lives with respect to the RPA ones.