Quenching of Gamow-Teller strengths and two particle -- two hole configurations

TL;DR

This paper investigates Gamow-Teller resonances using SSRPA with Skyrme functionals, revealing that including two particle-two hole configurations significantly quenches strength and aligns better with experimental data, especially in heavier nuclei.

Contribution

It demonstrates that two particle-two hole configurations are crucial for accurately modeling Gamow-Teller strengths and quenching effects in nuclear resonances.

Findings

SSRPA results show lower strength compared to ab-initio predictions.

Including 2p-2h configurations enhances quenching and agrees with experiments.

Strength is shifted to higher energies, reducing cumulative strength at lower excitation energies.

Abstract

We apply the charge-exchange subtracted second random-phase approximation (SSRPA), based on Skyrme functionals, to investigate Gamow-Teller resonances in several closed-shell and closed-subshell nuclei, located in different regions of the nuclear chart. After having discussed the SSRPA findings obtained within different approximation schemes in $^{48}$Ca, we compare our results with {\it{ab-initio}} coupled-cluster predictions available for C and O isotopes, where two-body currents are included. Our integrated strenghts, obtained by using one-body transition operators, are lower compared to the corresponding {\it{ab-initio}} results. This indicates that, within our model, quenching effects are mainly driven by the inclusion of two particle - two hole configurations and that the role of a two-body contribution in the transition operator is less important than in the coupled-cluster approach. By analyzing heavier nuclei, $^{90}$ Zr and $^{132}$Sn, we confirm the same conclusions that we have recently drawn for $^{48}$Ca: the inclusion of two particle - two hole configurations is very effective in our model for providing strengths which are significantly more quenched than in other theoretical models and, thus, in better agreement with the experimental measurements. This occurs because two particle - two hole configurations have a density which strongly increases with the excitation energy. Their inclusion thus pushes a significant amount of the strength to higher energies, compared to what happens in other theoretical models, reducing in this way the cumulative sum of the strength up to excitation energies around 20-30 MeV.