Second random-phase approximation with the Gogny force. First applications

TL;DR

This paper introduces the first application of the second random-phase approximation using the Gogny interaction, demonstrating significant shifts in response spectra and emphasizing the importance of neutron-proton matrix elements.

Contribution

It presents the novel implementation of the second RPA with the Gogny force and analyzes its impact on nuclear response spectra, highlighting the role of specific matrix elements.

Findings

Large downward shift of response centroids by several MeV.

Significant changes in strength distributions compared to RPA.

Large neutron-proton matrix elements influence results.

Abstract

We present the first applications of the second random-phase-approximation model with the finite-range Gogny interaction. We discuss the advantages of using such an interaction in this type of calculations where 2 particle-2 hole configurations are included. The results found in the present work confirm the well known general features of the second random-phase approximation spectra: we find a large shift, several MeV, of the response centroids to lower energies with respect to the corresponding random-phase-approximation values. As known, these results indicate that the effects of the 1 particle-1 hole/2 particle-2 hole and 2 particle-2 hole/2 particle-2 hole couplings are important. It has been found that the changes of the strength distributions with respect to the standard random-phase-approximation results are particularly large in the present case. This important effect is due to some large neutron-proton matrix elements of the interaction and indicates that these matrix elements (which do not contribute in the mean-field calculations employed in the conventional fit procedures of the force parameters) should be carefully constrained to perform calculations