Tensor and tensor-isospin terms in the effective Gogny interaction

TL;DR

This paper advocates for including tensor and tensor-isospin terms in the Gogny effective interaction to improve the description of neutron energy gap evolution in isotopes, demonstrating the importance of separate like-nucleon and neutron-proton contributions.

Contribution

It introduces a new parameterization of tensor terms in the Gogny interaction, enabling separate treatment of like-nucleon and neutron-proton effects, and analyzes their impact on neutron gap evolution.

Findings

Tensor terms improve neutron gap predictions.

Separate like-nucleon and neutron-proton contributions are crucial.

Parameterizations match experimental and shell-model trends.

Abstract

We discuss the need of including tensor terms in the effective Gogny interaction used in mean-field calculations. We show in one illustrative case that, with the usual tensor term that is employed in the Skyrme interaction (and that allows us to separate the like-nucleon and the neutron-proton tensor contributions), we can describe the evolution of the N=28 neutron gap in calcium isotopes. We propose to include a tensor and a tensor-isospin term in finite-range interactions of Gogny type. The parameters of the two tensor terms allow us to treat separately the like-nucleon and the neutron-proton contributions. Two parameterizations of the tensor terms have been chosen to reproduce different neutron single-particle properties in the 48Ca nucleus and the energy of the first 0- state in the 16O nucleus. By employing these two parameterizations we analyze the evolution of the N=14, 28, and 90 neutron energy gaps in oxygen, calcium and tin isotopes, respectively. We show that the combination of the parameters governing the like-nucleon contribution is crucial to correctly reproduce the experimental (where available) or shell-model trends for the evolution of the three neutron gaps under study.