Shell evolution and nuclear forces

TL;DR

This paper investigates how different components of the nucleon-nucleon interaction influence nuclear shell structure evolution, highlighting the dominant roles of central and tensor forces in shaping shell gaps.

Contribution

It introduces a spin-tensor decomposition method to distinguish contributions of various interaction components to shell evolution in nuclei.

Findings

Central component drives global single-particle energy variation.

Tensor component explains behavior of spin-orbit partner energies.

Analysis of realistic interactions clarifies shell gap formation in neutron-rich nuclei.

Abstract

We present a quantitative study of the role played by different components characterizing the nucleon-nucleon interaction in the evolution of the nuclear shell structure. It is based on the spin-tensor decomposition of an effective two-body shell-model interaction and the subsequent study of effective single-particle energy variations in a series of isotopes or isotones. The technique allows to separate unambiguously contributions of the central, vector and tensor components of the realistic effective interaction. We show that while the global variation of the single-particle energies is due to the central component of the effective interaction, the characteristic behavior of spin-orbit partners, noticed recently, is mainly due to its tensor part. Based on the analysis of a well-fitted realistic interaction in sdpf-shell model space, we analyze in detail the role played by the different terms in the formation and/or disappearance of N=16, N=20 and N=28 shell gaps in neutron-rich nuclei.