Three-body forces and shell structure in calcium isotopes

TL;DR

This paper demonstrates that three-nucleon forces are essential to accurately reproduce the shell structure and magic nature of calcium-48, resolving discrepancies in microscopic nuclear theories.

Contribution

It shows that including three-nucleon forces introduces repulsive interactions crucial for modeling calcium isotopes' shell structure.

Findings

Three-nucleon forces produce repulsive interactions between valence neutrons.

Including three-nucleon forces improves agreement with experimental binding energies.

Calcium-48 is confirmed as a magic nucleus with high 2+ excitation energy.

Abstract

Understanding and predicting the formation of shell structure from nuclear forces is a central challenge for nuclear physics. While the magic numbers N=2,8,20 are generally well understood, N=28 is the first standard magic number that is not reproduced in microscopic theories with two-nucleon forces. In this Letter, we show that three-nucleon forces give rise to repulsive interactions between two valence neutrons that are key to explain 48Ca as a magic nucleus, with a high 2+ excitation energy and a concentrated magnetic dipole transition strength. The repulsive three-nucleon mechanism improves the agreement with experimental binding energies.