Chiral three-nucleon forces and bound excited states in neutron-rich oxygen isotopes

TL;DR

This paper investigates neutron-rich oxygen isotopes using chiral two- and three-nucleon interactions, highlighting the importance of three-nucleon forces and extended valence spaces in accurately reproducing shell evolution and excited state spectra.

Contribution

It demonstrates the necessity of including chiral three-nucleon forces and extended valence spaces for accurate nuclear structure predictions in neutron-rich oxygen isotopes.

Findings

Three-nucleon forces significantly influence valence neutron interactions.

Extended valence space improves agreement with experimental signatures.

First calculations using nuclear forces without adjustments in this context.

Abstract

We study the spectra of neutron-rich oxygen isotopes based on chiral two- and three-nucleon interactions. First, we benchmark our many-body approach by comparing ground-state energies to coupled-cluster results for the same two-nucleon interaction, with overall good agreement. We then calculate bound excited states in 21,22,23O, focusing on the role of three-nucleon forces, in the standard sd shell and an extended sdf7/2p3/2 valence space. Chiral three-nucleon forces provide important one- and two-body contributions between valence neutrons. We find that both these contributions and an extended valence space are necessary to reproduce key signatures of novel shell evolution, such as the N = 14 magic number and the low-lying states in 21O and 23O, which are too compressed with two-nucleon interactions only. For the extended space calculations, this presents first work based on nuclear forces without adjustments. Future work is needed and open questions are discussed.