Angular-momentum projection in coupled-cluster theory: structure of $^{34}$Mg

TL;DR

This paper develops an angular-momentum projection method within coupled-cluster theory to accurately describe open-shell nuclei, demonstrating its effectiveness through comparisons with benchmarks and experimental data for exotic and well-studied nuclei.

Contribution

It introduces an angular-momentum projection technique in coupled-cluster theory using a Hermitian approach, improving the description of rotational states in open-shell nuclei.

Findings

Accurate reproduction of rotational bands in $^{34}$Mg.

Good agreement with benchmarks for $^8$Be and $^{20}$Ne.

Effective description of $pf$-shell nuclei.

Abstract

Single-reference coupled-cluster theory is an accurate and affordable computational method for the nuclear many-body problem. For open-shell nuclei, the reference state typically breaks rotational invariance and angular momentum must be restored as a good quantum number. We perform angular-momentum projection after variation and employ the disentangled coupled-cluster formalism and a Hermitian approach. We compare our results with benchmarks for $^8$Be and $^{20}$Ne using a two-nucleon interaction from chiral effective field theory and for $pf$-shell nuclei within the traditional shell model. We compute the rotational band in the exotic nucleus $^{34}$Mg and find agreement with data.