Shell-model coupled-cluster method for open-shell nuclei

TL;DR

This paper introduces a novel shell-model coupled-cluster approach that derives effective interactions from microscopic nuclear forces, accurately predicting properties of open-shell nuclei by including crucial three-body terms.

Contribution

The method combines similarity transformations with coupled-cluster theory to produce effective shell-model interactions directly from nuclear forces, improving accuracy for open-shell nuclei.

Findings

Accurately predicts low-lying states of helium and lithium isotopes.

Includes three-body terms for improved results.

Results agree with full configuration interaction benchmarks.

Abstract

We present an approach to derive effective shell-model interactions from microscopic nuclear forces. The similarity-transformed coupled-cluster Hamiltonian decouples the single-reference state of a closed-shell nucleus and provides us with a core for the shell model. We use a second similarity transformation to decouple a shell-model space from the excluded space. We show that the three-body terms induced by both similarity transformations are crucial for an accurate computation of ground and excited states. As a proof of principle we use a nucleon-nucleon interaction from chiral effective field theory, employ a $^4$He core, and compute low-lying states of $^{6-8}$He and $^{6-8}$Li in $p$-shell model spaces. Our results agree with benchmarks from full configuration interaction.