Factorized Approximation to the IMSRG(3)

TL;DR

This paper introduces a factorized approximation to the IMSRG(3) method that includes intermediate three-body effects, improving spectroscopic predictions and reducing valence space dependence in nuclear structure calculations.

Contribution

It presents a scalable factorized approximation to IMSRG(3) that captures key three-body effects with minimal additional computational cost.

Findings

Improved spectroscopy in carbon, sulfur, and nickel isotopes.

Reduced valence space dependence in calculations.

Provides insight into the importance of diagram topologies.

Abstract

We describe an approximation to the in-medium similarity renormalization group (IMSRG) method in which we include the effects of intermediate three-body operators arising within nested commutators. As an initial step, we present the relevant equations for two nested commutators, all of which can be factorized so that the method scales like the standard IMSRG(2) approximation, enabling large-scale calculations. We test the accuracy of this approximation scheme, and apply it to the isotopic chains of carbon, sulfur and nickel isotopic chains. We obtain an improved description of spectroscopy, and a reduced dependence on the choice of the valence space. In addition, we provide an explanation of the relative importance of the diagram topologies included, with an eye toward assessing the impact of remaining omitted terms.