Ab initio calculations of monopole sum rules: From finite nuclei to infinite nuclear matter

TL;DR

This paper uses ab initio methods to calculate monopole response moments in nuclei, comparing different many-body approaches and extrapolating to nuclear matter, providing insights into nuclear incompressibility.

Contribution

It introduces a comprehensive ab initio framework combining IMSRG and CC methods to compute monopole sum rules in nuclei and extrapolate to nuclear matter.

Findings

Good agreement between IMSRG and CC results across nuclei

RPA approximates correlated methods well for soft interactions

Extrapolated nuclear matter incompressibility values are consistent with phenomenology

Abstract

We compute moments of the isoscalar monopole response of N = Z closed-shell nuclei based on chiral nucleon-nucleon plus three-nucleon interactions. We employ the random phase approximation (RPA) and two ab initio many-body approaches, the in-medium similarity renormalization group (IMSRG) and coupled-cluster theory (CC). In the IMSRG framework, the moments are obtained as ground-state expectation values, whereas in the CC approach, they are evaluated through excited-state calculations. We find good agreement between the IMSRG and CC results across all nuclei studied. RPA provides a reasonable approximation to the correlated methods if the interaction is soft. From the calculated moments, we extract average energies of the monopole response, compute finite-nucleus incompressibilities, and estimate the incompressibility of symmetric nuclear matter by a fit to a leptodermous expansion. Our extrapolated values are lower than those obtained in nuclear matter calculations with the same interactions, but the values are consistent with phenomenological ranges.