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

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.