The Symmetry Energy: Current Status of Ab Initio Predictions vs. Empirical Constraints

TL;DR

This paper reviews the current status of ab initio theoretical predictions of the nuclear symmetry energy and compares them with recent empirical constraints, highlighting the importance of free-space NN data in constraining the equation of state of neutron-rich matter.

Contribution

It provides a comprehensive comparison between ab initio predictions and empirical data on the symmetry energy, emphasizing the role of free-space NN data in constraining the density dependence.

Findings

Free-space NN data strongly constrain the neutron matter equation of state.

Ab initio predictions are consistent with recent empirical constraints.

The slope of the symmetry energy at saturation is primarily determined by these constraints.

Abstract

Infinite nuclear matter is a suitable laboratory to learn about nuclear forces in many-body systems. Modern theoretical predictions of neutron-rich matter are particularly timely in view of recent and planned measurements of observables which are sensitive to the equation of state of isospin-asymmetric matter. For these reasons, over the past several years we have taken a broad look at the equation of state of neutron-rich matter and the closely related symmetry energy, which is the focal point of this article. Its density dependence is of paramount importance for a number of nuclear and astrophysical systems, ranging from neutron skins to the structure of neutron stars. We review and discuss ab initio predictions in relation to recent empirical constraints. We emphasize and demonstrate that free-space NN data pose stringent constraints on the density dependence of the neutron matter equation of state, which essentially determines the slope of the symmetry energy at saturation.