Constraints on the symmetry energy and neutron skins from experiments and theory

Abstract

The symmetry energy contribution to the nuclear equation of state impacts various phenomena in nuclear astrophysics, nuclear structure, and nuclear reactions. Its determination is a key objective of contemporary nuclear physics, with consequences for the understanding of dense matter within neutron stars. We examine the results of laboratory experiments that have provided initial constraints on the nuclear symmetry energy and on its density dependence at and somewhat below normal nuclear matter density. Even though some of these constraints have been derived from properties of nuclei while others have been derived from the nuclear response to electroweak and hadronic probes, within experimental uncertainties-they are consistent with each other. We also examine the most frequently used theoretical models that predict the symmetry energy and its slope parameter. By comparing existing constraints on the symmetry pressure to theories, we demonstrate how contributions of three-body forces, which are essential ingredients in neutron matter models, can be determined.

Density dependence of the nuclear symmetry energy from measurements of neutron radii in nuclei

“…Both results are much consistent with previous estimates, although the central value is larger than the typical value reported from the existing evidence on Δr np of 208 Pb [28]. As mentioned, a new run PREX-II has been scheduled at the Jefferson Lab [54] to improve the statistics of the measurement and reach the original 3% accuracy in A pv .…”

“…Different experimental evidences from nuclear masses, heavy-ion collisions, giant resonances and observational properties of neutron stars allow to constrain the value of the symmetry energy at saturation J in a range between approximately 29 MeV and 33 MeV [28,29]. These values are, in general, reproduced by well calibrated nuclear mean field models [30].…”

Comparative study of three-nucleon force models in nuclear matter

“…To compare our results with the value of the symmetry energy extracted from various nuclear experimental data [67,68], we report in Table VI E sym calculated at the empirical saturation density ρ 0 = 0.16 fm −3 for the different TNF models considered in this work. In the same table, we also report the so-called slope parameter As we can see (Table VI) our calculated E sym and L lies within the ranges of values extracted from experimental data [68]: E sym (ρ 0 ) = 29.0-32.7 MeV, and L = 40.5-61.9 MeV.…”

Self-consistent calculation of the nuclear composition in hot and dense stellar matter

“…Its actual value is still rather uncertain. Various predictions have been provided by the terrestrial nuclear experiments, theoretical analyses and astrophysical observations [38][39][40][41][42][43]. Unfortunately, these constraints do not overlap and the actual value is likely to be larger than 35 MeV and less than 131 MeV.…”