Constraints on the Nuclear Symmetry Energy from Experiments, Theory and Observations

Nuclear mass measurements and neutron matter theory tightly constrain the nuclear symmetry energy parameters $J$, $L$, $K_{sym}$ and $Q_{sym}$. Corroboration of these constraints on $J$ and $L$ can be found from measurements of the neutron skin thicknesses and dipole polarizabilities of neutron-rich nuclei. The experimental constraints on these parameters are compared with those obtained from consideration of astrophysical measurements of the neutron star radius, which we show is highly correlated with $L$. Attention is aimed at the recent PREX and CREX neutron skin measurements from Jefferson Lab, NICER neutron star radius measurements, and a new interpretation of the GW170817 tidal deformability measurement. We find joint satisfaction of PREX and CREX gives $J=32.2\pm1.7$ MeV and $L=52.9\pm13.2$ MeV, in excellent agreement with neutron matter predictions of $J=32.0\pm1.1$ MeV and $L=51.9\pm7.9$ MeV.