Abstract
The symmetry energy and its density dependence are pivotal for many nuclear physics and astrophysics applications, as they determine properties ranging from the neutron-skin thickness of nuclei to the crust thickness and the radius of neutron stars. Recently, PREX-II reported a value of fm for the neutron-skin thickness of , , implying a symmetry-energy slope parameter of MeV, larger than most ranges obtained from microscopic calculations and other nuclear experiments. We use a nonparametric equation of state representation based on Gaussian processes to constrain the symmetry energy , , and directly from observations of neutron stars with minimal modeling assumptions. The resulting astrophysical constraints from heavy pulsar masses, LIGO/Virgo, and NICER favor smaller values of the neutron skin and , as well as negative symmetry incompressibilities. Combining astrophysical data with chiral effective field theory () and PREX-II constraints yields MeV, MeV, and fm. We also examine the consistency of several individual calculations with astrophysical observations and terrestrial experiments. We find that there is only mild tension between , astrophysical data, and PREX-II's measurement ( value ) and that there is excellent agreement between , astrophysical data, and other nuclear experiments.
5 More- Received 15 July 2021
- Revised 29 October 2021
- Accepted 19 November 2021
DOI:https://doi.org/10.1103/PhysRevC.104.065804
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