Equation of State of nuclear matter in a Virial expansion of nucleons and nuclei

TL;DR

This paper develops a detailed equation of state for nuclear matter at subnuclear densities using a Virial expansion, covering a wide range of conditions relevant for astrophysical phenomena like supernovae and neutron star mergers.

Contribution

It introduces a comprehensive Virial expansion-based EOS including many nuclear species, smoothly connecting to relativistic mean field models at higher densities.

Findings

EOS tabulated at over 73,000 grid points

Accurate at low densities, matching relativistic mean field results at higher densities

Provides a detailed, exact low-density limit for nuclear matter

Abstract

We study the equation of state (EOS) of nuclear matter at subnuclear density in a Virial expansion for a nonideal gas. The gas consists of neutrons, protons, alpha particles, and 8980 species of nuclei with $A \ge 12$ and masses from the finite-range droplet model (FRDM). At very low density, the Virial expansion reduces to nuclear statistical equilibrium. At higher density, the Virial results match smoothly to the relativistic mean field results discussed in our previous paper. We tabulate the resulting EOS at over 73,000 grid points in the temperature range $T$ = 0.158 to 15.8 MeV, the density range $n_B$ = 10$^{-8}$ to 0.1 fm$^{-3}$, and the proton fraction range $Y_P$ = 0.05 to 0.56. In the future we plan to match these low density results to our earlier high density mean field results, and generate a full EOS table for use in supernova and neutron star merger simulations. This Virial EOS is exact in the low density limit.