Equation of state of nuclear matter in a virial expansion of nucleons and nuclei

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 ≥ 12 and masses from the finite-range droplet model. 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.