Variational study for the equation of state of asymmetric nuclear matter at finite temperatures

TL;DR

This paper develops a variational equation of state for asymmetric nuclear matter at both zero and finite temperatures, incorporating realistic nuclear potentials and comparing results with observational data and other models.

Contribution

It introduces a variational approach to derive the nuclear EOS at finite temperatures, including thermodynamic quantities, validated against fully minimized calculations.

Findings

EOS results are consistent with neutron star observations.

The quadratic proton-fraction dependence holds at zero temperature.

Deviations from quadratic dependence are significant at finite temperatures.

Abstract

An equation of state (EOS) for uniform asymmetric nuclear matter (ANM) is constructed at zero and finite temperatures by the variational method starting from the nuclear Hamiltonian that is composed of the Argonne v18 and Urbana IX potentials. At zero temperature, the two-body energy is calculated with the Jastrow wave function in the two-body cluster approximation which is supplemented by Mayer's condition and the healing-distance condition so as to reproduce the result by Akmal, Pandharipande and Ravenhall. The energy caused by the three-body force is treated somewhat phenomenologically so that the total energy reproduces the empirical saturation conditions. The masses and radii of neutron stars obtained with the EOS are consistent with recent observational data. At finite temperatures, thermodynamic quantities such as free energy, internal energy, entropy, pressure and chemical potentials are calculated with an extension of the method by Schmidt and Pandharipande. The validity of the frozen-correlation approximation employed in this work is confirmed as compared with the result of the fully minimized calculation. The quadratic proton-fraction-dependence of the energy of ANM is confirmed at zero temperature, whereas the free energy of ANM deviates from the quadratic proton-fraction-dependence markedly at finite temperatures. The obtained EOS of ANM will be an important ingredient of a new nuclear EOS for supernova numerical simulations.