Chiral thermodynamics of nuclear matter

The free energy and the equation of state of isospin-asymmetric nuclear matter are calculated at finite temperature up to three loop order in the framework of in-medium chiral perturbation theory, systematically incorporating one- and two-pion exchange dynamics to this order. Effects from the 2π-exchange with explicit Δ-isobar excitation are included, as well as three-body forces. We construct the phase diagram of nuclear matter for different proton fractions image and investigate the dependence of nuclear matter properties on the isospin-asymmetry. A detailed study of the liquid–gas phase transition is performed. For isospin-symmetric nuclear matter we find a critical temperature of 15.1 MeV; as the isospin-asymmetry is increased, the liquid–gas coexistence region decreases until it disappears at image, while nuclear matter becomes unbound at image. The quadratic expansion of the free energy in the asymmetry parameter δ is a good approximation at low temperature even for large δ. An estimate of chiral four-body correlations in nuclear and neutron matter is also performed and the corrections from such four-body interactions are found to be small.