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 xp 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 xp≃0.05, while nuclear matter becomes unbound at xp≃0.12. 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.