Neutron matter at finite temperature

We calculate the neutron matter equation of state at finite temperature based on low-momentum two- and three-nucleon interactions. The free energy is obtained from a loop expansion around the Hartree–Fock energy, including contributions from normal and anomalous diagrams. We focus on densities below saturation density with temperatures T⩽10MeV and compare our results to the model-independent virial equation of state and to variational calculations. Good agreement with the virial equation of state is found at low density. We provide simple estimates for the theoretical error, important for extrapolations to astrophysical conditions.