Variational Method for Nuclear Matter with an Explicit Energy Functional

We report on the status of two variational studies of the nuclear equation of state (EOS). One is the study of the variational method with an explicit energy functional (EEF). We have been studying the EEF with two-body central and tensor forces, and, in this paper, we extend the EEF to take into account the state-independent three-body force. The calculated energy of neutron matter with the two-body v6' potential and the repulsive part of the UIX potential is close to that with the Monte Carlo method using the full UIX. The maximum mass of the neutron star with this EOS is about 2.5M_ȯ. The other study is a construction of a new nuclear EOS table for supernova numerical simulations that is based on the cluster variational method. Starting from the nuclear Hamiltonian with the AV18 two-body force and the UIX three-body force, the EOS of uniform hot asymmetric nuclear matter is calculated using the method of Schmidt and Pandharipande. For non-uniform nuclear matter, the free energy of a Wigner-Seitz cell is calculated in the Thomas-Fermi approximation. At zero temperature, a reasonable phase diagram is obtained.