RELATIVISTIC FOCK DIAGRAMS AT FINITE DENSITY

Within a simple relativistic field theory coupling scalar mesons and nucleons, analytical expressions are derived for the Fock self-energy amplitudes at finite baryon density. The strong coupling required to model nuclear matter turns out to be near a critical value, beyond which a perturbation expansion in such a system breaks down. This has the effect of shifting the Landau ghost poles of the perturbative propagator to rather low energies. The removal of these unphysical poles can be achieved either at the level of propagators or at the level of self-energy amplitudes. In the latter case, the removal of the ghost poles is shown to have a big effect on the self-energies because of the coupling strength.