Chiral sigma model with pion mean field and the effect of Dirac Sea

We studied the properties of infinite matter and finite nuclei by using the chiral sigma model in the framework of the relativistic mean field theory. The chiral sigma model has the property which the omega meson mass is generated dynamically by the sigma condensation in the vacuum in the same way as the nucleon mass. By using the chiral sigma model in nuclear matter, we can reproduce the saturation property. In finite nucleus, we find that the energy differences between the spin-orbit partners are reproduced by the finite pion mean field which is completely a different mechanism from the standard spin-orbit interaction. The chiral sigma model is a renormalizable model, and it is important to include Dirac Sea. We study the effects of Dirac Sea in the chiral sigma model. (author)