sigma pi(0) condensation at finite density in the linear sigma model - art. no. 015205

Within the relativistic mean-field theory, we reinvestigate the Dautry-Nyma n instability of the normal many-panicle state in the linear sigma model (L sigmaM). It is shown that an "instability" due to an inappropriate quantiz ation of Dirac field inheres in the normal state of L sigmaM. Then we see t hat, in a wide class of models which are compatible with the nuclear-matter data at saturation, there generally exists a critical density above which a condensation of sigma and pi (o) with a finite wave vector takes place. I t has been known that the coupling of wave vector to nucleon spin causes th e dispersion relation of nucleons to dissolve into two distinct branches. I n case one of these branches lies sufficiently lower than the normal branch , the phase with sigma pi (o) condensation emerges with strong spin polariz ations.