Phase Transition in the chiral $\sigma$-$\omega$ model with dilatons
  We investigate the properties of different modifications to the linear $\sigma$-model (including a dilaton field associated with broken scale invariance) at finite baryon density $\rho$ and nonzero temperature $T$. The explicit breaking of chiral symmetry and the way the vector meson mass is generated are significant for the appearance of a phase of nearly vanishing nucleon mass besides the solution describing normal nuclear matter. The elimination of the abnormal solution prohibits the onset of a chiral phase transition but allows to lower the compressibility to a reasonable range. The repulsive contributions from the vector mesons are responsible for the wide range of stability of the normal phase in the $(\mu,T)$-plane. The abnormal solution becomes not only energetically preferable to the normal state at high temperature or density, but also mechanically stable due to the inclusion of dilatons. 
P. Papazoglou, J. Schaffner, S. Schramm, D. Zschiesche, H. St\"ocker,   W. Greiner