ar X iv : h ep - t h / 03 08 13 9 v 1 2 1 A ug 2 00 3 Particle density in zero temperature symmetry restoring phase transitions in four - fermion interaction models ∗

By means of critical behaviors of the dynamical fermion mass in four-fermion interaction models, we have shown by explicit calculations that when T = 0 the particle density will have a discontinuous jumping across the critical chemical potential µc in 2D and 3D Gross-Neveu (GN) model and these physically explain the first order feature of corresponding symmetry restoring phase transitions. For second order phase transitions in 3D GN model when T → 0 and in 4D Nambu-Jona-Lasinio (NJL) model when T = 0, it has been proven that the particle density itself will be continuous across µc but its derivative over the chemical potential µ will have a discontinuous jumping. The results give a physical explanation of implications of the tricritical point (T, µ) = (0, µc) in 3D GN model. The discussions also show effectiveness of the critical analysis approach of phase transitions.