Chiral-symmetry restoration in the linear sigma model at nonzero temperature and baryon density

We study the chiral phase transition in the linear sigma model with 2 quark flavors and $N_c$ colors. One-loop calculations predict a first-order phase transition at both $\mu =0$ and $\mu \mathrm{\ne }0$. We also discuss the phase diagram and make a comparison with a thermal parametrization of existing heavy-ion experimental data.