Superluminal pions in a hadronic fluid

Abstract

We study the propagation of pions at finite temperature and finite chemical potential in the framework of the linear sigma model with 2 quark flavors and $N_c$ colors. The velocity of massless pions in general differs from that of light. One-loop calculations show that in the chiral symmetry broken phase pions, under certain conditions, propagate faster than light.

Comments: 8 pages, 3 figures included. Considerably revised, discussions expanded, one figure added, typos corrected, results unchanged. To be published in Phys. Rev. D