Sigma Decay at Finite Temperature and Density

Sigma decay and its relation with chiral phase transition are discussed at finite temperature and density in the framework of the Nambu-Jona-Lasinio model. The decay rate for the process σ → 2π to first order in 1/N_c (inverse number of colors) expansion is calculated as a function of temperature T and baryon density n_b. In particular, only when the chiral phase transition happens around the tricritical point, the σ decay results in a non-thermal enhancement of pions in the final state distributions in relativistic heavy ion collisions.