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Abstract

In the search for possible signatures of the chiral phase transition in heavy ion collisions, pions are expected to play an important role. We investigate the impact of pion fluctuations on the relaxation of th echiral order parameter in the framework of nonequilibrium Langevin dynamics in the quark-meson model. Starting from the effective action and motivated by the influence functional formalism, we derive an equation of motion for the chiral fields coupled to a heat bath of quarks and hard meson modes. Thereby, we extend existing studies in which the pions have been neglected. We find that at the chiral phase transition the pion fluctuations have a noticeable effect on the dynamics of the sigma field. For a first order phase transition, the pion fluctuations can speed up or delay relaxation of the system, depending on the initial conditions. For a critical point scenario, the pion fluctuations shift the equilibrium expectation value of the order parameter at the phase transition. Further, we test our model in the context of heavy ion collision by imposing the temperature profile for an expanding plasma on the heat bath. We find that within this approximation, the model shows no effect from pion fluctuations.