Quenching an expanding chiral condensate

We simulate quenching in the O(4) σ model of hadronic matter expanding along the z axis, with randomly generated initial conditions imposed at a given boost invariant time ${\mathrm{\tau }}_0$= √${\mathit{t}}^2$-${\mathit{z}}^2$ . A comparison of our results with the simulations of Rajagopal and Wilczek for a nonexpanding case shows that the normalized power exhibits approximately the same frequency of oscillations in the laboratory time in both cases. However, the response of the expanding system depends on ${\mathrm{\tau }}_0$: e.g., for ${\mathrm{\tau }}_0$=1 fm it is about 2 orders of magnitude smaller than for the nonexpanding system. Also, the relaxation time becomes shorter with expansion present. When ${\mathrm{\tau }}_0$→∞ the two cases become identical. Kinematical windows for the production of a disoriented chiral condensate are also discussed.