Dynamical critical fluctuations near the QCD critical point with hydrodynamic cooling rate

Abstract

Within the model A in the Hohenberg's dynamical universality classification, we investigate the critical slowing down effects on the critical fluctuations driven by the expanding quark-gluon plasma, using a trajectory and cooling rate obtained from hydrodynamics. We numerically solved the Langevin dynamics of the non-conserved order parameter field and find that, compared with commonly used Hubble-like expansion, the cooling rate of a realistic hydrodynamic system is pretty large and the associated critical slowing down effects strongly suppress the higher-order cumulants of the order parameter field ({\it e.g.,} $C_4$). Furthermore, for an evolving system that approaches the critical point, such critical slowing down suppression overcomes the enhancement of the critical fluctuations, which indicates that the largest fluctuations of the order parameter field ({\it i.e.,} $C_2$) do not necessarily associate with the evolving trajectory closest to the critical point.