Transport properties near the QCD chiral critical point

by Eduardo Grossi




During the evolution of a heavy ion collision, the system passes close to the O(4) critical point. The order parameter that controls the chiral symmetry is the quark condensate. Due to the non-zero quark mass, there is a crossover (not a second-order phase transition) between the high and low-temperature phases. In this talk, we will introduce the hydrodynamic theory with the order parameter as an additional hydrodynamical variable and show the results of the real-time simulation of this model that shares the same universality class of QCD, the so-called Model G.

Due to the presence of the superfluid pion degrees of freedom, we compute the modification of the ordinary hydrodynamic transport coefficients and estimate the expected critical enhancement of soft pion yields, which provides a plausible explanation for the excess seen in the experiment relative to normal hydrodynamic computations. We extract the dynamical critical exponent of $zeta=1.47\pm (\text{stat.})$, which is compatible with the theoretical expectation of $zeta=d/2$.

Based on 2005.02885, 2101.10847 and 2111.03640