The evolution of a heavy ion collision passes close to the O(4) critical point of QCD, where fluctuations of the order parameter are expected to be enhanced. Using the appropriate stochastic hydrodynamic equations in mean field close to the
near the pseudo-critical point, we compute how these enhanced fluctuations modify the transport coefficients of QCD and make a phenomenological estimate for how chiral fluctuations could effect the momentum spectrum of soft pions. Finally, we estimate the expected critical enhancement of soft pion yields, which provides a plausible explanation for the excess seen in experiment relative to ordinary hydrodynamic computations.
Based on: arXiv:2005.02885 and 2101.10847