Supercooled Goldstones at the QCD chiral phase transition

Abstract: We discuss the universal non-equilibrium enhancement of long-wavelength Goldstone bosons induced by quenches to broken phase in Model G -- the dynamical universality class of an $O(4)$-antiferromagnet and chiral QCD phase transition. Generic scaling arguments predict a parametric enhancement in the infrared spectra of Goldstones, which is confirmed by fully-fledged stochastic simulations. The details of the enhancement are determined by the non-linear dynamics of a superfluid effective theory, which is a limit of Model G reflecting the broken $O(4)$ symmetry. Our results translate to a parametric enhancement of low-momentum pions in heavy-ion collisions at the LHC, which are underpredicted in current hydrodynamic models without critical dynamics.