Thoughts on non-perturbative thermalization and jet quenching in heavy ion collisions

We start by presenting physical arguments for the impossibility of perturbative thermalization leading to (non-viscous) Bjorken hydrodynamic description of heavy ion collisions. These arguments are complimentary to our more formal argument presented in [Yu.V. Kovchegov, hep-ph/0503038]. We argue that the success of hydrodynamic models in describing the quark–gluon system produced in heavy ion collisions could only be due to non-perturbative strong coupling effects. We continue by studying non-perturbative effects in heavy ion collisions at high energies. We model non-perturbative phenomena by an instanton ensemble. We show that non-perturbative instanton vacuum fields may significantly contribute to jet quenching in nuclear collisions. At the same time, the instanton ensemble contribution to thermalization is likely to be rather weak, leading to non-perturbative thermalization time comparable to the time of hadronization. This example illustrates that jet quenching is not necessarily a signal of a thermalized medium. Indeed, since the instanton models do not capture all the effects of QCD vacuum (e.g., they do not account for confinement), there may be other non-perturbative effects facilitating thermalization of the system.