Suppression of the Shear Viscosity in a "semi" Quark Gluon Plasma

TL;DR

This paper investigates how the shear viscosity of QCD near the deconfinement temperature is suppressed in the semi-QGP phase, impacting hydrodynamic behavior in heavy-ion collisions.

Contribution

It introduces a semi-classical model to compute shear viscosity in the semi-QGP, revealing suppression near Tc due to the Polyakov loop behavior.

Findings

Shear viscosity is suppressed by two powers of the Polyakov loop near Tc.

Hydrodynamic behavior at LHC may have higher shear viscosity than at RHIC.

Semi-QGP phase exists from below Tc to a few times above Tc.

Abstract

We consider QCD at temperatures T near Tc, where the theory deconfines. We distinguish between a "complete" Quark Gluon Plasma (QGP), where the vacuum expectation value of the renormalized Polyakov loop is near unity, essentially constant with T, and the "semi"-QGP, where the loop changes strongly with T. Lattice simulations indicate that in QCD, there is a semi-QGP from below Tc to a few times that. Using a semi-classical model, we compute the shear viscosity, eta, to leading order in perturbation theory. We find that near Tc, where the expectation value of the Polyakov loop is small, that eta/T^3 is suppressed by two powers of the loop. For heavy ions, this suggests that during the initial stages of the collision, hydrodynamic behavior at the LHC will be characterized by a shear viscosity which is significantly larger than that at RHIC.