Early-Stage Shear Viscosity far from Equilibrium via Holography

Abstract

Shear viscosity is a crucial property of QCD matter which determines the collective behavior of the the quark-gluon plasma (QGP) in ultrarelativistic heavy-ion collisions. Extending the near-equilibrium, high-precision investigations in theory and experiment, we take into account the fact that, in a collision, the QGP is generated far from equilibrium. We use the AdS/CFT correspondence to study a strongly coupled plasma and find a significant impact on the ratio of shear viscosity to entropy density, $\eta /s$. In particular, we investigate the initial heating phase and find a decrease reaching down to below 60% followed by an overshoot to 110% of the near-equilibrium value. This finding might be highly relevant for the extraction of transport coefficients from anisotropic flow measurements at RHIC and LHC.

Comments: 6 pages, 3 figures. Plenary Flash Talk given at the 28th International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2019) Wuhan, China, November 4-9, 2019