Viscosity of pure-glue QCD from the lattice

TL;DR

This study computes shear and bulk viscosities of pure-glue QCD at high temperature using lattice simulations, achieving high precision through advanced techniques and providing estimates relevant for understanding quark-gluon plasma properties.

Contribution

It introduces a novel lattice approach with gradient flow and blocking to accurately determine QCD viscosities from spectral functions.

Findings

Shear viscosity to entropy ratio: 0.15-0.48

Bulk viscosity to entropy ratio: 0.017-0.059

High-precision lattice estimates at 1.5 T_c

Abstract

We calculate shear viscosity and bulk viscosity in SU(3) gauge theory on the lattice at $1.5 \,T_c$. The viscosities are extracted via a Kubo formula from the reconstructed spectral function which we determine from the Euclidean-time dependence of the corresponding channel of the energy-momentum tensor correlators. We obtain unprecedented precision for the correlators by applying gradient flow and blocking methods. The correlators are extrapolated to the continuum and then to zero flow time. To extract the viscosities we fit theoretically inspired models to the lattice data and crosscheck the fit results using the Backus Gilbert method. The final estimates for shear and bulk viscosity are $\eta/s = 0.15-0.48$ and $\zeta/s = 0.017-0.059$.