Effective Shear and Bulk Viscosities of the Quark–Gluon Plasma: QCD Versus Heavy-ion Data

In recent years, there has been a significant effort to extract the temperature-dependent shear ($\eta/s$) and bulk ($\zeta/s$) viscosity over entropy ratios of quark-gluon plasma from global comparison heavy-ion data with results hydrodynamic simulations. However, anisotropic flow, which is arguably most sensitive probe viscosity, only an {\it effective\/} ratio, obtained by taking weighted average temperature, summing contributions bulk. We estimate this effective using existing first-principles calculations, give $0.17<(\eta/s)_{\rm eff}<0.21$, $(\zeta/s)_{\rm eff}<0.08$, implying that damping flow at LHC mostly due viscosity. The values extracted analyses are compatible these theory predictions.