Bulk viscosity of QCD matter near the critical temperature

Understand

Kubo's formula relates bulk viscosity to the retarded Green's function of the trace of the energy-momentum tensor.

• Using low energy theorems of QCD for the latter we derive the formula which relates the bulk viscosity to the energy density and pressure of hot matter.
• We then employ the available lattice QCD data to extract the bulk viscosity as a function of temperature.
• We find that close to the deconfinement temperature bulk viscosity becomes large, with viscosity-to-entropy ratio zeta/s about 1.