Informal Pizza Seminar

Comparing QCD and N=4 Super-Yang-Mills: Shear viscosity

Guy Moore

McGill University

I will begin by explaining briefly what a heavy ion collision is and what they may tell us about many-body QCD. It is claimed that they tell us that QCD at temperatures of ~300 MeV is a nearly ideal fluid--that is, that free paths are so short that thinking in terms of quarks and gluons almost doesn't make sense. It turns out that the shear viscosity of N=4 Super-Yang-Mills can be determined in closed form at strong coupling, and is very small. People have argued that N=4 SYM should therefore be a good analog theory for QCD if we want to learn about temperatures ~300 MeV. We address this proposal by comparing the theories at weak coupling — the conclusion is that the shear viscosity of QCD is almost surely well above that of N=4 SYM and it is hard to see how the theories could be quantitative analogs.