Viscosity of a net-baryon fluid near the QCD critical point

Abstract

In the dynamics of the QCD critical point, the net-baryon fluid, linked to the slow component of the order parameter, relaxes to a 3d Ising system in equilibrium. An analytical study of shear and bulk viscosity, with constraints imposed by the dynamics of the critical net-baryon fluid, the universality property and the requirements of a class of strong coupling theories, is performed in the neighbourhood of the critical point. It is found that the shear viscosity of the net-baryon fluid is restricted in the domain $1.6\le 4\pi \frac{\eta }{s}\le 3.7$ for $T_c<T\le 2T_c$ whereas the bulk viscosity is small, $4\pi \frac{\zeta }{s}<0.05$ (for $T>1.27T_c$) but rising towards the singularity at $T=T_c$.

Comments: 13 pages, 2 figures