Critical behavior of the bulk viscosity in QCD

Understand

We study the behavior of the bulk viscosity $\zeta$ in QCD near a possible critical endpoint in the phase diagram.

• We verify the expectation that $(\zeta/s)\sim a(\xi/\xi_0)^{x_\zeta}$, where $s$ is the entropy density, $\xi$ is the correlation length, $\xi_0$ is the non-critical correlation length, $a$ is a constant and $x_\zeta\simeq 3$.
• Using a recently developed equation of state that includes a critical point in the universality class of the Ising model we estimate the constant of proportionality $a$.
• We find that $a$ is typically quite small, $a\sim O(10^{-4})$.