  Strongly coupled N=4 supersymmetric Yang-Mills plasma at finite temperature
and chemical potential for an R-symmetry charge undergoes a second order phase
transition. We demonstrate that this phase transition is of the mean field
theory type. We explicitly show that the model is in the dynamical universality
class of 'model B' according to the classification of Hohenberg and Halperine,
with dynamical critical exponent z=4. We study bulk viscosity in the mass
deformed version of this theory in the vicinity of the phase transition. We
point out that all available models of bulk viscosity at continuous phase
transition are in conflict with our explicit holographic computations.
