  Recently Eling and Oz [1] proposed a simple formula for the bulk viscosity of
holographic plasma. They argued that the formula is valid in the high
temperature (near-conformal) regime, but is expected to break down at low
temperatures. We point out that the formula is in perfect agreement with the
previous computations of the bulk viscosity of the cascading plasma [2,3], as
well as with the previous computations of the bulk viscosity of N=2^* plasma
[4,5]. In the latter case it correctly reproduces the critical behaviour of the
bulk viscosity in the vicinity of the critical point with the vanishing speed
of sound.

High Energy Physics - Theory