Viscous hydrodynamics relaxation time from AdS/CFT correspondence

We consider an expanding boost-invariant plasma at strong coupling using the AdS/CFT correspondence for N=4 super Yang-Mills theory. We determine the relaxation time in second order viscous hydrodynamics and find that it is around 30 times shorter than weak coupling expectations. We find that the nonsingularity of the dual geometry in the string frame necessitates turning on the dilaton which leads to a nonvanishing expectation value for trF(2) behaving like tau(-10/3).