  At second order in gradients, conformal relativistic hydrodynamics depends on
the viscosity eta and on five additional "second-order" hydrodynamical
coefficients tauPi, kappa, lambda1, lambda2, and lambda3. We derive Kubo
relations for these coefficients, relating them to equilibrium, fully retarded
3-point correlation functions of the stress tensor. We show that the
coefficient lambda3 can be evaluated directly by Euclidean means and does not
in general vanish.
