Causal three-point functions and nonlinear second-order hydrodynamic coefficients in AdS/CFT

In the context of $\mathcal{N}=4$ SYM, we compute the finite 't Hooft coupling $\lambda$ correction to the non-linear second-order hydrodynamic coefficient $\lambda_3$ from a Kubo formula based on fully retarded three-point functions using AdS/CFT. Although $\lambda_3$ is known to vanish in the infinite 't Hooft coupling limit, we find that the finite $\lambda$ correction is non-zero. We also present a set of Kubo formulae for the non-linear coefficients $\lambda_{1,2,3}$, which is more convenient than the one that has appeared recently elsewhere.