Formula_5222

\[\left\langle f_{i}(\boldsymbol{k}, t) u_{j}(-\boldsymbol{k}, t)\right\rangle=\int_{0}^{t} d t^{\prime}\left\langle f_{i}(\boldsymbol{k}, t) f_{l}\left(-\boldsymbol{k}, t^{\prime}\right)\right\rangle\left\langle\delta u_{j}(\boldsymbol{k}, t) / \delta f_{l}\left(-\boldsymbol{k}, t^{\prime}\right)\right\rangle\]