  We systematically present a new approach for studying the coupled linear
transport of holographic systems. In this approach, the set of equations for
the linear perturbations can be reduced to a first-order nonlinear ordinary
differential equation expressed as the radial (renormalization group) flow
equation of the transport matrices. As an important application, we use this
approach to compute the DC and AC conductivities of a holographic model with
momentum dissipation, which can be easily read off from the nonlinear flow
equations. This method also works for transport in the presence of an external
magnetic field.

High Energy Physics - Theory