ac conductance through an interacting quantum dot

We investigate the linear ac conductance for tunneling through an arbitrary interacting quantum dot in the presence of a finite dc bias. In analogy to the well-known Meir-Wingreen formula for the dc case, we are able to derive a general formula for the ac conductance. It can be expressed entirely in terms of local correlations on the quantum dot in the form of a Keldysh block diagram with four external legs. We illustrate the use of this formula as a starting point for diagrammatic calculations by considering the ac conductance of the noninteracting resonant-level model and deriving the result for the lowest order of electron-phonon coupling. We show how known results are recovered in the appropriate limits.