Zero Bias Anomaly Out of Thermal Equlibrium

We consider the out-of-equilibrium tunneling density-of-states for a two-dimensional diffusive film. Starting from a Keldysh $sigma$-model formalism we have obtained an effective action capable of accounting for both real and virtual processes. The ensuing zero bias anomaly, obtained non-perturbatively in the interaction, exhibits a two-dip structure, whose singularity is rounded off by the electron-electron inelastic rate.