On solutions of the nonequilibrium x-ray edge problem

We rediscuss a nonequilibrium x-ray edge problem which in recent publications led to discrepancies between the results of the perturbative and of an extended Nozieres-De Dominicis approach. We show that the this problem results from an uncritical separation of momenta of the scattering potential, and we propose a corrected Nozieres-De Dominicis solution.