Fermi-edge singularity changes in a dramatic way in a nonequilibrium system, acquiring
features which reflect the structure of energy distribution. In particular, it splits into
several components if the energy distribution exhibits multiple steps. While conventional
approaches, such as bosonization, fail to describe the nonequilibrium problem, an exact
solution for a generic energy distribution can be obtained with the help of the method of
functional determinants. In the case of a split Fermi distribution, while the `open loop'
contribution to Green's function has power law singularities, the tunneling density of states
profile exhibits broadened peaks centered at Fermi sub-levels.
reference: D.A. Abanin, L.S. Levitov, Phys. Rev. Lett. 94, 186803 (2005)