Elementary Theory of Line Broadening and Four-wave Mixing in   Nonequilibrium Many-Particle Systems
  The basic results of optical line broadening and four-wave mixing are deduced from first principles based on time-dependent many-body purturbation theory. The formalism allows us to write all the results in terms of nonequilibrium distribution functions without the need to assume a quasiequilibrium temperature. The connection of these results to the quantum Boltzmann equation is shown, which is also derived from first principles. Last, specific predictions for electron-electron scattering are reviewed. 
David W. Snoke