Kinetic equations for electron excitations and phonons in a superconductor

A system of kinetic equations that describe the relaxation of the nonequilibrium system of electron excitations and phonons in a superconductor is obtained. It is shown that the complete system of equations in the weak-coupling approximation and the spatially homogeneous case includes, besides the kinetic equations for the electron excitations and phonons, a system of integral equations for the nonequilibrium energy gap and the energy renormalization function; these have the form of Eliashberg's equations.