title: Two-particle problem in a nonequilibrium many-particle system.
abstract: The two-particle problem within a nonequilibrium many-particle system is investigated in the framework of real-time Green's functions. Starting from the nonequilibrium Bethe-Salpeter equation on the Keldysh contour, a Dyson equation is given for two-time two-particle Green's functions. Thereby the well-known Kadanoff-Baym equations are generalized to the case of two-particle functions. The two-time structure of the equations is achieved in an exact way using the semigroup property of the free-particle propagators. The frequently used Shindo approximation is thus avoided. It turns out that results obtained earlier are valid only in limiting cases of a nondegenerate system or a static interaction, respectively. For the case of thermodynamic equilibrium, the differences to former results obtained for the effective two-particle Hamiltonian are discussed.
authors.affiliation: Fachbereich Physik, Universität Rostock, 18051 Rostock, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Bornath
authors.forename: D
authors.initials: D
authors.lastname: Kremp
authors.forename: M
authors.initials: M
authors.lastname: Schlanges