Article révisé par les pairs
| Résumé : | The fundamental equations of Kadanoff and Baym (K-B) relating Green's functions (g> and g<) and self-energy parts (Σ> and Σ<) are derived directly without going through the technique of imaginary-time Green's function. Explicit definitions for Σ> and Σ< are given in terms of diagrams. The derivation based on the perturbation theory suggests the possible use of Green's function defined with a more general density operator than the equilibrium one e.g. for the problem of approach to equilibrium. The method of K-B is compared with the existing theories of irreversible processes developed by different authors. The method agrees in principles with the perturbation method of Fujita. The self-energy parts (Σ<, Σ>) are related to (Wιι′ Gι) of Van Hove and ψ(z) of Prigogine-Résibois both responsible for localized collision processes but they contain also the information about the previous history of particles depending on a given initial condition. The separation of these apparently different processes is however one of the main points in the theories of Van Hove and Prigogine-Résibois. © 1957. |
