Special Methods

Abstract

The Green’s function self-energy formulation can describe the physics of interacting particles in a very wide variety of systems. Because of its generality, however, it is not always the most suitable method for any particular problem. The iteration series must be developed in many different directions in order to include the correct physical properties, and it is not always obvious which direction (or, alternatively, which subset of diagrams) will actually describe the system being studied. For this reason, a number of alternative formulations and special models have been developed that concentrate upon a particular physical property of the system to give either a useful alternate viewpoint or bring out the physics involved more clearly.