By making use of the renormalization group technique, we show that the compositeness conditions required for the equivalence of quantum chromodynamics and the corresponding four-fermion theory may be demonstrated for a large class of gauges. It is also pointed out from a study of soluble models...

We present a general formalism for doing the perturbation theory in the complex energy plane, where the notion of the generalized quantum mechanical systems is used. This formalism is applied to the Friedrichs-Lee model. It reproduces the results of the exact solution, where the spectrum of the...

Light is a quantum electrodynamic entity and hence bundles of rays must be describable in this framework. We demonstrate the duality in the description of elementary optical phenomena in terms of two-point correlation functions and in terms of collections of light rays. The generalizations...