Charged Particle Emission and Detection Sources in Quantum Field Theory and Infrared Photons

A study is carried out of the fundamental roles played by emission and detection sources of charged particles in quantum field theory by incorporating the unavoidable fact that charged particles feel the presence of each other even when they are widely separated at the emission and detection sites due to the long range effect of the electromagnetic interaction. It is shown that the emission and detection sources as amplitudes of emission and detection of charged particles are to have given specific coupling dependent phase factors for a correct formulation of the problem. Composite sources are introduced for emitting and detecting “clusters” of charged particles. Finally a complete cancellation of the so-called relativistic Dalitz phase factor occurs prior to computing transition rates and probabilities. This work generalizes our earlier work (Fortschr. Phys. 34 , 835 (1986)) dealing with the non-relativistic Coulomb problem.