HOW DO CONSTITUENT QUARKS ARISE IN QCD - PERTURBATION-THEORY AND THE INFRARED

We motivate the use of dressed charges by arguing that such objects ar e needed to describe, e.g., constituent quarks and, in general, physic al charged states in gauge theories. We give a short introduction to d ressings in both QED and QCD. We put special emphasis on the infra-red properties of a moving dressed charge. To be more precise, we demonst rate that the one loop propagator of a relativistic dressed charge can be renormalized in the mass shell scheme with no infra-red divergence showing up.