Physical charges in QED and QCD

Abstract

We show that the `dressing' approach, which describes physical charges as gauge invariant composites of matter and clouds of gauge bosons, arises naturally in gauge theories. We give perturbative examples of dressings for both asymptotic charges and for states in which the fields are confined to a compact volume as is required, for example, by causality in pair creation. In QCD, we use dressed states to demonstrate explicitly how Gribov copies obstruct the non-perturbative construction of colour charges.

Comments: Talk given at the International Workshop on QCD Green's Functions, Confinement and Phenomenology, September 7-11 2009, ECT Trento, Italy. 8 pages, 3 pdf figures. V2: references added, to appear in PoS