Charges from dressed matter: Physics and renormalisation

Gauge theories are characterised by long range interactions. Neglecting the se interactions at large limes and identifying the Lagrangian matter fields with the asymptotic physical fields leads to the infrared problem. In this paper we study the perturbative applications of a construction of physical charges in QED, where the matter fields are combined with the associated e lectromagnetic clouds. This has been formally shown, in a companion paper, to include these asymptotic interactions. It is explicitly demonstrated tha t the on-shell Green's functions and S-matrix elements describing these cha rged fields have, to all orders in the coupling, the pole structure associa ted with particle propagation and scattering. We show in derail that the re normalisation procedure may be carried out straightforwardly. II is shown t hat standard infrared finite predictions of QED are not altered and it is s peculated that the good infrared properties of our construction may open th e way to the calculation of previously uncalculable properties. Finally ext ensions of this approach to QCD are briefly discussed. (C) 2000 Academic Pr ess.