24 research outputs found
Charges from Dressed Matter: Physics and Renormalisation
Gauge theories are characterised by long range interactions. Neglecting these
interactions at large times, and identifying the Lagrangian matter fields with
the asymptotic physical fields, leads to the infra-red 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 electromagnetic
clouds. This has been formally shown, in a companion paper, to include these
asymptotic interactions. It is explicitly demonstrated that the on-shell
Green's functions and S-matrix elements describing these charged fields have,
to all orders in the coupling, the pole structure associated with particle
propagation and scattering. We show in detail that the renormalisation
procedure may be carried out straightforwardly. It is shown that standard
infra-red finite predictions of QED are not altered and it is speculated that
the good infra-red properties of our construction may open the way to the
calculation of previously uncalculable properties. Finally extensions of this
approach to QCD are briefly discussed.Comment: 34 pages, LaTeX, uses FeynMF, 17 figures, very minor wording change,
version to appear in Annals of Physic
Anti-Screening by Quarks and the Structure of the Inter-Quark Potential
The inter-quark potential is dominated by anti-screening effects which
underly asymptotic freedom. We calculate the order g^6 anti-screening
contribution from light fermions and demonstrate that these effects introduce a
non-local divergence. These divergences are shown to make it impossible to
define a coupling renormalisation scheme that renormalises this minimal,
anti-screening potential. Hence the beta function cannot be divided into
screening and anti-screening parts beyond lowest order. However, we then
demonstrate that renormalisation can be carried out in terms of the
anti-screening potential.Comment: 11 pages, some clarifications and typographical corrections, to
appear in Physics Letters
Charged Particles: A Builder's Guide
It is sometimes claimed that one cannot describe charged particles in gauge
theories. We identify the root of the problem and present an explicit
construction of charged particles. This is shown to have good perturbative
properties and, asymptotically before and after scattering, to recover particle
modes.Comment: 6 pages, LaTeX, to appear in proceedings of Sixth Workshop on
Non-Perturbative Quantum Chromodynamics, Paris, June 200
The Structure of the QCD Potential in 2+1 Dimensions
We calculate the screening and anti-screening contributions to the
inter-quark potential in 2+1 dimensions, which is relevant to the high
temperature limit of QCD. We demonstrate that the relative strength of
screening to anti-screening agrees with the 3+1 dimensional theory to better
than one percent accuracy.Comment: 9 pages, LaTeX, no figures, version to appear in Journa
Infra-Red Finite Charge Propagation
The Coulomb gauge has a long history and many uses. It is especially useful
in bound state applications. An important feature of this gauge is that the
matter fields have an infra-red finite propagator in an on-shell
renormalisation scheme. This is, however, only the case if the renormalisation
point is chosen to be the static point on the mass shell, p = (m, 0, 0, 0). In
this letter we show how to extend this key property of the Coulomb gauge to an
arbitrary relativistic renormalisation point. This is achieved through the
introduction of a new class of gauges of which the Coulomb gauge is a limiting
case. A physical explanation for this result is given.Comment: 8 pages, plain TeX, to appear in Modern Physics Letters
The Structure of Screening in QED
The possibility of constructing charged particles in gauge theories has long
been the subject of debate. In the context of QED we have shown how to
construct operators which have a particle description. In this paper we further
support this programme by showing how the screening interactions arise between
these charges. Unexpectedly we see that there are two different gauge invariant
contributions with opposite signs. Their difference gives the expected result.Comment: 8 pages, LaTe