1,811 research outputs found
Description of Gluon Propagation in the Presence of an A^2 Condensate
There is a good deal of current interest in the condensate A^2 which has been
seen to play an important role in calculations which make use of the operator
product expansion. That development has led to the publication of a large
number of papers which discuss how that condensate could play a role in a
gauge-invariant formulation. In the present work we consider gluon propagation
in the presence of such a condensate which we assume to be present in the
vacuum. We show that the gluon propagator has no on-mass-shell pole and,
therefore, a gluon cannot propagate over extended distances. That is, the gluon
is a nonpropagating mode in the gluon condensate. In the present work we
discuss the properties of both the Euclidean-space and Minkowski-space gluon
propagator. In the case of the Euclidean-space propagator we can make contact
with the results of QCD lattice calculations of the propagator in the Landau
gauge. With an appropriate choice of normalization constants, we present a
unified representation of the gluon propagator that describes both the
Minkowski-space and Euclidean-space dynamics in which the A^2 condensate plays
an important role.Comment: 28 pages, 11 figure
The Nielsen Identities for the Two-Point Functions of QED and QCD
We consider the Nielsen identities for the two-point functions of full QCD
and QED in the class of Lorentz gauges. For pedagogical reasons the identities
are first derived in QED to demonstrate the gauge independence of the photon
self-energy, and of the electron mass shell. In QCD we derive the general
identity and hence the identities for the quark, gluon and ghost propagators.
The explicit contributions to the gluon and ghost identities are calculated to
one-loop order, and then we show that the quark identity requires that in
on-shell schemes the quark mass renormalisation must be gauge independent.
Furthermore, we obtain formal solutions for the gluon self-energy and ghost
propagator in terms of the gauge dependence of other, independent Green
functions.Comment: 25 pages, plain TeX, 4 figures available upon request, MZ-TH/94-0
On the Significance of the Quantity "A Squared"
We consider the gauge potential A and argue that the minimum value of the
volume integral of A squared (in Euclidean space) may have physical meaning,
particularly in connection with the existence of topological structures. A
lattice simulation comparing compact and non-compact ``photodynamics'' shows a
jump in this quantity at the phase transition, supporting this idea.Comment: 6 pages, one figur
Comment on gauge choices and physical variables in QED
We consider possible definitions of physical variables in QED. We demonstrate
that the condition is the most convenient one because it
leads to path integral over physical components with local action. However,
other choices, as , are also possible. The standard expression for
configuration space path integral in gauge is obtained starting with
reduced phase space formulation. Contrary to the claims of the paper [M.Lavelle
and D.McMullan,Phys. Lett. B316 (1993)172] the gauge is not
overconstrained.Comment: 4 pages, SPbU-IP-94-8, Late
- âŠ