2,560 research outputs found
The Glue Around Quarks and the Interquark Potential
The quarks of quark models cannot be identified with the quarks of the QCD
Lagrangian. We review the restrictions that gauge field theories place on any
description of physical (colour) charges. A method to construct charged
particles is presented. The solutions are applied to a variety of applications.
Their Green's functions are shown to be free of infra-red divergences to all
orders in perturbation theory. The interquark potential is analysed and it is
shown that the interaction responsible for anti-screening results from the
force between two separately gauge invariant constituent quarks. A fundamental
limit on the applicability of quark models is identified.Comment: 4 pages, LaTeX, talk given at Montpellier meeting QCD9
Intermolecular C-H...N and C-H...O interactions in (2S,4S,5R)-(-)-3,4-dimethyl-5-phenyl-2-(1,3-thiazol-2-yl)-1,3-oxazolidine
The title compound, CââHââNâOS, prepared from
(1R,2S)-(-)-ephedrine, contains the oxazolidine ring
in an envelope conformation, with the nitrogen atom
0.623 (2) Ă
from the plane of the other four oxazolidine ring
atoms. Intermolecular C--H...N and C--H...O interactions
generate a two-dimensional hydrogen-bonded
network, with shortest C...N and C...O distances of
3.403 (3) and 3.463 (2) Ă
, respectively
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Improving decision-making and cognitive bias using innovative approaches to simulated scenario and debrief design
Colour, copies and confinement
In this paper we construct a wide class of Gribov copies in Coulomb gauge
SU(2) gauge theory. Infinitesimal copies are studied in some detail and their
non-perturbative nature is made manifest. As an application it is shown that
the copies prevent a non-perturbative definition of colour charge.Comment: 25 pages, 10 figures. Minor changes, two references added. Published
versio
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
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
Comment on ``A New Symmetry for QED'' and ``Relativistically Covariant Symmetry in QED''
We show that recently found symmetries in QED are just non-local versions of
standard BRST symmetry.Comment: 4 pages, revte
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
Concurrent optimization of airframe and engine design parameters
An integrated system for the multidisciplinary analysis and optimization of airframe and propulsion design parameters is being developed. This system is known as IPAS, the Integrated Propulsion/Airframe Analysis System. The traditional method of analysis is one in which the propulsion system analysis is loosely coupled to the overall mission performance analysis. This results in a time consuming iterative process. First, the engine is designed and analyzed. Then, the results from this analysis are used in a mission analysis to determine the overall aircraft performance. The results from the mission analysis are used as a guide as the engine is redesigned and the entire process repeated. In IPAS, the propulsion system, airframe, and mission are closely coupled. The propulsion system analysis code is directly integrated into the mission analysis code. This allows the propulsion design parameters to be optimized along with the airframe and mission design parameters, significantly reducing the time required to obtain an optimized solution
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