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Dryson equations, Ward identities, and the infrared behavior of Yang-Mills theories. [Schwinger-Dyson equations, Slavnov-Taylor identities]

Description: It was shown using the Schwinger-Dyson equations and the Slavnov-Taylor identities of Yang-Mills theory that no inconsistency arises if the gluon propagator behaves like (1/p/sup 2/)/sup 2/ for small p/sup 2/. To see whether the theory actually contains such singular long range behavior, a nonperturbative closed set of equations was formulated by neglecting the transverse parts of GAMMA and GAMMA/sub 4/ in the Schwinger-Dyson equations. This simplification preserves all the symmetries of the th… more
Date: January 1, 1979
Creator: Baker, M.
Partner: UNT Libraries Government Documents Department
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Vertex Sensitivity in the Schwinger-Dyson Equations of QCD

Description: The nonperturbative gluon and ghost propagators in Landau gauge QCD are obtained using the Schwinger-Dyson equation approach. The propagator equations are solved in Euclidean space using Landau gauge with a range of vertex inputs. Initially we solve for the ghost alone, using a model gluon input, which leads us to favour a finite ghost dressing in the nonperturbative region. In order to then solve the gluon and ghost equations simultaneously, we find that non-trivial vertices are required, part… more
Date: January 1, 2012
Creator: David J. Wilson, Michael R. Pennington
Partner: UNT Libraries Government Documents Department
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Can an infrared-vanishing gluon propagator confine quarks?

Description: It is shown that the solution of the quark Dyson-Schwinger equation in QCD obtained with a gluon propagator of the form D(q) {approximately} q{sup 2}/[q{sup 4}+b{sup 4}] and a quark-gluon vertex that is free of kinematic singularities does not describe a confined particle and that there is always a value of b{sup 2} = b{sub c}{sup 2} such that chiral symmetry is not dynamically broken for b{sup 2} > b{sub c}{sup 2}.
Date: September 1, 1994
Creator: Roberts, C. D.
Partner: UNT Libraries Government Documents Department
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Pion observables and QCD

Description: The Dyson-Schwinger equations (DSEs) are a tower of coupled integral equations that relate the Green functions of QCD to one another. Solving these equations provides the solution of QCD. This tower of equations includes the equation for the quark self-energy, which is the analogue of the gap equation in superconductivity, and the Bethe-Salpeter equation, the solution of which is the quark-antiquark bound state amplitude in QCD. The application of this approach to solving Abelian and non-Abelia… more
Date: September 1, 1994
Creator: Roberts, C. D.
Partner: UNT Libraries Government Documents Department
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The strong running coupling from an approximate gluon Dyson-Schwinger equation

Description: Using Mandelstam`s approximation to the gluon Dyson-Schwinger equation we calculate the gluon self-energy in a renormalisation group invariant fashion. We obtain a non-perturbative {Beta} function. The scaling behavior near the ultraviolet stable fixed point is in good agreement with perturbative QCD. No further fixed point for positive values of the coupling is found: {alpha}{sub S} increases without bound in the infrared.
Date: October 1, 1996
Creator: Alkofer, R.; Hauck, A. & Von Smekal, L.
Partner: UNT Libraries Government Documents Department
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A continuum order parameter for deconfinement

Description: Dyson-Schwinger equations are presented as a non-perturbative tool for the study and modeling of QCD at finite-{ital T}. An order parameter for deconfinement, applicable for both light and heavy quarks, is introduced. In a simple Dyson-Schwinger equation model of two-flavor QCD, coincident, 2nd-order chiral symmetry restoration and deconfinement transitions occur at {ital T} {approx} 150 MeV, with the same critical exponent, {Beta} {approx} 0.33.
Date: March 1, 1997
Creator: Roberts, C.D.
Partner: UNT Libraries Government Documents Department
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Confinement, diquarks and goldstone`s theorem

Description: Determinations of the gluon propagator in the continuum and in lattice simulations are compared. A systematic truncation procedure for the quark Dyson-Schwinger and bound state Bethe-Salpeter equations is described. The procedure ensures the flavor-octet axial- vector Ward identity is satisfied order-by-order, thereby guaranteeing the preservation of Goldstone`s theorem; and identifies a mechanism that simultaneously ensures the absence of diquarks in QCD and their presence in QCD{sup N{sub c}=… more
Date: December 31, 1996
Creator: Roberts, C.D.
Partner: UNT Libraries Government Documents Department
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Non-equilibrium QCD of high-energy multi-gluon dynamics

Description: A non-equilibrium QCD description of multiparticle dynamics in space-time is of both fundamental and phenomenological interest. Here the authors discusses an attempt to derive from first principles, a real-time formalism to study the dynamical interplay of quantum and statistical-kinetic properties of non-equilibrium multi-parton systems produced in high-energy QCD processes. The ultimate goal (from which one is still far away) is to have a practically applicable description of the space-time e… more
Date: December 31, 1996
Creator: Geiger, K.
Partner: UNT Libraries Government Documents Department
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Separable approximation to the Bethe-Salpeter equation in QCD

Description: We calculate the mass spectrum and decay constants of the pseudoscalar meson octet, and mass spectrum of the vector meson octet from a separable approximation to the Bethel-Salpeter equation. In the model, quark propagators inspired by earlier studies of QCD Dyson-Schwinger equations are taken as the only input.
Date: December 1, 1995
Creator: Burden, C.J.; Qian, L. & Roberts, C.D.
Partner: UNT Libraries Government Documents Department
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Temperature, chemical potential and the {rho}-meson

Description: Models of QCD must confront nonperturbative phenomena such as confinement, dynamical chiral symmetry breaking (DCSB) and the formation of bound states. In addition, a unified approach should describe the deconfinement and chiral symmetry restoring phase transition exhibited by strongly-interacting matter under extreme conditions of temperature and density. Nonperturbative Dyson-Schwinger equation (DSE) models provide insight into a wide range of zero temperature hadronic phenomena; e.g., non-ha… more
Date: February 17, 2000
Creator: Roberts, C. D. & Schmidt, S. M.
Partner: UNT Libraries Government Documents Department
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Anomalous {gamma} {r_arrow} 3{pi} amplitude in a bound-state approach

Description: The form factor for the anomalous process {gamma}{pi}{sup +} {r_arrow} pi{sub +}{pi}{sup 0}, which is presently being measured at CEBAF, is calculated in the Schwinger-Dyson approach in conjunction with an impulse approximation. The form factors obtained by the author are compared with the ones predicted by the simple constituent quark loop model, vector meson dominance and chiral perturbation theory, as well as the scarce already available data.
Date: January 1, 2000
Creator: Bistrovic, Bojan & Klabucar, Dubravko
Partner: UNT Libraries Government Documents Department
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