scholarly journals POSITIVITY VIOLATIONS IN QCD

2013 ◽  
Vol 28 (38) ◽  
pp. 1330035 ◽  
Author(s):  
JOHN M. CORNWALL
Keyword(s):  
Spectral Function ◽  
Physical Interpretation ◽  
Gluon Propagator ◽  
Landau Gauge ◽  
Asymptotic Freedom ◽  
Theoretical Studies ◽  
Gauge Invariant ◽  
Superconvergence Relation

Both lattice simulations and theoretical studies show that the spectral function of the gluon propagator of QCD (in various gauges, as well as for the gauge-invariant Pinch Technique, or PT, propagator) is not nonnegative everywhere, although it should be if it has a physical interpretation as in QED. Theory says moreover that the non-positive spectral function of the Landau-gauge or of the PT gluon propagator is further constrained to obey a superconvergence relation (the integral of the spectral function vanishes). We review the theoretical and lattice evidence for violation of positivity as well as various interpretations of this violation, and consider methods for checking superconvergence on the lattice (so far undone). The most common interpretation is that positivity violation implies confinement of gluons, so the gluon propagator does not describe processes with physical gluons. Another more direct and gauge-invariant interpretation arises from the PT: Asymptotic freedom alone demands non-positivity and superconvergence.

scholarly journals Reconstructing the gluon

2018 ◽  
Vol 5 (6) ◽  
Author(s):  
Anton K. Cyrol ◽  
Jan M. Pawlowski ◽  
Alexander Rothkopf ◽  
Nicolas Wink
Keyword(s):  
Spectral Function ◽  
Gluon Propagator ◽  
Low Frequency ◽  
Numerical Data ◽  
Systematic Errors ◽  
Landau Gauge ◽  
Careful Consideration ◽  
Functional Basis ◽  
Reconstruction Methods ◽  
Perturbative Regime

We reconstruct the gluon spectral function in Landau gauge QCD from numerical data for the gluon propagator. The reconstruction relies on two novel ingredients: Firstly we derive analytically the low frequency asymptotics of the spectral function. Secondly we construct a functional basis from a careful consideration of the analytic properties of the gluon propagator in Landau gauge. This allows us to reliably capture the non-perturbative regime of the gluon spectrum. We also compare different reconstruction methods and discuss the respective systematic errors.

scholarly journals LATTICE QCD GLUON PROPAGATORS NEAR TRANSITION TEMPERATURE

2012 ◽  
Vol 27 (09) ◽  
pp. 1250050 ◽  
Author(s):  
V. G. BORNYAKOV ◽  
V. K. MITRJUSHKIN
Keyword(s):  
Transition Temperature ◽  
Lattice Qcd ◽  
Finite Volume ◽  
Momentum Space ◽  
Transition Point ◽  
Gluon Propagator ◽  
Landau Gauge ◽  
Volume Dependence ◽  
Gauge Fixing ◽  
Two Phases

Landau gauge gluon propagators are studied numerically in the SU (3) gluodynamics as well as in the full QCD with the number of flavors nF = 2 using efficient gauge fixing technique. We compare these propagators at temperatures very close to the transition point in two phases: confinement and deconfinement. The electric mass mE has been determined from the momentum space longitudinal gluon propagator. Gribov copy effects are found to be rather strong in the gluodynamics, while in the full QCD case they are weak ("Gribov noise"). Also we analyze finite volume dependence of the transverse and longitudinal propagators.

GAUGE INDEPENDENCE OF THE FERMION DAMPING RATE IN A HOT PLASMA - LANDAU GAUGE VS COULOMB GAUGE

1993 ◽  
Vol 08 (08) ◽  
pp. 739-748
Author(s):  
H. NAKKAGAWA ◽  
A. NIÉGAWA ◽  
B. PIRE
Keyword(s):  
Perturbation Theory ◽  
Gluon Propagator ◽  
Landau Gauge ◽  
Coulomb Gauge ◽  
Leading Order ◽  
Loop Order ◽  
Hard Thermal Loop ◽  
Hot Plasma ◽  
Damping Rate

The damping rate of a heavy muon/quark in a hot QED/QCD plasma is calculated in the Landau gauge to the effective one-loop order in the resummed perturbation theory of Braaten and Pisarski. For both a muon/quark at rest and in an energetic case we obtain to leading order the same result as in the Coulomb gauge. Resummation of hard-thermal loop corrections to the photon/gluon propagator is of key importance for this gauge independence.

The interaction of molecular multipoles with the electromagnetic field in the canonical formulation of non-covariant quantum electrodynamics

1970 ◽  
Vol 319 (1539) ◽  
pp. 549-563 ◽  
Keyword(s):  
Electromagnetic Field ◽  
Physical Interpretation ◽  
Quantum Electrodynamics ◽  
Unitary Transformation ◽  
Canonical Quantization ◽  
Multipole Moments ◽  
Gauge Invariant ◽  
Covariant Quantum ◽  
Canonical Formulation ◽  
Gauge Conditions

The procedure devised by Dirac for the canonical quantization of systems described by degenerate lagrangians is used to construct the hamiltonian for molecules interacting with the electromagnetic field. The hamiltonian obtained is expressed in terms of the gauge invariant field strengths and the electric and magnetic multipole moments of the molecules. The Coulomb gauge is introduced but other gauge conditions could be used. Finally, a physical interpretation of the unitary transformation that may be used to generate the multipole hamiltonian is given.

CONFINEMENT OF QUARKS AND GLUONS

1994 ◽  
Vol 09 (21) ◽  
pp. 3799-3819 ◽  
Author(s):  
KAZUHIKO NISHIJIMA
Keyword(s):  
Quantum Chromodynamics ◽  
Spectral Function ◽  
Weak Coupling ◽  
Anomalous Dimension ◽  
Weak Coupling Limit ◽  
Superconvergence Relation

It is proved without recourse to any approximation that quarks and gluons are confined simultaneously when the anomalous dimension of the gluon field is negative in the weak coupling limit. The proof is based on the BRS invariance of quantum chromodynamics and the Oehme–Zimmermann superconvergence relation for the spectral function of the gluon field.

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