Infrared Behavior of Gluon and Ghost Propagators in Landau Gauge QCD (original) (raw)

The Infrared Behavior of Gluon, Ghost and Quark Propagators in Landau Gauge QCD

1999

A truncation scheme for the Dyson-Schwinger equations of QCD in Landau gauge is presented which implements the Slavnov-Taylor identities for the 3-point vertex functions. Neglecting contributions from 4-point correlations such as the 4-gluon vertex function and irreducible scattering kernels, a closed system of equations for the propagators is obtained. For the pure gauge theory without quarks this system of equations

Infrared gluon and ghost propagators from lattice QCD

The European Physical Journal A, 2007

We report on the infrared limit of the quenched lattice Landau gauge gluon and ghost propagators as well as the strong coupling constant computed from large asymmetric lattices. The infrared lattice propagators are compared with the pure power law solutions from Dyson-Schwinger equations (DSE). For the gluon propagator, the lattice data is compatible with the DSE solution. The preferred measured gluon exponent being ∼ 0.52, favouring a vanishing propagator at zero momentum. The lattice ghost propagator shows finite volume effects and, for the volumes considered, the propagator does not follow a pure power law. Furthermore, the strong coupling constant is computed and its infrared behaviour investigated.

Infrared exponent for gluon and ghost propagation in Landau gauge QCD

Physical Review D, 2002

In the covariant description of confinement, one expects the ghost correlations to be infrared enhanced. Assuming ghost dominance, the long-range behavior of gluon and ghost correlations in Landau gauge QCD is determined by one exponent κ. The gluon propagator is infrared finite (vanishing) for κ = 1/2 (κ > 1/2) which is still under debate. Here, we study critical exponent and coupling for the infrared conformal behavior from the asymptotic form of the solutions to the Dyson-Schwinger equations in an ultraviolet finite expansion scheme. The value for κ is directly related to the ghost-gluon vertex. Assuming that it is regular in the infrared, one obtains κ ≃ 0.595. This value maximizes the critical coupling αc(κ), yielding α max c ≃ (4π/Nc) 0.709 ≈ 2.97 for Nc = 3. For larger κ the vertex acquires an infrared singularity in the gluon momentum, smaller ones imply infrared singular ghost legs. Variations in αc remain within 5% from κ = 0.5 to 0.7. Above this range, αc decreases more rapidly with αc → 0 + as κ → 1 − which sets the upper bound on κ.

Infrared gluon and ghost propagator exponents from lattice QCD

The European Physical Journal C, 2009

The compatibility of the pure power law infrared solution of QCD and lattice data for the gluon and ghost propagators in Landau gauge is discussed. For the gluon propagator, the lattice data is well described by a pure power law with an infrared exponent κ ∼ 0.53, in the Dyson-Schwinger notation. κ is measured using a technique that suppresses finite volume effects. This value implies a vanishing zero momentum gluon propagator, in agreement with the Gribov-Zwanziger confinement scenario. For the ghost propagator, the lattice data seem not to follow a pure power law, at least for the range of momenta accessed in our simulation.

The infrared behavior of QCD propagators in Landau gauge

Nuclear Physics A, 2001

Some features of the solutions to the truncated Dyson-Schwinger equations(DSEs) for the propagators of QCD in Landau gauge are summarized. In particular, the Kugo-Ojima confinement criterion is realized, and positivity of transverse gluons is manifestly violated in these solutions. In Landau gauge, the gluon-ghost vertex function offers a convenient possibility to define a nonperturbative running coupling. The infrared fixed point obtained from this coupling which determines the 2-point interactions of color-octet quark currents implies the existence of unphysical massless states which are necessary to escape the cluster decomposition of colored clusters. The gluon and ghost propagators, and the nonperturbative running coupling, are compared to recent lattice simulations. A significant deviation of the running coupling from the infrared behavior extracted in simulations of 3-point functions is attributed to an inconsistency of asymmetric subtraction schemes due to a consequence of the Kugo-Ojima criterion: infrared enhanced ghosts.

The Infrared Behavior of Propagators in Landau Gauge QCD

1999

A closed system of equations for the propagators of Landau gauge QCD is obtained in a truncation scheme for their Dyson-Schwinger equations which implements the Slavnov-Taylor identities for the 3-point vertex functions while neglecting contributions from irreducible 4-point correlations. In the pure gauge theory without quarks, non-perturbative solutions for the gluon and ghost propagators are available in an approximation which

Exploring the infrared gluon and ghost propagators using large asymmetric lattices

Brazilian Journal of Physics, 2007

We report on the infrared limit of the quenched lattice Landau gauge gluon propagator computed from large asymmetric lattices. In particular, the compatibility of the pure power law infrared solution (q 2) 2κ of the Dyson-Schwinger equations is investigated and the exponent κ is measured. The lattice data favours κ ∼ 0.52, which would imply a vanishing zero momentum gluon propagator as predicted by the Kugo-Ojima confinement mechanism and the Zwanziger horizon condition. Results for the ghost propagator and for the running coupling constant are shown.

Studying the infrared behaviour of gluon and ghost propagators using large asymmetric lattices

AIP Conference Proceedings, 2007

We report on the infrared limit of the quenched lattice Landau gauge gluon propagator computed from large asymmetric lattices. In particular, the compatibility of the pure power law infrared solution (q 2) 2κ of the Dyson-Schwinger equations is investigated and the exponent κ is measured. Some results for the ghost propagator and for the running coupling constant will also be shown.

Ghost propagator and ghost-gluon vertex from Schwinger-Dyson equations

Physical Review D, 2013

We study an approximate version of the Schwinger-Dyson equation that controls the nonperturbative behavior of the ghost-gluon vertex, in the Landau gauge. In particular, we focus on the form factor that enters in the dynamical equation for the ghost dressing function, in the same gauge, and derive its integral equation, in the "one-loop dressed" approximation. We consider two special kinematic configurations, which simplify the momentum dependence of the unknown quantity; in particular, we study the soft gluon case, and the well-known Taylor limit. When coupled with the Schwinger-Dyson equation of the ghost dressing function, the contribution of this form factor provides considerable support to the relevant integral kernel. As a consequence, the solution of this coupled system of integral equations furnishes a ghost dressing function that reproduces the standard lattice results rather accurately, without the need to artificially increase the value of the gauge coupling.