Infrared Features of the Landau Gauge QCD

TL;DR

This study uses lattice QCD simulations to analyze infrared properties of Landau gauge QCD, revealing finite gluon propagator at zero momentum, strong ghost singularity, and evidence for an infrared fixed point in the running coupling.

Contribution

It provides new lattice simulation data on infrared features of Landau gauge QCD, including the behavior of gluon and ghost propagators and the running coupling, supporting the existence of an infrared fixed point.

Findings

Gluon propagator remains finite at zero momentum.

Ghost propagator exhibits stronger infrared singularity than tree level.

QCD running coupling peaks around 1 at 0.5 GeV and decreases towards zero momentum.

Abstract

The infrared features of Landau gauge QCD are studied by the lattice simulation of $\beta=6.0, 16^4, 24^4, 32^4$ and $\beta=6.4, 32^4, 48^4$. We adopt two definitions of the gauge field; 1) $U-$linear 2) $\log U$ and measured the gluon propagator and ghost propagator. Infrared singularity of the gluon propagator is less than that of tree level result but the gluon propagator at 0 momentum remains finite. The infrared singularity of ghost propagator is stronger than the tree level. The QCD running coupling measured by using the gluon propagator and the ghost propagator has a maximum $\alpha_s(p)\simeq 1$ at around $p=0.5GeV$ and decreases as $p$ approaches 0. The data are analyzed in use of formula of the principle of minimal sensitivity(PMS), the effective charge method and the contour-improved perturbation method, which suggest necessity of the resummation of perturbation series in the infrared region together with existence of the infrared fixed point. Kugo-Ojima parameter saturates at about -0.8 in contrast to the theoretically expected value -1.