Effective gluon mass and infrared fixed point in QCD

TL;DR

This paper investigates solutions to the gluon propagator in pure QCD, revealing an infrared finite effective gluon mass that decreases with momentum and leads to an infrared fixed point, enhancing understanding of QCD's low-energy behavior.

Contribution

It presents a novel class of solutions to the gluon propagator from Schwinger-Dyson equations, showing a momentum-dependent gluon mass and an infrared fixed point in QCD.

Findings

Gluon propagator solutions reach a finite infrared value.

The effective gluon mass decreases as the inverse square of momentum.

The effective charge exhibits asymptotic freedom and freezes at low energies.

Abstract

We report on a special type of solutions for the gluon propagator of pure QCD, obtained from the corresponding non-linear Schwinger-Dyson equation formulated in the Feynman gauge of the background field method. These solutions reach a finite value in the deep infrared and may be fitted using a massive propagator, with the crucial characteristic that the effective ``mass'' employed depends on the momentum transfer. Specifically, the gluon mass falls off as the inverse square of the momentum, as expected from the operator-product expansion. In addition, one may define a dimensionless quantity, which constitutes the generalization in a non-Abelian context of the universal QED effective charge. This strong effective charge displays asymptotic freedom in the ultraviolet whereas in the low-energy regime it freezes at a finite value, giving rise to an infrared fixed point for QCD.