Infrared features of KS fermion and Wilson fermion in Lattice Landau Gauge QCD

TL;DR

This study investigates infrared properties of lattice Landau gauge QCD using Wilson and KS fermions, revealing an infrared fixed point and condensate effects consistent with continuum theory and recent perturbative results.

Contribution

It provides new lattice simulation evidence for an infrared fixed point and condensate effects in unquenched Landau gauge QCD, comparing different fermion actions and with continuum perturbative results.

Findings

Infrared fixed point at α₀ ≈ 2-2.5 independent of fermion action.

Kugo-Ojima parameter c ≈ 1, with lattice asymmetry effects.

Presence of dimension 4 condensates with opposite sign to dimension 2 condensates.

Abstract

The running coupling and the Kugo-Ojima parameter of unquenched lattice Landau gauge are simulated and compared with the continuum theory. Presence of infrared fixed point of $\alpha_0\sim 2-2.5$ irrespective of the fermion actions (Wilson fermions and Kogut-Susskind(KS) fermions) in the continuum and in the chiral limit is suggested. Although there exists dependence on the polarization due to asymmetry of the lattice (time axis is longer than spacial axes), the Kugo-Ojima parameter $c$ is consistent with 1. Presence of $1+c_1/q^2$ correction factor in the running coupling depends on the lattice size and the sea quark mass. In the large lattice size and small sea quark mass, $c_1\sim 2.8$GeV is confirmed. The MILC configuration of $a=0.09$fm suggests also presence of dimension 4 condensates with sign opposite to the dimension 2 condensates. The gluon propagator, the ghost propagator and the running coupling are compared with recent pQCD results including anomalous dimension of fields up to the 4-loop level.