Quark-gluon vertex from Nf=2 lattice QCD

TL;DR

This study investigates the infrared behavior of the quark-gluon vertex in lattice QCD with two flavors, revealing significant enhancements in form factors compared to perturbative predictions, with weak dependence on lattice parameters.

Contribution

First lattice QCD study of the quark-gluon vertex with Nf=2, showing infrared enhancements of form factors beyond perturbative expectations.

Findings

Infrared strength observed in all three form factors.

Significant enhancement of $lambda_1$ and $lambda_3$ compared to one-loop predictions.

Weak dependence of results on lattice spacing and quark mass.

Abstract

We study the quark-gluon vertex in the limit of vanishing gluon momentum using lattice QCD with 2 flavors of O(a) improved Wilson fermions, for several lattice spacings and quark masses. We find that all three form factors in this kinematics have a significant infrared strength, and that both the leading form factor $\lambda_1$, multiplying the tree-level vertex structure, and the scalar, chiral symmetry breaking form factor $\lambda_3$ are significantly enhanced in the infrared compared to the quenched (Nf=0) case. These enhancements are orders of magnitude larger than predicted by one-loop perturbation theory. We find only a weak dependence on the lattice spacing and quark mass.