Quark-gluon vertex from Nf=2 lattice QCD

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.

Comments: 24 pages, many figures. Minor changes, matches version published in Phys.Rev.D