Quark-gluon vertex with an off-shell O(a)-improved chiral fermion action

TL;DR

This paper compares the quark-gluon vertex functions obtained from different lattice fermion actions, highlighting the superior behavior of domain wall fermions at high momentum and exploring off-shell improvement techniques for clover actions.

Contribution

It provides a detailed comparison of vertex functions for various fermion actions and demonstrates how off-shell improvements can enhance clover action results.

Findings

Domain wall vertex functions behave well at high momentum transfer.

Clover vertex functions show weak dependence on the clover coefficient.

Off-shell improvement rotations improve clover action results.

Abstract

We perform a study the quark-gluon vertex function with a quenched Wilson gauge action and a variety of fermion actions. These include the domain wall fermion action (with exponentially accurate chiral symmetry) and the Wilson clover action both with the non-perturbatively improved clover coefficient as well as with a number of different values for this coefficient. We find that the domain wall vertex function behaves very well in the large momentum transfer region. The off-shell vertex function for the on-shell improved clover class of actions does not behave as well as the domain wall case and, surprisingly, shows only a weak dependence on the clover coefficient $c_{SW}$ for all components of its Dirac decomposition and across all momenta. Including off-shell improvement rotations for the clover fields can make this action yield results consistent with those from the domain wall approach, as well as helping to determine the off-shell improved coefficient $c_q^\prime$.