Improved variational approach to QCD in Coulomb gauge

TL;DR

This paper enhances the variational approach to QCD in Coulomb gauge by expanding the quark vacuum wave functional, ensuring divergence cancellation, and examining the effects of unquenching on the gluon propagator.

Contribution

The authors introduce a new Dirac structure in the quark-gluon coupling, improving the variational ansatz and ensuring divergence cancellation in the quark gap equation.

Findings

All linear divergences cancel in the quark gap equation.

Unquenching the gluon propagator results in small effects.

The renormalized coupling reproduces the quark condensate phenomenology.

Abstract

The variational approach to QCD in Coulomb gauge developed previously by the T\"ubingen group is improved by enlarging the space of quark trial vacuum wave functionals through a new Dirac structure in the quark-gluon coupling. Our ansatz for the quark vacuum wave functional ensures that all linear divergences cancel in the quark gap equation resulting from the minimization of the energy calculated to two-loop order. The logarithmic divergences are absorbed in a renormalized coupling which is adjusted to reproduce the phenomenological value of the quark condensate. We also unquench the gluon propagator and show that the unquenching effects are generally small and amount to a small reduction in the mid-momentum regime.