The impact of transverse Slavnov-Taylor identities on dynamical chiral symmetry breaking

TL;DR

This paper investigates how transverse Slavnov-Taylor identities influence dynamical chiral symmetry breaking in QCD, deriving new form factors for the quark-gluon vertex and analyzing their impact on quark mass generation.

Contribution

It introduces a complete set of eight form factors for the transverse quark-gluon vertex constrained by Slavnov-Taylor identities and studies their effects on chiral symmetry breaking using Dyson-Schwinger equations.

Findings

Significant dynamical chiral symmetry breaking observed.

Quark mass gap around 500 MeV for light quarks.

Calculated quark condensate and pion decay constant match reference values.

Abstract

We extend earlier studies of transverse Ward-Fradkin-Green-Takahashi identities in QED, their usefulness to constrain the transverse fermion-boson vertex and their importance for multiplicative renormalizability, to the equivalent gauge identities in QCD. To this end, we consider transverse Slavnov-Taylor identities that constrain the transverse quark-gluon vertex and derive its eight associated scalar form factors. The complete vertex can be expressed in terms of the quark's mass and wave-renormalization functions, the ghost-dressing function, the quark-ghost scattering amplitude and a set of eight form factors. The latter parametrize the hitherto unknown nonlocal tensor structure in the transverse Slavnov-Taylor identity which arises from the Fourier transform of a four-point function involving a Wilson line in coordinate space. We determine the functional form of these eight form factors with the constraints provided by the Bashir-Bermudez vertex and study the effects of this novel vertex on the quark in the Dyson-Schwinger equation using lattice QCD input for the gluon and ghost propagators. We observe significant dynamical chiral symmetry breaking and a mass gap that leads to a constituent mass of the order of 500 MeV for the light quarks. The flavor dependence of the mass and wave-renormalization functions as well as their analytic behavior on the complex momentum plane is studied and as an application we calculate the quark condensate and the pion's weak decay constant in the chiral limit. Both are in very good agreement with their reference values.