Dirac indices and is in general a function of two non-orthogonal four vectors, $P$ and $q$ ($P\cdot q \neq 0$). On first appraisal, one might therefore expect that the complete set of sixteen Dirac matrices $\left\{{\bf1},\gamma _5,\gamma _{\mu },\gamma _5\gamma _{\mu },\sigma
_{\mu \nu}\right\}$ must be employed in its description. However, by limiting the gluon two-point function, $D$, to diagonal components in Lorentz indices, the tensor, $\sigma _{\mu \nu }$, is excluded. This is seen explicitly by rewriting the integrand of (\[IBS\]) using $$\begin{aligned}
\left[ \gamma _{\nu }G(K_+)\Gamma _{\mu }(P,q)G(K_-)\gamma _{\nu
}\right] _{il}&=&\left( \gamma _{\nu }\right) _{ij}\left[ G(K_+)\Gamma
_{\mu }(P,q)G(K_-)\right] _{jk}\left( \gamma _{\nu }\right) _{kl}\nonumber \\
&=&\frac{1}{4}M^a_{il}\mbox{tr}\left[ M^aG(K_+)\Gamma _{\mu
}(P,q)G(K_-)\right] ,\label{2.5}\end{aligned}$$ where the set of matrices $M^a\equiv \left\{ {\bf1},i\gamma _5,i\gamma
_{\mu }/\sqrt{2},i\gamma _5\gamma _{\mu }/\sqrt{2}\right\} $, from which $\sigma _{\mu \nu }$ is absent, are obtained through Fierz reordering, and the repeated indices are summed. Further, the pseudo-scalar matrix, $\gamma _5$, can be excluded by considering that the corresponding term in (\[2.5\]) has the form $\gamma _5\Lambda
^5_{\mu }(P,q)$, where the matrix structure has been completely factored. In order to contribute to the QPV, this term must form a four vector, which requires $\Lambda ^5_{\mu }(P,q)$ to be an axial 