Feynman-gauge adjoint propagator
= Feynman-gauge adjoint propagator
{c}
{title2=$D_{\mu\nu}^{ab}(p)=\frac{-i\eta_{\mu\nu}\delta^{ab}}{p^2-i\epsilon}$}
With a mostly-plus <metric signature>, $e^{iS}$, and gauge-fixing term $-(\partial\cdot A)^2/2$, the free adjoint gauge-field kernel is $-p^2\eta_{\mu\nu}\delta_{ab}$. Inverting it gives the displayed <Feynman propagator>. This convention uses the same denominator and sign as a massless real <scalar propagator>.