GhostPropagator[p, a, b] gives the ghost propagator where a and b are the color indices.
GhostPropagator[p] omits the \delta _{ab}.
GHP can be used as an abbreviation of GhostPropagator.
Overview, GluonPropagator, QCDFeynmanRuleConvention, GluonGhostVertex.
GhostPropagator[p, a, b]
Explicit[%]\Pi _{ab}(p)
\frac{i \delta ^{ab}}{p^2}
GHP[p]
Explicit[%]\Pi _u(p)
\frac{i}{p^2}