QGVertex[psi1[index1, momentum1], psi2[index2, momentum2], ...] is a placeholder for the interaction vertex of the fields psi1, psi2, .... It is introduced in the QGARF style file "feyncalc.sty".
QGVertex[psi1[index1, momentum1], psi2[index2, momentum2], ...]
psi1, psi2, ...
"feyncalc.sty"
Overview.