Colour-preserving gluon vertex
= Colour-preserving gluon vertex
{title2=$(T^3)_{rr}=1/2,\ (T^8)_{rr}=1/(2\sqrt3)$}
A <quark>-<gluon> <Feynman vertex> whose initial and final <quark> have the same chosen <color charge> basis label. Such vertices exist: the diagonal <Gell-Mann matrices> act nontrivially on the red basis vector. Their <gluons> are traceless colour-octet combinations, not <colour singlets>. A ninth singlet generator proportional to the identity is absent from <SU(3)>.