= Color factor
= Colour factor
{synonym}
The group-theoretic tensor multiplying the kinematic part of a <Feynman diagram> involving <color charge>. It is obtained by contracting internal indices among <gauge generators>, invariant tensors and <structure constants of a Lie algebra>. For instance, one <gluon> exchange on a single <quark> line contributes $\sum_aT^aT^a=C_F\mathbf1$; averaging or summing the squared tensor over external colour labels gives the corresponding <color average> in a squared <scattering amplitude>.
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