Quark contribution to the reggeon-reggeon-gluon vertex in QCD
V. S. Fadin, R. Fiore, A. Quartarolo
TL;DR
A remarkable but not complete cancellation between gluon and quark contributions to this new spin structure takes place for the case of three massless quark flavors.
Abstract
The quark loop contribution to the reggeon-reggeon-gluon vertex is calculated in QCD, where the reggeon is the reggeized gluon. Compared with the vertex in the Born approximation, this contribution exhibits a new spin structure as well as the gluon loop one. A remarkable but not complete cancellation between gluon and quark contributions to this new spin structure takes place for the case of three massless quark flavours.