Baryons in QCDAS at large Nc: A roundabout approach

QCDAS, a variant of large Nc QCD in which quarks transform under the color two-index antisymmetric representation, reduces to standard QCD at Nc=3 and provides an alternative to the usual large Nc extrapolation that uses fundamental representation quarks. Previous strong plausibility arguments assert that the QCDAS baryon mass scales as Nc2; however, the complicated combinatoric problem associated with quarks carrying two color indices impeded a complete demonstration. We develop a diagrammatic technique to solve this problem. The key ingredient is the introduction of an effective multigluon vertex: a "traffic circle" or roundabout diagram. We show that arbitrarily complicated diagrams can be reduced to simple ones with the same leading Nc scaling using this device, and that the leading contribution to baryon mass does, in fact, scale as Nc2.