Diquark condensation and the quark-quark interaction

We employ a bispinor gap equation to study superfluidity at nonzero chemical potential, mu not equal 0, in two- and three-color QCD, exploring the gap's sensitivity to the nature of the quark-quark interaction. The two-color theory, QC(2)D, is an excellent exemplar; the order of truncation of the quark-quark scattering kernel K has no qualitative impact, which allows a straightforward elucidation of the effects of mu when the coupling is strong. in the three-color theory the rainbow-ladder truncation admits diquark bound states, a defect that is eliminated by an improvement of K. The corrected gap equation describes a superfluid phase that is semiquantitatively similar to that obtained using the rainbow truncation. A model study suggests that the width of the superfluid gap and the transition point in QC(2)D provide reliable quantitative estimates of those quantities in QCD. [S0556-2813(99)07112-5].