Quark pair condensation and chiral symmetry breaking in QCD

If the effective qanti q interaction strength due to gluon exchange becomes at least moderately strong beyond some distance g2/4π > 9/8, the perturbative vacuum becomes unstable to the creation of color singlet qanti q pairs, which indicates that the true vacuum contains a condensate of such pairs. We analyze the condensation by a coherent state variational procedure modeled after the BCS superconductor, and show that this method is equivalent to a self-consistent Hartree-Fock approximation to the Schwinger-Dyson equation for the quark propagator. The condensate leads to a spontaneous breakdown of chiral symmetry in the manner discussed by Nambu and Jona-Lasinio. The massive pseudoparticles with quark quantum numbers are identified with the 'constituent' quarks. (orig.)