The axial anomaly and the bound-state spectrum in confining theories

Abstract

We show that the axial anomaly of three-point functions of colour singlet currents in quark confining theories implies the presence of zero-mass bound states in the physical spectrum. These can be either massless fermions or Goldstone bosons. This supplements an argument given by 't Hooft. We then show, for any number of colours (with more than two flavours), that Goldstone bosons actually follow. Various aspects of heavy quark decoupling are also discussed.