Chiral extrapolation, renormalization, and the viability of the quark model

The relationship of the quark model to the known chiral properties of QCD is a long-standing problem in the interpretation of low-energy QCD. In particular, how can the pion be viewed as both a collective Goldstone-boson quasiparticle and as a valence-quark-antiquark bound state? A comparison of the many-body solution of a simplified model of QCD to the constituent-quark model demonstrates that the quark model is sufficiently flexible to describe meson hyperfine splitting provided proper renormalization conditions and correct degrees of freedom are employed consistently.