Proton Spin and Chiral Dynamics

 Recent successful chiral models for the spin fractions of the proton rely on parametrizations that are inconsistent with deep inelastic lepton scattering unless the quark masses are neglected and inconsistent with chiral quark models based on constituent quarks, because only chiral spinflip transitions are considered. Non-spinflip transitions are important for constituent quarks as they depend on the quark masses. Therefore, the models are valid at a scale of about 0.63 GeV to Λ_χ, where dynamical quark masses are expected to be close to current quark masses, rather than Λ_QCD. When constituent quark masses are properly included, chiral quark models generate spin fractions that disagree with the proton spin data. Received July 1, 1998; accepted for publication January 30, 1999