Proton Structure Functions from Chiral Dynamics and QCD Constraints

The spin fractions and deep inelastic structure functions of the proton are analyzed using chiral field theory involving Goldstone bosons. A detailed comparison with recent chiral models sheds light on their successful description of the spin fractions of the proton as being due to neglecting helicity non-flip chiral transitions. This approximation is valid for zero mass quarks but not for constituent quarks. Since the chiral spin fraction models with the pure spin-flip approximation reproduce the measured spin fractions of the proton, axialvector constituent-quark-Goldstone boson coupling is found to be inconsistent with the proton spin data. Initial quark valence distributions are then constructed using quark counting constraints at Bjorken $x \to 1$ and Regge behavior at $x \to 0$. Sea quark distributions predicted by chiral field theory on this basis have correct order of magnitude and shape. The spin fractions agree with the data.