Regge phenomenology is used to infer the positivity of certain helicity-dependent quark distribution functions with their low-x behavior subtracted out. These forms adequately describe the data for muon scattering from polarized protons but violate the Ellis-Jaffe sum rule, casting doubt on the reliability of perturbative QCD. Predictions made earlier with the theory of quark geometrodynamics are in agreement with the data.
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Preparata et al. (1988) studied this question.
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