The Full Spin Structure of Quarks in the Nucleon

We discuss bounds on the distribution and fragmentation functions that appear at leading order in deep inelastic 1-particle inclusive leptoproduction or in Drell-Yan processes. These bounds simply follow from positivity of the quarkhadron scattering matrix elements and are an important guide in estimating the magnitude of the azimuthal and spin asymmetries in these processes. We focus on an example relevant for deep inelastic scattering at relatively low energies. 1 The spin structure in inclusive DIS In deep-inelastic scattering (DIS) the transition from hadrons to quarks and gluons is described in terms of distribution and fragmentation functions. In general, the distribution functions for a quark can be obtained from the lightcone correlation functions [1, 2, 3, 4]. Φij(x) = ∫ dξ 2π e 〈P, S|ψj(0)ψi(ξ)|P, S〉 ∣