Gluon topology and the spin structure of the constituent quark

has inspired much theoretical and experimental effort to understand the internal spin structure of the nucleon [ 1]. A key issue [ 2] is the role of the axial anomaly in the transition from parton to constituent quark degrees of freedom in low energy QCD. In this paper I explain why some fraction of proton’s spin may be carried by gluon topology. The topological contribution has support only at Bjorken x equal to zero. In deep inelastic processes the internal structure of the nucleon is described by the QCD parton model [ 3]. The deep inelastic structure functions may be written as the sum over the convolution of “soft” quark and gluon parton distributions with “hard” photon-parton scattering coefficients. The (target dependent) parton distributions describe a flux of quark and gluon partons carrying some fraction x = p+parton/p+proton of the proton’s momentum into the hard (target independent) photon-parton interaction which is described by the hard scattering coefficients. In low energy processes the nucleon behaves like a colour neutral system of three massive constituent quark quasi-particles interacting self consistently with a cloud of virtual pions which is induced by spontaneous chiral symmetry breaking [ 4, 5].