Role of the Axial Anomaly in Determining Spin-Dependent Parton Distributions.

摘要

It is shown that the forward matrix elements of j(sub 5)(sup (mu)), the flavor singlet axial vector current, do not measure the helicity carried by quarks and anti-quarks but also include a spin-dependent gluonic component due to the anomaly. Detailed phenomenological and field theoretic reasons are given for the necessity of a gluonic component in the matrix element of j(sub 5)(sup (mu)). The first higher order corrections to the basic box and triangle graphs are discussed and shown not to modify the conclusions drawn in the leading order calculation. We close with a few comments on the possible phenomenological implications of the anomalous contribution. 25 refs., 6 figs.