Nucleon spin structure from the instanton vacuum
Abstract
We discuss the evaluation of the nucleon isoscalar axial coupling, $g_A^{(0)}$, in the instanton vacuum, using the $1/N_c$ expansion. This approach allows a fully consistent treatment of the $U(1)_A$ anomaly. We compute the nucleon matrix element of the topological charge density, $\langle N  F\widetilde{F}  N \rangle$, and show that it reduces to the matrix element of the divergence of the isoscalar axial quark current. Our arguments show that the usual evaluation of $g_A^{(0)}$ in the chiral quark soliton model is consistent with the $U(1)_A$ anomaly in leading order of $1/N_c$. Such calculations give $g_A^{(0)} = 0.36$, which is in agreement with the recent estimate by Ellis and Karliner.
 Publication:

arXiv eprints
 Pub Date:
 April 1996
 arXiv:
 arXiv:hepph/9604324
 Bibcode:
 1996hep.ph....4324W
 Keywords:

 High Energy Physics  Phenomenology
 EPrint:
 8 pp, standard LaTeX