1999/01/26 by J. Balla, Balla, J., M. V. Polyakov +3
Physics and Astronomy · #FOS: Physical sciences #High Energy Physics - Phenomenology (hep-ph) #hep-ph
paper · pdf · doi:10.48550/arxiv.hep-ph/9901425
6 pages, LaTeX. Oral contribution to the 8th International Conference on the Structure of Baryons (Baryons '98), Bonn, Sep. 22-26, 1998; to appear in the Proceedings
arxiv created 1999/01/26 · arxiv updated 2009/11/30
The spin-dependent twist-3 and 4 nucleon matrix elements d^(2) and f^(2) describing power corrections to the Bjorken and Ellis-Jaffe sum rules are computed in the instanton vacuum. A systematic expansion in the small packing fraction of the instanton medium, rho / R << 1, is performed. We find that the twist-3 matrix element d^(2) is suppressed [of order (rho / R)4], while the twist-4 matrix element f^(2) is of order unity. Numerically, d^(2) << f^(2). The small value of d^(2) ∼ 10-3 obtained from instantons is consistent with the recent E143 measurements of the structure function g2, where d^(2) enters at the same level as the twist-2 contribution.