2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/48721The 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) \sim 10^{-3} obtained from instantons is consistent with the recent E143 measurements of the structure function g_2, where d^(2) enters at the same level as the twist-2 contribution.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 ProceedingsHigh Energy Physics - Phenomenologytext