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HK: Hadronen und Kerne

HK 68: Structure of Baryons, Mesons X, Theory

HK 68.6: Vortrag

Donnerstag, 19. März 1998, 16:00–16:15, J

Nucleon matrix elements of twist–3 and 4 operators from the instanton vacuum — •J. Balla¹, M.V. Polyakov^2,1, and C. Weiss¹ — ¹Institut f. Theoretische Physik II, Ruhr–Univ. Bochum — ²Petersburg Nuclear Physics Institute, St. Petersburg

We compute the nucleon matrix elements of QCD operators of twist 3 and 4 in the instanton vacuum. We consider the operators determining 1/Q²–power corrections to the Bjorken, Ellis–Jaffe and Gross–Llewellyn-Smith sum rules. The nucleon is described as a soliton of the effective chiral theory derived from instantons in the 1/N_c–expansion. QCD operators involving the gluon field are systematically represented by effective operators in the effective chiral theory. We find that twist–3 matrix elements are suppressed relative to twist–4 by a power of the packing fraction of the instanton medium. Numerical results for the spin–dependent (d⁽²⁾, f⁽²⁾) and spin–independent twist–3 and 4 matrix elements are compared with results of other approaches and with experimental estimates of power corrections.

[1] J. Balla, M.V. Polyakov and C. Weiss, Bochum University preprint RUB-TPII-6/97, hep-ph/9707515, Nucl. Phys. B, in press.