Freiburg 1998 – scientific programme

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T: Teilchenphysik

T 302: QCD III

T 302.7: Talk

Tuesday, March 24, 1998, 17:50–18:05, HS B

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

Nucleon matrix elements of QCD operators of twist 3 and 4 are computed 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. The methods developed can be used to evaluate a wide range of matrix elements relevant to DIS.

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