Nucleon matrix elements of higher – twist operators from the instanton vacuum

We compute the nucleon matrix elements of QCD operators of twist 3 and 4 in the instanton vacuum. We consider the operators determining 1/Q 2 –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.