Nucleon matrix elements of higher-twist operators from the instanton vacuum Original Research Article

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 1Nc 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.