Renormalization of Twist-Four Operators in QCD Bjorken and Ellis–Jaffe Sum Rules

The QCD effects of twist-four operators on the first moment of nucleon spin-dependent structure function g 1 (x,Q 2 ) are studied in the framework of operator product expansion and renormalization group method. We investigate the operator mixing through renormalization of the twist-four operators including those proportional to the equation of motion by evaluating off-shell Green's functions in the usual covariant gauge as well as in the background gauge. Through this procedure we extract the one-loop anomalous dimension of the spin-1 and twist-four operator which determines the logarithmic correction to the 1/Q 2 behavior of the contribution from the twist-four operators to the first moment of g 1 (x,Q 2 ).