Renormalization of gauge-invariant operators for the structure function g_2(x, Q^{2})
We investigate the nucleon's transverse spin-dependent structure function g_2(x, Q^{2}) in the framework of the operator product expansion and the renormalization group. We construct the complete set of the twist-3 operators for the flavor singlet channel, and give the relations among them. We develop an efficient, covariant approach to derive the anomalous dimension matrix of the twist-3 singlet operators by computing the off-shell Green's functions. As an application, we investigate the renormalization mixing for the lowest moment case, including the operators proportional to the equations of motion as well as the ``alien'' operators which are not gauge-invariant.