Spin Structure Function g_2(x,Q^2) and Twist-3 Operators in large-N_C QCD

Abstract

It is shown in the framework of the operator product expansion and the renormalization group method that the twist-3 part of flavour nonsinglet spin structure function g_2(x,Q^2) obeys a simple Dokshitzer-Gribov- Lipatov-Altarelli-Parisi (DGLAP) equation in the large N_C limit even in the case of massive quarks (N_C is the number of colours). There are four different types of twist-3 operators which contribute to g_2, including quark-mass-dependent operators and the ones proportional to the equation of motion. They are not all independent but are constrained by one relation. A new choice of the independent operator bases leads to a simple form of the evolution equation for g_2 at large N_C.