Evolution of twist-three parton distributions in QCD beyond the large-Nc limit

We formulate a consistent 1/Nc2 expansion of the QCD evolution equations for the twist-three quark distributions g2(x,Q2), hL(x,Q2) and e(x,Q2) based on the interpretation of the evolution as a three-particle quantum-mechanical problem with hermitian Hamiltonian. Each distribution amplitude can be decomposed in contributions of partonic components with DGLAP-type scale dependence. We calculate the 1/Nc2 corrections to the evolution of the dominant component with the lowest anomalous dimension – the only one that survives in the large-Nc limit – and observe a good agreement with the exact numerical results for Nc=3. The 1/Nc2 admixture of operators with higher anomalous dimensions is shown to be concentrated at a few lowest partonic components and in general is rather weak.