Renormalization of twist-four operators in QCD

Extending the work by Bukhvostov, Frolov, Lipatov and Kuraev (BFLK) on the renormalization of quasipartonic operators we derive a complete set of two-particle renormalization group kernels that enter QCD evolution equations to twist-four accuracy. To this end we develop a new technique which essentially bypasses calculation of Feynman diagrams. It is shown that the 2→22→2 evolution kernels which involve “non-partonic” components of field operators, and, most remarkably, also 2→32→3 kernels do not require independent calculation and can be restored from the known results for quasipartonic operators using conformal symmetry and Lorentz transformations. The kernels are presented for the renormalization of light-ray operators built of chiral fields in a particular basis such that the conformal symmetry is manifest. The results can easily be recast in momentum space, in the form of evolution equations for generalized parton distributions.