Altarelli–Parisi equations as renormalization-group equations for the coefficients of nonlocal expansion on the light cone

The relations between local and nonlocal expansions on the light cone are studied in the framework of renormalized perturbation theory. The case of forward scattering is also considered. It is shown that the Altarelli–Parisi equations are essentially the renormalization-group equations for the coefficients of the nonlocal expansion on the light cone.