RG-approach and mass factorization a la B.P.H.Z

The renormalization group (RG) approach to massive photon processes is developed in its most simple form. Assuming general g2 expansion of the RG-function we establish a direct connection between the RG-solution and order-by-order Feynman diagram calculation. Emphasis is placed on the next-to-leading corrections. A simple method is introduced of mass factorization, similar to Bogolyubov-Parasiuk-Hepp-Zimmermann-renormalization, where the mass singularities are subtracted by the counter terms which build up the operator matrix element (OME). It allows contruction of the deep-inelastic (DI)/Drell-Yan (DY) cut-graphs from the OMEs. Similar arguments applied on the DY coefficient function reveal its diagramatic form. Explicit examples in PHI63 theory illustrate the above insight. (author)