HARD-SOFT RENORMALIZATION AND THE EXACT RENORMALIZATION-GROUP

The Wilsonian exact renormalization group gives a natural framework in which ultraviolet and infrared divergences can be treated separately. In massless QED we introduce, as the only mass parameter, a renormali zation scale Lambda(R) > 0, We prove, using the flow equation techniqu e, that infrared convergence is a necessary consequence of any zero-mo mentum renormalization condition at Lambda(R) compatible with the effe ctive Ward identities and axial symmetry. The same formalism is applie d to renormalize gauge-invariant composite operators and to prove thei r infrared finiteness; in particular we consider the case of the axial current operator and its anomaly. (C) 1998 Elsevier Science B.V.