A simple approach to the ABJ axial anomaly

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Abstract
A very simple semi-quantitative derivation of the Adler-Bell-Jackiw (ABJ) axial anomaly is given, based on an investigation of the absorptive part of the VVA triangle graph and dispersion relations. Essential ingredients of the author's discussion are: normal Ward identities for the absorptive part of the relevant diagram, dimensional analysis, unitarity and energy-momentum conservation. An explanation of the physical origin of the axial anomaly, offered in some earlier treatments within such a dispersive framework, is critically examined. In particular, the interpretation of the ABJ anomaly as an analogue of the Lee-Nauenberg effect occurring in the massless limit of spinor electrodynamics is shown to be fallacious.