Do anomalies break the momentum routing invariance?

Abstract

The diagrammatic computation of anomalies is usually associated with the breaking of the momentum routing invariance. This is because the momentum routing is usually chosen to fulfill the desired Ward identity. In the case of the chiral anomaly, the momentum routing is chosen in order to fulfill the gauge Ward identity and break the chiral Ward identity. Although the chiral anomaly is physical because it is associated with the pion decay into two photons, this does not necessarily mean that the momentum routing invariance is broken because the momentum routing was chosen in the computation of the anomaly. The reciprocal is not true, i.e. anomalies do not imply in momentum routing invariance breaking. In this work, we show that if gauge invariance is assumed, the chiral and the scale anomalies are independent of the momentum routing chosen and as a result they are momentum routing invariant. This idea is applied to a QED with non-minimal CPT and Lorentz violation, where momentum routing invariance is used to find out what symmetry is broken in the Ward identities.