Discrete R Symmetries and Anomalies

Understand

We comment on aspects of discrete anomaly conditions focussing particularly on $R$ symmetries.

• We review the Green-Schwarz cancellation of discrete anomalies, providing a heuristic explanation why, in the heterotic string, only the "model-independent dilaton" transforms non-linearly under discrete symmetries; this argument suggests that, in other theories, multiple fields might play a role in anomaly cancellations, further weakening any anomaly constraints at low energies.
• We provide examples in open string theories of non-universal discrete anomalies at low energies.
• We then consider the fact that $R$ symmetries are necessarily broken at low energies.