= Solution
A <gauge anomaly> breaks a redundancy required to remove unphysical polarizations. It violates the Ward identities and makes the quantum gauge theory inconsistent, so all gauge anomalies must cancel. A <chiral anomaly>, or <Adler-Bell-Jackiw anomaly>, instead breaks a classically conserved global axial symmetry; it is physically allowed and explains effects such as anomalous pseudoscalar decays and instanton-induced charge violation. A <'t Hooft anomaly> is an obstruction to gauging a global symmetry. It is invariant under <renormalization-group flow>, so <'t Hooft anomaly matching> constrains the infrared theory to reproduce it through massless fields, symmetry breaking, or a topological sector.
Back to article page
