Slavnov–Taylor identities

In quantum field theory, a Slavnov–Taylor identity is the non-Abelian^[1] generalisation of a Ward–Takahashi identity, which in turn is an identity between correlation functions that follows from the global or gauged symmetries of a theory, and which remains valid after renormalization. The identity was originally discovered by Gerard 't Hooft,^[2] and it is named after Andrei Slavnov and John C. Taylor who rephrased the identity to hold off the mass shell.^[3][4]