Unitarity, Ward identities, and new quantization rules of supergravity

Using diagrammatic techniques, we prove that supergravity is unitary to all orders in perturbation theory, subject to a generalized Becchi-Rouet-Stora (BRS) invariance of the effective action. In particular we show that new nonphysical modes in the propagator, not canceled by ghosts, decouple from the S matrix through appropriate Ward identities. We establish the generalized BRS invariance to order 3 and give a general recipe for extension to higher order. This new invariance requires new quantization rules for supergravity: A quartic supersymmetry ghost coupling must be added to the action. The same term has been found previously by Fradkin and Vasiliev from a Hamiltonian formulation of supergravity.