Gauge invariant effective actions for dressed fields

A new fundamental form of the path integral for theories with local symmetry is introduced. It is utilised to construct effective actions that generate correlation functions of dressed fields in Yang-Mills theories and quantum gravity. The construction entails a novel BRST symmetric gauge fixing which imposes that the on-shell correlation functions are those of gauge invariant fields. We demonstrate that the effective actions are gauge and diffeomorphism invariant respectively, with appropriate transformations for the Faddeev-Popov ghosts and Nakanishi-Lautrup fields. As a consistency check, the on-shell one-loop effective actions are shown to take the expected gauge independent form. The effective action which satisfies Zinn-Justin's master equation is also gauge invariant with the anti-fields transforming accordingly. While our choice of gauge will in general be non-linear and non-local, we argue that these gauges are in fact stable under renormalisation if one allows for general renormalised field variables.