BRST structure for the mixed Weyl-diffeomorphism residual symmetry

In this paper, we show the compatibility of the so-called "dressing field method", which allows a systematic reduction of gauge symmetries, with the inclusion of diffeomorphisms in the BRST algebra of a gauge theory. The robustness of the scheme is illustrated on two examples where Cartan connections play a significant role. The former is General Relativity, while the latter concerns the second-order conformal structure where one ends up with a BRST algebra handling both the Weyl residual symmetry and diffeomorphisms of spacetime. We thereby provide a geometric counterpart to the BRST cohomological treatment used in~\cite{Boulanger1} in the construction of a Weyl covariant tensor calculus.