We give a formal treatment of the "correlated worldline" theory of quantum gravity. The generating functional is written as a product over multiple copies of the coupled matter and gravitational fields; paths for fields are correlated via gravity itself. In the limit where the gravitational coupling G → 0, conventional quantum field theory is recovered; in the classical limit ℏ → 0, general relativity is recovered. A formal loop expansion is derived, with all terms up to one-loop order ∼Oðl 2 P Þ given explicitly, where l P is the Planck length. We then derive the form of a perturbation expansion in l 2 P around a background field, with the correlation functions given explicitly up to ∼Oðl 2 P Þ. Finally, we explicitly demonstrate the on shell gauge independence of the theory, to order l 2 P in gravitational coupling and to all orders in matter loops, and derive the relevant Ward identities.

We consider the interaction between a matter system and soft gravitons. We use a functional eikonal expansion to deal with the infrared divergences, and introduce a "composite generating functional" which allows us to calculate a decoherence functional for the time evolution of the system. These techniques allow us to formulate scattering problems in a way which deals consistently with infrared effects, as well as being manifestly diffeomorphism invariant. We show how the asymptotic form of the decoherence functional can be written in terms of the infinitely many conserved charges associated with asymptotic BMS symmetries, and allow us to address the question of how much information is lost during the scattering.

We study scalar field configurations around Kerr black holes with a time-independent energymomentum tensor. These stationary 'scalar clouds', confined near the black hole (BH) by their own mass or a mirror at fixed radius, exist at the threshold for energy extraction via superradiance. Motivated by the electromagnetic Blandford-Znajek (BZ) mechanism, we explore whether scalar clouds could serve as a proxy for the force-free magnetosphere in the BZ process. We find that a stationary energy-extracting scalar cloud solution exists when the reflecting mirror is replaced by a semi-permeable surface which allows the cloud to radiate some energy to infinity while maintaining self-sustained superradiance. The radial energy flux displays the same behaviour for rapidly rotating holes as magnetohydrodynamic simulations predict for the BZ mechanism.