The Teukolsky scalar as a gateway for quantizing gravity on rotating black holes

Abstract: The quantization of linearized gravity on black hole spacetimes and the construction of states for that theory is a sought-after, yet difficult achievement. One of the main reasons is the difficulty of reconciling the positivity and gauge invariance of potential states. On Kerr spacetimes, the spin-2 Teukolsky scalars express the same degrees of freedom as the metric perturbations, up to pure gauge and radiative solutions, while avoiding the issue of gauge. In this work, we therefore explore the quantization of Teukolsky scalars on Kerr. We demonstrate that the theory can be written in terms of a formally hermitian Green-hyperbolic operator, allowing the construction of the algebra of observables. The reconstruction scheme for the metric perturbation allows us to keep track of the physical subalgebra. We indicate how this can be used to construct the Unruh state for this theory on any subextreme Kerr spacetime. This is based on a joint work with Dietrich H\"afner in preparation.