Classifying double copies and multicopies in AdS

Abstract

In this paper, we draw a parallel between solutions of pure three-dimensional gravity with a negative cosmological constant and classical double copies in four dimensions. In the former case, topological solutions, such as the BTZ black hole, deficit angles, and naked singularities, emerge from identifying points in AdS using elements from its isometry algebra $so(2,2)$. The type of solution corresponds one-to-one with the orbits of $so(2,2)$. We demonstrate how various double copies of four-dimensional AdS gravity similarly arise from the $so(2,3)$ isometry elements, which also correspond one-to-one with their orbits through a Penrose-type transform. We classify all such elements and generate the corresponding double copies, which include AdS black holes, black branes, and many others. The double-copy isometries originate from the centralizer of a given AdS isometry, allowing us to define canonical coordinates associated with its Abelian part. Additionally, the two Casimir invariants of $so(2,3)$ feature in the metrics. Our classification naturally extends to higher spins, providing nonequivalent multicopies at the linearized level.