FlatHolo · Towards a holographic approach for gravity in asymptotically flat spacetimes

Towards a holographic approach for gravity in asymptotically flat spacetimes

My proposed project broadly aimed to exploit the infinity of symmetries of gravity in four-dimensional asymptotically flat spacetimes (AFS) and the associated constraints to gain quantitative insight into non-perturbative aspects of gravitational scattering. AFS are interesting to study because they describe physical events in our universe on astrophysical timescales such as the gravitational radiation from a pair of merging black holes. Moreover, they were recently shown to host a set of precise equivalences relating spacetime symmetries to universal aspects of gravitational scattering. These ideas led to the Celestial Holography program, which aims to develop a holographic understanding of gravity in four-dimensional (4D) AFS. There is increasing evidence that dual theories in this case live on a 2D sphere at infinity (the celestial sphere) and that gravitational observables are encoded in correlation functions on the sphere (celestial amplitudes) obeying a wide range of constraints. The project had two main goals. The first objective (WP1) was to develop the foundations for systematically incorporating massive particles and ultimately black holes into the AFS holographic framework. On the one had, I proposed to initiate a study of celestial amplitudes involving massive particles. Such amplitudes are expected to carry information about observables associated with black hole scattering, including gravitational waves. On the other hand, I proposed the study of celestial amplitudes in shockwave and black hole backgrounds. Especially in the context of the Anti-de-Sitter/conformal field theory (AdS/CFT) correspondence, shockwave spacetimes have in the past served as toy models for black hole physics and chaos. It is currently not known whether these aspects are universally (ie. also in AFS) captured by observables (correlation functions) in a CFT. The second objective (WP2) was to derive certain aspects of celestial holography from a flat space limit of the much better understood holographic correspondence in asymptotically negatively curved spacetimes (AdS/CFT). The project proposed to first understand how celestial amplitudes emerge from correlation functions of a conformal field theory in one higher dimension. It then proposed to leverage some of the tools developed over many years in the study of AdS/CFT to gain new insights into flat space holography, including the implications of an infinity of symmetry constraints and the emergence of bulk subregions from the boundary celestial (C)CFT. Since the exterior of a black hole spacetime is a subregion, one of the aims of WP2 can be reformulated as searching for a missing entry in the flat space dictionary relating black hole observables to CCFT correlators.

Data: CORDIS, © European Union