A Unified Description of Flat Space Holography

One of the most challenging open questions in theoretical physics consists in describing quantum mechanics and gravity in a unified framework. Important progress has been made towards this goal with the development of the holographic principle, whose most concrete realization is the AdS/CFT correspondence. Although AdS/CFT is the duality that has attracted the most attention, the holographic principle is believed to be much more general and to hold for other kinds of asymptotics, including for the more realistic model of four-dimensional (4d) asymptotically flat spacetime. In this regard, two proposals of flat space holography have emerged. The first consists of a 4d/3d duality, where 4d gravity is dual to a 3d Carrollian CFT living on the null boundary of the spacetime. The second is a 4d/2d duality, where 4d gravity is dual to a 2d conformal field theory, called celestial CFT, living on the celestial sphere.

The aim of this research project is to make major steps towards a holographic description of quantum gravity in asymptotically flat spacetime. To do so, we plan to provide a unified description of flat space holography by exploring the relation between the two above proposals and connecting them with the AdS/CFT correspondence through a flat limit process. Four main lines of research will be investigated: (i) the relation between 3d Carrollian CFT and 2d celestial CFT, (ii) the representations of the BMS group acting in the dual theories, (iii) the flat limit of the AdS/CFT correspondence, and (iv) the construction of explicit candidates for the dual theories.

This project involves a transfer of knowledge between the host institutions and the researcher, who will receive training in new advanced techniques in the field. This unique exchange of skills and the collaborations that will emerge in this program are expected to generate major advances in the quest for flat space holography.