A Chapter on Celestial Holography

TL;DR

This chapter reviews recent progress in celestial holography, exploring how flat space holograms relate to conformal field theories on the celestial sphere, emphasizing symmetry structures and top-down approaches.

Contribution

It summarizes key developments in celestial holography, including the understanding of asymptotic symmetries and the formulation of top-down models using twisted holography insights.

Findings

Soft limits encode infinite-dimensional symmetries.

Progress in top-down celestial holography models.

Active research directions in the field.

Abstract

The Celestial Holography program encompasses recent efforts to understand the flat space hologram in terms of a CFT living on the celestial sphere. A key development instigating these efforts came from understanding how soft limits of scattering encode infinite dimensional symmetry enhancements corresponding to the asymptotic symmetry group of the bulk spacetime. Historically, the construction of the bulk-boundary dual pair has followed bottom up approach matching symmetries on both sides. Recently, however, there has been exciting progress in formulating top down descriptions using insights from twisted holography. This chapter reviews salient aspects of the celestial construction, the status of the dictionary, and active research directions. This is a preprint version of a chapter prepared for the Encyclopedia of Mathematical Physics 2nd edition.