We start by revisiting the task of constructing a holographic dual to quantum gravity in asymptotically flat spacetimes. Upon recasting the S-matrix in terms of data at the conformal boundary, we see that the two standard approaches (Carrollian and Celestial) amount to slicing up the bulk and boundary in different ways. In particular, the Celestial Hologram organizes scattering from the point of view of Rindler evolution.
Now the main motivation for Celestial Holography comes from the connection between soft theorems and asymptotic symmetries in asymptotically flat spacetimes, and our ability to recast soft operators as currents in a codimension 2 CFT. Taking radial = Rindler evolution provides a streamlined route from asymptotic symmetries in 4D asymptotically flat spacetimes to currents in a 2D celestial CFT in a manner that makes their relation to QFT soft theorems manifest. We use this to reconcile the construction of charges in CCFT with the more familiar construction from AdS/CFT, despite the differing codimension, and discuss the advantages of the celestial basis.
Based on 2201.06805 and 2202.11127