Extended BMS Algebra of Celestial CFT

Understand

We elaborate on the proposal of flat holography in which four-dimensional physics is encoded in two-dimensional celestial conformal field theory (CCFT).

• The symmetry underlying CCFT is the extended BMS symmetry of (asymptotically) flat spacetime.
• We use soft and collinear theorems of Einstein-Yang-Mills theory to derive the OPEs of BMS field operators generating superrotations and supertranslations.
• The energy-momentum tensor, given by a shadow transform of a soft graviton operator, implements superrotations in the Virasoro subalgebra of $\mathfrak{bms_4}$.