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Regular Seminar Andrea Puhm (CPHT, CNRS, Ecole polytechnique)
Novel insights into quantum gravity in asymptotically flat spacetimes evolving around soft theorems in scattering amplitudes, memory effects and asymptotic symmetries hint at an underlying holographic structure of Minkowski spacetime: information about 4D quantum gravity might be encoded in a 2D CFT on the celestial sphere at the conformal boundary of Minkowski spacetime. I will discuss recent progress on this attempted formulation of a flat space holography focusing on the 4D S-matrix which takes the form of a 2D correlator on the celestial sphere in a conformal basis. I will discuss how celestial conformal symmetry is generated by "conformally soft" gravitons and how insertions of the BMS supertranslation current in a correlator gives rise to the celestial analogue of Weinberg's soft graviton theorem.