Lecture notes prepared for the 2021 SAGEX PhD School in Amplitudes hosted by the
University of Copenhagen August 10th through 13th. Topics covered include: the …

We review the role that infinite-dimensional symmetries arising at the boundary of
asymptotically flat spacetimes play in the context of the celestial holography program. Once …

We show that a 3D sourced conformal Carrollian field theory has the right kinematic
properties to holographically describe gravity in 4D asymptotically flat spacetime. The …

These notes consist of 3 lectures on celestial holography given at the Pre-Strings school
2021. We start by reviewing how semiclassically, the subleading soft graviton theorem …

A bstract All 4D gauge and gravitational theories in asymptotically flat spacetimes contain an
infinite number of non-trivial symmetries. They can be succinctly characterized by …

It is shown that the infinite tower of tree-level plus-helicity soft graviton symmetries in
asymptotically flat 4D quantum gravity can be organized into a single chiral 2D Kac-Moody …

A bstract Celestial amplitudes represent 4D scattering of particles in boost, rather than the
usual energy-momentum, eigenstates and hence are sensitive to both UV and IR physics …

In this paper we extract from a large-r expansion of the vacuum Einstein's equations a
dynamical system governing the time evolution of an infinity of higher-spin charges. Upon …

A bstract The isomorphism between the (extended) BMS 4 algebra and the 1+ 2D Carrollian
conformal algebra hints towards a co-dimension one formalism of flat holography with the …

A bstract The operator product expansion of massless celestial primary operators of arbitrary
spin is investigated. Poincaré symmetry is found to imply a set of recursion relations on the …