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 …

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 …

Recent attempts at the construction of holography for asymptotically flat spacetime have
taken two different routes. Celestial holography, involving a two dimensional (2D) conformal …

We propose a holographic duality for a four dimensional Wess-Zumino-Witten model with
target manifold SO (8), coupled to scalar-flat Kähler gravity on an asymptotically flat, four …

A bstract We elaborate on various aspects of our top-down celestial holographic duality
wherein the semiclassical bulk spacetime is a 4d asymptotically flat, self-dual Kähler …

Gravity in 4 d asymptotically flat spacetime constitutes the archetypal example of a
gravitational system with leaky boundary conditions. Pursuing our previous analysis of …

A bstract We propose a new program for computing a certain integrand of scattering
amplitudes of four-dimensional gauge theories which we call the form factor integrand …