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 …

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 …

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

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 …

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 …