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 …

This review describes the duality between color and kinematics and its applications, with the
aim of gaining a deeper understanding of the perturbative structure of gauge and gravity …

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 …

A bstract Using a heavy-mass effective field theory (HEFT), we study gravitational-wave
emission in the scattering of two spinless black holes or neutron stars of arbitrary masses at …

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 …

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 show how to compute classical wave observables using quantum scattering amplitudes.
We discuss observables both with incoming and with outgoing waves. The required …

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 …