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 …

Motivated by conceptual problems in quantum theories of gravity, the gravitational eikonal
approach, inspired by its electromagnetic predecessor, has been successfully applied to the …

A bstract We re-examine the constraints imposed by causality and unitarity on the low-
energy effective field theory expansion of four-particle scattering amplitudes, exposing a …

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 …

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 …

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 …

Celestial holography proposes a duality between the gravitational $\mathcal {S} $-matrix
and correlators in a conformal field theory living on the celestial sphere. In this white paper …

The S-matrix Bootstrap originated on the idea that the S-matrix might be fully constrained by
global symmetries, crossing, unitarity, and analyticity without relying on an underlying …

A bstract Observables related to the real part of the gravitational eikonal, such as the
deflection angle and time delay, have been found so far to have a smooth post-Minkowskian …