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 …

The soft limits of scattering amplitudes have been extensively studied due to their essential
role in the computation of physical observables in collider physics. The universal …

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 …

A short, graduate-level synthesis of recent developments in theoretical physics, from a
pioneer in the field Lectures on the Infrared Structure of Gravity and Gauge Theory presents …

We provide evidence that the classical scattering of two spinning black holes is controlled by
the soft expansion of exchanged gravitons. We show how an exponentiation of Cachazo …

A bstract It is shown that black hole spacetimes in classical Einstein gravity are
characterized by, in addition to their ADM mass M, momentum\(\overrightarrow {P}\), angular …

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 …

A bstract We study two-dimensional celestial conformal field theory describing four-
dimensional\(\mathcal {N}\)= 1 supergravity/Yang-Mills systems and show that the …

A bstract We reformulate the scattering amplitudes of 4D flat space gauge theory and gravity
in the language of a 2D CFT on the celestial sphere. The resulting CFT structure exhibits an …

A bstract We systematically explore the space of scalar effective field theories (EFTs)
consistent with a Lorentz invariant and local S-matrix. To do so we define an EFT …