Topics in Asymptotic Symmetries and Infrared Effects

TL;DR

This thesis investigates how asymptotic symmetries at null infinity control infrared physics across gravity and gauge theories. It first consolidates the four‑dimensional picture—BMS symmetry, large gauge transformations, soft theorems, and memory—before extending the framework to spacetimes of arbitrary dimension and to higher spins, highlighting subtle interplays between radiation and Coulombic sectors. It develops methods to define finite charges and residual symmetries in higher dimensions, employing polyhomogeneous expansions and Lorenz‑gauge analyses, and uncovers higher‑dimensional analogs of memory phenomena such as color, phase, and kick memories. The work clarifies how soft theorems persist beyond four dimensions, informs flat space holography and higher‑spin infrared structure, and provides a unified view of memory, charges, and asymptotic symmetries across spin and dimensionality.

Abstract

Motivated by connections with observable phenomena, in particular with soft factorization theorems for scattering amplitudes and with memory effects, renewed interest has been recently shown in the subject of asymptotic symmetries at null infinity. The two main goals of this Ph.D. thesis are, first, to review the main aspects of the connection between such symmetries and observable effects in the context of gravity, electromagnetic and Yang-Mills theory in four dimensions and, second, to present results concerning the extension of this program to the case of spacetimes of arbitrary dimension, either even or odd, to the emission or absorption of soft scalar quanta, in connection with their dual description, and to theories containing massless higher-spin fields.