BMS Symmetries of Gravitational Scattering

TL;DR

This paper reviews the BMS group and its role in understanding the asymptotic structure of flat spacetimes, exploring connections between symmetries, soft theorems, and gravitational memory effects, with implications for quantum gravity.

Contribution

It explicitly constructs the BMS symmetry group in 3+1 dimensions and links asymptotic symmetries to infrared phenomena and quantum gravity insights.

Findings

Explicit construction of BMS group in 3+1 dimensions

Connections established between asymptotic symmetries and soft theorems

Discussion of implications for quantum gravity and black hole information

Abstract

After motivating the relevance of the Bondi-Metzner-Sachs (BMS) group over the last decades, we review how concepts such as Penrose diagrams and the covariant phase space formalism can be used to understand the asymptotic structure of asymptotically flat spacetimes (AFS). We then explicitly construct the asymptotic symmetry group of AFS in $3+1$ dimensions, the BMS group. Next, we apply this knowledge to the usual far-field scattering problem in general relativity, which leads to the unravelling of the intrinsic features of gravity in the infrared. In particular, we work out the connections between asymptotic symmetries, soft theorems in quantum field theories and gravitational memory effects. We restrict to the study of this infrared triangle through the lens of supertranslations here, but the analogous features that can be found in the case of superrotations or for other gauge theories are also motivated at the end of our discussion. We conclude with an overview of the implications of the infrared triangle of gravity for the formulation of an approach to quantum gravity through holography, as well as a brief discussion of its potential in tackling the black hole information paradox.