Gravitational memory in the bulk

TL;DR

This paper proposes a new method for detecting gravitational memory using ingoing null geodesics, extending the BMS symmetry-memory connection from null infinity to the bulk of spacetime.

Contribution

It introduces a novel approach utilizing ingoing null geodesics for gravitational memory detection and generalizes BMS symmetry interpretations to the spacetime bulk.

Findings

Method applicable in the bulk of spacetime

BMS generators have bulk memory interpretation

Extends null infinity memory results to the entire spacetime

Abstract

A method for detecting gravitational memory is proposed. It makes use of ingoing null geodesics instead of timelike geodesics in the original formulation by Christodoulou. It is argued that the method is applicable in the bulk of a spacetime. In addition, it is shown that BMS symmetry generators in Newman-Unti gauge have an interpretation in terms of the memory effect. This generalises the connection between BMS supertranslations and gravitational memory, discovered by Strominger and Zhiboedov at null infinity, to the bulk.