Displacement memory and BMS symmetries

TL;DR

This paper reviews the gravitational memory effect and its connection with BMS symmetries near black hole horizons, highlighting models and methods to compute displacement memory in these regions.

Contribution

It introduces a realistic approach to compute displacement memory associated with near-horizon BMS symmetries, extending previous asymptotic analyses.

Findings

Displacement memory causes permanent test particle displacements.

Near-horizon BMS symmetries relate to gravitational memory effects.

A new method for calculating memory at black hole horizons is proposed.

Abstract

This article reviews one of the most intriguing properties of black hole spacetimes known in the literature -- gravitational memory effect, and its connection with asymptotic symmetries, also termed as Bondi-van der Burg-Metzner-Sachs (BMS) symmetries, emerging near the horizon of black holes. Gravitational memory is a non-oscillatory part of the gravitational wave amplitude which generates a permanent displacement for freely falling test particles or test detectors. We highlight a model scenario where asymptotic symmetries appear as a soldering freedom in the context of stitching of two black hole spacetimes, and examine the impact of the interaction between test detectors and horizon shells. Further, we provide a more realistic approach of computing displacement memory for near-horizon asymptotic symmetries which is analogous to the conventional memory originally obtained at asymptotic null infinity.