# Asymptotically flat spacetimes with BMS$_3$ symmetry

## TL;DR

This paper constructs the phase space of 3D asymptotically flat spacetimes with BMS symmetry, revealing holographic properties and antipodal identification of bulk fields at null infinity.

## Contribution

It provides a detailed phase space construction for 3D flat spacetimes with BMS$_3$ symmetry, highlighting holographic causality and boundary parametrization.

## Key findings

- BMS group acts at both null and spatial infinity
- Phase space obeys holographic causality
- Bulk fields are antipodally identified between past and future null infinity

## Abstract

We construct the phase space of 3-dimensional asymptotically flat spacetimes that forms the bulk metric representation of the BMS group consisting of both supertranslations and superrotations. The asymptotic symmetry group is a unique copy of the BMS group at both null infinities and spatial infinity. The BMS phase space obeys a notion of holographic causality and can be parametrized by boundary null fields. This automatically leads to the antipodal identification of bulk fields between past and future null infinity in the absence of a global conical defect.