A Covariant Formulation of Logarithmic Supertranslations at Spatial Infinity

TL;DR

This paper develops a covariant framework for logarithmic supertranslations at spatial infinity, extending the BMS algebra with new symmetries and conserved charges, revealing novel physical insights in asymptotically flat spacetimes.

Contribution

It introduces a new symplectic structure and boundary conditions that incorporate log-supertranslations, extending previous asymptotic symmetry analyses at spatial infinity.

Findings

Extended BMS algebra with abelian sectors including log-supertranslations.

Finite, conserved charges associated with new symmetries.

Central extension in the algebra between supertranslations and log-supertranslations.

Abstract

We investigate the asymptotic symmetries of asymptotically flat spacetimes at spatial infinity. We propose a new symplectic structure and conservative boundary conditions in a polyhomogeneous Beig-Schmidt expansion. The asymptotic symmetries extend the BMS algebra by abelian sectors, notably incorporating regular log-translations and log-supertranslations. The associated charges are finite and conserved, and we show that their algebra admits a central extension between supertranslations and log-supertranslations, and between the singular translations and regular log-translations. Our analysis is compatible with, and extends, both the work of arXiv:1106.4045 and arXiv:2211.10941 : it extends the former by incorporating log-supertranslations, and the latter by allowing both parities of the log-supertranslations in the same phase space. These newly identified symmetries at spatial infinity encode novel physical information that has not been revealed in other regions of asymptotically flat spacetimes, thereby opening the door to new observables to consider at null and timelike infinity.