Subleading BMS charges and fake news near null infinity

TL;DR

This paper links subleading BMS charges in asymptotically-flat spacetimes to Newman-Penrose charges, revealing the existence of 'fake news' obstructions to charge integrability at null infinity.

Contribution

It introduces a novel definition of subleading BMS charges via a $1/r$-expansion, connecting them to Newman-Penrose charges and identifying 'fake news' obstructions.

Findings

Subleading BMS charges relate to Newman-Penrose charges.

Obstructions to charge integrability are interpreted as 'fake news'.

At order $r^{-3}$, integrable charges matching Newman-Penrose charges are found.

Abstract

In this paper we establish a relation between the non-linearly conserved Newman-Penrose charges and certain subleading terms in a large-$r$ expansion of the BMS charges in an asymptotically-flat spacetime. We define the subleading BMS charges by considering a $1/r$-expansion of the Barnich-Brandt prescription for defining asymptotic charges in an asymptotically-flat spacetime. At the leading order, i.e. $1/r^0$, one obtains the standard BMS charges, which would be integrable and conserved in the absence of a flux term at null infinity, corresponding to gravitational radiation, or Bondi news. At subleading orders, analogous terms in general provide obstructions to the integrability of the corresponding charges. Since the subleading terms are defined close to null infinity, but vanish actually at infinity, the analogous obstructions are not associated with genuine Bondi news. One may instead describe them as corresponding to "fake news." At order $r^{-3}$, we find that a set of integrable charges can be defined and that these are related to the ten non-linearly conserved Newman-Penrose charges.