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Advances in Mathematical Physics
Volume 2012 (2012), Article ID 197385, 16 pages
Research Article

A Note on the Newman-Unti Group and the BMS Charge Algebra in Terms of Newman-Penrose Coefficients

1Physique Théorique et Mathématique, Université Libre de Bruxelles, Campus Plaine, CP 231, 1050 Bruxelles, Belgium
2International Solvay Institutes, Campus Plaine, CP 231, 1050 Bruxelles, Belgium

Received 27 September 2012; Accepted 30 November 2012

Academic Editor: Andrei D. Mironov

Copyright © 2012 Glenn Barnich and Pierre-Henry Lambert. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The symmetry algebra of asymptotically flat spacetimes at null infinity in four dimensions in the sense of Newman and Unti is revisited. As in the Bondi-Metzner-Sachs gauge, it is shown to be isomorphic to the direct sum of the abelian algebra of infinitesimal conformal rescalings with . The latter algebra is the semidirect sum of infinitesimal supertranslations with the conformal Killing vectors of the Riemann sphere. Infinitesimal local conformal transformations can then consistently be included. We work out the local conformal properties of the relevant Newman-Penrose coefficients, construct the surface charges, and derive their algebra.