A Note on the Newman-Unti Group and the BMS Charge Algebra in Terms of Newman-Penrose Coefficients by Glenn Barnich, Pierre-Henry Lambert

“…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 𝔟𝔪𝔰4. …”
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