Aspects of the BMS/CFT correspondence

TL;DR

The paper advances the BMS/CFT program by promoting local conformal transformations to a central role in the asymptotic symmetry analysis of both 3D and 4D gravity. By exploiting Fefferman-Graham-type formalisms and covariant surface charges, it derives how extended conformal symmetries act on solution spaces, including the Bondi data such as mass, angular momentum, and News. In 3D, it recovers the ${\rm BMS}_3$ algebra with a Brown-Henneaux-type central extension, while in 4D it proposes a ${\rm BMS}_4/CFT_2$ structure with two Virasoro-like sectors acting on the sphere at null infinity and a semidirect supertranslation part. The work sets the stage for detailed central-charge analyses and holographic explorations of flat-space gravity, with potential implications for black hole entropy, S-matrix structure, and Kerr/CFT-like correspondences.

Abstract

After a review of symmetries and classical solutions involved in the AdS3/CFT2 correspondence, we apply a similar analysis to asymptotically flat spacetimes at null infinity in 3 and 4 dimensions. In the spirit of two dimensional conformal field theory, the symmetry algebra of asymptotically flat spacetimes at null infinity in 4 dimensions is taken to be the semi-direct sum of supertranslations with infinitesimal local conformal transformations and not, as usually done, with the Lorentz algebra. As a first application, we derive how the symmetry algebra is realized on solution space. In particular, we work out the behavior of Bondi's news tensor, mass and angular momentum aspects under local conformal transformations.