Near-Horizon BMS Symmetry, Dimensional Reduction, and Black Hole Entropy

TL;DR

This paper explores how near-horizon symmetries of black holes, specifically BMS symmetries, can be used to understand and derive black hole entropy through dimensional reduction and boundary condition analysis.

Contribution

It extends previous work by providing detailed analysis of near-horizon BMS symmetries, including boundary condition relaxation and dimensional reduction, to better understand black hole entropy.

Findings

Near-horizon BMS symmetries determine black hole entropy.

Relaxed boundary conditions expand the class of symmetries.

Dimensional reduction clarifies the role of symmetries in entropy calculation.

Abstract

In an earlier short paper [Phys.\ Rev.\ Lett.\ 120 (2018) 101301, arXiv:1702.04439], I argued that the horizon-preserving diffeomorphisms of a generic black hole are enhanced to a larger BMS${}_3$ symmetry, which is powerful enough to determine the Bekenstein-Hawking entropy. Here I provide details and extensions of that argument, including a loosening of horizon boundary conditions and a more thorough treatment of dimensional reduction and meaning of a "near-horizon symmetry."