Extremal and nonextremal Kerr/CFT correspondences

TL;DR

This paper rederives the Kerr/CFT correspondence without the extremal limit, extends it to nonextremal black holes, and proposes a stretched horizon approach to recover the full entropy with well-behaved thermodynamic quantities.

Contribution

It introduces a new method to derive Kerr/CFT correspondence without extremality and presents an alternative approach using a stretched horizon for nonextremal black holes.

Findings

Reproduces half of the Bekenstein-Hawking entropy in nonextremal cases.

Suggests a connection between the inner horizon and conformal field theory.

Provides a full entropy calculation using a stretched horizon approach.

Abstract

I rederive the Kerr/CFT correspondence without first taking the near-horizon extremal Kerr limit. This method extends easily to nonextremal black holes, for which the temperature and central charge behave poorly at the horizon but the entropy remains finite. A computation yields one-half of the standard Bekenstein-Hawking entropy, with hints that the other half may be related to a conformal field theory at the inner horizon. I then present an alternative approach, based on a stretched Killing horizon, in which the full entropy is obtained and the temperature and central charge remain well-behaved even in the nonextremal case.