Magnetised Kerr/CFT correspondence

TL;DR

This paper extends the Kerr/CFT correspondence to magnetised Kerr black holes, demonstrating how external magnetic fields influence the dual CFT description and entropy calculations, and exploring the Meissner effect at extremality.

Contribution

It introduces a dual CFT framework for magnetised Kerr black holes, incorporating magnetic field effects and the Meissner effect, and generalizes the approach to Kerr-Newman black holes.

Findings

Reproduces Bekenstein-Hawking entropy via Cardy formula

Identifies a second dual CFT based on electromagnetic symmetry

Shows magnetic field expulsion at extremality (Meissner effect)

Abstract

The tools of Kerr/CFT correspondence are applied to the Kerr black hole embedded in an axial external magnetic field. Its extremal near horizon geometry remains a warped and twisted product of $AdS_2\times S^2$. The central charge of the Virasoro algebra, generating the asymptotic symmetries of the near horizon geometry, is found. It is used to reproduce, via the Cardy formula, the Bekenstein-Hawking entropy of the magnetised Kerr black hole as the statistical microscopic entropy of a dual CFT. The presence of the background magnetic field makes available also a second dual CFT picture, based on the $U(1)$ electromagnetic symmetry, instead of the only rotational one of the standard non-magnetised Kerr spacetime. A Meissner-like effect, where at extremality the external magnetic field is expelled out of the black hole, allows us to infer the value of the mass for these magnetised extremal black holes. The generalisation to the CFT dual for the magnetised extreme Kerr-Newman black hole is also presented.