Black Hole Superradiance From Kerr/CFT

TL;DR

The paper tests Kerr/CFT by studying superradiant scattering of a scalar on near-extremal Kerr, showing that in a scaling limit near the superradiant bound the gravity absorption cross section matches a finite-temperature 2D CFT prediction. This match requires a right-moving current algebra and a constraint L0 = Q0 in the dual CFT, yielding a nonchiral but thermally populated sector that reproduces both the m- and β-dependent structure of the greybody factors. The analysis extends to five-dimensional rotating black holes, where the near-horizon geometry yields a similar AdS_3 × S^3 structure and the CFT reproduces the near-superradiant scattering, including conformal weights and CFT greybody factors. Together, these results provide strong support for Kerr/CFT and its extension to near-extremal regimes, connecting gravity scattering amplitudes to precise CFT correlators across dimensions.

Abstract

The superradiant scattering of a scalar field with frequency and angular momentum (ω,m) by a near-extreme Kerr black hole with mass and spin (M,J) was derived in the seventies by Starobinsky, Churilov, Press and Teukolsky. In this paper we show that for frequencies scaled to the superradiant bound the full functional dependence on (ω,m,M,J) of the scattering amplitudes is precisely reproduced by a dual two-dimensional conformal field theory in which the black hole corresponds to a specific thermal state and the scalar field to a specific operator. This striking agreement corroborates a conjectured Kerr/CFT correspondence.