Pole Structure of Kerr Green's Function

TL;DR

This paper analyzes the pole structure of Kerr black-hole perturbations in the frequency domain, revealing Matsubara poles and zero-frequency singularities in the Green's function, which clarify the response of Kerr black holes.

Contribution

It explicitly establishes the Matsubara pole structure within the Teukolsky formalism for Kerr black holes and explains the cancellation of singularities in the Green's function.

Findings

Homogeneous solutions develop simple poles at Matsubara frequencies.

Local connection coefficients have poles that cancel in the Green's function ratio.

Zero-frequency singularities scale as ω^{-2l-1} and cancel in total Green's function.

Abstract

We investigate the pole structure of Kerr black-hole perturbations in the frequency domain, focusing on the building blocks of the Green's function for the radial Teukolsky equation: the homogeneous radial solutions, the connection coefficients, and the Green's function itself. We show that the homogeneous solutions and the local connection coefficients develop simple poles at the Matsubara frequencies, thereby establishing the Matsubara pole structure explicitly within the Teukolsky formalism for asymptotically flat subextremal Kerr black holes. At the level of the local fixed-sector connection formula, the explicit Matsubara-pole factors cancel in the ratio of connection coefficients entering a decomposed Green-function contribution. We also identify higher-order zero-frequency singularities in the decomposed Green-function contributions, which scale as $\omega^{-2l-1}$ and cancel collectively in the total radial Green's function. These results clarify how Matsubara poles and sectoral zero-frequency singularities arise in the Teukolsky formalism and provide a frequency-domain foundation for understanding prompt response in time-domain ringdown waveforms in Kerr spacetime.