A note on the instability of the Kerr Cauchy horizon under linearised gravitational perturbations

TL;DR

This paper enhances previous findings on the linear instability of the Kerr Cauchy horizon, providing a stronger result that supports the proof of its non-linear instability.

Contribution

It improves the linear instability result of the Kerr Cauchy horizon, which is crucial for establishing its non-linear instability.

Findings

Strengthened the linear instability result of the Kerr Cauchy horizon.

Provided a key step for proving non-linear instability.

Supports the understanding of horizon stability in rotating black holes.

Abstract

This note slightly strengthens the result of arXiv:2201.12295 on the linear instability of the Kerr Cauchy horizon. This strengthened result is used in the proof arXiv:2604.04877 of the non-linear instability of the Kerr Cauchy horizon.