Stability study of a model for the Klein-Gordon equation in Kerr space-time II

The present paper is a follow-up of our previous paper that derives a slightly simplified model equation for the Klein-Gordon equation, describing the propagation of a scalar field of mass \(\mu\) in the background of a rotating black hole and, among others, supports the instability of the field down to \(a/M \approx 0.97\). The latter result was derived numerically. This paper gives corresponding rigorous results, supporting instability of the field down to \(a/M \approx 0.979796\).