paper

Exponentially growing finite energy solutions for the Klein-Gordon equation on sub-extremal Kerr spacetimes

arXiv:1302.3448 · doi:10.1007/s00220-014-2033-x

Abstract

For any sub-extremal Kerr spacetime with non-zero angular momentum, we find an open family of non-zero masses for which there exist smooth, finite energy, and exponentially growing solutions to the corresponding Klein-Gordon equation. If desired, for any non-zero integer m, an exponentially growing solution can be found with mass arbitrarily close to |am|/2Mr_+. In addition to its direct relevance for the stability of Kerr as a solution to the Einstein-Klein-Gordon system, our result provides the first rigorous construction of a superradiant instability. Finally, we note that this linear instability for the Klein-Gordon equation contrasts strongly with recent work establishing linear stability for the wave equation.

Final version, to appear in Comm. Math. Phys

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