On the global stability of the wave-map equation in Kerr spaces with   small angular momentum
  This paper is motivated by the problem of the nonlinear stability of the Kerr solution for axially symmetric perturbations. We consider a model problem concerning the axially symmetric perturbations of a wave map $\Phi$ defined from a fixed Kerr solution $\KK(M,a)$, $0\le a < M $, with values in the two dimensional hyperbolic space $\HHH^2$. A particular such wave map is given by the complex Ernst potential associated to the axial Killing vectorfield $\Z$ of $\KK(M,a)$. We conjecture that this stationary solution is stable, under small axially symmetric perturbations, in the domain of outer communication (DOC) of $\KK(M,a)$, for all $0\le a<M$ and we provide preliminary support for its validity, by deriving convincing stability estimates for the linearized system. 
A. D. Ionescu and S. Klainerman
math.AP gr-qc