Stability and Instability of Extreme Reissner-Nordström Black Hole Spacetimes for Linear Scalar Perturbations II
Stefanos Aretakis
TL;DR
This work provides a complete description of linear scalar perturbations on extreme Reissner–Nordström spacetimes, establishing rigorous energy and pointwise decay, non-decay, and blow-up phenomena up to the horizon. A key technical advance is the introduction of a horizon-friendly vector field $P$ that yields degeneracy-aware energy decay near $ ext{H}^+$, complemented by a hierarchy of conservation laws $H_l[]$ on degenerate horizons for each angular frequency $l$. The results reveal a sharp separation by angular frequency: transversal derivatives up to order $l$ decay while order $l+1$ typically converges to a nonzero limit along $ ext{H}^+$ and higher orders blow up, signaling dynamical instability in the extreme case. The paper also develops sharp higher-order $L^{2}$ estimates, precise commutator analyses, and dyadic decay arguments, culminating in detailed energy decay, pointwise decay, and blow-up statements for both degenerate and non-degenerate energies. These findings refine the stability/instability picture for extreme black holes and set the stage for extensions to more general spacetimes and coupled systems.
Abstract
This paper contains the second part of a two-part series on the stability and instability of extreme Reissner-Nordstrom spacetimes for linear scalar perturbations. We continue our study of solutions to the linear wave equation on a suitable globally hyperbolic subset of such a spacetime, arising from regular initial data prescribed on a Cauchy hypersurface crossing the future event horizon. We here obtain definitive energy and pointwise decay, non-decay and blow-up results. Our estimates hold up to and including the horizon. A hierarchy of conservations laws on degenerate horizons is also derived.
