A new gauge for gravitational perturbations of Kerr spacetimes II: The linear stability of Schwarzschild revisited
Gabriele Benomio
TL;DR
<3-5 sentence high-level summary> This paper establishes linear stability of the Schwarzschild solution to gravitational perturbations within a new geometric gauge tailored to linearised gravity. It achieves uniform boundedness and decay without any future gauge normalisation by exploiting red-shift transport structures, and it treats both gauge-invariant (Teukolsky/Regge-Wheeler) and gauge-dependent sectors with a refined initial-data normalisation. The analysis strengthens the role of horizon red-shift in stabilising the gauge-dependent part and provides a framework that aligns with, and extends, the prior DHR approach in a way that is compatible with future Kerr stability and nonlinear problems. The work thereby advances the understanding of gauge choices in black hole stability, with potential impact on sub-extremal Kerr and nonlinear stability programs.
Abstract
We present a new proof of linear stability of the Schwarzschild solution to gravitational perturbations. Our approach employs the system of linearised gravity in the new geometric gauge of \cite{benomio_kerr}, specialised to the $|a|=0$ case. The proof fundamentally relies on the novel structure of the transport equations in the system. Indeed, while exploiting the well-known decoupling of two gauge invariant linearised quantities into spin $\pm 2$ Teukolsky equations, we make enhanced use of the red-shifted transport equations and their stabilising properties to control the gauge dependent part of the system. As a result, an initial-data gauge normalisation suffices to establish both orbital and asymptotic stability for all the linearised quantities in the system. The absence of future gauge normalisations is a novel element in the linear stability analysis of black hole spacetimes in geometric gauges governed by transport equations. In particular, our approach simplifies the proof of \cite{DHR}, which requires a future normalised (double-null) gauge to establish asymptotic stability for the full system.
