Mode analysis for the linearized Einstein equations on the Kerr metric : the large $\mathfrak{a}$ case

TL;DR

This paper thoroughly analyzes mode solutions of the linearized Einstein equations on Kerr spacetime in the large angular momentum case, establishing their absence for non-zero frequencies and classifying zero modes.

Contribution

It provides a complete mode analysis for the linearized Einstein equations on Kerr with large angular momentum, including the classification of zero modes and the absence of non-zero modes.

Findings

No mode solutions for Im σ ≥ 0, σ ≠ 0.

Zero modes correspond to Coulomb and linearized Kerr solutions plus gauge terms.

The analysis applies the framework of Vasy and previous mode classification results.

Abstract

We give a complete analysis of mode solutions for the linearized Einstein equations and the $1-$form wave operator on the Kerr metric in the large $\mathfrak{a}$ case. By mode solutions we mean solutions of the form $e^{-it_*\sigma}\tilde{h}(r,\theta,\varphi)$ where $t_*$ is a suitable time variable. The corresponding Fourier transformed $1-$form wave operator and linearized Einstein operator are shown to be Fredholm between suitable function spaces and $\tilde{h}$ has to lie in the domain of these operators. These spaces are constructed following the general framework of Vasy. No mode solutions exist for ${\Im}\, \sigma\ge 0,\, \sigma\neq 0$. For $\sigma=0$ mode solutions are Coulomb solutions for the $1-$form wave operator and linearized Kerr solutions plus pure gauge terms in the case of the linearized Einstein equations. If we fix a De Turck/wave map gauge, then the zero mode solutions for the linearized Einstein equations lie in a fixed $7-$dimensional space. The proof relies on the absence of modes for the Teukolsky equation shown by the third author and a complete classification of the gauge invariants of linearized gravity on the Kerr spacetime due to Aksteiner et al.