Rotating scalarized black holes in scalar couplings to two topological terms

TL;DR

This paper investigates the stability of Kerr black holes in Einstein-scalar theory with quadratic couplings to topological terms, identifying conditions for instability and deriving threshold curves for different coupling signs.

Contribution

It introduces a detailed analysis of tachyonic instability in Kerr black holes with scalar couplings to topological terms, including new bounds and stability thresholds.

Findings

Positive coupling: derived threshold curve for stability boundary.

Negative coupling: found a new bound of a ≥ 0.26 for instability.

Identified stability conditions for Kerr black holes with scalar couplings.

Abstract

The tachyonic instability of the Kerr black holes is analyzed in the Einstein-scalar theory with the quadratic scalar couplings to two topological terms which are parity-even Gauss-Bonnet and parity-odd Chern-Simons terms. For positive coupling $\alpha$, we use the (2+1)-dimensional hyperboloidal foliation method to derive the threshold curve which is the boundary between stable and unstable Kerr black holes by considering a spherically symmetric scalar-mode perturbation. In case of negative coupling, a newly bound of $a\ge0.26$ with $a$ the rotation parameter is found for unstable Kerr black holes and its threshold curve is derived.