Spin-induced scalarization of Kerr-Newman black holes in Einstein-Maxwell-scalar theory

TL;DR

This paper investigates the spontaneous scalarization of Kerr-Newman black holes in Einstein-Maxwell-scalar theory, identifying conditions for instability and demonstrating scalarization through analytical bounds and numerical evolution.

Contribution

It provides the first analytical bound on the spin parameter for instability and performs numerical simulations to confirm scalarization in EMS theory.

Findings

Bound on spin parameter: a/r_+ ≥ 0.4142 for instability.

Numerical evidence of spontaneous scalarization.

Threshold curves delineate scalarized and bald black holes.

Abstract

In this paper, we consider the tachyonic instability of Kerr-Newman (KN) black holes in the Einstein-Maxwell-scalar (EMS) theory with nonminimal negative scalar coupling to Maxwell term, and then obtain a bound $(\frac{a}{r_+}\geq0.4142)$ for spin parameter $a$ of KN black hole in the limit of coupling constant $\alpha\rightarrow-\infty$ by using analytical method. In addition, we perform a $(2+1)$-dimensional time evolution of linearized scalar field perturbation on the KN black hole background by implementing the hyperboloidal foliation method numerically in the EMS theory. It recovers the \textit{spontaneous scalarization} phenomenon for KN black hole in some certain regions of the parameter spaces. We further plot corresponding threshold curves $\alpha(a)$ which describe a boundary between bald KN black holes and scalarized spinning black holes in the EMS theory.