Spin-induced scalarization of Kerr-Newman black hole in extended scalar-tensor theory

TL;DR

This paper investigates how non-minimal coupling in extended scalar-tensor-Gauss-Bonnet theory induces scalarization in Kerr-Newman black holes, revealing critical conditions and the possibility of scalarization at zero spin.

Contribution

It provides analytical and numerical analysis of the conditions under which Kerr-Newman black holes become scalarized in extended scalar-tensor-Gauss-Bonnet theory, including critical spin, charge, and coupling strength.

Findings

Critical spin and charge for scalarization are calculated.

Analytical formula for the critical coupling-dependent line is derived.

Kerr-Newman black holes can be scalarized even at zero spin.

Abstract

With certain non-minimal coupling between a massless scalar field and the Gauss-Bonnet curvature invariant in the extended scalar-tensor-Gauss-Bonnet (ESTGB) field theory, tachyonic instability of Kerr-Newman (KN) black hole is promoted. Critical spin and charge for the onset of the spontaneous scalarization phenomenon for the KN black hole are calculated in the infinitely large coupling limit. Then analytical formula for the coupling-strength-dependent critical existence line is obtained for the black-hole-scalar-field configuration in a finite large coupling regime. Moreover, numerical methods are used to perform threshold curves which are boundaries between bald KN black holes and their hairy counterparts. Intriguingly, we get to know KN black hole can be scalarized in the vanishing spin limit in ESTGB theory.