Scalarized black holes in new massive gravity dressed by a nonminimally coupled scalar

TL;DR

This paper explores the conditions under which scalarized black holes can form in new massive gravity with a nonminimally coupled scalar, analyzing stability bounds and deriving analytical solutions for scalar hair.

Contribution

It provides new analytical bounds for scalarized black holes in new massive gravity, including stability, solution, and thermodynamic bounds, without relying on the Gregory-Laflamme instability limit.

Findings

Derived bounds for scalar hair formation in new massive gravity.

Identified narrow parameter range for stable scalarized black holes.

Analyzed stability conditions using linearized theory and thermodynamics.

Abstract

We investigate scalarized black holes in new massive gravity dressed by a nonminimally coupled scalar. For this purpose, we find the Gregory-Laflamme (GL) and tachyonic instability bounds of bald BTZ black hole expressed in terms of $ m^2$ a massive spin-2 parameter and $\alpha$ a scalar coupling parameter to Ricci scalar by making use of the linearized theory around black hole. On the other hand, we obtain a solution bound of $0.161<\alpha <3/16$ for achieving non-BTZ black holes with scalar hair analytically and a thermodynamic bound of $1/8<\alpha <13/80$ for obtaining consistent thermodynamic quantities. Without imposing the GL instability bound ($m^2<1/2\ell^2$), we find a very narrow bound of $0.161<\alpha<0.1625$ which is located inside tachyonic instability bound of $\alpha>1/8+m^2_\Phi \ell^2/6$ for obtaining scalarized black holes where $m^2_\Phi$ is a scalar mass parameter.