Searcharxiv⌕ Search

arXiv subjects

Yun Soo Myung

Publications and source records attributed to Yun Soo Myung.

At least 73 records · Page 4Linked to original sources
arXiv2020

Scalarized black holes in the Einstein-Maxwell-scalar theory with a quasi-topological term

We investigate the Einstein-Maxwell-scalar theory with a quasi-topological term. Considering exponential couplings to Maxwell term, quasi-topological term, and both terms, we obtain three sets of infinite scalarized charged black holes by taking into account tachyonic instability of dyonic Reissner-Nordström black hole. Each set of infinite scalarized charged black holes is classified by the number of $n=0,1,2,\cdots$, where $n=0$ is called the fundamental black hole and $n=1,2,\cdots$ denote the $n$-excited black holes. All $n=0$ black holes are stable against the radial perturbation, while all $n=1,2$ black holes are unstable.

gr-qc↗
arXiv2020

Onset of rotating scalarized black holes in Einstein-Chern-Simons-Scalar theory

We perform the stability analysis of the Kerr black hole in the Einstein-Chern-Simons-Scalar theory with quadratic scalar coupling. For positive coupling parameter ($α>0$), we introduce the (2+1)-dimensional hyperboloidal foliation method to show that the Kerr black hole is unstable against scalar-mode perturbation. In case of $α<0$, it is shown that the Kerr black hole is unstable without any $α$-independent bound on the rotation parameter $a$ when using the the hyperboloidal foliation method. The disappearance of the $a$-bound is confirmed analytically by implementing the (1+1)-dimensional linearized scalar equation.

gr-qc↗
arXiv2020

Scalarized charged black holes in the Einstein-Maxwell-Scalar theory with two U(1) fields

We investigate scalarized charged black holes in the Einstein-Maxwell-Scalar theory with two U(1) fields inspired by the $N=4$ supergravity. From the onset of the spontaneous scalarization (tachyonic instability of Reissner-Nordström black hole), these black holes are classified by the number of $n=0,1,2,\cdots$, where $n=0$ is called the fundamental black hole and $n=1,2,\cdots$ denote the $n$-excited black holes. Adopting radial perturbations, we show that the $n=0$ black hole is stable against the $s(l=0)$-mode scalar perturbation, whereas the $n=1,2$ excited black holes are unstable. This implies that the $n=0$ black hole is considered as an endpoint of the Reissner-Nordström black hole.

gr-qc↗
arXiv2020

Radial perturbations of the scalarized black holes in Einstein-Maxwell-conformally coupled scalar theory

We perform the stability analysis for the scalarized charged black holes obtained from Einstein-Maxwell-conformally coupled scalar (EMCS) theory by employing the radial perturbations. The targeting black holes include a single branch of scalarized charged black hole with the coupling parameter $α>0$ inspired by the constant scalar hairy black hole as well as infinite branches of $n=0(α\ge 8.019),1(α\ge 40.84),2(α\ge 99.89),\cdots$ scalarized charged black holes found through the spontaneous scalarization on the Reissner-Nordström black hole. It turns out that the black hole in the single branch and the $n = 0$ black hole are stable against radial perturbations, while the $n = 1, 2$ excited black holes are unstable in the EMCS theory with both quadratic and exponential couplings.

gr-qc↗
arXiv2020

Black hole with primary scalar hair in Einstein-Weyl-Maxwell-conformal scalar theory

We obtain a newly charged BBMB (Bocharova-Bronnikov-Melnikov-Bekenstein) black hole solution from the Einstein-Weyl-Maxwell-conformal (conformally coupled) scalar theory with a positive Weyl coupling parameter $m^2_2$ numerically. This solution has a primary scalar hair, compared to a secondary scalar hair in the charged BBMB black hole solution. The limiting case of $m_2^2\to\infty$ leads to the series form of the charged BBMB black hole solution. However, for $m^2_2<0$, we could not obtain any asymptotically flat black hole solution with scalar hair.

gr-qc↗
arXiv2020

Scalar hairy black holes in Einstein-Maxwell-conformally coupled scalar theory

We obtain scalar hairy black holes from Einstein-Maxwell-conformally coupled scalar (EMCS) theory with the scalar coupling parameter $α$ to the Maxwell term. In case of $α=0$, the $α=0$ EMCS theory provides constant (charged) scalar hairy black hole and charged BBMB (Bocharova-Bronnikov-Melnikov-Bekenstein) black hole where the former is stable against full perturbations, while the latter remains unstable because it belongs to an extremal black hole. It is noted that for $α\not=0$, the unstable Reissner-Nordström black holes without scalar hair imply infinite branches of $n=0(α\ge 8.019),1(α\ge 40.84),2(α\ge 99.89),\cdots$ scalarized charged black holes. In addition, for $α>0$, we develop a single branch of scalarized charged black hole solutions inspired by the constant scalar hairy black hole. Finally, we obtain the numerical charged BBMB black hole solution from the $α=0$ EMCS theory.

gr-qc↗
arXiv2019

Scalarized charged black holes with scalar mass term

We study the scalarized charged black holes in the Einstein-Maxwell-Scalar (EMS) theory with scalar mass term. In this work, the scalar mass term is chosen to be $m^2_ϕ=α/β$, where $α$ is a coupling parameter and $β$ is a mass-like parameter. It turns out that any scalarized charged black holes are not allowed for the case of $β\le 4.4$ with $q=0.7(M=0.5,Q=0.35)$ because this case implies the stable Reissner-Nodström (RN) black holes. In the massless limit of $β\to \infty$, one recovers the case of the EMS theory. We note that the unstable RN black hole implies the appearance of scalarized charged black holes. The other unstable case of $β>4.4$ with $q=0.7$ allows us to obtain the $n=0,1,2,\cdots$ scalarized charged black holes for $α(β)\ge α_{\rm th}(β)$ where $α_{\rm th}(β)$ represents the threshold of instability for the RN black hole. Furthermore, it is shown that the $n=0$ black hole is stable against radial perturbations, while the $n=1$ black hole is unstable. This stability result is independent of the mass parameter $β$.

gr-qc↗
arXiv2019

Black holes in new massive conformal gravity

We investigate the black holes in the new massive conformal gravity which is not invariant under conformal transformations because of the presence of the Einstein-Hilbert term. First, we show that the small Schwarzschild black hole is unstable against the $s$-mode of linearized Ricci tensor by solving the Lichnerowicz-Ricci tensor equation. This instability induces the appearance of the non-BBMB (Bocharova-Bronnikov-Melnikov-Bekenstein) black hole that has both Ricci tensor and conformal scalar hair.

gr-qc↗
arXiv2019

Stability of scalarized charged black holes in the Einstein-Maxwell-Scalar theory

We analyze the stability of scalarized charged black holes in the Einstein-Maxwell-Scalar (EMS) theory with quadratic coupling. These black holes are labelled by the number of $n=0,1,2,\cdots$, where $n=0$ is called the fundamental black hole and $n=1,2,\cdots$ denote the $n$-excited black holes. We show that the $n=0$ black hole is stable against full perturbations, whereas the $n=1,2$ excited black holes are unstable against the $s(l=0)$-mode scalar perturbation. This is consistent with the EMS theory with exponential coupling, but it contrasts to the $n=0$ scalarized black hole in the Einstein-Gauss-Bonnet-Scalar theory with quadratic coupling. This implies that the endpoint of unstable Reissner-Nordström black holes with $α>8.019$ is the $n=0$ black hole with the same $q$. Furthermore, we study the scalarized charged black holes in the EMS theory with scalar mass $m^2_ϕ=α/β$.

gr-qc↗
arXiv2019

Black holes in Gauss-Bonnet and Chern-Simons-scalar theory

We carry out the stability analysis of the Schwarzschild black hole in Gauss-Bonnet and Chern-Simons-scalar theory. Here, we introduce two quadratic scalar couplings ($ϕ_1^2,ϕ_2^2$) to Gauss-Bonnet and Chern-Simons terms, where the former term is parity-even, while the latter one is parity-odd. The perturbation equation for the scalar $ϕ_1$ is the Klein-Gordon equation with an effective mass, while the perturbation equation for $ϕ_2$ is coupled to the parity-odd metric perturbation, providing a system of two coupled equations. It turns out that the Schwarzschild black hole is unstable against $ϕ_1$ perturbation, leading to scalarized black holes, while the black hole is stable against $ϕ_2$ and metric perturbations, implying no scalarized black holes.

gr-qc↗
arXiv2019

Quasinormal modes of scalarized black holes in the Einstein-Maxwell-Scalar theory

We perform the stability analysis on scalarized charged black holes in the Einstein-Maxwell-Scalar (EMS) theory by computing quasinormal mode spectrum. It is noted that the appearance of these black holes with scalar hair is closely related to the instability of Reissner-Nordström black holes without scalar hair in the EMS theory. The scalarized black hole solutions are classified by the node number of $n=0,1,2,\cdots$, where $n=0$ is called the fundamental branch and $n=1,2,\cdots$ denote the $n$ excited branches. Here, we show that the $n=1,2$ excited black holes are unstable against against the $s(l=0)$-mode scalar perturbation, while the $n=0$ fundamental black hole is stable against all scalar-vector-tensor perturbations. This is consistent with other scalarized black holes without charge found in the Einstein-Scalar-Gauss-Bonnet theory.

gr-qc↗
arXiv2018

Gregory-Laflamme instability of black hole in Einstein-scalar-Gauss-Bonnet theories

We investigate the stability analysis of Schwarzschild black hole in Einstein-scalar-Gauss-Bonnet (ESGB) theory because the instability of Schwarzschild black hole without scalar hair implies the Gauss-Bonnet black hole with scalar hair. The linearized scalar equation is compared to the Lichnerowicz-Ricci tensor equation in the Einstein-Weyl gravity. It turns out that the instability of Schwarzschild black hole in ESGB theory is interpreted as not the tachyonic instability, but the Gregory-Laflamme instability of black string. In the small mass regime of $1/λ<1.174/r_+$, the Schwarzschild solution becomes unstable and a new branch of solution with scalar hair bifurcates from the Schwarzschild one. This is very similar to finding a newly non-Schwarzschild black hole in Einstein-Weyl gravity.

gr-qc↗
arXiv2018

Black-hole stability in non-local gravity

We prove that Ricci-flat vacuum exact solutions are stable under linear perturbations in a new class of weakly non-local gravitational theories finite at the quantum level.

gr-qc↗
arXiv2018

Mass-induced instability of SAdS black hole in Einstein-Ricci cubic gravity

We perform the stability analysis of Schwarzschild-AdS (SAdS) black hole in the Einstein-Ricci cubic gravity. It shows that the Ricci tensor perturbations exhibit unstable modes for small black holes. We call this the mass-induced instability of SAdS black hole because the instability of small black holes arises from the massiveness in the linearized Einstein-Ricci cubic gravity, but not a feature of higher-order derivative theory giving ghost states. Also, we point out that the correlated stability conjecture holds for the SAdS black hole by computing the Wald entropy of SAdS black hole in Einstein-Ricci cubic gravity.

gr-qc↗
arXiv2018

Renormalizability and Newtonian potential in scale-invariant gravity

There is a conjecture that renormalizable higher-derivative gravity has a finite classical potential at the origin. In this work we show clearly that the scale-invariant gravity (SIG) satisfies the conjecture. This gravity produces the better-behaved $1/k^4$ UV behavior as needed for renormalizability. It turns out that the SIG has the linear classical potential of $V\propto r$ and it is a UV complete theory.

gr-qc↗
arXiv2018

Stability issues of black hole in non-local gravity

We discuss stability issues of Schwarzschild black hole in non-local gravity. It is shown that the stability analysis of black hole for the unitary and renormalizable non-local gravity with $γ_2=-2γ_0$ cannot be performed in the Lichnerowicz operator approach. On the other hand, for the unitary and non-renormalizable case with $γ_2=0$, the black hole is stable against the metric perturbations. For non-unitary and renormalizable local gravity with $γ_2=-2γ_0={\rm const}$ (fourth-order gravity), the small black holes are unstable against the metric perturbations. This implies that what makes the problem difficult in stability analysis of black hole is the simultaneous requirement of unitarity and renormalizability around the Minkowski spacetime.

gr-qc↗
arXiv2017

Universality of the Unruh effect

In this paper we prove the universal nature of the Unruh effect in a general class of weakly non-local field theories. At the same time we solve the tension between two conflicting claims published in literature. Our universality statement is based on two independent computations based on the canonical formulation as well as path integral formulation of the quantum theory.

gr-qc↗