arXiv subjects

Yun Soo Myung

Publications and source records attributed to Yun Soo Myung.

At least 37 records · Page 2Linked to original sources

arXiv2025

Newly scalarization of the Einstein-Euler-Heisenberg black hole

Th spontaneous scalarization of the Einstein-Euler-Heisenberg (EEH) black hole is performed in the EEH-scalar theory by introducing an exponential scalar coupling (with $α$ coupling constant) to the Maxwell term.Here, the EEH black hole as a blad black hole is described by mass $M$ and magnetic charge $q$ with an action parameter $μ$. A choice of $μ=0.3$ gurantees a single horizon with unrestricted magnetic charge $q$. The onset scalarization of this black hole appears for a positive coupling $α$ with an unlimited magnetic charge $q$. However, there exists a difference between $q\le1$ and $q>1$ onset scalarizations. We notify the presence of infinite branches labeled by the number of $n=0,1,2,\cdots$ of scalarized charged black holes by taking into account the scalar seeds around the EEH black hole. We find that the $n=0$ fundamental branch of all scalarized black holes is stable against the radial perturbations, while the $n=1$ excited branch is unstable.

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arXiv2025

Scalar-hairy AdS Black Hole in the Einstein-Maxwell-Scalar Theory: first-order phase transition with a critical point

In asymptotically anti-de Sitter (AdS) spacetime, we consider a real massiver scalar field in the Einstein-Maxwell-scalar (EMS) model and examine both scalar-hairy black hole solutions induced by the nonminimal coupling to the Maxwell field and tachyonic-hairy solutions driven by the scalar potential. When the scalar potential vanishes, scalar-hairy black holes emerge with profiles and properties similar to those observed in flat spacetime. The presence of the scalar potential additionally induces tachyonic-hairy solutions, leading to the coexistence of these two distinct hairy phases in different regions of the parameter space. The phase diagram reveals a first-order phase transition line between the tachyonic-hairy and scalar-hairy phases, originating at a critical point in the extreme temperature and chemical potential regime. Our detailed analysis shows that this phase transition is directly associated with the self-overlap region of the scalar-hairy phase and its start point. Moreover, increasing the coupling strength $λ$ shifts the critical point to higher temperature and chemical potential.

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arXiv2025

Scalarizations of qOS-extremal black hole and Aretakis instability

We study scalarization of quantum Oppenheimer-Snyder (qOS)-extremal black hole in the Einstein-Gauss-Bonnet-scalar theory. This black hole is described by mass ($M=4\sqrtα/3\sqrt{3}$) with $α$ quantum parameter. From studying onset of scalarization, we find the appearance of the single branch of scalarized qOS-extremal black holes. To obtain the tachyonic scalar cloud being a seed to generate the single branch of scalarized qOS-extremal black holes, we consider the near-horizon geometry of the Bertotti-Bobinson (BR) spacetime. In this case, we find that the appearance of a large scalar cloud at the horizon ($ρ=0$) is a new feature to represent onset scalarization of extremal black holes for tachyon with negative mass, but it is not related to the Aretakis instability of a propagating scalar with standard mass around the BR spacetime, showing polynomial instability of the ingoing time $v$. The Aretakis instability is connected to the scalar cloud with standard mass, indicating the blow-up at the horizon.

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arXiv2025

Thermodynamic analysis and shadow bound of black holes surrounded by a dark matter halo

We perform the thermodynamic analysis of a black hole (BH) immersed in a dark matter halo (DMH). It is shown that the BH could not be in thermal equilibrium with the DMH in any regions outside the event horizon. This means that the thermodynamic influence of the environment (DMH) is relatively small on the BH. Importantly, it does not alter the nature of the negative heat capacity for the BH. We stress that the Newtonian ($1/a_0$) approximation gives us a correct thermodynamic description for the BH surrounded by DMH because the first law of thermodynamics and Smarr formula are satisfied. Hence, the Newtonian Helmholtz free energy is employed to reveal that there is the absence of phase transition to other BH with a positive heat capacity. Finally, we investigate the shadow bound of favored region for the BH immersed in the DMH by comparing EHT observations.

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arXiv2025

Shadow radius and classical scattering analysis of two secondary hair Horndeski black holes

We perform the shadow radius analysis of a charged Horndeski black hole (CHB) and the naked singularity (NS) with secondary scalar hair obtained from the Einstein-Horndeski-Maxwell theory. For this analysis, we include the beyond Horndeski black hole (bH) with secondary scalar hair and the magnetically charged black hole (MC) found from the Einstein-Euler-Heisenberg theory. It is worth noting that the NS versions of CHB and bH arise from the charge extension of their photon spheres, while there is no NS version for MC. One branch (i) from the CHB is a point in the horizon realization but it shows up on the photon sphere and shadow radius. The shadow radius for the CHB is the nearly same as that for the MC with a single horizon and the charge of the NS is constrained by the EHT observation. From classical scattering analysis, it turns out that i-NS and NS play different roles from CHB, bH, and MC.

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arXiv2025

Negative potential-induced scalarization in the Einstein-Euler-Heisenberg black hole

We investigate a negative potential-induced scalarization of the Einstein-Euler-Heisenberg (EEH) black hole in the EEH-scalar (EEHS) theory, characterized by mass $M$, Euler-Heisenberg parameter $μ$, and magnetic charge $q$. Within this framework, the charge $q$ can exceed the extremal bound $q/M > 1$, and a single event horizon is maintained provided the parameter $μ$ exceeds the $μ_{\text{max}} = 0.019$, with the ADM mass fixed at $M = 1/2$. We obtain a single branch of scalarized EEH (sEEH) black holes for $q > 0$ which is considered as the simplest model for scalarization of EEH black holes. We found that this class of hairy black holes is not thermodynamically favored, and their quasinormal modes indicate they are dynamically unstable. An interesting feature is that when $q < 1/2$, the scalar charge varies only slightly with $q$ for a fixed mass. In contrast, for $q>1/2$, the scalar charge increases more rapidly as $q$ increases. This distinct behavior suggests that the scalar charge exhibits the characteristics of a primary charge for $q < 1/2$, and of a secondary charge for $q > 1/2$. This finding reveals notable features of hairy black holes in EEH theory, specifically in the overcharging regime.

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arXiv2025

Two scalarizations of magnetically charged black holes

We study two scalarizations of magnetically charged black holes in the Einstein-Gauss-Bonnet-scalar theory with the nonlinear electrodynamics (NED) term. For this purpose, two scalar coupling functions $f_1(ϕ)$ and $f_2(ϕ)$ are introduced to couple to Gauss-Bonnet (GB) and NED terms. The bald black hole is described by mass ($M$) and action parameter ($α$) with magnetic charge ($P$), which becomes the quantum Oppenheimer-Snyder black hole for $P=M$ whose action is still unknown. We derive Smarr formula which describes a correct thermodynamics for the charged black hole. Two Davies points of heat capacity are not identified with two critical onset mass and action parameter for GB$^-$ scalarization with $f_1(ϕ)$. Furthermore, the shadow radius analysis of charged black hole is performed to include naked singularities and it is compared to the EHT observation. There is no constraints on the action parameter, whereas new mass constraints are found. Finally, the NED$^+$ spontaneous scalarization with $f_2(ϕ)$ leads to infinite branches of scalarized charged black holes.

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arXiv2025

Quantum parameter-mass induced scalarization of qOS-black hole in the Einstein-Gauss-Bonnet-scalar theory

We obtain quantum parameter ($α$)-mass ($M$) induced spontaneous scalarization of quantum Oppenheimer-Snyder (qOS)-black hole in the Einstein-Gauss-Bonnet-scalar theory with the unknown qOS action. We derive Smarr formula which describes a correct thermodynamics for the bald qOS-black hole. It is turned out that two Davies points of heat capacity are identified with two critical onset mass and quantum parameter for spontaneous scalarization. However, we do not obtain such connections from the Einstein-Gauss-Bonnet-scalar theory with the nonlinear electrodynamics action. Furthermore, the shadow radius analysis of qOS-black hole is performed to distinguish quantum parameter from mass by comparing them with the EHT observation. There is no constraints on the quantum parameter, but new constraints are found for the mass. This work is considered as the first example to show a close connection between thermodynamics of bald black hole and spontaneous scalarization.

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arXiv2025

Smarr formula for black holes with primary and secondary scalar hair

In this work, we revisit the thermodynamics of black holes endowed with primary and secondary scalar hair in the shift and ${\rm Z}_2$ symmetric subclass of beyond Horndeski gravity. Under a specific fine-tuning of the scalar parameter $q$ in terms of the black hole mass, the singular black-hole solution with primary scalar hair reduces to the regular Bardeen solution featuring secondary scalar hair. We first demonstrate that the traditional thermodynamic approach fails to yield a consistent Smarr formula for both solutions under consideration. To address this issue, we adopt the approach introduced in [Phys$.$Rev$.$Lett. 132 (2024) 19, 191401], and we derive both the first law of black hole thermodynamics and the Smarr formula, offering a consistent thermodynamic description for scalar-hairy black holes. As an additional outcome, our analysis reveals a connection between the solutions with primary and secondary scalar hair.

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arXiv2025

Extended thermodynamic analysis of a charged Horndeski black hole

We perform the thermodynamic analysis of a charged Horndeski black hole (CHB) with mass $m$ and charge $q$ obtained from the Einstein-Horndeski-Maxwell theory. There are two solution branches: one is for the CHB and the other is for the naked singularity (NS). Thermodynamic behavior for the CHB is similar to that for the Reissner-Nordström black hole but its Helmholtz free energy is always positive. If the NS point is included as an extremal point, then the Helmholtz free energy is always negative, implying that the globally stable region is achieved anywhere. For the NS, its temperature has a maximum point, its heat capacity remains negative without having Davies point, and its free energy decreases without limitation as the charge $q$ increases.

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arXiv2025

Shadow and geometric scattering analysis of a new black hole with magnetic charge

We obtain a newly charged black hole with magnetic charge $q$ and coupling constant $μ$ from the Einstein-nonlinear electrodynamics theory inspired by quasi-topological terms. We perform the shadow and geometric scattering analysis of this black hole. For $μ=0.01$, we have four solution branches labelled by $2\pm$, 3, and 4 of the horizon, while there exists a single branch labelled by 2 for $μ=0.1$. There is the naked singularity (NS) arisen from the magnetic charge extension of the photon spheres for the 3 and 4-branches. In case of $q<1$, shadow radii of the $2$-branch with $μ$=0.01 and 0.1 are the same as that of the Reissner-Nordström black hole, while the 3-NS branch of $q>1$ is constrained by the EHT observation. The geometric scattering analysis is performed to understand the peculiar forms of the critical impact factors.

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arXiv2025

Thermodynamic and shadow radius analysis of the charged Einstein-Euler-Heisenberg black hole

We perform the thermodynamic and shadow radius analysis of an electrically charged black hole (EC) with electric charge $q$ and coupling constant $μ$ obtained from the Einstein-Euler-Heisenberg nonlinear electodynamics. For $μ=0.03$, we have four solution branches of the horizon including low, hot, negative, and cold ones, while for $μ=0.3,3$ there exist single branches without limitation on $q$. The shadow radius for the low branch is the nearly same as that for the Reissner-Norström black hole for $q<1$ case, while one finds the $q>1$ negative branch which is constrained by the EHT observation.

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arXiv2024

Spontaneous scalarization of Bardeen black holes

We study the spontaneous scalarization of Bardeen black holes, whose tachyonic instability triggers the formation of scalarized charged black holes (SCBHs). In this case, we find infinite ($n=0,1,2,\cdots$) branches of SCBHs with magnetic charge $g$. The $n = 0$ branch of SCBHs can be found for the coupling parameter $α\geq α_{n=0}(g)$ with both quadratic (1-$αφ^2$) and exponential ($e^{-αφ^2}$) couplings, where $α_{n=0}(g)$ represents the threshold of tachyonic instability for the Bardeen black holes. Furthermore, it is shown that the $n = 0$ branch for both couplings is stable against radial perturbations. This stability shows that this branch can be used for further observational implications.

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arXiv2024

The simplest model of a scalarized black hole in the Einstein-Klein-Gordon theory

We investigate scalarized black holes in the Einstein-minimally coupled scalar theory with a negative potential $V(ϕ)=-α^2ϕ^6$. The tachyonic instability is absent from analyzing the linearized scalar equation, which could not allow for spontaneous scalarization. However, we obtain the black hole solutions with scalar hair by solving three full equations because this scalar potential violates the weak energy condition. This shows clearly that scalarized black holes can be obtained without introducing a non-minimal scalar coupling term. We perform the stability analysis for scalarized black holes by adopting radial perturbations, implying that all scalarized black holes belonging to a single branch are unstable.

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arXiv2024

Photon ring bounds of scalar hairy charged black holes

We study photon rings of constant scalar hairy black holes with mass $m$, charge $Q$, and scalar hair $S$ obtained from the Einstein-Maxwell-conformally coupled scalar theory. These black holes are classified as scalar hairy Reissner-Nordström (SHRN) black hole, scalar hairy charged black hole with $S> -Q^2$, and mutated-RN black hole. The first two respect both dominant and strong energy conditions and have positive ADM mass and entropy, while the last does not respect two energy conditions and has negative ADM mass and entropy. We find that all of these black holes respect the lower bound ($r_γ\ge 1.2 r_+$) of photon rings. We obtain all real bounds of photon rings for these black holes and discuss physical and observational properties of real bounds. It is shown that the observationally favored region based on the shadow radius includes SHRN black hole, scalar hairy charged black hole, and mutated-RN black hole.

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arXiv2024

Shadow bound of black holes with dark matter halo

We investigate the shadow cast of black holes immersed in a dark matter halo. We use the M87* shadow data obtained by the EHT collaboration to constrain two parameters ($M,a$) of dark matter halo surrounding a black hole with mass $M_{\rm bh}$. For $a\ge10.8M$, we find the favored region (shadow bound), while the disfavored region is found for $a<10.8M$ when imposing the EHT results. This shadow bound is much less than the observation bound of galaxies ($a\ge 10^4 M$).

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arXiv2024

Scalarization of Kerr-Newman black holes in the Einstein-Chern-Simons-scalar theory

We investigate the tachyonic instability of Kerr-Newman (KN) black hole with a rotation parameter $a$ in the Einstein-Chern-Simons-scalar theory coupled with a quadratic massive scalar field. This instability analysis corresponds to exploring the onset of spontaneous scalarization for KN black holes. First, we find no $a$-bound for $α<0$ case by considering (1+1)-dimensional analytical method. A direct numerical method is adopted to explore (2+1)-dimensional time evolution of a massive scalar perturbation with positive and negative $α$ to obtain threshold curves numerically. We obtain threshold curves $α_{\rm th}(a)$ of tachyonic instability for positive $α$ without any $a$-bounds. We expect to find the same threshold curves $α_{\rm th}(a)$ of tachyonic instability for negative $α$ without any $a$-bound because its linearized scalar theory is invariant under the transformation of $α\to -α$ and $θ\to -θ$. In addition, it is found that the scalar mass term suppresses tachyonic instability of KN black holes.

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arXiv2023

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

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 $α$ 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 $0.161<α<3/16$ for achieving non-BTZ black holes with scalar hair analytically and a thermodynamic bound of $1/8<α<13/80$ for obtaining consistent thermodynamic quantities. Without imposing the GL instability bound ($m^2<1/2\ell^2$), we find a very narrow bound of $0.161<α<0.1625$ which is located inside tachyonic instability bound of $α>1/8+m^2_Φ\ell^2/6$ for obtaining scalarized black holes where $m^2_Φ$ is a scalar mass parameter.

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