arXiv subjects

Yun Soo Myung

Publications and source records attributed to Yun Soo Myung.

At least 19 recordsLinked to original sources

arXiv2026

Time-domain analysis of scalar perturbations of Kerr--Newman black holes with Chern--Simons and Maxwell couplings

To study the onset of scalarization, we investigate linear scalar perturbations around Kerr--Newman black holes in the Einstein-Chern-Simons-Maxwell-scalar theory with quadratic Chern--Simons (CS) coupling $γ$ ($\hatγ=γ/M^2$) and Maxwell coupling $η$. For this purpose, we employ hyperboloidal Rácz--Tóth evolution and a stationary axisymmetric zero-mode computation. The resulting thresholds are compared with the time-domain response at representative points. For $\hatγ=0$, we find two asymmetric threshold branches in $η$, while for $\hatγ=η$, the two branches have opposite signs and unequal magnitudes. For unequal CS and Maxwell couplings, the two real threshold branches merge as the spin or CS coupling increases.

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arXiv2026

Nonlinear scalarization and thermodynamics in Einstein-Phantom scalar-Gauss-Bonnet theory

We study nonlinear scalarization of Schwarzschild black-holes for a phantom scalar coupled to the Gauss--Bonnet invariant. Three polynomial couplings satisfying $ζ''(0)=0$ are introduced to investigate its nonlinear coupling dependence. Since the phantom factor $ε$ disappears in the probe scalar equation, its nonlinear evolution is the same as in the canonical scalar theory. We construct nodeless probe solutions and fully backreacted two branches of lower and primary. At equal mass and equal temperature, respectively, the lower branches have higher Wald entropy and lower Helmholtz free energy than primary branch, but their heat capacities are negative. This implies that lower branch favors than primary branch. Finally, we show that there is no nonlinerly stable scalar phase for a phantom kinetic theory.

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arXiv2026

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

We study scalarized extremal black holes in the Einstein-Maxwell-scalar (EMS) theory with two different scalar couplings to two U(1) fields. This theory is inspired by the dyonic EMS theory. Two scalarzied extremal black holes are found with constant scalar hair. We confirm that these are exactly obtained from the extremal scalarization and entropy function approaches. This may imply that it is not easy to find extremal black holes with primary scalar hair.

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arXiv2026

Quasinormal modes of type II-perturbation for dilaton-Euler-Heisenberg black holes

We study the quasinormal modes (QNMs) of Type II perturbations for dilaton-Euler-Heisenberg (dEH) black holes. These perturbations consist of coupled even-parity gravitational and dilaton perturbations together with odd-parity electromagnetic perturbations. The background is described by mass $M$, magnetic charge $Q_m$, and dilaton coupling difference $ζ=α-β$ to the Euler-Heisenberg term. To find the QNM frequencies, we need to find the parameter space of $(ζ, Q_m/M)$ that is free from vector ghosts. For the $\ell=1$ mode, the radiative block couples the dilaton and axial electromagnetic amplitudes, whereas the $\ell=2$ mode also contains metric amplitudes, so the frequencies are obtained from matrix-valued boundary-value problems. We calculate QNM frequencies for the fundamental ($n=0$) branch with direct integration and the Chebyshev pseudospectral method, and compare the two computations wherever their charge intervals overlap. We find that the $\ell=1,2$ modes in the $n=0$ branch remain damped over the ghost-free parameter domain, supporting the stability of dEH black holes against Type II perturbations. The Type I sector will be presented elsewhere; no claim is made here about that sector, higher multipoles, or overtones.

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arXiv2026

Charge-dependent scalarization of Einstein- Euler-Heisenberg black holes

Charge-dependent scalarization of the Einstein-Euler-Heisenberg (EEH) black hole is carried out in the EEH-scalar theory by introducing an exponential scalar coupling with coupling constant $α$ to the Maxwell and nonlinear electrodynamic terms. The bald black hole (EEHBH) is described by mass $M$ and arbitrary magnetic charge $q$ and has a single horizon when choosing the action parameter $μ=0.3$. Here, we find the critical onset charge $q_c=r_+^2/\sqrt{2μ}$ with $r_+(M,q_c)$ the outer horizon radius from the resonance condition. The spontaneous scalarization ($α^+$) of this black hole is available for charge $0 q_c$ and negative $α$. The former case of $q=0.5$ implies infinite branches of scalarized EEHBHs but its fundamental branch ($n=0$) is stable against the $l=0$ modes considered here, while for $q=2$ and $q=20$, one stable scalarized branch is found for each charge within the explored parameter ranges.

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arXiv2026

Extremal Scalarization of Charged Black Holes: Miransky Scaling across Reissner-Nordström Extremality

We study spontaneous scalarization near and at extremality in Einstein-Maxwell-scalar theory. As Reissner-Nordström (RN) extremality is approached from below, the nonextremal scalarization existence curves collapse toward a common critical threshold $α_c=1/4$ given by the Breitenlohner-Freedman bound for the near-horizon throat (AdS$_2\times S^2$) of its extremal black hole. For a polynomial coupling, we construct extremal black holes with nonconstant scalar hair, satisfying $M^2+Q_s^2=Q^2$, which places them in the overcharged region $Q/M>1$ beyond the RN bound. A common near-region phase mechanism predicts accumulation toward the RN extremality from both sides, yielding Miransky-type scaling. In the extremal sector, the logarithmic phase interval doubles, halving the exponent which denotes the geometric spacing of successive node scales.

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arXiv2026

Critical Scalarization for a Self-Gravitating Bosonic Condensate

We establish a minimal nonrelativistic realization of scalarization in a self-gravitating bosonic condensate coupled to a scalar response field. A local effective-mass shift and nonlinear saturation generate a multibranch structure with two distinct transition routes. In the linearly stable regime, a finite perturbation drives a first-order transition with type-I logarithmic scaling near threshold. Beyond the linear onset, small perturbations grow tachyonically, and the response time controls both the growth and the subsequent breathing dynamics. These results identify a common mechanism for scalarization across relativistic compact objects and nonrelativistic condensates, and point toward laboratory analogues in coherent media.

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arXiv2026

Scalarized Einstein-Euler-Heisenberg black holes at the approach to extremality

We investigate extremal black holes with scalar hair in the generic Einstein-Euler-Heisenberg (EEH)-scalar theory with two scalar couplings to the Maxwell term. One is an exponential coupling with coupling constant $α$ and the other is its polynomial coupling. We first construct scalarized black holes on the cold (C)-horizon of EEH black holes described by mass $M$ and magnetic charge $P$ both at the linear level, through the existence curves $α_n(q)$ with $q=P/M$, and as fully backreaction solutions. As extremality ($q=q_e$) is approached, all existence curves accumulate, following $α_n-α_c\sim 1/\ln^2(q_e-q)$, at the critical branch $α_c$ fixed by the Breitenlohner-Freedman bound for the near-horizon (AdS$_2\times S^2$) throat. We obtain scalarized extremal black hole (SEBH) with constant secondary hair and it is recovered exactly from the entropy function approach working on the near-horizon throat. Its entropy is an attractor invariant, being independent of the asymptotic modulus, so the scalar hair remains secondary. Exploiting this constant scalar, we seek further SEBHs with scalar hair keeping its charge $Q_s$ for the zero asymptotic scalar ($ϕ_\infty=0$). In the $(q,α)$ plane, we observe that these extremal solutions occupy $q\ge q_e$. Hence, the existence curves $α_n(q)$ existing for $q\le q_e$ and the extremal branches bound the scalarized domain from opposite sides and they meet only at $q=q_e$.

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arXiv2026

Curvature-induced scalarization of charged AdS black holes

We investigate how a negative cosmological constant affects the Gauss-Bonnet (GB) scalarization in the Einstein-Maxwell-scalar-Gauss-Bonnet theory with a scalar coupling constant $η$ to GB term. We focus on the instability of Reissner-Nordström-AdS (RN-AdS) black holes under a scalar perturbation governed by an effective mass $μ^2_{\text{eff}}$ sourced by the GB term. Unlike the asymptotically flat spacetime case, the onset of scalarization is not merely determined by $μ^2_{\text{eff}} < 0$, but it is constrained by the Breitenlohner-Freedman (BF) bound. In case that the BF bound is violated ($η>2.25$ with $Λ=-0.5$), one may find AdS-tachyonic instability. We find that for $0<η<2.25$, the GB$^+$ scalarization may be performed through spontaneous scalarization, while for $η<0$ the GB$^-$ scalarization is found to give the single branch of scalarized AdS black holes. For the GB$^+$ scalarization in $η_{th}\leη<2.25$ with $η_{th}$ threshold instability, we obtain the single branch ($n=0$ fundamental branch) of scalarized AdS black holes, in contrast to the infinite branches in asymptotically flat spacetime. A bulk fixed-charge thermodynamic analysis is performed thoroughly for GB$^\pm$ scalarizations.

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arXiv2026

Scalarization of Einstein-Euler-Heisenberg black hole with multiple horizons

Scalarizations of the Einstein-Euler-Heisenberg (EEH) black hole (EEHBH) with multiple horizons are investigated in the EEH-scalar theory by introducing a quadratic scalar coupling to the Maxwell term. For mass $M=1$ and Euler-Heisenberg parameter $μ=0.03$, the magnetically charged EEHBH admits four horizon families (low, cold, negative, and hot), with triple horizons appearing in the narrow band of magnetic charge $q\in[0.95,1.0065]$. The onset scalarization around the low, cold, and high horizons is then analyzed for the magnetic charge $q=0.5,\,1,\,2$, implying infinite branches of scalarized black holes for each case. We construct the three fundamental branches of scalarized black holes. From the positivity condition of their mass, we find the upper bounds on primary scalar charges $q_{s}$ for scalarized low and cold horizons. These bounds determine the allowable regions for the Hawking temperature and entropy. Furthermore, we perform a time-domain stability analysis and find that the instabilities arise only at small scalar charge regime. Therefore, stable and physically viable scalarized black holes exist in an intermediate window of the primary scalar charge for low and cold horizon solutions and a lower bound for hot horizon solution.

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arXiv2026

Polar perturbations of dilaton-Euler-Heisenberg black holes

We investigate the quasinormal modes of polar metric-dilaton perturbations around the dilaton-Euler-Heisenberg (dEH) black holes with dilaton hair. The dEH black holes are obtained from the Einstein-Maxwell-dilaton theory with two dilaton coupling parameters ($α,β$) to the nonlinear Euler-Heisenberg term. We compute the quasinormal mode spectra by making use of two numerical techniques: direct integration and matrix values continued fraction methods. An excellent agreement is found between two approaches, confirming the robustness of our computation. We present the fundamental quasinormal frequencies for both gravitational and dilaton modes and analyze their dependence on the magnetic charge ($Q_m$), angular momentum quantum number ($l$), and coupling parameter ($ε=α-β$). All negative imaginary quasinormal frequencies for polar metric-dilaton perturbations imply that the dEH black hole with dilaton hair is stable against dilaton with $l=0,1,2,3$ and gravitational modes with $l=2,3$. Also, our results reveal distinct qualitative behaviors between $ε=1$ and $ε=-1$, particularly in the damping rates near the extremality.

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arXiv2026

Gauss-Bonnet scalarization of charged qOS-black holes

The Gauss-Bonnet (GB) scalarization for charged quantum Oppenheimer-Snyder (cqOS)-black holes is investigated in the Einstein-Gauss-Bonnet-scalar theory with the nonlinear electrodynamics (NED) term. Here, the scalar coupling function to GB term is given by $f(ϕ)=2λϕ^2$ with a coupling constant $λ$. Three parameters of mass ($M$), action parameter ($α$), and magnetic charge ($P$) are necessary to describe the cqOS-black hole, and it may become the qOS-black hole when $P=M$. The GB scalarization of cqOS-black holes comes into two cases GB$^\pm$, depending on the sign of GB term which triggers the different phenomena. For $α=0$ and $λ>0$, GB$^+$ scalarization is allowed, while for $α\not=0$ and $λ<0$, GB$^-$ scalarization appears for a narrow band of $3.5653\le α\le 4.6875$. After discussing the onset GB$^-$ scalarization, we construct scalarized cqOS-black holes which belong to the single branch. The scalar field decays much more rapidly compared to the GB$^+$ case. Stability analysis shows these scalarized black holes are linearly stable under scalar perturbations.

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arXiv2026

Anisotropic matter and nonlinear electromagnetics black holes

It is shown that anisotropic matter black holes with two parameters $w$ and $K$ correspond to nonlinear electrodynamics (NED) black holes with power-index $s$ and charge term $ξ(s,q)$ by introducing a NED term. These NED black holes include dark matter ($s=3/4$), constant scalar hair ($s=1$), charged quantum Oppenheimer-Snyder ($s=3/2$), and Einstein-Euler-Heisenberg ($s=2$) black holes derived from their known actions. Rotating NED black holes can be obtained from rotating anisotropic matter black holes when replacing $w$ and $K$ by $2s-1$ and $ξ(s,q)$. The extremal rotating NED black holes being the boundary between rotating charged NED black hole and naked singularity are derived as functions of the rotation parameter $a(q)$.

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arXiv2026

Spin-Induced Nonlinear Scalarization of Kerr Black Holes in Einstein-scalar-Gauss-Bonnet Gravity

We investigate spin-induced scalarization of Kerr black holes in an Einstein-scalar-Gauss-Bonnet (EsGB) model that does not admit a linear tachyonic instability of the scalar-free solution. The scalarization mechanism is therefore genuinely nonlinear. We first analyze the decoupled scalar dynamics on fixed Kerr backgrounds and show that sufficiently rapid rotation modifies the Gauss-Bonnet invariant such that a negative near-horizon region develops near the poles. This region provides a geometric trapping mechanism for nonlinear scalar growth, which becomes effective above a threshold spin $χ=0.5$. We then construct stationary scalarized black hole solutions with full backreaction and determine their domain of existence. We find that the solutions occupy a finite low-mass high-spin wedge in the spin-mass plane. This is in contrast to spin-induced spontaneous scalarization, where the scalarized solutions form a narrow band. In this wedge, toward the high-spin end, the scalar hair becomes stronger, and the solutions approach a near-extremal regime, while toward the low-spin boundary, the scalar field is strongly suppressed and approaches a weak-hair limit as $χ\to 0.5$.

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arXiv2026

Thermodynamics and phase transitions of nonlinearly scalarized black holes in Einstein-scalar-Gauss-Bonnet theory

We investigate the thermodynamic properties of static nonlinearly scalarized black holes in Einstein-scalar-Gauss-Bonnet theory with polynomial coupling functions. Based on the scalarized solutions constructed previously, we compute thermodynamical quantities of these scalarized black holes. Moreover, we examine the first law of black hole thermodynamics and consider the phase transitions between Schwarzschild and scalarized black holes. It shows that a phase transition from Schwarzschild black hole to scalarized black hole is a first-order with non-zero latent heat.

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arXiv2026

Spin-charge induced scalarization of Kerr-Newman black holes in the Einstein-Maxwell-scalar theory with scalar potential

We investigate the spin-charge-induced scalarization of Kerr--Newman (KN) black holes in the Einstein--Maxwell-scalar (EMS) theory with a scalar potential and positive coupling parameter. In the linearized theory, there exists a bound of $0<a<a_0$ with onset spin $a_c$ for the negative region signaling instability by analyzing the effective scalar mass term in the $θ$-direction. Solving the $(2+1)$-dimensional evolution equation numerically, we find the region where the KN black hole becomes unstable, giving rise to scalarized KN black holes. The threshold curve for representing the boundary between stable and unstable KN black holes depends on charge $Q$, scalar mass $m_ϕ$, coupling parameter $α$, and spin parameter $a$ with upper bound $a^2\le M^2-Q^2$.

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arXiv2026

Existence of nonlinearly scalarized black holes in Einstein-scalar-Gauss-Bonnet theory with polynomial couplings

Nonlinearly scalarized black holes are investigated in Einstein-scalar-Gauss-Bonnet (EsGB) theory with polynomial coupling functions $ζ(ϕ)$ satisfying $ζ''(0) = 0$, where $ζ'(ϕ) = 0$ features besides $ϕ=0$ solutions with constant $ϕ_{\rm s} \ne 0$. We determine the threshold amplitudes for Gaussian pulses, above which Schwarzschild black holes (SBHs) %become unstable and may transition to scalarized black holes for two coupling functions: $ζ(ϕ)=αϕ^4-βϕ^8$ and $ζ(ϕ)=αϕ^4-βϕ^6$. In contrast, for the quartic coupling function $ζ(ϕ)=αϕ^4$ SBHs are stable. Treating $ζ(ϕ)R_{GB}^2$ as an effective potential $V_\text{eff}$ provides an explanation for the ``plateau" and the divergence observed in the time evolution. We then construct the branches of nonlinearly scalarized black holes in the probe limit and with backreaction. While the pattern of the solution branches in the probe limit exhibits universal features, the presence of backreaction reveals a distinct dependence on the coupling strength $β$.

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arXiv2026

Charged qOS-extremal black hole and its scalarization by entropy function approach

We investigate scalarization of charged quantum Oppenheimer-Snyder extremal (cqOSe)-black hole in the Einstein-Gauss-Bonnet-scalar theory with a nonlinear electrodynamics term. This black hole is described by quantum parameter $α$ and magnetic charge $P$. It is equivalent to the qOS-extremal black hole whose action is still unknown when imposing a relation of $(3αP^2)^{1/4}\to 3M/2$. Focusing on the onset of scalarization, we find the single branch of scalarized cqOS extremal (scqOSe)-black holes. To obtain a scalar cloud (seed) for the single branch, however, we have to consider its near-horizon geometry of the Bertotti-Bobinson (BR) spacetime. In this case, two scalar clouds for positive and negative coupling constant $λ$ are found to represent two branches. Applying Sen's entropy function approach to this theory, we obtain the entropy which is the only physical quantity to describe the scqOSe-black holes. We find that the positive branch is preferred than the negative branch.

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