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Wonwoo Lee

Publications and source records attributed to Wonwoo Lee.

At least 19 recordsLinked to original sources
arXiv2026

Phase transition for a black hole with matter fields and the relation with the Lyapunov exponent

We construct static black hole solutions coexisting with anisotropic matter in asymptotically (anti-)de Sitter spacetime and investigate how the matter field modifies their thermodynamic and dynamical properties. The anisotropic matter generates an exponentially decaying charge-like contribution to the metric, causing the geometry to interpolate between the Schwarzschild black hole in anti-de Sitter spacetime and the Reissner-Nordström black hole in anti-de Sitter spacetime. In anti-de Sitter black hole spacetime, we derive the complete thermodynamic description, including the Hawking temperature, heat capacity, Smarr relation, generalized first law, and Helmholtz free energy. The system exhibits a van der Waals-type small/large black hole phase transition with a critical point determined by the matter field parameters. Local thermodynamic stability is characterized by the heat capacity, whereas global stability is determined through the free energy. We further investigate unstable homoclinic orbits by evaluating the Lyapunov exponent associated with null geodesics. Our analysis reveals that different thermodynamic branches possess distinct dynamical instabilities, and that the thermodynamically preferred phase is accompanied by a smaller Lyapunov exponent. These results demonstrate that thermodynamic stability and geodesic instability are correlated because both originate from the same underlying spacetime geometry.

gr-qc↗
arXiv2026

Chaotic behaviors of particles around the black hole with an anisotropic matter immersed in a magnetic field

We present an exact solution to the Einstein-Maxwell equations that describes a static black hole coexisting with anisotropic matter immersed in an external magnetic field, obtained via the Harrison transformation. Our findings reveal that an increase in the anisotropic matter parameter systematically suppresses the local chaotic behavior, as indicated by a reduction in the Lyapunov exponent. Conversely, variations in the external magnetic field lead to qualitative changes in global chaotic behavior. This is analyzed through Poincaré sections, which demonstrate transitions between regular and chaotic trajectories resulting from the nonlinear gravitational-magnetic interactions. These factors play distinct yet complementary roles in shaping chaotic particle dynamics around black holes. This study would offer a new theoretical framework for exploring non-integrable particle motion within magnetized black hole spacetimes and for probing a black hole at the galactic center, where magnetic fields may arise from plasma effects surrounding astrophysical black holes.

gr-qc↗
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 $a(q)$.

gr-qc↗
arXiv2026

Resonant transmission of scalar waves through rotating traversable wormhole

The viability of traversable wormholes as exotic compact objects requires the identification of signatures that distinguish them from other compact objects. Given recent advances in observing rotating black hole signatures, identifying characteristic imprints that reflect the absence of an event horizon and the presence of a throat structure is of considerable significance. Motivated by this, in the present work, we analyze the propagation of a massless scalar field in a rotating traversable wormhole spacetime described by Teo's class of solutions. We numerically compute the transmission (greybody) factor and the corresponding absorption spectrum across a broad range of frequencies. The spectrum exhibits a series of sharp peaks in the amplitudes, which we identify as Breit-Wigner-type resonances. The emergence of such peaks can be attributed to the scalar modes temporarily trapped within the potential well formed by barriers on either side of the throat. These resonant features, previously identified in static wormhole backgrounds, persist in the rotating case. In particular, for Teo's class of wormholes, we find that rotation enhances the strength of the resonances. Overall, our results demonstrate the role of rotation in shaping the resonance effect and indicate these features as characteristic signatures of wormhole geometries.

gr-qc↗
arXiv2026

Stationary axisymmetric systems that allow for a separability structure

We develop a systematic framework for formulating and solving the conditions that lead to separability in stationary, axisymmetric spacetimes in the presence of matter fields. Guided by Carter's metric form, we introduce a general stationary, axisymmetric metric ansatz that allows for a transparent separation of radial and angular variables. This construction yields a broad family of stationary rotating solutions admitting separability structures. To illustrate the applicability of the formalism, we explicitly construct several examples, including a rotating black hole with a global monopole supported by anisotropic matter, as well as a new class of rotating wormhole geometries.

gr-qc↗
arXiv2026

Charged traversable wormholes: charge without charge

We present and investigate charged wormhole solutions of the Einstein-Maxwell equations supported by anisotropic matter fields, with the purpose of establishing their physical plausibility as traversable wormholes. To this end, we examine the flare-out condition and evaluate tidal forces to confirm their traversability. We also analyze light deflection around these wormholes to provide observational implications. Additionally, we attempt to construct rotating generalizations of the solutions by applying and modifying the Newman-Janis algorithm. Our results suggest that the obtained geometries offer a concrete realization of the concept of ``charge without charge".

gr-qc↗
arXiv2026

Charged wormholes in (anti-)de Sitter spacetime

We present a family of charged, traversable wormhole solutions in the presence of a cosmological constant. In de Sitter spacetime, two types of wormhole throats can exist--referred to as typical and cosmological throat--located at small and large radial values, respectively. In anti-de Sitter spacetime, the throat geometry allows for positive, zero, or negative curvature, enabling the possibility of an infinite throat area. We analyze the flare-out condition, a key requirement for the existence of traversable wormholes, which imposes constraints on the equation of state parameters governing the supporting matter. These solutions are shown to be of Petrov type D. Furthermore, we examine radial geodesics of null and timelike particles. In the de Sitter case, particles traverse the wormhole, passing from one throat to the other. In contrast, in the anti-de Sitter case, particles exhibit recurrent oscillatory motion between two asymptotic regions, cyclically disappearing and reappearing across the throats.

gr-qc↗
arXiv2025

Dressing rotating black holes with anisotropic matter

We present a new rotating black hole solution to the Einstein equations as an extension of the Kerr spacetime. Interestingly, the solution we find may not be uniquely characterized by asymptotic parameters such as mass, angular momentum, and charge, thereby it would be the additional hair. We also analyze in detail how this additional characteristics or this hair affects the thermodynamic properties of the black hole.

gr-qc↗
arXiv2025

Stability and topological nature of charged Gauss-Bonnet AdS black holes in five dimensions

We investigate the thermodynamics of Reissner-Nordstrom Gauss-Bonnet (RN-GB) black holes in anti-de Sitter (AdS) space with three horizon geometries (k=+1,0,-1) within the grand canonical ensemble. Using the recently developed topological approach to black hole thermodynamics, inspired by Duan's $ϕ$-mapping theory, we analyze the black holes by treating both critical points in the phase diagram and black hole solutions as defects in the thermodynamic parameter space. Our results show that the Gauss-Bonnet coupling significantly alters the topological classification of RN-GB AdS black holes, distinguishing them from their RN AdS counterparts in the grand canonical ensemble, while aligning with their canonical ensemble counterparts. Complementary analyses of local stability using specific heat validate the implication of topological analysis. Furthermore, an evaluation of global stability via Gibbs free energy provides a comprehensive understanding on the system's phase structure. Notably, for k=+1, topological analysis suggests liquid-gas type phase transitions, whereas global analysis favors Hawking-Page transitions. For k=-1, topology indicates a single stable black hole branch, yet the global analysis reveals the presence of Hawking-Page transition.

hep-th↗
arXiv2024

Gauss-Bonnet Cosmology: large-temperature behaviour and bounds from Gravitational Waves

We provide a transparent discussion of the high temperature asymptotic behaviour of Cosmology in a dilaton-Einstein-Gauss-Bonnet (dEGB) scenario of modified gravity with vanishing scalar potential. In particular, we show that it has a clear interpretation in terms of only three attractors (stable critical points) of a set of autonomous differential equations: $w=-\frac{1}{3}$, $w=1$ and $1<w<\frac{7}{3}$, where $w\equiv p/ρ$ is the equation of state, defined as the ratio of the total pressure and the total energy density. All the possible different high-temperature evolution histories of the model are exhausted by only eight paths in the flow of the set of the autonomous differential equations. Our discussion clearly explains why five out of them are characterized by a swift transition of the system toward the attractor, while the remaining three show a more convoluted evolution, where the system follows a meta-stable equation of state at intermediate temperatures before eventually jumping to the real attractor at higher temperatures. Compared to standard Cosmology, the regions of the dEGB parameter space with $w=-\frac{1}{3}$ show a strong enhancement of the expected Gravitational Wave stochastic background produced by the primordial plasma of relativistic particles of the Standard Model. This is due to the very peculiar fact that dEGB allows to have an epoch when the energy density $ρ_{\rm rad}$ of the relativistic plasma dominates the energy of the Universe while at the same time the rate of dilution with $T$ of the total energy density is slower than what usually expected during radiation dominance. This allows to use the bound from BBN to put in dEGB a constraint $T_{\rm RH}\lesssim 10^8 - 10^9$ GeV on the reheating temperature of the Universe $T_{\rm RH}$. Such BBN bound is complementary to late-time constraints from compact binary mergers.

hep-ph↗
arXiv2024

Induced Cosmological Anisotropies and CMB Anomalies by a non-Abelian Gauge-Gravity Interaction

We present a non-abelian cousin of the model presented in \cite{Lee:2022rtz} which induces cosmological anisotropies on top of standard FLRW geometry. This is in some sense doing a cosmological mean field approximation, where the mean field cosmological model under consideration would be the standard FLRW, and the induced anisotropies are small perturbative corrections on top of it. Here we mostly focus on the non-abelian $SU(2)$ gauge fields coupled to the gravity to generate the anisotropies, which can be a viable model for the axion-like particle (ALP) dark sector. The induced anisotropies are consequences of the non-trivial back-reaction of the gauge fields on the gravity sector, and by a clever choice of the parametrization, one can generate the Bianchi model we have studied in this note. We also show that the anisotropies influence the Sachs-Wolfe effect and we discuss the implications.

gr-qc↗
arXiv2024

Induced cosmological anisotropy by a gauge-gravity interaction

We present a simple model which generates cosmological anisotropies on top of standard FLRW geometry. This is in some sense reminiscent of the mean field approximation, where the mean field cosmological model under consideration would be the standard FLRW, and the anisotropy is a small perturbative correction on top of it. Using a supergravity-inspired model, we confirm that the stable fixed point of our model corresponds to standard FLRW cosmology. We use a Bianchi VII$_0$-type model supplemented with a scalar and $U(1)$ gauge fields, and we show that the anisotropies of the geometry are generated by the non-trivial interaction between the gravity sector and the $U(1)$ gauge sector. Studying the attractor flow, we show that the anisotropies are present at early times (high redshift) and decay asymptotically to an FLRW attractor fixed point. With such a mechanism, observations of non-isotropy are not contradictory to FLRW geometry or indeed the $Λ$CDM model. Such models could in principle shed some insights on the present cosmological tensions.

gr-qc↗
arXiv2023

Superradiance in the Kerr-Taub-NUT spacetime

Superradiance is the effect of field waves being amplified during reflection from a charged or rotating black hole. In this paper, we study the low-energy dynamics of super-radiant scattering of massive scalar and massless higher spin field perturbations in a generic axisymmetric stationary Kerr-Taub-NUT (Newman-Unti-Tamburino) spacetime, which represents sources with both gravitomagnetic monopole moment (magnetic mass) and gravitomagnetic dipole moment (angular momentum). We obtain a generalized Teukolsky master equation for all spin perturbation fields. The equations are separated into their angular and radial parts. The angular equations lead to spin-weighted spheroidal harmonic functions that generalize those in Kerr spacetime. We identify an effective spin as a coupling between frequency (or energy) and the NUT parameter. The behaviors of the radial wave function near the horizon and at the infinite boundary are studied. We provide analytical expressions for low-energy observables such as emission rates and cross sections of all massless fields with spin, including scalar, neutrino, electromagnetic, Rarita-Schwinger, and gravitational waves.

gr-qc↗
arXiv2023

WIMPs in Dilatonic Einstein Gauss-Bonnet Cosmology

We use the Weakly Interacting Massive Particle (WIMP) thermal decoupling scenario to probe Cosmologies in dilatonic Einstein Gauss-Bonnet (dEGB) gravity, where the Gauss-Bonnet term is non-minimally coupled to a scalar field with vanishing potential. We put constraints on the model parameters when the ensuing modified cosmological scenario drives the WIMP annihilation cross section beyond the present bounds from DM indirect detection searches. In our analysis we assumed WIMPs that annihilate to Standard Model particles through an s-wave process. For the class of solutions that comply with WIMP indirect detection bounds, we find that dEGB typically plays a mitigating role on the scalar field dynamics at high temperature, slowing down the speed of its evolution and reducing the enhancement of the Hubble constant compared to its standard value. For such solutions, we observe that the corresponding boundary conditions at high temperature correspond asymptotically to a vanishing deceleration parameter q, so that the effect of dEGB is to add an accelerating term that exactly cancels the deceleration predicted by General Relativity. The bounds from WIMP indirect detection are nicely complementary to late-time constraints from compact binary mergers. This suggest that it could be interesting to use other Early Cosmology processes to probe the dEGB scenario.

hep-ph↗
arXiv2023

Homoclinic orbit and the violation of the chaos bound around a black hole with anisotropic matter fields

We study the homoclinic orbit and the violation of chaos bound, which are obtained by particle motions around a black hole that coexist with anisotropic matter fields. The homoclinic one is associated with an unstable local maximum of the effective potential. By perturbing a particle located slightly away from the homoclinic one, we numerically compute Lyapunov exponents indicating the sensitivity of the initial value. Our results demonstrate that the violation of the chaos bound increases with higher angular momentum, and the anisotropic matter gives rise to violating the chaos bound further, even in the case of the nonextremal black hole. We utilize the Hamiltonian-Jacobi formalism to explicitly illustrate how the geodesic motion of a particle can be integrable in the procedure of obtaining our findings.

gr-qc↗
arXiv2022

Hairy black holes in dilatonic Einstein-Gauss-Bonnet theory

We study black hole solutions in dilatonic Einstein-Gauss-Bonnet theory with a coupling constant $α$ between the dilaton field and the Gauss-Bonnet term. In a previous study, we considered the black hole with the vanishing cosmological constant in this theory and constructed the hairy black hole solution with the negative $α$. In this study, we present black hole solutions numerically with various physical properties in anti-de Sitter spacetime. We describe the procedure for constructing the black hole solutions in detail.

gr-qc↗
arXiv2022

Gravitational waves from the vacuum decay with LISA

We investigate the gravitational wave spectrum resulted from the cosmological first-order phase transition. We compare two models; one is a scalar field model without gravitation, while the other is a scalar field model with gravitation. Based on the sensitivity curves of the LISA space-based interferometer on the stochastic gravitational-wave background, we compare the difference between the gravitational wave spectra of the former and the latter cases resulted from the bubble collision process. Especially, we calculated the speed of the bubble wall before collision for the two models numerically. We show that the difference between the amplitudes of those spectra can clearly distinguish between the two models. We expect that the LISA with Signal to Noise Ratio =10 could observe the spectrum as the fast first-order phase transition.

gr-qc↗