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Y. S. Myung

Publications and source records attributed to Y. S. Myung.

At least 73 records · Page 4Linked to original sources
arXiv1998

Probing the BTZ black hole with test fields

We introduce a set of scalar fields as test fields to study the dynamical behaviors of the BTZ (Banados-Teitelboim-Zanelli) black hole. These include minimally coupled scalar, conformally coupled scalar, dilaton, and tachyon. To calculate the decay rate of the BTZ black hole, we consider both the Dirichlet boundary condition at spatial infinity and the stability condition. It turns out that the tachyon may be a relevant field to get information of the BTZ black hole.

hep-th↗
arXiv1998

Stability analysis and absorption cross-section in three-dimensional black string

It is shown that all string fields except dilaton are non-propagating in the (2+1)-dimensional black string. One finds that the perturbation around the black string reveals a mixing between the dilaton and other fields. Under the new gauge(dilaton gauge), we disentangle this mixing and obtain one decoupled dilaton equation. It turns out that this black string is stable. From the scattering of dilaton off the neutral black string(N=0), we find the absorption cross-section. Further the absorption cross-section for minimally coupled scalar is obtained and we compared it with that of dilaton.

hep-th↗
arXiv1997

Negative modes in the four-dimensional stringy wormholes

We study the Giddings-Strominger wormholes in string theories. We found negative modes among O(4)-symmetric fluctuations about the non-singular wormhole background. Hence the stringy wormhole contribution to the euclidean functional integral is purely imaginary. This means that the stringy wormhole is a bounce (not an instanton) and describes the nucleation and growth of wormholes in the Minkowski spacetime.

hep-th↗
arXiv1997

Black holes in the Brans-Dicke-Maxwell theory

The black hole solutions in the higher dimensional Brans-Dicke-Maxwell theory are investigated. We find that the presence of the nontrivial scalar field depends on the spacetime dimensions (D). When D=4, the solution corresponds to the Reissner-Nordström black hole with a constant scalar field. In higher dimensions (D>4), one finds the charged black hole solutions with the nontrivial scalar field. The thermal properties of the charged black holes are discussed and the reason why the nontrivial scalar field exists are explained. Also the solutions for higher dimensional Brans-Dicke theory are given for comparison.

gr-qc↗
arXiv1997

Absorption of fixed scalar in scattering off 4D N=4 black holes

We perform the perturbation analysis of the black holes in the 4D, N=4 supergravity. Analysis around the black holes reveals a complicated mixing between the dilaton and other fields (metric and two U(1) Maxwell fields). It turns out that considering both s-wave (l=0) and higher momentum modes (l \neq 0), the dilaton as a fixed scalar is the only propagating mode with $P=Q, h_1=h_2=0$ and $F = -G = 2ϕ$. We calculate the absorption cross-section for scattering of low frequency waves of fixed scalar and U(1) Maxwell fields off the extremal black hole.

hep-th↗
arXiv1997

Propagating waves in an extremal black string

We investigate the black string in the context of the string theories. It is shown that the graviton is the only propagating mode in the (2+1)--dimensional extremal black string background. Both the dilation and axion turn out to be non-propagating modes.

hep-th↗
arXiv1997

Critical behavior for the dilaton black holes

We study the critical behavior in the black p-branes and four dimensional charged dilaton black holes. We calculate the thermodynamic fluctuations in the various (microcanonical, canonical, and grandcanonical) ensembles. It is found that the extremal limit of some black configurations has a critical point and a phase transition takes place from the extremal to nonextremal black configurations. Some critical exponents are obtained, which satisfy the scaling laws. This is related to the fact that the entropy of these black configurations is a homogeneous function.

hep-th↗
arXiv1996

Higher dimensional extremal black strings

We investigate the five and six-dimensional black strings within Einstein-Maxwell theory. The extremal black strings are endowed with the null Killing symmetry. We study the propagation of Einstein-Maxwell modes in the extremal black string background by using this symmetry. It turns out that one graviton is a propagating mode, while both the Maxwell $F$ and three-form $H$ fields are non-propagating modes. Further we discuss the stability and classical hair of the extremal black strings.

hep-th↗
arXiv1996

Comment on "Background thermal contributions in testing the Unruh effect"

Costa and Matsas (gr-qc/9412030) claimed in their recent paper that a thermal bath does not affect substantially the transition probability for fast moving inertial Unruh detector. It is shown that their claim holds only for small $βΔE$. We show that, for large enough $βΔE$, the transition probability is not monotonically decreasing function of the detector's speed contrary to their claim.

hep-th↗
arXiv1996

New divergences of tachyon in the two-dimensional charged black holes

We quantize the tachyon field in the two-dimensional (2D), $ε<2$ charged black holes where $ε$ is the dilaton coupling parameter for the Maxwell term. Especially the expectation value of the stress-energy tensor $\langle T_{ab}\rangle$, observed by a freely falling observer, is computed. This shows that new divergences such as $\ln f$ and ${1 \over f}$ arises near the horizon ($f \to 0$), compared with conformal matter case.

hep-th↗
arXiv1996

Chiral boson, $W_\infty$-coherent state and edge states in the quantum Hall effect

We perform consistently the Gupta-Bleuler quantization combined with Dirac procedure for a chiral boson with the parameter ($α$) on the circle, the boundary of the circular droplet. For $α=1$, we obtain the holomorphic constraints. Using the representation of Bargmann-Fock space and the Schrödinger equation, we construct the holomorphic wave functions. In order to interpret these functions, we introduce the $W_\infty$-coherent state to account for the infinite-dimensional translation symmetry for the Fourier (edge) modes. The $α=1$ wave functions explain the neutral edge states for $ν=1$ quantum Hall fluid very well. In the case of $α= -1$, we obtain the new wave functions which may describe the higher modes (radial excitations) of edge states. Finally, the charged edge states are described by the $|α| \not=1$ wave functions.

hep-th↗
arXiv1995

Two-dimensional extremal black holes

We discuss the two-dimensional (2D), $ε<2$ extremal ground states of charged black hole. Here $ε$ is the dilaton coupling parameter for the Maxwell term. The complete analysis of stability is carried out for all these extremal black holes. It is found that they are all unstable. To understand this instability, we study the non-extremal charged black hole with two (inner and outer) horizons. The extremal black holes appear when two horizons coalesce. It conjectures that the instability originates from the inner horizon.

hep-th↗
arXiv1995

Unstable two-dimensional extremal black holes

We obtain the $ε<2$ new extremal ground states of a two-dimensional (2D) charged black hole where $ε$ is the dilaton coupling parameter for the Maxwell term. The stability analysis is carried out for all these extremal black holes. It is found that the shape of potentials to an on-coming tachyon (as a spectator) take all barrier-well types. These provide the bound state solutions, which imply that they are unstable. We conclude that the 2D, $ε<2$ extremal black holes should not be considered as a toy model for the stable endpoint of the Hawking evaporation.

hep-th↗
arXiv1995

On the stability of two-dimensional extremal black holes

We discuss the stability of the extremal ground states of a two-dimensional (2D) charged black hole which carries both electric ($Q_E$) and magnetic ($Q_M$) charges. The method is first to find the physical field and then to derive the equation of the Schrödinger type. It is found that the presenting potential to an on-coming tachyon (as a spectator) takes a barrier-well type. This provides the bound state solution, which implies an exponentially growing mode with respect to time. The 2D extremal ground states all are classically unstable. We conclude that the 2D extremal charged black holes are not considered as the candidates for the stable endpoint of the Hawking evaporation.

hep-th↗
arXiv1995

An infinite number of potentials surrounding 2d black hole

We found an infinite number of potentials surrounding 2d black hole. According to the transmission ${\cal T}$ and reflection ${\cal R}$ coefficients for scattering of string fields off 2d black hole, we can classify an infinite number of potentials into three : graviton-dilaton, tachyon and the other types. We suggest that the discrete states from all the Virasoro levels be candidates for new potentials (modes).

hep-th↗
arXiv1995

Blushift of a tachyon in the charged 2D black hole

We study the propagation of string fields (metric $G_{μν}$, Mawxell gauge potential $A_μ$, dilaton $Φ$, and tachyon $T$) in a two-dimensional (2D) charged black hole. It is shown that the tachyon is a propagating field both inside and outside the black hole. This becomes infinitely blueshifted at the inner horizon. We confirm that the inner horizon is unstable, whereas the outer horizon is stable.

hep-th↗
arXiv1995

Instability of a two-dimensional extremal black hole

We consider the perturbation of tachyon about the extremal ground state of a two-dimensional (2D) electrically charged black hole. It is found that the presenting potential to on-coming tachyonic wave takes a double-humped barrier well. This allows an exponentially growing mode with respect to time. This extremal ground state is classically unstable. We conclude that the 2D extremal electrically charged black hole cannot be a candidate for the stable endpoint of the Hawking evaporation.

hep-th↗