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H. W. Lee

Publications and source records attributed to H. W. Lee.

52 records · Page 3Linked to original sources
arXiv1998

Greybody Factors in the $AdS_3$/CFT Correspondence

We propose a new method to calculate the greybody factor in the $AdS_3$. This is based on both the non-normalizable modes of a test field($Φ_i$) and $AdS_3$/CFT correspondence. Such non-normalizable modes serve as classical, non-fluctuating background and encode the choice of operator insertion(${\cal O}^i$) in the boundary. Actually specifying the boundary condition at infinity of $AdS_3$ corresponds to turning on these non-normalizable modes. Hence we can calculate the greybody factor of test fields without the Dirichlet(or Neumann) boundary condition. The result is consistent with those of the boundary CFT and effective string calculations.

hep-th↗
arXiv1998

Potential analysis and absorption cross section in the D1-D5 brane system

We analyze the potentials which arise from the D1--D5 brane (5D black hole). In the sufficiently low energy ($ω\ll 1$), we can derive the Schrodinger-type equation with potential $V_N$ from the linearized equations. In this case one can understand the difference between absorption cross section for a free and two fixed scalars intuitively in terms of their potentials. In the low temperature limit ($ω\gg T_H$), one expects the logarithmic correction to the cross section of a free scalar. However, we cannot obtain the Schrodinger equation with potential for this case. Finally we comment on the stability of 5D black hole.

hep-th↗
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

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↗
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↗
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

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

Hawking temperature from scattering off the charged 2D black hole

The charged 2D black hole is visualized as presenting an potential barrier $V^{OUT}(r^*)$ to on-coming tachyon wave. Since this takes the complicated form, an approximate form $V^{APP}(r^*)$ is used for scattering analysis. We calculate the reflection and transmission coefficients for scattering of tachyon off the charged 2D black hole. The Hawking temperature is also derived from the reflection coefficient by Bogoliubov transformation. In the limit of $Q \to 0$, we recover the Hawking temperature of the 2D dilaton black hole.

hep-th↗
arXiv1993

Orthogonality catastrophe in a mesoscopic conductor due to a time-dependent flux

We consider quantum fluctuations of current in a metallic loop induced by varying magnetic flux. The dependence of the fluctuations on the flux change $Φ$ contains a logarithmically divergent term periodic in $Φ$ with the period $Φ_0=hc/e$. The fluctuation is smallest near $Φ=nΦ_0$. The divergence is explained by a comparison with the orthogonality catastrophe problem. The $Φ_0-$periodicity is related with the discreteness of "attempts" in the binomial statistics picture of charge fluctuations.

cond-mat↗