arXiv subjects

H. T. Cho

Publications and source records attributed to H. T. Cho.

32 records · Page 2Linked to original sources

arXiv2007

Fermion excitations of a tense brane black hole

By finding the spinor eigenvalues for a single deficit angle (d-2)-sphere, we derive the radial potential for fermions on a d-dimensional black hole background that is embedded on a codimension two brane with conical singularity, where the deficit angle is related to the brane tension. From this we obtain the quasi-normal mode spectrum for bulk fermions on such a background. As a byproduct of our method, this also gives a rigorous proof for integer spin fields on the deficit 2-sphere.

hep-th↗

arXiv2007

Bulk dominated fermion emission on a Schwarzschild background

Using the WKBJ approximation, and the Unruh method, we obtain semi-analytic expressions for the absorption probability (in all energy regimes) for Dirac fermions on a higher dimensional Schwarzschild background. We present an analytic expression relating the absorption probability to the absorption cross-section, and then use these results to plot the emission rates to third order in the WKBJ approximation. The set-up we use is sufficiently general such that it could also easily be applied to any spherically symmetric background in $d$-dimensions. Our results lead to the interesting conclusion that for $d>5$ bulk fermion emission dominates brane localised emission. This is an example contrary to the conjecture that black holes radiate mainly on the brane.

hep-th↗

arXiv2007

Split fermion quasi-normal modes

In this paper we use the conformal properties of the spinor field to show how we can obtain the fermion quasi-normal modes for a higher dimensional Schwarzschild black hole. These modes are of interest in so called split fermion models, where quarks and leptons are required to exist on different branes in order to keep the proton stable. As has been previously shown, for brane localized fields, the larger the number of dimensions the faster the black hole damping rate. Moreover, we also present the analytic forms of the quasi-normal frequencies in both the large angular momentum and the large mode number limits.

hep-th↗

arXiv2005

Asymptotic Quasinormal Frequencies of Different Spin Fields in Spherically Symmetric Black Holes

We consider the asymptotic quasinormal frequencies of various spin fields in Schwarzschild and Reissner-Nordström black holes. In the Schwarzschild case, the real part of the asymptotic frequency is ln3 for the spin 0 and the spin 2 fields, while for the spin 1/2, the spin 1, and the spin 3/2 fields it is zero. For the non-extreme charged black holes, the spin 3/2 Rarita-Schwinger field has the same asymptotic frequency as that of the integral spin fields. However, the asymptotic frequency of the Dirac field is different, and its real part is zero. For the extremal case, which is relevant to the supersymmetric consideration, all the spin fields have the same asymptotic frequency, the real part of which is zero. For the imaginary parts of the asymptotic frequencies, it is interesting to see that it has a universal spacing of $1/4M$ for all the spin fields in the single-horizon cases of the Schwarzschild and the extreme Reissner-Nordström black holes. The implications of these results to the universality of the asymptotic quasinormal frequencies are discussed.

gr-qc↗

arXiv2005

Vacuum Structure of Two-Dimensional $ϕ^4$ Theory on the Orbifold $S^{1}/Z_{2}$

We consider the vacuum structure of two-dimensional $ϕ^4$ theory on $S^{1}/Z_{2}$ both in the bosonic and the supersymmetric cases. When the size of the orbifold is varied, a phase transition occurs at $L_{c}=2π/m$, where $m$ is the mass of $ϕ$. For $L L_{c}$, there are two degenerate vacua. We also obtain the 1-loop quantum corrections around these vacuum solutions, exactly in the case of $L L_{c}$. As for the quantum corrections, the fermionic contributions cancel the singular part of the bosonic contributions at L=0. Then the total quantum correction has a minimum at the critical length $L_{c}$.

hep-th↗

arXiv2004

WKB Analysis of the Scattering of Massive Dirac Fields in Schwarzschild Black Hole Spacetimes

We analysis the radial equations for massive Dirac fields in Schwarzschild black hole spacetimes. Different approximation formulae under the WKB scheme are developed for the transmission probability ${\cal T}$ of the radial wavefunction with $E^{2}\gg V_{m}$, $E^{2}\approx V_{m}$, and $E^{2}\ll V_{m}$, where $E$ is the energy of the field and $V_{m}$ is the maximum value of the effective potential. Explicit results of ${\cal T}$ in these approximations are given for various values of $E$, the mass $m$, and the angular momentum parameter $κ$ of the fields. We also discuss the dependence of ${\cal T}$ on these parameters.

gr-qc↗

arXiv2004

The Onset of Chaotic Motion of a Spinning Particle around the Schwarzchild Black Hole

In the Schwarzchild black hole spacetime, we show that chaotic motion can be triggered by the spin of a particle. Taking the spin of the particle as a perturbation and using the Melnikov method, we find that the perturbed stable and unstable orbits are entangled with each other and that illustrates the onset of chaotic behavior in the motion of the particle.

gr-qc↗

arXiv2003

The Onset of Chaos in Spinning Particle Models

The onset of chaos in one-dimensional spinning particle models derived from pseudoclassical mechanical hamiltonians with a bosonic Duffing potential is examined. Using the Melnikov method, we indicate the presence of homoclinic entanglements in models with general potentials for the spins, and thus show that chaotic motions occur in these models.

nlin.CD↗

arXiv2000

Vilkovisky-DeWitt Effective Action for Einstein Gravity on Kaluza-Klein Spacetimes $M^4\times S^N$

We evaluate the divergent part of the Vilkovisky-DeWitt effective action for Einstein gravity on even-dimensional Kaluza-Klein spacetimes of the form $M^{4}\times S^{N}$. Explicit results are given for $N$=2, 4, and 6. Trace anomalies for gravitons are also given for these cases. Stable Kaluza-Klein configurations are sought, unsuccessfully, assuming the divergent part of the effective action dominates the dynamics.

hep-th↗

arXiv1995

Zeta-Functions for Non-Minimal Operators

We evaluate zeta-functions $ζ(s)$ at $s=0$ for invariant non-minimal 2nd-order vector and tensor operators defined on maximally symmetric even dimensional spaces. We decompose the operators into their irreducible parts and obtain their corresponding eigenvalues. Using these eigenvalues, we are able to explicitly calculate $ζ(0)$ for the cases of Euclidean spaces and $N$-spheres. In the $N$-sphere case, we make use of the Euler-Maclaurin formula to develop asymptotic expansions for the required sums. The resulting $ζ(0)$ values for dimensions 2 to 10 are given in the Appendix.

hep-th↗

arXiv1995

Gauge Independent Trace Anomaly for Gravitons

We show that the trace anomaly for gravitons calculated using the usual effective action formalism depends on the choice of gauge when the background spacetime is not a solution of the classical equation of motion, that is, when off-shell. We then use the gauge independent Vilkovisky-DeWitt effective action to restore gauge independence to the off-shell case. Additionally we explicitly evaluate trace anomalies for some N-sphere background spacetimes.

hep-th↗

arXiv1995

Gravitational Waves in Bianchi Type-I Universes I: The Classical Theory

The propagation of classical gravitational waves in Bianchi Type-I universes is studied. We find that gravitational waves in Bianchi Type-I universes are not equivalent to two minimally coupled massless scalar fields as it is for the Robertson-Walker universe. Due to its tensorial nature, the gravitational wave is much more sensitive to the anisotropy of the spacetime than the scalar field is and it gains an effective mass term. Moreover, we find a coupling between the two polarization states of the gravitational wave which is also not present in the Robertson-Walker universe.

gr-qc↗

arXiv1994

A Measure on a Subspace of FRW Solutions and ``The Flatness Problem" of Standard Cosmology

We use the metric on the space of gravity fields given by DeWitt to construct a unique kinematic measure on the space of FRW simple fluids and show that when the mass parameter $Ω$ is used as a coordinate this measure is singular at $Ω= 1$. This singularity, combined with the time evolution of $Ω$, distorts distributions of $Ω$ values to be concentrated in the neighborhood of 1 at early times. It is a distorted distribution of $Ω$ values that sometimes misleads the casual observer to conclude that $Ω$ must be exactly equal to 1.

hep-th↗

arXiv1993

A Hydrodynamical Analysis of the Burning of a Neutron Star

The burning of a neutron star by strange matter is analyzed using relativistic combustion theory with a planar geometry. It is shown that such burning is probably neither slow combustion nor simple detonation. Fast combustion without detonation is possible under certain circumstances, but would involve very efficient heat transfer mechanisms. It is found, however, that the burning is most likely absolutely unstable with no well defined burn front.

astro-ph↗