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Sang Pyo Kim

Publications and source records attributed to Sang Pyo Kim.

At least 163 records · Page 9Linked to original sources
arXiv1998

Nonequilibrium Self-Interacting Quantum Fields in Cosmology: The Liouville-Neumann Approach

We present the so-called Liouville-Neumann (LN) approach to nonequilibrium quantum fields. The LN approach unifies the functional Schrödinger equation and the LN equation for time-independent or time-dependent quantum systems and for equilibrium or nonequilibrium quantum systems. The LN approach is nonperturbative in that at the lowest order of coupling constant it gives the same results as those of the Gaussian effective potential at the zero and finite temperature in a Minkowski spacetime. We study a self-interacting quantum field in an expanding Friedmann-Robertson-Walker Universe. By studying a toy model of anharmonic oscillator and finding the underlying algebraic structure we propose a scheme to go beyond the Gaussian approximation.

hep-th↗
arXiv1998

Loss of Quantum Coherence and Positivity of Energy Density in Semiclassical Quantum Gravity

In the semiclassical quantum gravity derived from the Wheeler-DeWitt equation, the energy density of a matter field loses quantum coherence due to the induced gauge potential from the parametric interaction with gravity in a non-static spacetime. It is further shown that the energy density takes only positive values and makes superposition principle hold true. By studying a minimal massive scalar field in a FRW spacetime background, we illustrate the positivity of energy density and obtain the classical Hamiltonian of a complex field from the energy density in coherent states.

gr-qc↗
arXiv1998

Factorization and q-Deformed Algebra of Quantum Anharmonic Oscillator

We have studied the underlying algebraic structure of the anharmonic oscillator by using the variational perturbation theory. To the first order of the variational perturbation, the Hamiltonian is found to be factorized into a supersymmetric form in terms of the annihilation and creation operators, which satisfy a q-deformed algebra. This algebraic structure is used to construct all the eigenstates of the Hamiltonian.

hep-th↗
arXiv1998

Quantum Inflaton Dynamics

We show that the quantum dynamics of a real scalar field for a large class of potentials in the symmetric Gaussian state, where the nonperturbative quantum contributions are taken into account, can be described equivalently by a two-dimensional nonlinear dynamical system with a definite angular momentum (U(1) charge of a complex theory). It is found that the Gaussian state with a nearly minimal uncertainty and a large quantum fluctuation, as an initial condition, naturally explains the most of the essential features of the early stage of the inflationary Universe.

gr-qc↗
arXiv1998

Fractal Diffraction Grating

We consider an optical diffraction grating in which the spatial distribution of open slits forms a fractal set. The Fraunhofer diffraction patterns through the fractal grating are obtained analytically for the simplest triad Cantor type and its generalized version. The resulting interference patterns exhibit characteristics of the original fractals and their scaling properties.

physics.optics↗
arXiv1997

Electromagnetic fields in a 3D cavity and in a waveguide with oscillating walls

We consider classical and quantum electromagnetic fields in a three-dimensional (3D) cavity and in a waveguide with oscillating boundaries of the frequency $Ω$. The photons created by the parametric resonance are distributed in the wave number space around $Ω/2 $ along the axis of the oscillation. When classical waves propagate along the waveguide in the one direction, we observe the amplification of the original waves and another wave generation in the opposite direction by the oscillation of side walls. This can be understood as the classical counterpart of the photon production. In the case of two opposite walls oscillating with the same frequency but with a phase difference, the interferences are shown to occur due to the phase difference in the photon numbers and in the intensity of the generated waves.

quant-ph↗
arXiv1997

Boundary degrees of freedom in fractional quantum Hall effect: Excitations on common boundary of two samples

Using the Carlip's method we have derived the boundary action for the fermion Chern-Simons theory of quantum Hall effects on a planar region with a boundary. We have computed both the bulk and edge responses of currents to the external electric field. From this we obtain the well-known anomaly relation and the boundary Hall current without introducing any ad hoc assumptions such as the chirality condition. In addition, the edge current on the common boundary of two samples is found to be proportional to the difference between Chern-Simons coupling strengths.

cond-mat↗
arXiv1997

Liouville-Neumann Approach to the Nonperturbative Quantum Field Theory

We present a nonperturbative field theoretic method based on the Liouville-Neumann (LN) equation. The LN approach provides a unified formulation of nonperturbative quantum fields and also nonequilibrium quantum fields, which makes use of mean-field type equations and whose results at the lowest level are identically the same as those of the Gaussian effective potential approach and the mean-field approach. The great advantageous point of this formulation is its readiness of applicability to time-dependent quantum systems and to finite temperature field theory, and its possibility to go beyond the Gaussian approximation.

hep-th↗
arXiv1997

Coherence and Emergence of Classical Spacetime

Using the coherent-state representation we show that the classical Einstein equation for the FRW cosmological model with a general minimal scalar field can be derived from the semiclassical quantum Einstein equation.

gr-qc↗
arXiv1997

Problem of Unitarity and Quantum Corrections in Semiclassical Quantum Gravity

Using both the Born-Oppenheimer idea and the de Broglie-Bohm interpretation of wavefunction we represent in a different way the semiclassical quantum gravity from the Wheeler-DeWitt equation in an oscillating regime which can preserve completely the unitary quantum evolution of a matter field at the expense of a nonlinear gravitational field equation, but has the same asymptotic limit as the others. We apply the de Broglie-Bohm interpretation to the nonlinear gravitational field equation to develop a perturbation method to find the quantum corrections of a matter field to the gravity. The semiclassical Einstein equation with the quantum corrections is found for a minimal quantum FRW cosmological model.

gr-qc↗
arXiv1997

Quantum Potential and Cosmological Singularities

We apply the de Broglie-Bohm interpretation to the Wheeler-DeWitt equation for the quantum FRW cosmological model with a minimal massless scalar field. We find that the quantum FRW cosmological model has quantum potential dominated solutions that avoid the initial and the final cosmological singularities. It is suggested that the quantum potential and the back-reaction of geometry and matter fields may change the property of the cosmological singularities of the Universe.

gr-qc↗
arXiv1996

Renormalized Thermodynamic Entropy of Black Holes in Higher Dimensions

We study the ultraviolet divergent structures of the matter (scalar) field in a higher D-dimensional Reissner-Nordström black hole and compute the matter field contribution to the Bekenstein-Hawking entropy by using the Pauli-Villars regularization method. We find that the matter field contribution to the black hole entropy does not, in general, yield the correct renormalization of the gravitational coupling constants. In particular we show that the matter field contribution in odd dimensions does not give the term proportional to the area of the black hole event horizon.

gr-qc↗
arXiv1996

Quantum Fluctuations and Particle Production of Coherently Oscillating Inflaton

We study a massive inflaton minimally coupled to the FRW Universe using the semiclassical gravity derived from canonical quantum gravity. It is found that the semiclassical quantum gravity leads to the power-law expansion $t^{2/3}$ in an oscillatory phase of the inflaton. The particle production of the inflaton in the expanding Universe restricts the duration of stable coherent oscillations and parametric resonance. The semiclassical gravity shows a significant difference that the Hubble constant does not oscillate in contrast with the oscillatory behavior in classical gravity.

hep-ph↗
arXiv1996

Coherent State Representation of Semiclassical Quantum Gravity

We elaborate the recently introduced asymptotically exact semiclassical quantum gravity derived from the Wheeler-DeWitt equation by finding a particular coherent state representation of a quantum scalar field in which the back-reaction of the scalar field Hamiltonian exactly gives rise to the classical one. In this coherent state representation classical spacetime emerges naturally from semiclassical quantum gravity.

gr-qc↗
arXiv1996

Classical Spacetime from Quantum Gravity

We show how classical spacetime emerges from quantum gravity through the study of a quantum FRW cosmological model coupled to a free massive scalar field using a new asymptotic expansion method of the Wheeler-DeWitt equation. It is shown that the coherent states of the nonadiabatic basis of a particular generalized invariant give rise to the quantum back reaction of matter field proportional to classical energy and the Einstein-Hamilton-Jacobi with matter becomes equivalent to the classical Einstein equation.

gr-qc↗
arXiv1996

The Effect of Brick Walls on the Black Hole Radiation

In order to understand the physical effect of the brick wall boundary condition, we compute the distribution of the zero-point energy of the massless scalar fields minimally coupled to the Schwarzschild and Reissner-Nordström black hole backgrounds. We find that the black hole radiation spectrum depends on the positions of the brick wall and the observer, and reveals the interference effect due to the reflected field by the brick wall.

gr-qc↗
arXiv1996

Remarks on Renormalization of Black Hole Entropy

We elaborate the renormalization process of entropy of a nonextremal and an extremal Reissner-Nordström black hole by using the Pauli-Villars regularization method, in which the regulator fields obey either the Bose-Einstein or Fermi-Dirac distribution depending on their spin-statistics. The black hole entropy involves only two renormalization constants. We also discuss the entropy and temperature of the extremal black hole.

gr-qc↗