804 citations · 3.3k across the 158 of their papers we have counts for
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Nonequilibrium Self-Interacting Quantum Fields in Cosmology: The Liouville-Neumann Approach
Sang Pyo Kim
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-…
Factorization and q-Deformed Algebra of Quantum Anharmonic Oscillator
Dongsu Bak, Sang Pyo Kim, Sung Ku Kim +2
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, th…
Perturbation Method beyond the Variational Gaussian Approximation: The Liouville-Neumann Approach
Dongsu Bak, Sang Pyo Kim, Sung Ku Kim +2
We have developed a variational perturbation theory based on the Liouville-Neumann equation, which enables one to systematically compute the perturbative correction terms to the va…
Loss of Quantum Coherence and Positivity of Energy Density in Semiclassical Quantum Gravity
Sang Pyo Kim, Kwang-Sup Soh
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…
One-Parameter Squeezed Gaussian States of Time-Dependent Harmonic Oscillator and Selection Rule for Vacuum States
Jung Kon Kim, Sang Pyo Kim
By using the invariant method we find one-parameter squeezed Gaussian states for both time-independent and time-dependent oscillators. The squeezing parameter is expressed in terms…
Quantum Inflaton Dynamics
Dongsu Bak, Sang Pyo Kim, Sung Ku Kim +2
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…
Fractal Diffraction Grating
Dongsu Bak, Sang Pyo Kim, Sung Ku Kim +2
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…