arXiv subjects

Chul H. Lee

Publications and source records attributed to Chul H. Lee.

27 records · Page 2Linked to original sources

arXiv2000

Nonequilibrium Quantum Dynamics of Second Order Phase Transitions

We use the so-called Liouville-von Neumann (LvN) approach to study the nonequilibrium quantum dynamics of time-dependent second order phase transitions. The LvN approach is a canonical method that unifies the functional Schrödinger equation for the quantum evolution of pure states and the LvN equation for the quantum description of mixed states of either equilibrium or nonequilibrium. As nonequilibrium quantum mechanical systems we study a time-dependent harmonic and an anharmonic oscillator and find the exact Fock space and density operator for the harmonic oscillator and the nonperturbative Gaussian Fock space and density operator for the anharmonic oscillator. The density matrix and the coherent, thermal and coherent-thermal states are found in terms of their classical solutions, for which the effective Hamiltonians and equations of motion are derived. The LvN approach is further extended to quantum fields undergoing time-dependent second order phase transitions. We study an exactly solvable model with a finite smooth quench and find the two-point correlation functions. Due to the spinodal instability of long wavelength modes the two-point correlation functions lead to the $t^{1/4}$-scaling relation during the quench and the Cahn-Allen scaling relation $t^{1/2}$ after the completion of quench. Further, after the finite quench the domain formation shows a time-lag behavior at the cubic power of quench period. Finally we study the time-dependent phase transition of a self-interacting scalar field.

hep-ph↗

arXiv2000

Cosmic Microwave Background Radiation anisotropy with primordial magnetic fields

Galactic magnetic fields are observed of order $\sim 10^{-6}G$, but their origin is not definitely known yet. In this paper we consider the primordial magnetic fields generated in the early universe and analyse their effects on the density perturbations and the CMBR anisotropy. We assume that the random magnetic fields have the power law spectrum and satisfy the force-free field condition. The peak heights of the CMBR anisotropy are shown to be shifted upward depending on the magnetic field strengths relative to the no-magnetic field case.

astro-ph↗

arXiv1999

Radiation Damping at a Bubble Wall

The first order phase transition proceeds via nucleation and growth of true vacuum bubbles. When charged particles collide with the bubble they could radiate electromagnetic wave. We show that, due to an energy loss of the particles by the radiation, the damping pressure acting on the bubble wall depends on the velocity of the wall even in a thermal equilibrium state.

hep-ph↗

arXiv1999

Oscillating Inflation with a non-minimally coupled scalar field

The oscillating inflation model recently proposed by Damour and Mukhanov is investigated with a non-minimal coupling. Numerical study confirms an inflationary behavior and the density perturbation is obtained. A successful inflation requires the gravity-dilaton coupling to be small.

hep-th↗

arXiv1999

Relics of cosmological quark-hadron phase transition

We propose that the amplified density fluctuations by the vanishing sound velocity effect during the cosmological quark-hadron phase transition lead to quark-gluon plasma lumps decoupled from the expansion of the universe, which may evolve to quark nuggets (QNs). Assuming power-law spectrum of density fluctuations, we investigate the parameter ranges for the QNs to play the role of baryonic dark matter and give inhomogeneities which could affect big-bang nucleosynthesis within the observational bounds of CMBR anisotropy. The QNs can give the strongest constraint ever found on the spectral index.

astro-ph↗

arXiv1999

Diffuse $γ$-ray background and primordial black hole constraints on the spectral index of density fluctuations

We calculate the flux of $γ$-rays emitted from primordial black holes (PBHs) which are formed by a ``blue'' power-law spectrum of density fluctuations in the early universe. Gamma-ray emission from such PBHs may contribute significantly to the observed extragalactic diffuse $γ$-ray background (DGB). Using the observed DGB flux from the imaging Compton Telescope (COMPTEL) and the Energetic Gamma Ray Experiment Telescope (EGRET) as the upper limit of $γ$-ray flux from PBHs, we derive the upper limit on the spectral index $n$ of the density fluctuations. The range of initial PBH masses which can contribute to the DGB is $2\times 10^{13}\g - 5\times 10^{14}\g$, corresponding to a cosmic reheating temperature of $7\times 10^{7}\gev - 4\times 10^{8} \gev$. In this range, we find the upper limit to be $n \lsim 1.23-1.25$. This limit is stronger than those derived from the energy density in PBHs or PBH relics and matches the value of $n$ required to explain the cosmic microwave background anisotropy.

astro-ph↗

arXiv1998

Open Inflation With Scalar-tensor Gravity

The open inflation model recently proposed by Hawking and Turok is investigated in scalar-tensor gravity context. If the dilaton-like field has no potential, the instanton of our model is singular but has a finite action. The Gibbons-Hawking surface term vanishes and hence, can not be used to make $Ω_0$ nonzero. To obtain a successful open inflation one should introduce other matter fields or a potential for the dilaton-like fields.

hep-th↗

arXiv1998

Axion Emissivity from the Conversion of a Neutron Star into a Strange Star

The conversion of neutron matter into strange matter in a neutron star occurs through the non-leptonic weak-interaction process. We study the energy loss of the neutron star by the emission of axions in that process. Owing to that process, the neutron star will liberate the energy which can in no way be negligible as an axion burst.

astro-ph↗

arXiv1994

Static Solution of the General Relativistic Nonlinear $σ$-Model Equation

The nonlinear $σ$-model is considered to be useful in describing hadrons (Skyrmions) in low energy hadron physics and the approximate behavior of the global texture. Here we investigate the properties of the static solution of the nonlinear $σ$-model equation coupled with gravity. As in the case where gravity is ignored, there is still no scale parameter that determines the size of the static solution and the winding number of the solution is $1/2$. The geometry of the spatial hyperspace in the asymptotic region of large $r$ is explicitly shown to be that of a flat space with some missing solid angle.

hep-th↗