arXiv subjects

Hyun Kyu Lee

Publications and source records attributed to Hyun Kyu Lee.

82 records · Page 5Linked to original sources

arXiv1999

Can precessing jets explain the light curves of Gamma-ray Bursts?

We present a phenomenological model to explain the light curves of gamma-ray bursts. In the model a black hole is orbited by a precessing accretion disc which is fed by a neutron star. Gamma-rays are produced in a highly collimated beam via the Blandford-Znajek mechanism. The gamma-ray beam sweeps through space due to the precession of the slaved accretion disc. The light curve expected from such a precessing luminosity cone can explain the complex temporal behavior of observed bright gamma-ray bursts.

astro-ph↗

arXiv1997

Primordial Abundances of ^6Li, ^9Be, and ^11B with Neutrino Degeneracy and Gravitational Constant Variation

Recent measurements of deuterium abundances from QSO absorption spectra show two conflicting numbers, which differ by an order of magnitude. Allowing the neutrino degeneracy together with gravitational constant variation at the epoch of primordial nucleosynthesis, the implication of these observations on the ^6Li, ^9Be and ^11B abundances will be discussed. Within the permitted ranges consistent with D, ^4He and ^7Li, we observe the strong ηdependence of ^11B as in SBBN but no significant dependence of ^6Li and ^9Be on the baryon number density is observed. The predictions of ^6Li and ^9Be for low and high deuterium differ by an order of magnitude and predictions for ^11B differ by several orders of magnitude at most and vary with η.

hep-ph↗

arXiv1997

Baryon Density and the Dilated Chiral Quark Model

We calculate perturbatively the effect of density on hadronic properties using the chiral quark model implemented by the QCD trace anomaly to see the possibility of constructing Lorentz invariant Lagrangian at finite density. We calculate the density dependent masses of the constituent quark, the scalar field and the pion in one-loop order using the technique of thermo field dynamics. In the chiral limit, the pion remains massless at finite density. It is found that the tadpole type corrections lead to the decreasing masses with increasing baryon density, while the radiative corrections induce Lorentz-symmetry-breaking terms. We found in the large $N_c$ limit with large scalar mass that the tadpoles dominate and the mean-field approximation is reliable, giving rise a Lorentz-invariant Lagrangian with masses decreasing as the baryon density increases.

nucl-th↗

arXiv1997

Electron-Neutrino Degeneracy and Primordial Nucleosynthesis

We discuss the possible ranges of electron neutrino degeneracy which is consistent with the inferred primordial abundances of the light elements. It is found that the electron neutrino degeneracy, $|ξ_e|$, up to order of $10^{-1}$ is consistent with the present data.

astro-ph↗

arXiv1995

Finite-Temperature Corrections in the Dilated Chiral Quark Model

We calculate the finite-temperature corrections in the dilated chiral quark model using the effective potential formalism. Assuming that the dilaton limit is applicable at some short length scale, we interpret the results to represent the behavior of hadrons in dense {\it and} hot matter. We obtain the scaling law, $\frac{f_π(T)}{f_π} = \frac{m_Q (T)}{m_Q} \simeq \frac{m_σ(T)}{m_σ}$ while we argue, using PCAC, that pion mass does not scale within the temperature range involved in our Lagrangian. It is found that the hadron masses and the pion decay constant drop faster with temperature in the dilated chiral quark model than in the conventional linear sigma model that does not take into account the QCD scale anomaly. We attribute the difference in scaling in heat bath to the effect of baryonic medium on thermal properties of the hadrons. Our finding would imply that the AGS experiments (dense {\it and} hot matter) and the RHIC experiments (hot and dilute matter) will ``see" different hadron properties in the hadronization phase.

hep-ph↗

arXiv1994

Renormalization-Group Flow Analysis of Meson Condensations in Dense Matter

We present a renormalization-group (RG) flow argument for s-wave kaon condensation in dense nuclear-star matter predicted in chiral perturbation theory. It is shown that it is the {\it relevant} mass term together with {\it any} attractive interaction for the kaon in medium that triggers the instability. We show that a saddle point of multi-dimensional RG flow can imply a phase transition. Pion condensation is also analyzed along the same line of reasoning.

hep-ph↗

arXiv1994

Characteristics of QCD Phase Transitions in an Extended Skyrme Model on $S^3$

We study the characteristics of the QCD phase transitions in dense hadronic matter using the Skyrme model constructed on S^3. We find numerically the localized solutions on $S^3$ using the extended Skyrme model which implements correctly the scale symmetry of QCD. The transition from the localized phase to the delocalized phase is found to be of first order at the critical radius of the hypersphere, $L_c$. The chiral restoration and the gluon decondensation also take place at the same critical size.

hep-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↗

arXiv1993

Vanishing of Nonabelian Berry Phases in Heavy Solitonic Baryons

In this article, we show -- using a reasoning applicable to both the excitation spectrum in the chiral bag model and the hyperfine structure of diatomic molecules -- that the generic form of a non- abelian Berry potential appears in heavy-quark effective theory (HQET) and that the Berry potential vanishes for the soliton- heavy meson bound state in the heavy-quark limit. The vanishing of the Berry potential in HQET is shown to be related to the restoration of heavy-quark symmetry in infinite heavy-quark-mass limit in close analogy to diatomic molecules at infinite internuclear separation.

hep-ph↗

arXiv1992

Rotation Symmetry and Nonabelian Berry Potential

We study the role of rotational symmetry in the systems where nonabelian Berry potentials emerge as a result of integrating out fast degrees of freedom. The conserved angular momentum is constructed in the presence of a non-abelian Berry potential, which is formulated using Grassmann variables. The modifications on conventional angular momentum are discussed in close analogy with monopole systems. The diatomic molecular system discussed by Zygelman is found to have a similar structure to that of a non-abelian $SU(2)$ charge coupled to a 't Hooft - Polyakov monopole. The abelian limit of the Berry potential in diatomic systems is shown to be the same as $U(1)$ monopole and in a large separation limit, we observe the decoupling associated with a vanishing field tensor.

hep-th↗