arXiv subjects

Dae Sung Hwang

Publications and source records attributed to Dae Sung Hwang.

48 records · Page 3Linked to original sources

arXiv1997

Decay Constant Ratios $f_{η_c}/f_{J/ψ}$ and $f_{η_b}/f_Υ$

We calculate the decay constant ratios $f_{η_c}/f_{J/ψ}$ and $f_{η_b}/f_Υ$. In the calculation we take into account the mock meson structures of the mesons, as well as the difference of the wave functions at origin of the vector and pseudoscalar mesons studied by Ahmady and Mendel. We find that the different spin structures of the mesons much affect the ratios. We incorporate our results in the prediction of the branching ratios of $B\to K η_c$.

hep-ph↗

arXiv1997

Solving the Puzzle of ${M_{D^}-M_{D}\over M_{D_s^}-M_{D_s}}$ $\simeq$ ${M_{B^}-M_{B}\over M_{B_s^}-M_{B_s}}$ $\simeq$ $1$

The commonly used Hamiltonian of the chromomagnetic hyperfine splitting is inversely proportional to the product of the masses of two constituent quarks composing the meson. So it is expected to have $(M_{D^*}-M_{D})/(M_{D_s^*}-M_{D_s})$ $\simeq$ $(M_{B^*}-M_{B})/(M_{B_s^*}-M_{B_s})$ $\simeq$ $1.6$, when the constituent quark masses $m_{u,d}=0.33$ GeV and $m_s=0.53$ GeV are used. However, the experimental results show that the above ratios are very close to 1. We solve this puzzle by employing the Hamiltonian recently proposed by Scora and Isgur.

hep-ph↗

arXiv1997

Magnetic Field Dependence of Macroscopic Quantum Tunneling and Coherence of Ferromagnetic Particle

We calculate the quantum tunneling rate of a ferromagnetic particle of $\sim 100 Å$ diameter in a magnetic field of arbitrary angle. We consider the magnetocrystalline anisotropy with the biaxial symmetry and that with the tetragonal symmetry. Using the spin-coherent-state path integral, we obtain approximate analytic formulas of the tunneling rates in the small $ε(=1- H/H_c)$-limit for the magnetic field normal to the easy axis ($θ_H = π/2$), for the field opposite to the initial easy axis ($θ_H = π$), and for the field at an angle between these two orientations ($π/2 << θ_H << π$). In addition, we obtain numerically the tunneling rates for the biaxial symmetry in the full range of the angle $θ_H$ of the magnetic field ($π/2 < θ_H \leq π$), for the values of ε=0.01 and 0.001.

cond-mat.soft↗

arXiv1996

Particle dynamics in a class of 2-dimensional gravity theories

We provide a method to determine the motion of a classical massive particle in a background geometry of 2-dimensional gravity theories, for which the Birkhoff theorem holds. In particular, we get the particle trajectory in a continuous class of 2-dimensional dilaton gravity theories that includes the Callan-Giddings-Harvey-Strominger (CGHS) model, the Jackiw-Teitelboim (JT) model, and the $d$-dimensional $s$-wave Einstein gravity. The explicit trajectory expressions for these theories are given along with the discussions on the results.

gr-qc↗

arXiv1996

Average Kinetic Energy of Heavy Quark in Semileptonic B Decay

Within the ACCMM model the average kinetic energy of heavy quark in a heavy-light meson is calculated as $\langle {\bf p}^2 \rangle = {3 \over 2} {p_{_F}}^2$, solely from the fact that the Gaussian momentum probability distribution has been taken in the ACCMM model. Therefore, the Fermi momentum parameter $p_{_F}$ of the ACCMM model is not a truly free parameter, but is closely related to the average kinetic energy of heavy quark, which is theoretically calculable in principle. In this context, we determine $p_{_F}$ by comparing the theoretical prediction of the ACCMM model with the model independent lepton energy spectrum of $B \rightarrow e νX$ from the recent CLEO analysis, and find that $p_{_F}=0.54~\pm~^{0.16}_{0.15}$ GeV. We also calculate $p_{_F}$ in the relativistic quark model by applying the quantum mechanical variational method, and obtained $p_{_F}=0.5\sim 0.6$ GeV. We show the correspondences between the relativistic quark model and the heavy quark effective theory. We then clarify the importance of the value of $p_{_F}$ in the determination of $|V_{ub}/V_{cb}|$.

hep-ph↗

arXiv1996

Decay Constants of $B$, $B^$ and $D$, $D^$ Mesons in Relativistic Mock Meson Model

We derive formulas for the decay constants $f_P$ and $f_V$ of pseudoscalar and vector mesons in the relativistic mock meson model. Using these formulas, we obtain $f_P$ and $f_V$ of $B_s$, $B_d$, $D_s$, and $D_d$ mesons as functions of the mock meson parameter $β$. Then by using the values of $β$ which are obtained by the variational method in the relativistic quark model, we obtain the decay constants $f_P$ and $f_V$ of the heavy mesons, and the corresponding ratios $f_V/f_P$. The results are compared with other calculations and existing experimental results.

hep-ph↗

arXiv1995

BRST Quantization of Gauge Theory in Noncommutative Geometry: Matrix Derivative Approach

The BRST quantization of a gauge theory in noncommutative geometry is carried out in the ``matrix derivative" approach. BRST/anti-BRST transformation rules are obtained by applying the horizontality condition, in the superconnection formalism. A BRST/anti-BRST invariant quantum action is then constructed, using an adaptation of the method devised by Baulieu and Thierry-Mieg for the Yang-Mills case. The resulting quantum action turns out to be the same as that of a gauge theory in the 't Hooft gauge with spontaneously broken symmetry. Our result shows that only the even part of the supergroup acts as a gauge symmetry, while the odd part effectively provides a global symmetry. We treat the general formalism first, then work out the $SU(2/1)$ and $SU(2/2)$ cases explicitly.

hep-th↗

arXiv1995

Nonabelian Topological Mass Generation in 4 Dimensions

We study the topological mass generation in the 4 dimensional nonabelian gauge theory, which is the extension of the Allen $et$ $al.$'s work in the abelian theory. It is crucial to introduce a one form auxiliary field in constructing the gauge invariant nonabelian action which contains both the one form vector gauge field $A$ and the two form antisymmetric tensor field $B$. As in the abelian case, the topological coupling $m B\wedge F$, where $F$ is the field strength of $A$, makes the transmutation among $A$ and $B$ possible, and consequently we see that the gauge field becomes massive. We find the BRST/anti-BRST transformation rule using the horizontality condition, and construct a BRST/anti-BRST invariant quantum action.

hep-th↗

arXiv1995

Ratios of $B$ and $D$ Meson Decay Constants in Improved Mock Meson Model

We calculate the ratio $f_{B_s}/f_{B_d}$ by following the Oakes' method which is based on chiral symmetry breaking, but we improve his calculation by performing the calculation of the factor $<0|{\bar{b}}γ_5s|B_s>$/$<0|{\bar{b}}γ_5d|B_d>$ in the mock meson model. In this calculation we improved the mock meson model by using the value of the parameter $β$ which is obtained by the variational method in the relativistic quark model. We also calculate $f_{D_s}/f_{D_d}$, and then $(f_{B_s}/f_{B_d})\, /\, (f_{D_s}/f_{D_d})$. In this method we also obtain the ratio $f_{B_s}/f_{D_s}$ and $f_{B_d}/f_{D_d}$ which are important for the knowledge of CP violation and $B$-$\bar{B}$ mixing.

hep-ph↗

arXiv1995

Ratios of $B$ and $D$ Meson Decay Constants in Relativistic Quark Model

We calculate the ratios of $B$ and $D$ meson decay constants by applying the variational method to the relativistic hamiltonian of the heavy meson. We adopt the Gaussian and hydrogen-type trial wave functions, and use six different potentials of the potential model. We obtain reliable results for the ratios, which are similar for different trial wave functions and different potentials. The obtained ratios show the deviation from the nonrelativistic scaling law, and they are in a pretty good agreement with the results of the Lattice calculations.

hep-ph↗

arXiv1995

Decay Constants and Semileptonic Decays of Heavy Mesons in Relativistic Quark Model

We investigate the $B$ and $D$ mesons in the relativistic quark model by applying the variational method with the Gaussian wave function. We calculate the Fermi momentum parameter $p_{_F}$, and obtain $p_{_F} = 0.50 \sim 0.54$ GeV, which is almost independent of the input parameters, $α_s$, $m_b$, $m_c$ and $m_{sp}$. We then calculate the ratio $f_B$/$f_D$, and obtain the result which is larger, by the factor of about 1.3, than $\sqrt{M_D / M_B}$ given by the naive nonrelativistic analogy. This result is in a good agreement with the recent Lattice calculations. We also calculate the ratio $(M_{B^*}-M_{B})$/$(M_{D^*}-M_{D})$. In these calculations the wave function at origin $ψ(0)$ is essential. We also determine $p_{_F}$ by comparing the theoretical prediction of the ACCMM model with the lepton energy spectrum of $B \rightarrow e νX$ from the recent ARGUS analysis, and find that $p_{_F}=0.27~\pm~^{0.22}_{0.27}$ GeV, when we use $m_c=1.5$ GeV. However, this experimentally determined value of $p_{_F}$ is strongly dependent on the value of input parameter $m_c$.

hep-ph↗

arXiv1995

Dependence of $|V_{ub}/V_{cb}|$ on Fermi momentum $p_{_F}$ in ACCMM model

The Gaussian width of Fermi momentum, $p_{_F}$, is the most important parameter of the ACCMM model, and its value is essential in the determination of $|V_{ub}/V_{cb}|$ because the experimental analysis is allowed only at the end-point region of inclusive semileptonic $B$-decay spectrum. We extract the value of $|V_{ub}/V_{cb}|$ as a function of $p_{_F}$. We also calculate the parameter $p_{_F}$ in the relativistic quark model using the variational method, and obtain $p_{_F} = 0.54$ GeV which is much larger than the commonly used value, $\sim 0.3$ GeV, in experimental analyses. When we use $p_{_F} = 0.5$ GeV instead of 0.3 GeV, the value of $|V_{ub}/V_{cb}|$ from ACCMM model is increased by a factor 1.81, and can give a good agreement with Isgur {\it et al.} model.

hep-ph↗