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Ho-Meoyng Choi

Publications and source records attributed to Ho-Meoyng Choi.

At least 73 records · Page 4Linked to original sources
arXiv2003

Transition Form Factors between Pseudoscalar and Vector Mesons in Light-Front Dynamics

We study the transition form factors between pseudoscalar and vector mesons using a covariant fermion field theory model in $(3+1)$ dimensions. Performing the light-front calculation in the $q^+ =0$ frame in parallel with the manifestly covariant calculation, we note that the suspected nonvanishing zero-mode contribution to the light-front current $J^+$ does not exist in our analysis of transition form factors. We also perform the light-front calculation in a purely longitudinal $q^+ > 0$ frame and confirm that the form factors obtained directly from the timelike region are identical to the ones obtained by the analytic continuation from the spacelike region. Our results for the $B \to D^* l ν_l$ decay process satisfy the constraints on the heavy-to-heavy semileptonic decays imposed by the flavor independence in the heavy quark limit.

hep-ph↗
arXiv2002

Continuity of generalized parton distributions for the pion virtual Compton scattering

We discuss a consistent treatment of the light-front gauge-boson and meson wave functions in the analyses of the generalized parton distributions(GPDs) and the scattering amplitudes in deeply virtual Compton scattering(DVCS) for the pion. The continuity of the GPDs at the crossover, where the longitudinal momentum fraction of the probed quark is same with the skewedness parameter, and the finiteness of the DVCS amplitude are ensured if the same light-front radial wave function as that of the meson bound state wave function is used for the gauge boson bound state arising from the pair-creation(or nonvalence) diagram. The frame-independence of our model calculation is also guaranteed by the constraint from the sum rule between the GPDs and the form factors.

hep-ph↗
arXiv2002

The Vector Meson Form Factor Analysis in Light-Front Dynamics

We study the form factors of vector mesons using a covariant fermion field theory model in $(3+1)$ dimensions. Performing a light-front calculation in the $q^+ =0$ frame in parallel with a manifestly covariant calculation, we note the existence of a nonvanishing zero-mode contribution to the light-front current $J^+$ and find a way of avoiding the zero-mode in the form factor calculations. Upon choosing the light-front gauge ($\ep^+_{h=\pm}=0$) with circular polarization and with spin projection $h=\uparrow\downarrow=\pm$, only the helicity zero to zero matrix element of the plus current receives zero-mode contributions. Therefore, one can obtain the exact light-front solution of the form factors using only the valence contribution if only the helicity components, $(h'h)=(++),(+-)$, and $(+0)$, are used. We also compare our results obtained from the light-front gauge in the light-front helicity basis (i.e. $h=\pm,0$) with those obtained from the non-LF gauge in the instant form linear polarization basis (i.e. $h=x,y,z$) where the zero-mode contributions to the form factors are unavoidable.

hep-ph↗
arXiv2002

Light-front quark model analysis of rare $B\to K\ell^+\ell^-$ decays

Using the light-front quark model, we calculate the transition form factors, decay rates, and longitudinal lepton polarization asymmetries for the exclusive rare $B\to K\ell^+\ell^-(\ell=e,μ,τ$) decays within the standard model. Evaluating the timelike form factors, we use the analytic continuation method in $q^+=0$ frame to obtain the form factors $F_+$ and $F_T$, which are free from zero-mode. The form factor $F_-$ which is not free from zero-mode in $q^+ = 0$ frame and contaminated by the higher(or nonvalence) Fock states in $q^+ \neq 0$ frame is obtained from an effective treatment for handling the nonvalence contribution based on the Bethe-Salpeter formalism. The covariance(i.e. frame-independence) of our model calculation is discussed. We obtain the branching ratios for ${\rm BR}(B\to K\ell^+\ell^-)$ as $4.96\times10^{-7}|V_{ts}/V_{cb}|^2$ for $\ell=e,μ$ and $1.27\times 10^{-7}|V_{ts}/V_{cb}|^2$ for $\ell=τ$.

hep-ph↗
arXiv2001

Light-Front QCD Hamiltonian Dynamics and Constituent Quark Picture in Exclusive Processes

After reviewing a connection between quantum chromodynamics and contituent quark model pictures in the light-front quantization with some comparison and contrast to the ordinary equal-time bridge a la Bogoliubov-Valatin transformation, we discuss some newer development of the light-front quark model phenomenology in exclusive processes including the embedded state. The skewed parton distribution appears to be a good testing ground for our new effective treatment of the light-front nonvalence contributions in timelike exclusive processes.

hep-ph↗
arXiv2001

New Progress in Time-Like Exclusive Processes

We discuss a necessary nonvalence contribution in timelike exclusive processes. Following a Schwinger-Dyson type of approach, we relate the nonvalence contribution to an ordinary light-front wave function that has been extensively tested in the spacelike exclusive processes. A complicate multi-body energy denominator is exactly cancelled in summing the light-front time-ordered amplitudes. Applying our method to $K_{\ell3}$ and $D^0\to K^- \ell^+ ν_l$ where a rather substantial nonvalence contribution is expected, we find not only an improvement in comparing with the experimental data but also a covariance(i.e. frame-indepndence) of existing light-front constituent quark model.

hep-ph↗
arXiv2001

Skewed quark distribution of the pion in the light-front quark model

We calculate the skewed quark distributions(SQDs) of the pion in the light-front quark model, and discuss the calculation of the nonvalence contribution to the SQDs in this model. The frame-independence of our model calculation is guaranteed by the constraint of the sum rule between the SQDs and form factor. Our numerical results show large nonvalence contributions to the SQDs at small momentum transfer region as the skewedness increases.

hep-ph↗
arXiv2001

Exploring timelike exclusive processes in the light-front approach

We discuss a necessary nonvalence contribution in timelike exclusive processes. Utilizing a Schwinger-Dyson type of approach, we relate the nonvalence contribution to an ordinary light-front wave function that has been extensively tested in the spacelike exclusive processes. An application to $K_{\ell3}$ decays provides encouraging results.

hep-ph↗
arXiv2001

New effective treatment of the light-front nonvalence contribution in timelike exclusive processes

We discuss a necessary nonvalence contribution in timelike exclusive processes. Following a Schwinger-Dyson type of approach, we relate the nonvalence contribution to an ordinary light-front wave function that has been extensively tested in the spacelike exclusive processes. A complicate four-body energy denominator is exactly cancelled in summing the light-front time-ordered amplitudes. Applying our method to $K_{\ell3}$ and $D^0\to K^- \ell^+ ν_l$ where a rather substantial nonvalence contribution is expected, we find not only an improvement in comparing with the experimental data but also a covariance(i.e. frame-independence) of existing light-front constituent quark model.

hep-ph↗
arXiv2001

Pion Form Factor and Quark Mass Evolution in a Light-Front Bethe-Salpeter Model

We discuss the soft contribution to the elastic pion form factor with the mass evolution from current to constituent quark being taken into account using a light-front Bethe-Salpeter (LFBS) model, which is a light-front quark model (LFQM) with a running mass. It is shown that partial conservation of the axial-vector current (PCAC) is satisfied with a running quark mass. We examine the sensitivity of the pion form factor using two different functional forms of the quark propagator. The Ball-Chiu ansatz is used to maintain local gauge invariance of the quark-photon vertex. The extension of our model to the hard contribution is also discussed.

hep-ph↗
arXiv2000

Regularizing the Divergent Structure of the Light-Front Currents

The divergences appearing in the 3+1 dimensional fermion-loop calculations are often regulated by smearing the vertices in a covariant manner. Performing a parallel light-front calculation, we corroborate the similarity between the vertex-smearing-technique and the Pauli-Villars regularization. In the light-front calculation of the electromagnetic meson current, we find that the persistent end-point singularity that appears in the case of point vertices is removed even if the smeared-vertex is taken to the limit of the point-vertex. Recapitulating the current conservation, we substantiate the finiteness of both valence and non-valence contributions in all components of the current with the regularized bound-state vertex. However, we stress that each contribution, valence or non-valence, depends on the reference-frame even though the sum is always frame-independent. The numerical taxonomy of each contribution including the instantaneous contribution and the zero-mode contribution is presented in the $π$, $K$, and $D$-meson form factors.

hep-ph↗
arXiv2000

Higher-Fock States and the Covariance of the Light-Front Quark Model

The light-front quark model has been successful in describing various meson properties. We apply the model to the meson weak decays and discuss the covariance of the model. We find that the inclusion of the higher-Fock state(i.e. nonvalence or so called Z-graph) contributions is necessary to recover the covariance of the light-front quark model. We present the possibility of the effective calculation of the higher-Fock state contributions to restore the covarince in the light-front model.

hep-ph↗
arXiv2000

Exploring the timelike region for the elastic form factor in the light-front quantization

Even though the Drell-Yan-West formulation is the most rigorous and well-established framework to compute the exclusive processes, its utility has been limited only to the spacelike region because of the intrinsic kinematic constraint $q^+=0$. We present an explicit example demonstrating how one may obtain the necessary information (i.e. nonvalence or so called Z-graph contribution) in the timelike region of exclusive process without encountering a formidable task of direct calculation that has hindered so far the progress in this area. In the analysis of $q\bar{Q}$ bound state form factors using an exactly solvable model of $(3+1)$ dimensional scalar field theory interacting with gauge fields, the results analytically continued from the spacelike region coincide exactly with the direct results in the timelike region. This example verifies that the method of analytic continuation is capable of yielding the effect of complicate nonvalence contributions. The meson peaks analogous to the vector meson dominance(VMD) phenomena are also generated at the usual VMD positions.

hep-ph↗
arXiv1999

Light-Front Quark Model Analysis of Electroweak Decays of Pseudoscalar and Vector Mesons

We investigate the electroweak form factors and semileptonic decay rates of pseudoscalar and vector mesons using the light-front constituent quark model. Our method of analytic continuation in the Drell-Yan-West (q^+=q^0+q^3=0) frame to obtain the weak form factors avoids the difficulty associated with the contributions from the nonvalence quark-antiquark pair creation. This method seems to provide a promising step forward to handle the exclusive processes in the timelike region. Our calculation reveals that the zero mode contribution is crucial to obtaining the correct values of the light-front current J^{-} in the q^+=0 frame. Our numerical results are overall in a very good agreement with the available exprimental data.

hep-ph↗
arXiv1999

Exploring Timelike Region of QCD Exclusive Processes in Relativistic Quark Model

We investigate the form factors and decay rates of exclusive $0^{-}\to0^{-}$ semileptonic meson decays using the constituent quark model based on the light-front quantization. Our model is constrained by the variational principle for the linear plus Coulomb interaction motivated by QCD. Our numerical results are in a good agreement with the available experimental data.

hep-ph↗