Ho-Meoyng Choi

Mixing angles and electromagnetic properties of ground state pseudoscalar and vector meson nonets in the light cone quark model

Both the mass spectra and the wave functions of the light pseudoscalar ({pi},K,{eta},{eta}{sup {prime}}) and vector({rho},K{sup {asterisk}},{omega},{phi}) mesons are analyzed within the framework of the light-cone constituent quark model. A Gaussian radial wave function is used as a trial function of the variational principle for a QCD-motivated Hamiltonian which includes not only the Coulomb plus confining potential but also the hyperfine interaction to obtain the correct {rho}-{pi} splitting. For the confining potential, we use the (1) harmonic oscillator potential and (2) linear potential and compare the numerical results for these two cases. The mixing angles of {omega}-{phi} and {eta}-{eta}{sup {prime}} are predicted and various physical observables such as decay constants, charge radii, and radiative decay rates, etc., are calculated. Our numerical results in the two cases (1) and (2) are overall not much different from each other and are in good agreement with the available experimental data. {copyright} {ital 1999} {ital The American Physical Society}

Decay constants and radiative decays of heavy mesons in light-front quark model

We investigate the magnetic dipole decays V{yields}P{gamma} of various heavy-flavored mesons such as (D,D*,D{sub s},D{sub s}*,{eta}{sub c},J/{psi}) and (B,B*,B{sub s},B{sub s}*,{eta}{sub b},{upsilon}) using the light-front quark model constrained by the variational principle for the QCD-motivated effective Hamiltonian. The momentum dependent form factors F{sub VP}(q{sup 2}) for V{yields}P{gamma}* decays are obtained in the q{sup +}=0 frame and then analytically continued to the timelike region by changing q{sub perpendicular} to iq{sub perpendicular} in the form factors. The coupling constant g{sub VP{gamma}} for real photon case is then obtained in the limit as q{sup 2}{yields}0, i.e. g{sub VP{gamma}}=F{sub VP}(q{sup 2}=0). The weak decay constants of heavy pseudoscalar and vector mesons are also calculated. Our numerical results for the decay constants and radiative decay widths for the heavy-flavored mesons are overall in good agreement with the available experimental data as well as other theoretical model calculations.

Regularizing the divergent structure of light-front currents

~Received 15 August 2000; revised manuscript received 7 December 2000; published 7 March 2001! The divergences appearing in the ~311!-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 nonvalence contributions in all components of the current with the regularized bound-state vertex. However, we stress that each contribution, valence or nonvalence, 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 p, K, and D-meson form factors.

Electromagnetic structure of the {rho} meson in the light-front quark model

We investigate the elastic form factors of the {rho} meson in the light-front quark model (LFQM). With the phenomenologically accessible meson vertices including the one obtained by the Melosh transformation frequently used in the LFQM, we find that only the helicity 0{yields}0 matrix element of the plus current receives the zero-mode contribution. We quantify the zero-mode contribution in the helicity 0{yields}0 amplitude using the angular condition of spin-1 system.After taking care of the zero-mode issue, we obtain the magnetic ({mu})and quadrupole (Q) moments of the {rho} meson as {mu}=1.92 and Q=0.43, respectively, in the LFQM consistent with the Melosh transformation and compare our results with other available theoretical predictions.

Light-front quark model analysis of exclusive 0−→0− semileptonic heavy meson decays

Abstract We present the analysis of exclusive 0 − →0 − semileptonic heavy meson decays using the constituent quark model based on the light-front quantization. Our model is constrained by the variational principle for the well-known linear plus Coulomb interaction motivated by QCD. Our method of analytic continuation to obtain the weak form factors avoids the difficulty associated with the contribution from the nonvalence quark-antiquark pair creation. Our numerical results for the heavy-to-heavy and heavy-to-light meson decays are in a good agreement with the available experimental data and the lattice QCD results. In addition, our model predicts the two unmeasured mass spectra of 1 S 0 (b b ) and 3 S 1 (b s ) systems as M b b =9657 MeV and M b s =5424 MeV.

Electromagnetic structure of theρmesonin the light-front quark model

We investigate the elastic form factors of the {rho} meson in the light-front quark model (LFQM). With the phenomenologically accessible meson vertices including the one obtained by the Melosh transformation frequently used in the LFQM, we find that only the helicity 0{yields}0 matrix element of the plus current receives the zero-mode contribution. We quantify the zero-mode contribution in the helicity 0{yields}0 amplitude using the angular condition of spin-1 system.After taking care of the zero-mode issue, we obtain the magnetic ({mu})and quadrupole (Q) moments of the {rho} meson as {mu}=1.92 and Q=0.43, respectively, in the LFQM consistent with the Melosh transformation and compare our results with other available theoretical predictions.

Non-leptonic two-body decays of the B(c) meson in light-front quark model and QCD factorization approach

We study exclusive nonleptonic two-body B{sub c}{yields}(D{sub (s)},{eta}{sub c},B{sub (s)})+F decays with F (pseudoscalar or vector mesons) factored out in the QCD factorization approach. The nonleptonic decay amplitudes are related to the product of meson decay constants and the form factors for semileptonic B{sub c} decays. As inputs in obtaining the branching ratios for a large set of nonleptonic B{sub c} decays, we use the weak form factors for the semileptonic B{sub c}{yields}(D{sub (s)},{eta}{sub c},B{sub (s)}) decays in the whole kinematical region and the unmeasured meson decay constants obtained from our previous light-front quark model. We compare our results for the branching ratios with those of other theoretical studies.

Distribution amplitudes and decay constants for (π, K, ρ, K*) mesons in the light-front quark model

We present a calculation of the quark distribution amplitudes (DAs), the Gegenbauer moments, and decay constants for {pi}, {rho}, K, and K* mesons using the light-front quark model. While the quark DA for {pi} is somewhat broader than the asymptotic one, that for {rho} meson is very close to the asymptotic one. The quark DAs for K and K* show asymmetric form due to the flavor SU(3)-symmetry breaking effect. The decay constants for the transversely polarized {rho} and K* mesons (f{sub {rho}}{sup T} and f{sub K*}{sup T}) as well as the longitudinally polarized ones (f{sub {rho}} and f{sub K*}) are also obtained. Our averaged values for f{sub V}{sup T}/f{sub V}, i.e. (f{sub {rho}}{sup T}/f{sub {rho}}){sub av}=0.78 and (f{sub K*}{sup T}/f{sub K*}){sub av}=0.84, are found to be consistent with other model predictions. Especially, our results for the decay constants are in good agreement with the SU(6) symmetry relation, f{sub {rho}}{sub (K*)}{sup T}=(f{sub {pi}}{sub (K)}+f{sub {rho}}{sub (K*)})/2.

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

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.