arXiv subjects

Hyun-Chul Kim

Publications and source records attributed to Hyun-Chul Kim.

At least 181 records · Page 10Linked to original sources

arXiv2007

A new candidate for non-strangeness pentaquarks: N*(1675)

We study a new nucleon resonance from eta photoproduction, which was observed at sqrt{s}=1675 MeV with a narrow decay width (~10 MeV) by the Tohoku LNS group as well as the GRAAL collaboration. Using an effective Lagrangian approach, we compute differential cross sections for the eta photoproduction. In addition to N*(1675,1/2+-,3/2+-), we employ six other nucleon resonances, i.e. N*(1520,1535,1650,1675,1710,1720) and vector meson exchanges which are the most relevant ones to this reaction process. As a result, we can reproduce the GRAAL data qualitatively well and observe obvious isospin asymmetry between the transition magnetic moments of N*(1675): mu_{gamma nn*} >> mu_{gamma pp*}, which indicates that the newly found nucleon resonance may be identified as a non-strange pentaquark state.

hep-ph↗

arXiv2007

Quark spin content of the proton, hyperon semileptonic decays, and the decay width of the $Θ^{+}$ pentaquark

Using the exisiting experimental data for hyperon semileptonic decays and the flavor-singlet axial-vector charge $g_{A}^{(0)}$ from polarized deep inelastic scattering of the proton, we derive the decay width of the $Θ^{+}$ pentaquark baryon. We take into account the effects of flavor SU(3) symmetry breaking within the framework of the chiral quark-soliton model. All dynamical parameters of the model are fixed by using the five experimental hyperon semileptonic decay constants and flavor singlet axial-vector charge. We obtain the numerical results of the decay width of the $Θ^{+}$ pentaquark baryon as a function of the pion-nucleon sigma term $Σ_{πN}$ and investigate the dependence of the decay width of the $Θ^{+}$ on the $g_{A}^{(0)}$, varying the $g_{A}^{(0)}$ within the range of the experimental uncertainty. We demonstrate that the combined values of all known semileptonic decays with the generally accepted value of $g_{A}^{(0)} \approx 0.3$ for the proton are compatible with a small decay width $Γ_{ΘKN}$ of the $Θ^{+}$ pentaquark, i.e. $Γ_{ΘKN} \leq 1$ MeV.

hep-ph↗

arXiv2007

Kaon semileptonic decay (K_{l3}) form factors from the instanton vacuum

We investigate the kaon semileptonic decay (K_{l3}) form factors within the framework of the nonlocal chiral quark model from the instanton vacuum, taking into account the effects of flavor SU(3) symmetry breaking. We also consider the problem of gauge invariance arising from the momentum-dependent quark mass in the present work. All theoretical calculations are carried out without any adjustable parameter, the average instanton size (rho ~ 1/3 fm) and the inter-instanton distance (R ~ 1 fm) having been fixed. We also show that the present results satisfy the Callan-Treiman low-energy theorem as well as the Ademollo-Gatto theorem. Using the K_{l3} form factors, we evaluate relevant physical quantities. It turns out that the effects of flavor SU(3) symmetry breaking are essential in reproducing the kaon semileptonic form factors. The present results are in a good agreement with experiments, and are compatible with other model calculations.

hep-ph↗

arXiv2007

QCD condensates with flavor SU(3) symmetry breaking from the instanton vacuum

We investigate the effects of flavor SU(3)-symmetry breaking on the quark, gluon, and mixed quark-gluon condensates, based on the nonlocal effective chiral action from the instanton vacuum. We employ two different parameterizations for the dependence of the momentum-dependent dynamical quark mass on the strange current quark mass. With a proper choice of the current-quark mass dependence of the dynamical quark mass, we show that the gluon condensate is independent of the current quark mass. We obtain the ratios of the quark and mixed condensates, respectively: $[<\bar{s}s>/< \bar{u}u>]^{1/3}=0.75$ and $[<\bar{s}σ_{μν}G^{μν}s > <\bar{u}σ_{μν}G^{μν}u>]^{1/5}=0.87$. It turns out that the dimensional parameter $m^2_0=<\bar{q} σ_{μν}G^{μν}q>/ <\bar{q}q> =1.60\sim 1.92 {\rm GeV}^2$.

hep-ph↗

arXiv2007

Test of the reaction mechanism for gamma N -> K Lambda(1520) using the polarized photon

We study the reaction mechanism for the photoproduction of the Lambda(1520), based on an effective Lagrangian approach. We investigate each contribution of the s-, u-, t-channel processes and contact term, separately. One of the most characteristic features of this reaction is the contact-term dominance which governs the photoproduction from the proton, when the K*-exchange contribution is possibly not too large. We suggest several different ways of the polarizations and arrangement of the beam and target to make to understand the role of each contribution separately in future experiments.

hep-ph↗

arXiv2006

Twist-3 pion and kaon distribution amplitudes from the instanton vacuum with flavor SU(3) symmetry breaking

We investigate the twist-3 pion and kaon distribution amplitudes of the pseudoscalar (phi^p_{pi,K}) and pseudotensor (phi^{sigma}_{pi,K}) types, based on the effective chiral action from the instanton vacuum. Effects of flavor SU(3) symmetry breaking are explicitly taken into account. The Gegenbauer moments and the moments of the distribution amplitudes ( ) are also computed. Our results are summarized as follows: a^p_{2,pi} ~ 0.4, a^p_{1,K} ~ 0.02 and a^p_{2,K} ~ 0.14, and a^{sigma}_{2,pi} ~ 0.02 and a^{sigma}_{1,K} ~ a^{sigma}_{2,K} ~ 0; ^p_π ~ ^p_K ~ 0.37 and ^p_K ~ 0, and ^{sigma}_{pi} ~ ^{sigma}_K ~ 0.20 and ^{sigma}_K ~ 0. We compare our results with those from the QCD sum rules. We also discuss the relevant Wilson coefficients which were analyzed recently in chiral perturbation theory.

hep-ph↗

arXiv2006

Leading-twist pion and kaon distribution amplitudes in the gauge-invariant nonlocal chiral quark model from the instanton vacuum

We investigate the leading-twist light-cone distribution amplitudes for the pion and kaon based on the gauge-invariant nonlocal chiral quark model from the instanton vacuum in the presence of external axial-vector currents. We find that the nonlocal contribution from the gauge invariance has much effects on the pion distribution amplitudes, while it changes mildly the kaon ones. We also study the Gegenbauer moments of the distribution amplitudes and compare them with the empirical analysis of the CLEO data.

hep-ph↗

arXiv2006

Strange nucleon form factors: Solitonic approach to $G_{M}^{s}$, $G_{E}^{s}$, $\tilde{G}_{A}^{p}$ and $\tilde{G}_{A}^{n}$ and comparison with world data

We summarize the results of the chiral quark-soliton model ($χ$QSM) concerning basically all form factors necessary to interpret the present data of the parity violating electron scattering experiments SAMPLE, HAPPEX, A4 and G0. The results particularly focus on the recently measured asymmetries and the detailed data for various combinations of $G_{M}^{s}$, $G_{E}^{s}$, $\tilde{G}_{A}^{p}$ and $\tilde{G}_{A}^{n}$ at $Q^2=0.1$ GeV$^2$. The calculations yield positive strange magnetic and electric form factors and a negative axial vector one, all being rather small. The results are very close to the combined experimental world data from parity violating electron scattering and elastic $νp$- and $\bar{νp}$- scattering.

hep-ph↗

arXiv2006

Pentaquark Theta^+ production via gamma N ->K^*bar Theta^+(3/2^(+-))

We study the photoproduction of the exotic pentaquark Theta^+ baryon with the vector kaon, assuming that the quantum numbers of the Theta^+ to be J^P=3/2^(+-) and J^P=1/2^+. Scalar meson kappa(800)-exchange is also taken into account. In contrast with the gamma N -> Kbar Theta^+(3/2^(+-)) process, the large suppression from the proton target is not observed in the total cross sections. We also suggest a method to determine which meson exchange is the most dominant by analyzing the polarizations of incident photon and outgoing K^*. We find that kappa-exchange turns out to be prominent when the polarizations of the photon and K^* are aligned to be parallel, whereas K-exchange does when they are perpendicular to each other.

hep-ph↗

arXiv2006

The leading-twist pion and kaon distribution amplitudes from the QCD instanton vacuum

We investigate the leading-twist light-cone distribution amplitudes for the pion and kaon, based on the nonlocal chiral quark model from the instanton vacuum. Effects of explicit flavor SU(3)-symmetry breaking are taken into account. The Gegenbauer moments are computed, analyzed and compared with those of other models. The one-loop QCD evolution of the moments is briefly discussed. The transverse momentum distributions are also discussed for the pion and kaon light-cone wave functions.

hep-ph↗

arXiv2006

QCD condensates with flavor SU(3) symmetry breaking

We investigate the effects of flavor SU(3)-symmetry breaking on the QCD condensates, based on the nonlocal effective chiral action from the instanton vacuum, focusing on the quark-gluon mixed one. We employ two different parameterizations for the dependence of the momentum-dependent dynamical quark mass on the strange current quark mass. We obtain the ratios of the mixed condensates:$[<\bar{s}σ_{μν}G^{μν}s><\bar{u}\sig ma_{μν}G^{μν}u>]^{1/5}=0.87$. It turns out that the dimensional parameter $m^2_0=<\bar{q} σ_{μν}G^{μν}q>/ <\bar{q}q> =1.60\sim 1.92 {\rm GeV}^2$.

hep-ph↗

arXiv2006

Electric properties of the baryon anti-decuplet in the SU(3) chiral quark-soliton model

We investigate the electric form factors and charge radii of the pentaquark baryons within the framework of the chiral quark-soliton model. We consider the rotational $1/N_c$ and linear $m_s$ corrections, assuming isospin symmetry and employing the symmetry-conserving quantization. The flavor-decomposed charge densities of the $Θ^+$ are presented. The electric form factors and charge radii of the charged pentaquark baryons turn out to be very similar to those of the corresponding octet baryons. The charge radii of the neutral pentaquark baryons are obtained to be very tiny and positive. The strange electric form factor of the pentaquark proton is shown to be larger than the corresponding one of the proton by around 20%. We also present the charge radii of the baryon decuplet for comparison.

hep-ph↗

arXiv2006

A new $N^*(1675)$ resonance in the $γN\toηN$ reaction

We study the $η$-photoproduction focusing on the new nucleon resonance which was observed at $\sqrt{s}=1675$ MeV with a narrow decay width ($\sim 10$ MeV) in the recent GRAAL experiment. Using an effective Lagrangian approach, we compute differential cross sections for the $η$-photoproduction. In addition to $N^*(1675)$, we employ three other nucleon resonances, i.e. $N^*(1535)$, $N^*(1650)$ and $N^*(1710)$, and vector meson exchanges which are the most relevant ones to this reaction process. As a result, we can reproduce the GRAAL data qualitatively well and observe obvious isospin asymmetry between the transition magnetic moments of $N^*(1675)$: $μ_{γnn^*}\ggμ_{γpp^*}$.

hep-ph↗

arXiv2006

Parity-violating aysmmetries in elastic $\vec{e}p$ scattering in the chiral quark-soliton model: Comparison with A4, G0, HAPPEX and SAMPLE

We investigate parity-violating electroweak asymmetries in the elastic scattering of polarized electrons off protons within the framework of the chiral quark-soliton model ($χ$QSM). We use as input the former results of the electromagnetic and strange form factors and newly calculated SU(3) axial-vector form factors, all evaluated with the same set of four parameters adjusted several years ago to general mesonic and baryonic properties. Based on this scheme, which yields positive electric and magnetic strange form factors with a $μ_s=(0.08-0.13)μ_N$, we determine the parity-violating asymmetries of elastic polarized electron-proton scattering. The results are in a good agreement with the data of the A4, HAPPEX, and SAMPLE experiments and reproduce the full $Q^2$-range of the G0-data. We also predict the parity-violating asymmetries for the backward G0 experiment.

hep-ph↗

arXiv2005

Meson-loop contributions to the quark condensate from the instanton vacuum

We investigate the quark condensate of the QCD vacuum within the instanton vacuum model. We calculate the meson-loop contributions to the dynamical quark mass and quark condensate to ${\cal O}(1/N_c)$-, ${\cal O}(m/N_c)$-, and ${\cal O}((m\ln m) /N_c)$-order corrections. We find that the meson (especially pion) loops provide substantial contributions to the dynamical quark mass and as a result to the quark condensate. The results indicate that the $1/N_c$ corrections should be reconsidered in the systematical way. The present results are consistent with those from chiral perturbation theory.

hep-ph↗

arXiv2005

Is there a crystalline state of nuclear matter?

A possibility of the crystalline state of nuclear matter is discussed in a medium--modified Skyrme model. The interaction energy per nucleon in nuclear matter is evaluated by taking into account the medium influence on single nucleon--skyrmion properties and the tensor part of the nucleon--nucleon potential, and by using a variational method of Hartree--Fock type including zero--point quantum fluctuations. It is shown that in this approach the ground state of nuclear matter has no crystalline structure due to quantum fluctuations as well as medium modifications of hadron properties.

nucl-th↗

arXiv2005

Lambda(1520,3/2^-) photoproduction reaction via gamma N -> K Lambda(1520)

We investigate Lambda(1520,3/2^-,D_03) photoproduction via the gamma N -> K Lambda^* reaction process. Using effective Lagrangians, we compute the total and differential cross sections as well as the dependence on the momentum transfer for the photoproduction at the tree-level. We employ two different form factors: The four-dimensional gauge-invariant type and the three dimensional one depending on the external momenta. We find that the total cross sections for the proton target are well reproduced as compared with the experimental data. It turns out that the total cross sections for the neutron target are significantly smaller than those for the proton target. We also compare the present results with the gamma N -> bar{K} Theta^+ reaction in order to extract information of Theta^+. Finally the role of K^*--exchange in the production reaction is discussed.

hep-ph↗

arXiv2005

Suppression of Theta^+(J^P=3/2^(+,-)) photoproduction from the proton

We investigate the photoproduction of Theta^+ from the proton and neutron, gamma N -> Kbar Theta^+. Assuming that spin and parity of Theta^+ are J^P = 3/2^(+,-), it is shown that the production from the proton is strongly suppressed as compared with that from the neutron. This could provide a possible explanation for the null results of the recent CLAS experiment in finding Theta^+ via the reaction gamma p -> Kbar^0 Theta^+.

hep-ph↗