arXiv subjects

Hyun-Chul Kim

Publications and source records attributed to Hyun-Chul Kim.

At least 163 records · Page 9Linked to original sources

arXiv2008

Hybrid exotic meson with J^{PC}=1^{-+} in AdS/QCD

We investigate the hybrid exotic meson with $J^{PC}=1^{-+}$ within the framework of an AdS/QCD model. Introducing a holographic field dual to the operator for hybrid exotic meson, we obtain the eigen-value equation for its mass. Fixing all free parameters by QCD observables such as the $ρ$-meson mass, we predict the masses of the hybrid exotic meson. The results turn out to be $1476 \mathrm{MeV}$ for the ground state, and $2611 \mathrm{MeV}$ for the first excited one. Being compared with the existing experimental data for the $π_1(1400)$, which is known to be $m_{π_1} = 1351\pm30 \mathrm{MeV}$, the present result seems to be qualitative in agreement with it. We also predict the decay constant of $π_1$(1400): $F_{π_1}= 10.6$ MeV.

hep-ph↗

arXiv2008

Pion and kaon structures from the instanton vacuum

In this presentation, we briefly review recent investigations on pion and kaon structures from the instanton vacuum. Starting from the low-energy QCD partition function, we have computed the Gasser-Leutwyler low-energy constants, electromagnetic form factors of the pion and kaon, semileptonic decay form factors of the kaon, and light-cone distribution amplitues of the pion and kaon. The results are in good agreement with the experimental and empirical data.

hep-ph↗

arXiv2008

Pion properties at finite density

In this talk, we report our recent work on the pion weak decay constant (F_pi) and pion mass (m_pi) using the nonlocal chiral quark model with the finite quark-number chemical potential (mu) taken into account. Considering the breakdown of Lorentz invariance at finite density, the time and space components are computed separately, and the corresponding results turn out to be: F^t_pi = 82.96 MeV and F^s_pi = 80.29 MeV at mu_c ~ 320 MeV, respectively. Using the in-medium Gell-Mann Oakes-Renner (GOR) relation, we show that the pion mass increases by about 15% at mu_c.

hep-ph↗

arXiv2008

Quark-gluon mixed condensate of the QCD vacuum in Holographic QCD

We investigate the quark-gluon mixed condensate based on an AdS/QCD model. Introducing a holographic field dual to the operator for the quark-gluon mixed condensate, we obtain the corresponding classical equation of motion. Taking the mixed condensate as an additional free parameter, we show that the present scheme reproduces very well experimental data. A fixed value of the mixed condensate is in good agreement with that of the QCD sum rules.

hep-ph↗

arXiv2008

Pion weak decay constant at finite density from the instanton vacuum

We investigate the pion weak decay constant (F_pi) and pion mass (m_pi) at finite density within the framework of the nonlocal chiral quark model from the instanton vacuum with the finite quark-number chemical potential (mu) taken into account. We mainly focus on the Nambu-Goldstone phase below the critical value of the chemical potential mu_c ~ 320 MeV, which is determined consistently within the present framework. The breakdown of Lorentz invariance at finite density being considered, the time (F^t_pi) and space (F^s_pi) components are computed separately, and the corresponding results turn out to be: F^t_pi = 82.96 MeV and F^s_pi = 80.29 MeV at mu_c, respectively. Using the in-medium Gell-Mann-Oakes-Renner (GOR) relation, we show that the pion mass increases by about 15% at mu_c.

hep-ph↗

arXiv2008

Semileptonic hyperon decays in the self-consistent SU(3) chiral quark-soliton model

We investigate the semileptonic hyperon decays within the framework of the self-consistent SU(3) chiral quark-soliton model ($χ$QSM). We take linear $1/N_c$ rotational as well as linear $m_s$ corrections into account and apply the symmetry conserving quantization. We present the results for the form factors $f_1(Q^2)$, $f_2(Q^2)$ and $g_1(Q^2)$ in addition to the semileptonic decay constants of hyperons. We also have calculated the radii and dipole masses of these form factors for all relevant strangeness-conserving and strangeness-changing transitions.

hep-ph↗

arXiv2008

Axial-vector transitions and strong decays of the baryon antidecuplet in the self-consistent SU(3) chiral quark-soliton model

We investigate the axial-vector transition constants of the baryon antidecuplet to the octet and decuplet within the framework of the self-consistent SU(3) chiral quark-soliton model. Taking into account rotational 1/N_c and linear m_s corrections and using the symmetry-conserving quantization, we calculate the axial-vector transition constants. It is found that the leading-order contributions are generally almost canceled by the rotational 1/N_c corrections. Thus, the m_s corrections turn out to be essential contributions to the axial-vector constants. The decay width of the Theta^+ to NK transition is determined to be Gamma(Theta -> NK)=0.71, MeV, based on the result of the axial-vector transition constant g_A^* (Theta -> NK)=0.05. In addition, other strong decays of the baryon antidecuplet are investigated.

hep-ph↗

arXiv2008

Vector and axial-vector structures of the Theta^+

We present in this talk recent results of the vector and axial-vector transitions of the nucleon to the pentaquark baryon Theta^{+}, based on the SU(3) chiral quark-soliton model. The results are summarized as follows: K^{*}-N-Theta vector and tensor coupling constants turn out to be g_{K^{*}N Theta} = 0.81 and f_{K^{*}N Theta}=0.84, respectively, and the KN Theta axial-vector coupling constant to be g_{A}^* = 0.05. As a result, the total decay width for Theta^+ to NK becomes very small: Gamma_{Theta -> NK} = 0.71 MeV, which is consistent with the DIANA result Gamma_{Theta -> NK}=0.36 +- 0.11 MeV.

hep-ph↗

arXiv2008

Vector transition form factors of the $N K^\toΘ^+ $ and $N \bar{K}^\to Σ_{\bar{10}}^{*-}$ in the SU(3) chiral quark-soliton model

We investigate the vector transition form factors of the nucleon and vector meson K^* to the pentaquark baryon Theta^+ within the framework of the SU(3) chiral quark-soliton model. We take into account the rotational 1/N_c and linear $m_{\rm s}$ corrections, assuming isospin symmetry and employing the symmetry-conserving quantization. It turns out that the leading-order contributions to the form factors are almost cancelled by the rotational corrections. Because of this, the flavor SU(3) symmetry-breaking terms yield sizeable effects on the vector transition form factors. In particular, the main contribution to the electric-like transition form factor comes from the wave-function corrections, which is a consequence of the generalized Ademollo-Gatto theorem derived in the present work. We estimate with the help of the vector meson dominance the K^* vector and tensor coupling constants for the Theta^+: $g_{K^{*}NΘ}=0.74 - 0.87$ and $f_{K^{*}NΘ}=0.53 - 1.16$. We argue that the outcome of the present work is consistent with the null results of the CLAS experiments in the reactions gamma n -> K^- Theta^+ and gamma p ->bar{K}^0 Theta^+. The results of the present work are also consistent with the recent experiments at KEK. In addition, we present the results of the $Σ_{\bar{10}}\to N\bar{K}^*$ transition form factors and its $\bar{K}^*NΣ_{\bar{10}}$ coupling constants.

hep-ph↗

arXiv2008

Electromagnetic form factors of the pion and kaon from the instanton vacuum

We investigate the pion and kaon (pi^+, K^+, K^0) electromagnetic form factors in the space-like region: Q^2 ~< 1 GeV, based on the gauged low-energy effective chiral action from the instanton vacuum in the large N_c limit. Explicit flavor SU(3) symmetry breaking is taken into account. The nonlocal contributions turn out to be crucial to reproduce the experimental data. While the pion electromagnetic form factor is in good agreement with the data, the kaon one seems underestimated. We also calculate the electromagnetic charge radii for the pion and kaon: _{pi^+}=0.455 fm^2, _{K^+}=0.486 fm^2 and _{K^0}=-0.055 fm^2 without any adjustable free parameter except for the average instanton size and inter-instanton distance, and they are compatible with the experimental data. The low-energy constant L_9 in the large N_c limit is estimated to be 8.42*10^{-3} from the pion charge radius.

hep-ph↗

arXiv2008

Magnetic susceptibility of QCD vacuum at finite density from the nonlocal chiral quark model

We present in this talk a recent investigation on the magnetic susceptibility (chi) of the QCD vacuum at finite density, utilizing the nonlocal chiral quark model from the instanton vacuum. We take into account the nonzero current-quark mass (m_q) explicitly to consider the effect of explicit flavor SU(3) symmetry breaking. It turns out that, when we turn on the current-quark mass, chi becomes smaller, indicating less response to the externally induced electromagnetic field, in comparison to that for m_q=0.

hep-ph↗

arXiv2008

Pion electromagnetic charge radii and rho-meson mass shift at finite density

We investigate the pion electromagnetic charge radii and mass dropping of the rho meson at finite density. We first calculate the pion charge radii within the framework of the nonlocal chiral quark model from the instanton vacuum both at zero and finite densities. In order to relate the change of the pion charge radius to that of the rho-meson mass at finite density, we employ the vector-meson dominance for the pion electromagnetic form factor. It turns out that the pion charge radius is getting larger as the quark chemical potential increases. As a result, the rho-meson mass falls off as the quark chemical potential grows and is found to be dropped by about 10% at normal nuclear matter density: m*_rho/m_rho ~ 1 - 0.12 mu_B/mu_0, which is compatible to the results of the measurement at the KEK recently.

hep-ph↗

arXiv2008

Production of the pentaquark exotic baryon Xi_5 in bar{K} N scattering : bar{K} N -> K Xi_5 and bar{K} N -> K* Xi_5

We investigate the production of the newly found pentaquark exotic baryon Xi_5 in the bar{K} N -> K Xi_5 and the bar{K} N -> K* Xi_5 reactions at the tree level. We consider both positive- and negative parities of the Xi_5. The reactions are dominated by the s- and u-channel processes, and the resulting cross sections depend very much on the parity of Xi_5 and on the type of form factor. We have seen that the cross sections for the positive-parity Xi_5 are generally about a hundred times larger than those of the negative-parity one. This large difference in the cross sections will be useful for further study of pentaquark baryons.

hep-ph↗

arXiv2007

Pion electromagnetic form factor at finite density

In this talk, we introduce an effective chiral action, derived from the instanton QCD vacuum configuration, in order to study the modification of mesonic properties in medium. We present our recent theoretical results on the electromagnetic from factor and rho-meson mass shift at finite density. We observe that the rho-meson mass is dropped by about 10%: m*_rho/m_rho ~ 1-0.12 mu_B/mu_0, which is compatible with that estimated by the QCD sum rule as well as by Brown and Rho.

hep-ph↗

arXiv2007

1/N_c corrections to the magnetic susceptibility of the QCD vacuum

We investigate the magnetic susceptibility of the QCD vacuum with the $1/N_c$ corrections taken into account, based on the instanton vacuum. Starting from the instanton liquid model we derive the gauged light-quark partition function in the presence of the current quark mass as well as of external Abelian vector and tensor fields. We consider the $1/N_c$ meson-loop corrections which are shown to contribute to the magnetic susceptibility by around 15% for the up (and down) quarks. We also take into account the tensor terms of the quark-quark interaction from the instanton vacuum as well as the finite-width effects, both of which are of order $\mathcal{O}(1/N_c)$. The effects of the tensor terms and finite width turn out to be negligibly small. The final results for the up-quarks are given as: $χ< iψ^\dagger ψ>_0 \simeq 35-40 \mathrm{MeV}$ with the quark condensate $ _0$. We also discuss the pion mass dependence of the magnetic susceptibility in order to give a qualitative guideline for the chiral extrapolation of lattice data.

hep-ph↗

arXiv2007

The Electric Dipole Moment of the Nucleons in Holographic QCD

We introduce the strong CP-violation in the framework of AdS/QCD model and calculate the electric dipole moments of nucleons as well as the CP-violating pion-nucleon coupling. Our holographic estimate of the electric dipole moments gives for the neutron d_n=1.08 X 10^{-16} theta (e cm), which is comparable with previous estimates. We also predict that the electric dipole moment of the proton should be precisely the minus of the neutron electric dipole moment, thus leading to a new sum rule on the electric dipole moments of baryons.

hep-ph↗

arXiv2007

A new nucleon resonance in eta photoproduction

We present in this talk recent investigations on the nucleon-like resonance N*(1675) newly found in eta photoproduction by the GRAAL, Tohoku LNS-gamma and CB-ELSA collaborations. We focus on the production mechanism of the N*(1675), examining its spin and parity theoretically within the framework of the effective Lagrangian method. We expliucitly consider D_{13}(1520), S_{11}(1535), S_{11}(1650), D_{15}(1675), P_{11}(1710), P_{13}(1720) as well as possible background contributions. We calculate the differential cross sections and beam asymmetries for the neutron and proton targets. It turns out that there is manifest isospin asymmetry in eta photoproduction, which can be explained by the asymmetry in the transition magnetic moments: mu_{gamma p p*} =<mu_{gamma n n*}. Moreover, we find that the spin-1/2 state is preferred and this observation implies that the new resonance may be identified as a non-strangeness member of the baryon antidecuplet.

hep-ph↗

arXiv2007

Kaon semileptonic decay (K_{l3}) form factor in the nonlocal chiral quark model

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. All theoretical calculations are carried out without any adjustable parameter. We also show that the present results satisfy the Callan-Treiman low-energy theorem as well as the Ademollo-Gatto theorem. 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.

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