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Ghil-Seok Yang

Publications and source records attributed to Ghil-Seok Yang.

29 records · Page 2Linked to original sources

Hidden Local Symmetry and Infinite Tower of Vector Mesons for Baryons

In an effort to access dense baryonic matter relevant for compact stars in a unified framework that handles both single baryon and multibaryon systems on the same footing, we first address a holographic dual action for a single baryon focusing on the role of the infinite tower of vector mesons deconstructed from five dimensions. To leading order in 't Hooft coupling $λ=N_c g_{\rm YM}^2$, one has the Bogomol'nyi-Prasad-Sommerfield (BPS) Skyrmion that results when the warping of the bulk background and the Chern-Simons term in the Sakai-Sugimoto D4/D8-${\bar{\rm D8}}$ model are ignored. The infinite tower was found by Sutcliffe to induce flow to a conformal theory, i.e., the BPS. We compare this structure to that of the SS model consisting of a 5D Yang-Mills action in warped space and the Chern-Simons term in which higher vector mesons are integrated out while preserving hidden local symmetry and valid to $O(λ^0)$ and $O(p^4)$ in the chiral counting. We point out the surprisingly important role of the $ω$ meson that figures in the Chern-Simons term that encodes chiral anomaly in the baryon structure and that may be closely tied to short-range repulsion in nuclear interactions.

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Mass splittings of SU(3) baryons within a chiral soliton model

Considering simultaneously isospin and SU(3) flavor symmetry breakings, we investigate the complete mass splittings of SU(3) baryons within a chiral soliton model, a {}"model-independent approach" being employed. In linear order several new mass relations are derived, which are mostly generalizations of existing mass formulae. The dynamical quantities appearing in the expressions for the masses are fixed by fitting them to the masses of the baryon octet and the masses of $Ω^{-}$ and $Θ^{+}$ as input rather than by extracting them from a calculated self-consistent soliton profile. In particular, the consideration of isospin symmetry breaking allows us to use the experimental data of the whole octet baryon masses as input. We predict the masses of the baryon decuplet and antidecuplet without any further adjustable free parameter. In addition, we also obtain the pion-nucleon sigma term which turns out to be $Σ_{πN} = 36.4\pm3.9\,\mathrm{MeV}$. We get the ratio of the current light quark masses $R = 58.1\pm1.3$. The present results indicate that the recent experimental data for the $Θ^{+}(1524)$ are compatible with the experimental data of the octet and decuplet masses.

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Mass splittings of the baryon decuplet and antidecuplet with the second-order flavor symmetry breakings within a chiral soliton model

We revisit the mass splittings of SU(3) baryons, taking into account the second-order effects of isospin and SU(3) flavor symmetry breakings within the framework of a chiral soliton model. The masses of the baryon decuplet turn out to be improved, compared to those with the first-order corrections. The mass of the N^* as a member of the baryon antidecuplet is obtained as M_{n^*}=1687 MeV, which is in agreement with the recent experimental data. The pion-nucleon sigma term becomes Σ_{πN}=(50.5\pm 5.4) MeV.

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$Θ^+$ baryon, $N^* (1685)$ resonance, and $πN$ sigma term in the context of the LEPS and DIANA experiments

We reexamine properties of the baryon antidecuplet $Θ^+$ and $N^*$, and the $πN$ sigma term within the framework of a chiral soliton model, focusing on their dependence on the $Θ^+$ mass. It turns out that the measured value of the $N^*$ mass, $M_{N^*}=1686$ MeV, is consistent with that of the $Θ^+$ mass $M_{Θ^+}=1524$ MeV by the LEPS collaboration. The $N^*\to Nγ$ magnetic transition moments are almost independent of the $Θ^+$ mass. The ratio of the radiative decay width $Γ_{nn^*}$ to $Γ_{pp^*}$ turns out to be around 5. The decay width for $Θ^+\to NK$ is studied in the context of the LEPS and DIANA experiments. When the LEPS value of the $Θ^+$ mass is employed, we obtain $Γ_{ΘNK} =(0.5\pm0.1)$ MeV. The $πN$ sigma term is found to be almost independent of the $Θ^+$ mass. In addition, we derive a new expression for the $πN$ sigma term in terms of the isospin mass splittings of the hyperon octet as well as that of the antidecuplet $N^*$.

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Electromagnetic mass differences of SU(3) baryons within a chiral soliton model

We investigate the electromagnetic mass differences of SU(3) baryons, using an "model-independent approach" within a chiral soliton model. The electromagnetic self-energy corrections to the masses of the baryon are expressed as the baryonic two-point correlation function of the electromagnetic currents. Using the fact that the electromagnetic current can be treated as an octet operator, and considering possible irreducible representations of the correlation function, we are able to construct a general collective operator for the electromagnetic self-energies, which consists of three unknown parameters. These parameters are fixed, the empirical data for the electromagnetic mass differences of the baryon octet being employed. We predict those of the baryon decuplet and antidecuplet. In addition, we obtain various mass relations between baryon masses within the corresponding representation with isospin symmetry breaking considered. We also predict the physical mass differences of the baryon decuplet. The results are in good agreement with the exisiting data.

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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.

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Exotic and nonexotic magnetic transitions in the context of the SELEX and GRAAL experiments

We calculate magnetic transition moments in the chiral quark-soliton model, with explicit SU(3)-symmetry breaking taken into account. The dynamical model parameters are fixed by experimental data for the magnetic moments of the baryon octet and from the recent measurements of $Θ^{+}$ mass. Known magnetic transition moments $μ_{ΛΣ}$, $μ_{NΔ}$ are reproduced and predictions for other octet-decuplet and octet-antidecuplet transitions are given. In particular $μ_{ΣΣ^{\ast}}$ recently constrained by SELEX is shown to be below $0.82 μ_N$. The recent GRAAL data on $η$ photoproduction off the nucleon are explained in terms of a new narrow antidecuplet neutron-like resonance.

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Magnetic moments of exotic pentaquark baryons

In this talk, we present our recent investigation on the magnetic moments of the exotic pentaquark states, based on the chiral quark-soliton model, all relevant intrinsic parameters being fixed by using empirical data.

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Magnetic moments of the pentaquarks

We present in this talk a recent analysis for the magnetic moments of the baryon antidecuplet within the framework of the chiral quark-soliton model with linear $m_s$ corrections considered. We take into account the mixing of higher representations to the collective magnetic moment operator, which comes from the SU(3) symmetry breaking. Dynamical parameters of the model are fixed by experimental data for the magnetic moments of the baryon octet as well as by the masses of the octet, decuplet and of $Θ^{+}$. The magnetic moment of $Θ^{+}$ is rather sensitive to the pion-nucleon sigma term and ranges from $-1.19 {\rm n.m.}$ to $-0.33 {\rm n.m.}$ as the sigma term is varied from $Σ_{πN} = 45$ to 75 MeV, respectively. On top of them, we obtained that the strange magnetic moment of the nucleon has the value of $μ^{(s)}_N =+0.39$ n.m. within this scheme and turns out to be almost independent of the sigma term.

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Pentaquarks: Review on Models and Solitonic Calculations of Antidecuplet Magnetic Moments

After a quick look at the present status of experiments we shortly review in a first step the ongoing discussions on some of the basic theoretical approaches to pentaquarks: Chiral solitons, Large-$N_c$ considerations, quark models, and lattice gauge approaches. In a second step we apply the chiral quark-soliton approach including linear $m_s$-corrections to the calculation of magnetic moments of the baryons of the anti-decuplet. In this approach the parameters are fixed solely by experimental data for the magnetic moments of the baryon octet and for the masses of the octet, decuplet and of $Θ^{+}$. The magnetic moment of $Θ^{+}$ depends rather strongly on the pion-nucleon sigma term and reads $-1.19 {\rm n.m.}$ to $-0.33 {\rm n.m.}$ for $Σ_{πN} = 45$ and 75 MeV respectively. As a byproduct the strange magnetic moment of the nucleon is obtained with a value of $μ^{(s)}_N =+0.39$ n.m.

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Octet, decuplet and antidecuplet magnetic moments in the chiral quark soliton model revisited

We reanalyse the magnetic moments of the baryon octet, decuplet, and antidecuplet within the framework of the chiral quark-soliton model, with SU(3) symmetry breaking taken into account. We consider the contributions of the mixing of higher representations to the magnetic moment operator arising from the SU(3) symmetry breaking. Dynamical parameters of the model are fixed by experimental data for the magnetic moments of the baryon octet and from the masses of the octet, decuplet and of $Θ^{+}$. The magnetic moment of $Θ^{+}$ depends rather strongly on the pion-nucleon sigma term and reads $-1.19 {\rm n.m.}$ to $-0.33 {\rm n.m.}$ for $Σ_{πN} = 45$ and 75 MeV respectively. The recently reported mass of $Ξ^{--}_{\bar{10}}(1862)$ is compatible with $Σ_{πN} = 73$ MeV. As a byproduct the strange magnetic moment of the nucleon is obtained with a value of $μ^{(s)}_N =+0.39$ n.m.

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