arXiv subjects

Yongseok Oh

Publications and source records attributed to Yongseok Oh.

At least 55 records · Page 3Linked to original sources

arXiv2014

Model-independent aspects of the reaction $\bar{K} + N \to K + Ξ$

Various model-independent aspects of the $\bar{K} N \to K Ξ$ reaction are investigated, starting from the determination of the most general structure of the reaction amplitude for $Ξ$ baryons with $J^P=\frac12^\pm$ and $\frac32^\pm$ and the observables that allow a complete determination of these amplitudes. Polarization observables are constructed in terms of spin-density matrix elements. Reflection symmetry about the reaction plane is exploited, in particular, to determine the parity of the produced $Ξ$ in a model-independent way. In addition, extending the work of Biagi $\mathrm{\textit{et al. } [Z. Phys.\ C \textbf{34}, 175 (1987)]}$, a way is presented of determining simultaneously the spin and parity of the ground state of $Ξ$ baryon as well as those of the excited $Ξ$ states.

hep-ph↗

arXiv2014

Hadronic description for Omega baryon photoproduction

In the present work, we investigate subsequential production of three kaons and $Ω^-$ baryon based on an effective Lagrangian approach. We only consider the intermediate states with the light mass baryon to suggest the minimum of the total cross section. Coupling constants for verteces of meson-octet baryons are fixed from the empirical data and/or quark models together with SU(3) symmetry considerations and these for meson-decouplet are predicted not only quark model but also Chiral-quark soliton model calculation. Gauge invariance of the resulting amplitude is maintained by introducing the contact currents by extending the gauge-invariant approach of Haberzettl for one-meson photoproduction to two-meson photoproduction.

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arXiv2014

${}_{ΛΛ}^{4}$H in halo effective field theory

The ${}_{ΛΛ}^{\ \ 4}$H bound state and the $S$-wave hypertriton(${}_Λ^{ \, 3}$H)-$Λ$ scattering in spin singlet and triplet channels below the hypertriton breakup momentum scale are studied in halo/cluster effective field theory at leading order by treating the ${}_{ΛΛ}^{\ \ 4}$H system as a three-cluster ($Λ$-$Λ$-deuteron) system. In the spin singlet channel, the amplitude is insensitive to the cutoff parameter $Λ_c$ introduced in the integral equation, and we find that there is no bound state. In this case, the scattering length of the hypertriton-$Λ$ scattering is found to be $a_0^{} = 16.0\pm 3.0$ fm. In the spin triplet channel, however, the amplitude obtained by the coupled integral equations is sensitive to $Λ_c$, and we introduce the three-body contact interaction $g_1^{} (Λ_c)$. After phenomenologically fixing $g_1^{} (Λ_c)$, we find that the correlation between the two-$Λ$ separation energy $B_{ΛΛ}$ from the $_{ΛΛ}^{\ \ 4}$H bound state and the scattering length $a_{ΛΛ}^{}$ of the $S$-wave $Λ$-$Λ$ scattering is significantly sensitive to the value of $Λ_c$.

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arXiv2013

Skyrmions, half-skyrmions and nucleon mass in dense baryonic matter

We explore the hadron properties in dense baryonic matter in a unified way by using a Skyrme model constructed with an effective Lagrangian which includes the $ρ$ and $ω$ vector mesons as hidden gauge bosons and is valid up to $O(p^4)$ in chiral expansion including the homogeneous Wess-Zumino terms. With the two input values of pion decay constant and the lowest lying vector meson mass which can be fixed in free space, all the other low energy constants in the effective Lagrangian are determined by their master formulas derived from holographic QCD models, which allows us to study the baryonic matter properties with no additional free parameters and thus without ambiguities. We find that the $ω$ field that figures in the homogeneous Wess-Zumino term plays a crucial role in the skyrmion structure and its matter properties. The most striking and intriguing observation is that the pion decay constant that smoothly drops with increasing density in the Skyrmion phase stops decreasing at $n_{1/2}^{}$ at which the skyrmions in medium fractionize into half-skyrmions and remains nearly constant in the half-skyrmion phase. In accordance with the large $N_c$ consideration, the baryon mass also stays non-scaling in the half-skyrmion phase. This feature is supported by the nuclear effective field theory with the parameters of the Lagrangian scaling modified at the skyrmion--half-skyrmion phase transition. Our exploration also uncovers the crucial role of the $ω$ meson in multi-baryon systems as well as in the structure of a single skyrmion.

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arXiv2013

Dense Baryonic Matter in Hidden Local Symmetry Approach: Half-Skyrmions and Nucleon Mass

Hadron properties in dense medium are treated in a unified way in a skyrmion model constructed with an effective Lagrangian, in which the rho and omega vector mesons are introduced as hidden gauge bosons, valid up to O(p^4) terms in chiral expansion including the homogeneous Wess-Zumino terms. All the low energy constants - apart from f_pi and m_rho - are fixed by the master formula derived from the relation between 5-D hQCD and 4-D HLS. This allows one to pin down the density n_1/2 at which the skyrmions in medium fractionize into half-skyrmions, bringing in a drastic change in the EoS of dense matter. We find that the U(1) field that figures in the CS term in the hQCD action or equivalently the omega field in the hWZ term in the dimensionally reduced HLS action plays a crucial role in the half-skyrmion phase. The importance of the omega degree of freedom may be connected to what happens in the instanton structure of elementary baryon noticed in hQCD. The most striking and intriguing in what is found in the model is that f_pi that smoothly drops with increasing density in the skyrmion phase stops decreasing at n_1/2 and remains nearly constant in the half-skyrmion phase. In accordance with the large N_c consideration, the baryon mass also stays non-scaling in the half-skyrmion phase. This feature which is reminiscent of the parity-doublet baryon model with a chirally invariant mass m_0 is supported by the nuclear EFT with the parameters of the Lagrangian scaling modified at the skyrmion-half-skyrmion phase transition. It also matches with one-loop RG analysis based on HLS. A link between a non-vanishing m_0 and the origin of nucleon mass distinctive from dynamically generated mass is suggested. We briefly discuss the possible consequences of the topology change found in this paper on the forthcoming experiments at the RIB machines under construction.

hep-ph↗

arXiv2013

QCD sum rule study on the $f_0(980)$ structure as a pure $K \bar{K}$ bound state

We perform a QCD sum rule analysis for the scalar $f_0(980)$ meson to investigate whether it can be described as a pure bound state of $K$ and $\bar{K}$ mesons. Based on the QCD sum rule with the operators of up to dimension 10 within the operator product expansion, we found that it is hard to treat the $f_0(980)$ as a simple $K\bar{K}$ bound state, which implies that the $f_0(980)$ scalar meson has more complicated structure being mixed states of various configurations.

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arXiv2013

Baryonic Matter in the Hidden Local Symmetry Induced from Holographic QCD Models

Baryonic matter is studied in the Skyrme model by taking into account the roles of $π,$ $ρ$, and $ω$ mesons through the hidden local symmetry up to $\mathcal{O}(p^4)$ terms including the homogeneous Wess-Zumino (hWZ) terms. Using the master formulas for the low energy constants derived from holographic QCD models the skyrmion matter properties can be quantitatively calculated with the input values of the pion decay constant $f_π$ and the vector meson mass $m_ρ^{}$. We find that the hWZ terms are responsible for the repulsive interactions of the $ω$ meson. In addition, the self-consistently included $\mathcal{O}(p^4)$ terms with the hWZ terms is found to increase the half skyrmion phase transition point above the normal nucleon density.

hep-ph↗

arXiv2013

Skyrmions with vector mesons in the hidden local symmetry approach

The roles of light $ρ$ and $ω$ vector mesons in the Skyrmion are investigated in a chiral Lagrangian derived from the hidden local symmetry (HLS) up to $O(p^4)$ including the homogeneous Wess-Zumino (hWZ) terms. We write a general "master formula" that allows us to determine the parameters of the HLS Lagrangian from a class of holographic QCD models valid at large $N_c$ and $λ$ ('t Hooft constant) limit by integrating out the infinite towers of vector and axial-vector mesons other than the lowest $ρ$ and $ω$ mesons. Within this approach we find that the physical properties of the Skyrmion as the solitonic description of baryons are \textit{independent} of the HLS parameter $a$. Therefore the only parameters of the model are the pion decay constant and the vector meson mass. Once determined in the meson sector, we have a totally parameter-free theory that allows us to study unequivocally the role of light vector mesons in the Skyrmion structure. We find, as suggested by Sutcliffe, that inclusion of the $ρ$ meson reduces the soliton mass, which makes the Skyrmion come closer to the Bogomol'nyi-Prasad-Sommerfield (BPS) soliton, but the role of the $ω$ meson is found to increase the soliton mass. In a stark contrast, the $Δ$-$N$ mass difference, which is determined by the moment of inertia in adiabatic collective quantization of the Skyrmion, is increased by the $ρ$ vector meson, while it is reduced by the inclusion of the $ω$ meson. All these observations show the importance of the $ω$ meson in the properties of the nucleon and nuclear matter in the Skyrme model.

hep-ph↗

arXiv2012

Gauge-invariant theory of two-pion photo- and electro-production off the nucleon

A field-theoretical description of the photoproduction of two pions off the nucleon is presented that applies to real as well as virtual photons in the one-photon approximation. The Lorentz-covariant theory is complete at the level of all explicit Faddeev-type three-body final-state mechanisms of dressed interacting hadrons, including those of the nonlinear Dyson-Schwinger type. All electromagnetic currents are constructed to satisfy their respective (generalized) Ward-Takahashi identities and thus satisfy local gauge invariance as a matter of course. The Faddeev-type ordering structure results in a natural expansion of the full two-pion photoproduction current $\Mpp^μ$ in terms of multiple loops that preserve gauge invariance order by order in the number of loops, which in turn lends itself naturally to practical applications of increasing sophistication with increasing number of loops.

nucl-th↗

arXiv2012

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.

hep-ph↗

arXiv2012

Production and parity determination of $Ξ$ baryons

To understand the structure of hadrons and their production mechanisms, it is very important to be able to identify their quantum numbers. For investigating the spin and parity quantum numbers of $Ξ$ and $Ω$ baryons, in particular, it is very important to understand strong interactions in the strangeness sector. At present, such quantum numbers are known for only a few of the $Ξ$ baryons, and even the parity of the ground state $Ξ(1318)$ has never been measured. In this article, we present a novel, model-independent way to determine the parity of $Ξ$ baryons solely based on symmetry considerations for the hadronic reaction $\bar{K} N \to K Ξ$.

nucl-th↗

arXiv2012

Model-independent determination of the parity of $Ξ$ hyperons

Based on reflection symmetry in the reaction plane, it is shown that measuring the transverse spin-transfer coefficient $K_{yy}$ in the $\bar{K}N \to KΞ$ reaction directly determines the parity of the produced cascade hyperon in a model-independent way as $π_Ξ=K_{yy}$, where $π_Ξ=\pm 1$ is the parity. This result based on Bohr's theorem provides a completely general, universal relationship that applies to the entire hyperon spectrum. A similar expression is obtained for the photoreaction $γN \to K K Ξ$ by measuring both the double-polarization observable $K_{yy}$ and the photon-beam asymmetry $Σ$. Regarding the feasibility of such experiments, it is pointed out that the self-analyzing property of the $Ξ$'s can be invoked, thus requiring only a polarized nucleon target.

hep-ph↗

arXiv2012

Axial anomaly and the delta_{LT} puzzle

The axial anomaly contribution to generalized longitudinal-transverse polarizability $δ_{LT}^{}$ is calculated within Regge approach. It is shown that the contribution from the exchange of the $a_1^{}(1260)$ Regge trajectory is nontrivial and might have the key role to explain the large difference between the predictions of chiral perturbation theory and the experimental data for the neutron $δ_{LT}^{}$. We also present the prediction for the proton $δ_{LT}^{}$, which will be measured at the Thomas Jefferson National Accelerator Facility in near future.

hep-ph↗

arXiv2011

Hyperons analogous to the Λ(1405)

The low mass of the $Λ(1405)$ hyperon with $j^P = 1/2^-$, which is higher than the ground state $Λ(1116)$ mass by 290 MeV, is difficult to understand in quark models. We analyze the hyperon spectrum in the bound state approach of the Skyrme model that successfully describes both the $Λ(1116)$ and the $Λ(1405)$. This model predicts that several hyperon resonances of the same spin but with opposite parity form parity doublets that have a mass difference of around 300 MeV, which is indeed realized in the observed hyperon spectrum. Furthermore, the existence of the $Ξ(1620)$ and the $Ξ(1690)$ of $j^P=1/2^-$ is predicted by this model. Comments on the $Ω$ baryons and heavy quark baryons are made as well.

nucl-th↗

arXiv2011

Contribution of higher nucleon resonances to K*Λ photoproduction

We investigate K*Λ(1116) photoproduction off the proton and neutron targets in the effective Lagrangian method in the tree-level Born approximation. In addition to the K, K*, and κ exchanges which are the main contributions to the reaction, we consider the contributions from the higher nucleon resonances D13(2080) and the D15(2200). We find that the D13(2080) plays a crucial role in explaining the enhancement of the near-threshold production rate, which results in a good agreement with the experimental data for the proton targets, while the contribution of the D15(2200) is rather small. A similar conclusion is drawn for K* photoproduction off the neutron targets. In addition to the energy and angular dependence of the cross sections, we present the predictions on the photon-beam asymmetry.

hep-ph↗

arXiv2011

Combined analysis of eta meson hadro- and photo-production off nucleons

The $η$-meson production in photon- and hadron-induced reactions, namely, $γp \to p η$, $π^- p \to n η$, $pp \to ppη$, and $pn \to pnη$, are investigated in a combined analysis in order to learn about the relevant production mechanisms and the possible role of nucleon resonances in these reactions. We consider the nucleonic, mesonic, and nucleon resonance currents constructed within an effective Lagrangian approach and compare the results with the available data for cross sections and spin asymmetries for these reactions. We found that the reaction $γp \to p η$ could be described well with the inclusion of the well-established $S_{11}(1535)$, $S_{11}(1650)$, $D_{13}(1520)$, and $D_{13}(1700)$ resonances, in addition to the mesonic current. Consideration of other well-established resonances in the same mass region, including the spin-5/2 resonances, $D_{15}(1675)$ and $F_{15}(1680)$, does not further improve the results qualitatively. For the reaction $π^- p \to n η$, the $P_{13}(1720)$ resonance is found to be important for reproducing the structure observed in the differential cross section data. Our model also improves the description of the reaction $NN \to NNη$ to a large extent compared to the earlier results by Nakayama \textit{et al.} [Phys.\ Rev.\ C \textbf{68}, 045201 (2003)]. For this reaction, we address two cases where either the $S_{11}(1535)$ or the $D_{13}$ dominates. Further improvement in the description of these reactions and the difficulty to uniquely determine the nucleon resonance parameters in the present type of analysis are discussed.

hep-ph↗

arXiv2011

K*Lambda(1116) photoproduction and nucleon resonances

We study the reaction mechanism of K*Lambda(1116) photoproduction off the proton target near threshold considering the contributions from nucleon-resonances. Employing the effective Lagrangian method at the tree-level Born approximation, we investigate the role of the D13(2080) and the D15(2200). We found that the D13 plays a crucial role to reproduce the experimental data well in the forward scattering region at low energy. We also present theoretical predictions on the single photon-beam asymmetry as well as the energy and angular dependence for the cross sections of this reaction.

hep-ph↗

arXiv2011

K*Λ(1116) photoproduction and nucleon resonances

In this presentation, we report our recent studies on the $K^*Λ(1116)$ photoproduction off the proton target, using the tree-level Born approximation, via the effective Lagrangian approach. In addition, we include the nine (three- or four-star confirmed) nucleon resonances below the threshold $\sqrt{s}_\mathrm{th}\approx2008$ MeV, to interpret the discrepancy between the experiment and previous theoretical studies, in the vicinity of the threshold region. From the numerical studies, we observe that the $S_{11}(1535)$ and $S_{11}(1650)$ play an important role for the cross-section enhancement near the $\sqrt{s}_\mathrm{th}$. It also turns out that, in order to reproduce the data, we have the vector coupling constants $g_{K^*S_{11}(1535)Λ}=(7.0\sim9.0)$ and $g_{K^*S_{11}(1650)Λ}=(5.0\sim6.0)$.

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