arXiv subjects

Ghil-Seok Yang

Publications and source records attributed to Ghil-Seok Yang.

At least 19 recordsLinked to original sources

arXiv2025

Properties of neutron stars and strangeness-mixed stars from a pion mean-field approach

We investigate the properties of the static neutron stars and strangeness-mixed stars, based on the equations of state derived from a pion mean-field approach. Using the empirical data on the pion-nucleus scattering and bulk properties of nuclear matter, we have already fixed all the parameters in a previous work, where the nucleons and hyperons were shown to be modified in various nuclear medium. In the current work, we first examine the energy and pressure inside a neutron star. We show that the central densities in various neutron stars vary within the range of $(3-4)ρ_0$, where $ρ_0$ is the normal nuclear matter density. The mass-radius relations are obtained and discussed. As the slope parameter for neutron matter increases, the radii of the neutron stars increase with their masses fixed. We also study the strangeness-mixed stars or the hyperon stars using the same sets of the parameters. As the strangeness content of strange matter increases, the binding energy per nucleon is saturated and the corresponding equation of state becomes softened. Consequently, the central densities of the strangeness-mixed stars increase. Assuming that recently observed neutron stars are the strangeness-mixed ones, we find that the central densities increase.

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arXiv2022

Medium modification of singly heavy baryons in a pion-mean field approach

We investigate how the masses of singly heavy baryons undergo changes in nuclear matter. The mass spectrum of the singly heavy baryons was successfully described in a pion-mean field approach even with isospin symmetry breaking, based on which we extend the investigation to the medium modification of the singly heavy baryons. Since all dynamical parameters were determined by explaining the mass spectrum of the SU(3) light and singly heavy baryons in free space, we can directly implement the density-dependent functionals for the dynamical parameters, of which the density dependence was already fixed by reproducing the bulk properties of nuclear matter and medium modification of the SU(3) light baryons. We predict and discuss the density dependence of the masses of the singly heavy baryons.

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arXiv2022

Quark spin content of SU(3) light and singly heavy baryons

We investigate the quark spin content of the SU(3) baryon octet, decuplet, antitriplet, and sextet in a pion mean-field approach or the chiral quark-soliton model, considering the $1/N_c$ rotational corrections and SU(3) symmetry breaking effects. We compare the present results with those from various theoretical works and lattice QCD.

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arXiv2021

Baryonic matter and the medium modification of the baryon masses

We investigate the properties of baryonic matter within the framework of the in-medium modified chiral soliton model by taking into account the effects of surrounding baryonic environment on the properties of in-medium baryons. The internal parameters of the model are determined based on nuclear phenomenology at nonstrange sector and fitted by reproducing nuclear matter properties near the saturation point. We discuss the equations of state in different nuclear environments such as symmetric nuclear matter, neutron and strange matters. We show that the results for the equations of state are in good agreement with the phenomenology of nuclear matter. We also discuss how the SU(3) baryons masses undergo changes in these various types of nuclear matter.

nucl-th↗

arXiv2021

Electromagnetic transitions of the singly charmed baryons with spin 3/2

We investigate the electromagnetic transitions of the singly charmed baryons with spin 3/2, based on a pion mean-field approach, also known as the chiral quark-soliton model, taking into account the rotational $1/N_c$ corrections and the effects of flavor SU(3) symmetry breaking. We examine the valence- and sea-quark contributions to the electromagnetic transition form factors and find that the quadrupole form factors of the sea-quark contributions dominate over those of the valence-quark ones in the smaller $Q^2$ region, whereas the sea quarks only provide marginal contributions to the magnetic dipole transition form factors of the baryon sextet with spin 3/2. The effects of the flavor SU(3) symmetry breaking are in general very small except for the forbidden transition $Ξ_c^0γ\to Ξ_c^{*0}$ by $U$-spin symmetry. We also discuss the widths of the radiative decays for the baryon sextet with spin 3/2, comparing the present results with those from other works.

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arXiv2020

Isospin mass differences of singly heavy baryons

We study the isospin mass differences of singly heavy baryons, based on a pion mean-field approach. We consider both the electromagnetic interactions and the hadronic contributions that arise from the mass difference of the up and down quarks. The relevant parameters have been already fixed by the baryon octet. In addition, we introduce the strong hyperfine interactions between the light quarks inside a chiral soliton and the Coulomb interactions between the chiral soliton and a heavy quark. The numerical results are in good agreement with the experimental data. In particular, the results for the neutral mass relations, which contain only the electromagnetic contributions, are in remarkable agreement with the data, which implies that the pion mean field approach provides a good description of the singly heavy baryons.

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arXiv2019

Magnetic transitions and radiative decays of singly heavy baryons

A pion mean-field approach allows one to investigate light and singly heavy baryons on an equal footing. In the large $N_c$ limit, the light and singly heavy baryons are viewed respectively as $N_c$ and $N_c-1$ valence quarks bound by the pion mean fields created self-consistently, since a heavy quark can be regarded as a static color source in the limit of the infinitely heavy quark mass. The transition magnetic moments of the baryon sextet are determined entirely by using the parameters fixed in the light-baryon sector without any additional parameters introduced. Assuming that the transition $E2$ moments are small, we are able to compute the radiative decay rates of the baryon sextet. The numerical results are discussed, being compared with those from other approaches.

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arXiv2019

New narrow nucleon resonances $N^{\ast}(1685)$ and $N^{\ast}(1726)$ within the chiral quark-soliton model

We investigate the strong and radiative decay widths of the narrow nucleon resonances $N^*(1685)$ and $N^{\ast}(1726)$ within the framework of the SU(3) chiral quark-soliton model. All the relevant parameters are taken from those used to describe the properties of the baryon octet and decuplet in previous works. The masses of the antidecuplet nucleon and the eikosiheptaplet (27-plet) nucleon with spin 3/2 are determined respectively to be $(1690.2\pm 10.5)\, \mathrm{MeV}$ and $(1719.6\pm7.4)\,\mathrm{MeV}$. The decay width for $N^{\ast}(1685)\to η+ N$ is found to be approximately three times larger than that for $N^{\ast}(1685)\to π+N$. The width of the decay $N^{\ast}\left(1726\right)3/2^+\to η+N$ is even about 31 times larger than that of $N^{\ast}\left(1726\right)3/2^+\to π+ N$. The ratio of the radiative decays for $N^*(1685)$ is obtained to be $Γ_{nn^*(1685)}/Γ_{pp^*(1685)}=8.62\pm3.45$ which explains very well the neutron anomaly. In contrast, we find $Γ_{pp^*(1726)}/Γ_{nn^*(1726)}=3.72\pm0.64$, which indicates that the production of $N^*(1726)$ is more likely to be observed in the proton channel. We also examined the decay modes of these narrow nucleon resonances with the strangeness hadrons involved.

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arXiv2018

Mass spectra of singly heavy baryons in a self-consistent chiral quark-soliton model

We investigate the mass spectra of the lowest-lying singly heavy baryons, based on the self-consistent chiral quark-soliton model. We take into account the rotational $1/N_c$ and strange current quark mass ($m_{\mathrm{s}}$) corrections. Regarding $m_{\mathrm{s}}$ as a small perturbation, we expand the effective chiral action to the second order with respect to $m_{s}$. The mass spectra of heavy baryons are computed and compared with the experimental data. Fitting the classical masses of the heavy baryon to the center mass of each representation, we determine the masses of all the lowest-lying singly heavy baryons. We predict the mass of the $Ω_b^*$ baryon to be 6081.9 MeV, when the second-order $m_{\mathrm{s}}$ corrections are included.

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arXiv2018

Meson-baryon coupling constants of the SU(3) baryons with flavor SU(3) symmetry breaking

We investigate the strong coupling constants for the baryon octet-octet, decuplet-octet, and decuplet-decuplet vertices with pseudoscalar mesons within a general framework of the chiral quark-soliton model, taking into account the effects of flavor SU(3) symmetry breaking to linear order in the expansion of the strange current quark mass. All relevant dynamical parameters are fixed by using the experimental data on hyperon semileptonic decays and the singlet axial-vector constant of the nucleon. The results of the strong coupling constants for the baryon octet and the pseudoscalar meson octet are compared with those determined from the Jülich-Bonn potential and the Nijmegen extended soft-core potential for hyperon-nucleon scattering. The results of the strong decay widths of the baryon decuplet are in good agreement with the experimental data. The effects of $SU_f(3)$ symmetry breaking are sizable on the $η'$ coupling constants. We predict also the strong coupling constants for the $Ω$ baryons.

hep-ph↗

arXiv2018

Magnetic moments of the lowest-lying singly heavy baryons

A light baryon is viewed as $N_c$ valence quarks bound by meson mean fields in the large $N_c$ limit. In much the same way a singly heavy baryon is regarded as $N_c-1$ valence quarks bound by the same mean fields, which makes it possible to use the properties of light baryons to investigate those of the heavy baryons. A heavy quark being regarded as a static color source in the limit of the infinitely heavy quark mass, the magnetic moments of the heavy baryon are determined entirely by the chiral soliton consisting of a light-quark pair. The magnetic moments of the baryon sextet are obtained by using the parameters fixed in the light-baryon sector. In this mean-field approach, the numerical results of the magnetic moments of the baryon sextet with spin $3/2$ are just 3/2 larger than those with spin $1/2$. The magnetic moments of the bottom baryons are the same as those of the corresponding charmed baryons.

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arXiv2017

Strong decays of exotic and non-exotic heavy baryons in the chiral quark-soliton model

In the large $N_c$ limit both heavy and light baryons are described by the universal mean field, which allows us to relate the properties of heavy baryons to light ones. With the only input from the decays of light octet baryons (due to the universality of the chiral mean field), excellent description of strong decays of both charm and bottom sextets is obtained. The parameter-free prediction for the widths of exotic anti-decapentaplet ($\overline{\boldsymbol{15}}$) baryons is also made. The exotic heavy baryons should be anomalously narrow despite of large phase space available. In particular, the widths of $Ω_c(3050)$ and $Ω_c(3119)$, interpreted as members of $\overline{\boldsymbol{15}}$-plet, are very small: 0.48~MeV and 1.12~MeV respectivly. This result is in very good agreement with the measurements of the LHCb Collaboration and provides natural and parameter free explanation of the LHCb observation that $Ω_c(3050)$ and $Ω_c(3119)$ have anomalously small widths among five recently observed states.

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arXiv2016

Pion mean fields and heavy baryons

We show that the masses of the lowest-lying heavy baryons can be very well described in a pion mean-field approach. We consider a heavy baryon as a system consisting of the $N_c-1$ light quarks that induce the pion mean field, and a heavy quark as a static color source under the influence of this mean field. In this approach we derive a number of \textit{model-independent} relations and calculate the heavy baryon masses using those of the lowest-lying light baryons as input. The results are in remarkable agreement with the experimental data. In addition, the mass of the $Ω_b^*$ baryon is predicted.

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arXiv2015

Hyperon Semileptonic decay constants with flavor SU(3) symmetry breaking

We investigate the hyperon semileptonic decay constants, $f_2/f_1$, and $g_1/f_1$, within a general framework of a chiral soliton model. All relevant parameters for the SU(3) baryon wave functions were unambiguously determined by using the experimental data for the masses of the baryon octet and the decuplet. Using then the existing experimental data for the magnetic moments of the baryon octet and the decay constants of hyperon semileptonic decays, we are able to determine all the hyperon semileptonic decay constants $f_2/f_1$ and $g_1/f_1$ of the baryon octet unequivocally. In addition, we also present the results of the axial-vector transition constants from the baryon decuplet to the octet.

hep-ph↗

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 $Λ_c$.

nucl-th↗

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.

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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.

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