arXiv subjects

June-Young Kim

Publications and source records attributed to June-Young Kim.

At least 37 records · Page 2Linked to original sources

arXiv2023

Instanton effects in twist-3 generalized parton distributions

The instanton vacuum picture is used to study hadronic matrix elements of the twist-3 (dimension-4, spin-1) QCD operators measuring the quark spin density and spin-orbit correlations. The QCD operators are converted to effective operators in the low-energy effective theory emerging after chiral symmetry breaking, in a systematic approach based on the diluteness of the instanton medium and the $1/N_c$ expansion. The instanton fields induce spin-flavor-dependent "potential" terms in the effective operators, complementing the "kinetic" terms from the quark field momenta. As a result, the effective operators obey the same equation-of-motion relations as the original QCD operators. The spin-orbit correlations are qualitatively different from naive quark model expectations.

hep-ph↗

arXiv2023

Quark distribution functions and spin-flavor structures in $N \to Δ$ transitions

Transition generalized parton distributions have emerged as a novel tool for studying the quantum chromodynamics (QCD) structure of resonances. They provide an integrated picture of the transition form factors and the transition parton distribution functions. In this study, we delve into the angular momentum (AM) properties for the $N\to Δ$ transition and its decomposition into the orbital angular momentum and the intrinsic spin in the context of the quark distribution functions. First, we explore the spin-flavor structures within the framework of both the overlap representations of the three-quark light-cone wave functions and the large $N_c$ limit of QCD. We then estimate the AM quark distribution functions for the $N\to Δ$ transition. Our analysis reveals a substantial flavor asymmetry present in both the orbital angular momentum and intrinsic spin components.

hep-ph↗

arXiv2023

Role of strange quarks in the $D$-term and cosmological constant term of the proton

We investigate the mechanics of the proton by examining the flavor-decomposed proton cosmological constants and generalized vector form factors. The interplay of up, down, and strange quarks within the proton is explored, shedding light on its internal structure. The contributions of strange quarks play a crucial role in the $D$-term and cosmological constants. We find that the flavor blindness of the isovector $D$-term form factor is only valid in flavor SU(3) symmetry.

hep-ph↗

arXiv2023

QCD angular momentum in $N \rightarrow Δ$ transitions

$N \rightarrow Δ$ transitions offer new possibilities for exploring the isovector component of the QCD quark angular momentum (AM) operator causing the $J^{u - d}$ flavor asymmetry in the nucleon. We extend the concept of QCD AM to transitions between baryon states, using light-front densities of the energy-momentum tensor in transversely localized states. We calculate the $N \rightarrow Δ$ transition AM in the $1/N_c$ expansion, connect it with the $J^{u - d}$ flavor asymmetry in the nucleon, and estimate the values using lattice QCD results. In the same setup we connect the transition AM to the transition GPDs sampled in hard exclusive electroproduction processes with $N \rightarrow Δ$ transitions, enabling experimental study of the transition AM.

hep-ph↗

arXiv2023

Two-dimensional charge distributions of the $Δ$ baryon: Interpolation between the nonrelativistic and ultrarelativistic limit

We investigate how the charge distributions of both the unpolarized and transversely polarized $Δ$ baryon change as the longitudinal momentum~($P_{z}$) of the $Δ$ baryon increases from $P_{z}=0$ to $P_{z}=\infty$ in a Wigner phase-space perspective. When the $Δ$ baryon is longitudinally polarized, its two-dimensional charge distribution is kept to be spherically symmetric with $P_{z}$ varied, whereas when the $Δ$ baryon is transversely polarized along the $x$-axis, the quadrupole contribution emerges at the rest frame ($P_{z}=0$). When $P_{z}$ grows, the electric dipole and octupole moments are induced. The induced dipole moment dominates over other higher multipole contributions and governs the deformation of the charge distribution of the $Δ$ baryon.

hep-ph↗

arXiv2022

Gravitational form factors of the baryon octet with flavor SU(3) symmetry breaking

We investigate the gravitational form factors of the baryon octet within the framework of the SU(3) chiral quark-soliton model, considering the effects of flavor SU(3) symmetry breaking, and the corresponding energy-momentum tensor distributions. We examine the effects of flavor SU(3) symmetry breaking to the mass, angular momentum, pressure, and shear force distributions of the baryon octet. We first find that a heavier baryon is energetically more compact than a lighter one. For the spin distributions of the baryon octet, they are properly normalized to their spins and are decomposed into the flavor-singlet axial charge and the orbital angular momentum even when the flavor SU(3) symmetry is broken. While the effects of the flavor SU(3) symmetry breaking differently contribute to the angular momentum distributions for the octet baryons, they are found to be rather small. The spin and orbital angular momentum almost equally contribute to the angular momentum distributions for the octet baryons. We also estimate the effects of the flavor SU(3) symmetry breaking to the pressure and shear force distributions. Interestingly, even if we include the effects of the SU(3) flavor symmetry breaking, the shear force distributions are kept to be positive over $r$. It indicates that the Polyakov & Schweitzer local stability condition is kept to be intact with the flavor SU(3) symmetry broken. Lastly, we discuss how much the gravitational form factors vary with the effects of flavor SU(3) symmetry breaking considered.

hep-ph↗

arXiv2022

Parametrization of transition energy-momentum tensor form factors

While the Lorentz structures of the $N \to Δ$ transition matrix element of the vector current is well-known, that of the symmetric energy-momentum tensor current is unknown. In this letter, we first reproduce the Lorentz structures of the $\frac{1}{2}^{\pm} \to \frac{1}{2}^{\pm}$, $\frac{1}{2}^{\mp} \to \frac{1}{2}^{\pm}$, and $\frac{1}{2}^{\mp} \to \frac{3}{2}^{\pm}$ transition matrix elements of the vector current. We also repeat the parametrizations of the symmetric energy-momentum tensor current for the $\frac{1}{2}^{\pm} \to \frac{1}{2}^{\pm}$ and $\frac{1}{2}^{\mp} \to \frac{1}{2}^{\pm}$ transitions. We then consider both $\frac{1}{2}^{\pm} \to \frac{3}{2}^{\pm}$ and $\frac{1}{2}^{\mp} \to \frac{3}{2}^{\pm}$ matrix elements of the symmetric energy-momentum tensor current (say, $N \to Δ$ transition) for the first time. We found that there are five independent conserved and four independent non-conserved energy-momentum tensor form factors.

hep-ph↗

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.

hep-ph↗

arXiv2022

Mechanical structure of a spin-1 particle

We investigate the mechanical structure of a spin-1 particle. Introducing three different frameworks, i.e., the three-dimensional (3D) Breit frame, the two-dimensional (2D) Breit frame, and the 2D infinite momentum frame (equivalently the two-dimensional Drell-Yan frame), we scrutinize the 2D and 3D energy-momentum tensor (EMT) distributions in these frames. We first derive the EMT distributions in the 2D Breit frame by performing the Abel transformation. The mass distribution in the 2D Breit frame contains an additional monopole contribution induced geometrically. The pressure distribution in the 2D Breit frame also gets an induced monopole structure. When the Lorentz boost is carried out, the mass distribution in the 2D infinite-momentum frame acquires the induced dipole term. Similarly, we also have the induced dipole contributions to the pressure and shear-force densities. We visualize the 2D mass distributions when the spin-1 particle is polarized along the $x$- and $z$-axes. We observe that the 2D mass distribution in the infinite momentum frame exhibit clearly the induced dipole structure when the spin-1 particle is polarized along the $x$-axis. We also discuss the strong force fields inside a polarized spin-1 particle.

hep-ph↗

arXiv2022

Medium modification of the nucleon mechanical properties: Abel tomography case

We investigate how the gravitational form factors of the nucleon undergo changes in nuclear matter, emphasizing the Abel transformation from the three-dimensional (3D) Breit frame to the two-dimensional (2D) light-front frame. Since the gravitational form factors reveal the mechanical structure of the nucleon, we examine also the medium modifications of the energy-momentum, pressure, and shear-force distributions. We scrutinize the stabilities of the nucleon in nuclear matter. For this purpose, we employ the in-medium modified SU(2) Skyrme model to study these mechanical quantities of the nucleon, since it provides a simple but clear framework. In this in-medium modified SU(2) Skyrme model, the modification of pionic properties is performed by using low-energy pion-nucleus scattering data and the saturation properties of nuclear matter near the normal nuclear matter density, $ρ_0=0.5m_π^3$. The results reveal how the nucleon swells in nuclear matter as the mass distribution of the nucleon is broadened in medium. We also show that the mean square radii corresponding to the mass and angular momentum distributions increase in nuclear medium. This feature is kept both in 3D and 2D cases. We visualize how the strong force fields inside the nucleon in the 2D plane are distributed and illustrate how these forces undergo change in nuclear matter.

hep-ph↗

arXiv2022

Electromagnetic multipole structure of a spin-one particle: Abel tomography case

We investigate the three-dimensional~(3D) and two-dimensional~(2D) charge distributions of a spin-one particle in terms of the multipole expansion. On account of the geometrical difference between 2D and 3D spaces, projecting the 3D electric distribution to the 2D one in the Breit frame brings about the influence of the quadrupole distribution upon the monopole one. Thus, the 2D charge distribution becomes spin-dependent. This effect should be sorted out from the relativistic effects arising from the Lorentz boost. We first provide the connections between the 2D and 3D distributions in the Breit frame in terms of the angle-dependent Abel transformation. We then provide the differential equations that enable us to map 2D distributions in the Breit frame to those in the infinite momentum frame.

hep-ph↗

arXiv2022

Structure of the $Ω$ baryon and the kaon cloud

We investigate the effects of the kaon cloud on the electromagnetic and axial-vector form factors of the $Ω^-$ baryon within the framework of the chiral quark-soliton model. We first derive the profile function of the chiral soliton in such a way that the kaon Yukawa tail is properly produced self-consistently. Then, we compute the electromagnetic form factors of the $Ω^-$ baryon. The results for the electromagnetic form factors are compared with the lattice data. We find that the results with the kaon tail employed are in better agreement with the lattice data, compared with those obtained with the pion tail. We also study the axial-vector form factors of the $Ω^-$ baryon, examining the effects of the kaon cloud.

hep-ph↗

arXiv2021

Light-cone distribution amplitudes of the nucleon and $Δ$ baryon

We investigate the light-cone wave functions and leading-twist distribution amplitudes for the nucleon and $Δ$ baryon within the framework of the chiral quark-soliton model. The baryon wave function consists of the valence quark and vacuum wave functions. The vacuum wave functions generate all possible higher Fock states by expanding them. We find that it is essential to consider the five-quark component and relativistic corrections to evaluate the distribution amplitudes of the nucleon and $Δ$ isobar. Having taken into account them, we derive the distribution amplitudes. The results are in good agreement with the lattice data.

hep-ph↗

arXiv2021

Transverse charge distributions of the nucleon and their Abel images

We investigate the two-dimensional transverse charge distributions of the transversely polarized nucleon. As the longitudinal momentum ($P_z$) of the nucleon increases, the electric dipole moment is induced, which causes the displacement of the transverse charge and magnetization distributions of the nucleon. The induced dipole moment of the proton reaches its maximum value at around $P_z \approx 3.2$ GeV due to the kinematical reason. We also investigate how the Abel transformations map the three-dimensional charge and magnetization distributions in the Breit frame on to the transverse charge and magnetization ones in the infinite momentum frame.

hep-ph↗

arXiv2021

Pion mass dependence of the electromagnetic form factors of singly heavy baryons

We study the electromagnetic form factors of the lowest-lying singly heavy baryons with spin 1/2 within the framework of the chiral quark-soliton model, focusing on the comparison with recent lattice data. To compare the present results quantitatively with the lattice data, it is essential to treat the pion mass as a variable parameter, i.e., to employ the unphysical values of the pion mass, which are used in lattice calculations. While the results with the physical value of the pion mass fall off faster than those from the lattice calculations as the momentum transfer increases, the extrapolated results with larger pion masses get closer to the lattice data.

hep-ph↗

arXiv2021

Energy-momentum tensor of the nucleon on the light front: Abel tomography case

We investigate the two-dimensional energy-momentum-tensor (EMT) distributions of the nucleon on the light front, using the Abel transforms of the three-dimensional EMT ones. We explicitly show that the main features of all EMT distributions are kept intact in the course of the Abel transform. We also examine the equivalence between the global and local conditions for the nucleon stability in the three-dimensional Breit frame and in the two-dimensional transverse plane on the light front. We also discuss the two-dimensional force fields inside a nucleon on the light front.

hep-ph↗

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.

hep-ph↗

arXiv2020

Electric quadrupole form factors of singly heavy baryons with spin 3/2

We study the electromagnetic form factors of the lowest-lying singly heavy baryons in a pion mean-field approach, which is also known as the SU(3) chiral quark-soliton model. In the limit of the heavy-quark mass, the dynamics inside a singly heavy baryon is governed by the $N_c-1$ valence quarks, while the heavy quark remains as a mere static color source. In this framework, a singly heavy baryon is described by combining the colored soliton with the singly heavy quark. In the infinitely heavy-quark mass limit, we can compute the electric quadrupole form factors of the baryon sextet with spin 3/2 with the rotational $1/N_c$ and linear corrections of the explicit flavor SU(3) symmetry breaking taken into account. We find that the sea-quark contributions or the Dirac-sea level contributions dominate over the valence-quark contributions in lower $Q^2$ region. We examined the effects of explicit flavor SU(3) symmetry breaking in detail. The numerical results are also compared with the recent data from the lattice calculation with the unphysical value of the pion mass considered, which was used in the lattice calculation.

hep-ph↗