arXiv subjects

Chueng-Ryong Ji

Publications and source records attributed to Chueng-Ryong Ji.

At least 37 records · Page 2Linked to original sources

arXiv2024

Consistency of pion form factor and unpolarized transverse momentum dependent parton distributions beyond leading twist in the light-front quark model

We investigate the interplay among the pion's form factor, transverse momentum dependent distributions (TMDs), and parton distribution functions (PDFs) extending our light-front quark model (LFQM) computation based on the Bakamjian-Thomas construction for the two-point function[41,42] to the three-point and four-point functions. Ensuring the four-momentum conservation at the meson-quark vertex from the Bakamjian-Thomas construction, the meson mass is taken consistently as the corresponding invariant meson mass both in the matrix element and the Lorentz factor in our LFQM computation. We achieve the current-component independence in the physical observables such as the pion form factor and delve into the derivation of unpolarized TMDs and PDFs associated with the forward matrix element. We address the challenges posed by twist-4 TMDs and exhibit the fulfillment of the sum rule. Effectively, our LFQM successfully handles the light-front zero modes and offers insights for broader three-point and four-point functions and related observables.

hep-ph↗

arXiv2023

Pseudoscalar meson decay constants and distribution amplitudes up to twist-4 in the light-front quark model

In the light-front quark model (LFQM) amenable to the simultaneous study of both the mass spectroscopy and the wave function related observables, we examine the decay constants and distribution amplitudes (DAs) up to the twist-4. The analysis of the heavy pseudoscalar mesons is carried out both in the $1S$ and $2S$ states. This investigation involves calculating the local and nonlocal matrix elements $\langle 0 |{\bar q}Γ q|P \rangle$ using three distinct current operators $Γ=(γ^μγ_5, iγ_5,σ^{μν}γ_5)$. Considering a general reference frame where ${\bf P}_\perp\neq 0$ and investigating all available current components, we examine not only the frame-independence but also the component-independence of the decay constants. The explicit findings from our study provide the evidence for the equality of the three pseudoscalar meson decay constants obtained from the three distinct current operators $Γ$. The notable agreement in decay constants is attained by imposing the Bakamjian-Thomas construction of the LFQM, namely the meson state is constructed by the noninteracting quark and antiquark representations while the interaction is added to the mass operator, which provides the self-consistency condition replacing the physical mass $M$ with the invariant mass $M_0$ for the noninteracting quark-antiquark representation of the meson state. In addition to obtaining the process-independent pseudoscalar meson decay constant, regardless of the choice of current operators $Γ$, we further demonstrate its explicit Lorentz and rotation invariance. In particular, we present the analysis conducted on the twist-4 DA derived from the minus component of the axial-vector current. Finally, we discuss the various twist DAs and their $ξ$-moments associated with the $1S$ and $2S$ heavy pseudoscalar mesons.

hep-ph↗

arXiv2023

Octet and decuplet baryon $σ$-terms and mass decompositions

We present a comprehensive analysis of the SU(3) octet and decuplet baryon masses and $σ$-terms using high-precision lattice QCD data and chiral SU(3) effective theory with finite range regularization. The effects of various systematic uncertainties, including from the scale setting of the lattice data and the regularization prescriptions, are quantified. We find the pion-nucleon and strange nucleon $σ$-terms to be $σ_{πN} = 44(3)(3)$ MeV and $σ_{N s} = 50(6)(1)$ MeV, respectively. The results provide constraints on the energy-momentum tensor mass decompositions of the SU(3) octet and decuplet baryons, where we find the trace anomaly and quark/gluon energies decrease for strange baryons due to their larger strange $σ$-terms.

nucl-th↗

arXiv2023

The case for an EIC Theory Alliance: Theoretical Challenges of the EIC

We outline the physics opportunities provided by the Electron Ion Collider (EIC). These include the study of the parton structure of the nucleon and nuclei, the onset of gluon saturation, the production of jets and heavy flavor, hadron spectroscopy and tests of fundamental symmetries. We review the present status and future challenges in EIC theory that have to be addressed in order to realize this ambitious and impactful physics program, including how to engage a diverse and inclusive workforce. In order to address these many-fold challenges, we propose a coordinated effort involving theory groups with differing expertise is needed. We discuss the scientific goals and scope of such an EIC Theory Alliance.

hep-ph↗

arXiv2023

Independence of current components, polarization vectors, and reference frames in the light-front quark model analysis of meson decay constants

The issue of resulting in the same physical observables with different current components, in particular from the minus current, has been challenging in the light-front quark model (LFQM) even for the computation of the two-point functions such as meson decay constants. At the level of one-body current matrix element computation, we show the uniqueness of pseudoscalar and vector meson decay constants using all available components including the minus component of the current in the LFQM consistent with the Bakamjian-Thomas construction. Regardless of the current components, the polarization vectors, and the reference frames, the meson decay constants are uniquely determined in the non-interacting constituent quark and antiquark basis while the interactions of the constituents are added to the meson mass operator in the LFQM.

hep-ph↗

arXiv2022

Generalized parton distributions of sea quarks in the proton from nonlocal chiral effective theory

We calculate the spin-averaged generalized parton distributions (GPDs) of sea quarks in the proton at zero skewness from nonlocal covariant chiral effective theory, including one-loop contributions from intermediate states with pseudoscalar mesons and octet and decuplet baryons. A relativistic regulator is generated from the nonlocal Lagrangian where a gauge link is introduced to guarantee local gauge invariance, with additional diagrams from the expansion of the gauge link ensuring conservation of electric charge and strangeness. Flavor asymmetries for sea quarks at zero and finite momentum transfer, as well as strange form factors, are obtained from the calculated GPDs, and results compared with phenomenological extractions and lattice QCD.

hep-ph↗

arXiv2022

Nucleon form factors and parton distributions in nonlocal chiral effective theory

We present a review of recent applications of nonlocal chiral effective theory to hadron structure studies. Starting from a nonlocal meson--baryon effective chiral Lagrangian, we show how the introduction of a correlation function representing the finite extent of hadrons regularizes the meson loop integrals and introduces momentum dependence in vertex form factors in a gauge invariant manner. We apply the framework to the calculation of nucleon electromagnetic form factors, unpolarized and polarized parton distributions, as well as transverse momentum dependent distributions and generalized parton distributions. Assuming that the nonlocal behavior is a general property of all interactions, we also discuss the application to the lepton anomalous magnetic moment in nonlocal QED.

hep-ph↗

arXiv2022

Helicity-dependent distribution of strange quarks in the proton from nonlocal chiral effective theory

The helicity-dependent strange quark distribution in the proton, $Δs$, is calculated in a nonlocal chiral SU(3) effective field theory. The hadronic proton to meson plus octet or decuplet baryon splitting functions are derived at the one-loop level, with loop integrals rendered finite by correlation functions introduced in the nonlocal Lagrangian. Within the convolution framework, the proton strange helicity distribution is obtained using spin-flavor symmetry to constrain the input valence quark distributions in the hadronic intermediate states. The polarized strange quark distribution is found to be quite small, with the lowest moment of $Δs$ negative, but consistent with recent global QCD analyses.

hep-ph↗

arXiv2021

Analysis of virtual meson production in solvable (1+1) dimensional scalar field theory

Light-front time-ordered amplitudes are investigated in the virtual scalar meson production process in (1+1) dimensions using the solvable scalar field theory extended from the conventional Wick-Cutkosky model. There is only one Compton form factor (CFF) in the (1+1) dimensional computation of the virtual meson production process, and we compute both the real and imaginary parts of the CFF for the entire kinematic regions of $Q^2>0$ and $t<0$. We then analyze the contribution of each and every light-front time-ordered amplitude to the CFF as a function of $Q^2$ and $t$. In particular, we discuss the significance of the "cat's ears" contributions for gauge invariance and the validity of the "handbag dominance" in the formulation of the generalized parton distribution (GPD) function used typically in the analysis of deeply virtual meson production processes. We explicitly derive the GPD from the "handbag" light-front time-ordered amplitudes in the $-t/Q^2<<1$ limit and verify that the integrations of the GPD over the light-front longitudinal momentum fraction for the DGLAP and ERBL regions correspond to the valence and nonvalence contributions of the electromagnetic form factor that we have recently reported [Phys. Rev. D $\textbf{103}$, 076002 (2021)]. We also discuss the correspondence of the GPD to the parton distribution function for the analysis of the deep inelastic lepton-hadron scattering process and the utility of the new light-front longitudinal spatial variable $\tilde{z}$.

hep-ph↗

arXiv2021

Global QCD Analysis of Pion Parton Distributions with Threshold Resummation

We perform the first global QCD analysis of pion valence, sea quark, and gluon distributions within a Bayesian Monte Carlo framework with threshold resummation on Drell-Yan cross sections at next-to-leading log accuracy. Exploring various treatments of resummation, we find that the large-$x$ asymptotics of the valence quark distribution $\sim (1-x)^{β_v}$ can differ significantly, with $β_v$ ranging from $\approx 1$ to $> 2.5$ at the input scale. Regardless of the specific implementation, however, the resummation induced redistribution of the momentum between valence quarks and gluons boosts the total momentum carried by gluons to $\approx 40\%$, increasing the gluon contribution to the pion mass to $\approx 40$ MeV.

hep-ph↗

arXiv2021

Interpolating 't Hooft model between instant and front forms

The 't Hooft model, i.e. the two-dimensional quantum chromodynamics in the limit of infinite number of colors, is interpolated by an angle parameter $δ$ between $δ=0$ for the instant form dynamics (IFD) and $δ=π/4$ for the light-front dynamics (LFD). With this parameter $δ$, we formulate the interpolating mass gap equation which takes into account the non-trivial vacuum effect on the bare fermion mass to find the dressed fermion mass. Our interpolating mass gap solutions link the IFD and LFD results with the $δ$ parameter. We find the interpolation angle independent characteristic energy function which satisfies the energy-momentum dispersion relation of the dressed fermion, identifying the renormalized fermion mass function and the wave function renormalization factor. Using the dressed fermion propagator interpolating between IFD and LFD, we derive the corresponding quark-antiquark bound-state equation in the interpolating formulation. The mass spectra of mesons bearing the feature of the Regge trajectories are found independent of the $δ$-parameter for the equal mass quark and antiquark bound-states. The Gell-Mann - Oakes - Renner relation for the pionic ground-state in the zero fermion mass limit is confirmed indicating that the spontaneous breaking of the chiral symmetry occurs regardless of the quantization for $0 \le δ\le π/4$. We obtain the corresponding bound-state wave functions and discuss their reference frame dependence. Applying them for the computation of the so-called quasi parton distribution functions, we note a possibility of utilizing not only the reference frame dependence but also the interpolation angle dependence to get an alternative effective approach to the LFD-like results.

hep-ph↗

arXiv2021

Light-front dynamic analysis of the longitudinal charge density using the solvable scalar field model in (1+1) dimensions

We investigate the electromagnetic form factor $F(q^2)$ of the meson by using the solvable $ϕ^{3}$ scalar field model in $(1+1)$ dimensions. As the transverse rotations are absent in $(1+1)$ dimensions, the advantage of the light-front dynamics (LFD) with the light-front time $x^+ = x^0 + x^3$ as the evolution parameter is maximized in contrast to the usual instant form dynamics (IFD) with the ordinary time $x^0$ as the evolution parameter. In LFD, the individual $x^+$-ordered amplitudes contributing to $F(q^2)$ are invariant under the boost, i.e., frame-independent, while the individual $x^0$-ordered amplitudes in IFD are not invariant under the boost but dependent on the reference frame. The LFD allows to get the analytic result for the one-loop triangle diagram which covers not only the spacelike ($q^{2}<0$) but also timelike region ($q^{2}>0$). Using the analytic results, we verify that the real and imaginary parts of the form factor satisfy the dispersion relations in the entire $q^{2}$ space. Comparing with the results in $(3+1)$ dimensions, we discuss the transverse momentum effects on $F(q^2)$ . We also discuss the longitudinal charge density in terms of the boost invariant variable $\tilde z = p^+ x^-$ in LFD.

hep-ph↗

arXiv2020

Strange quark helicity in the proton from chiral effective theory

We compute the helicity-dependent strange quark distribution in the proton in the framework of chiral effective theory. Starting from the most general chiral SU(3) Lagrangian that respects Lorentz and gauge invariance, we derive the complete set of hadronic splitting functions at the one meson loop level, including the octet and decuplet rainbow, tadpole, Kroll-Ruderman and octet-decuplet transition configurations. By matching hadronic and quark level operators, we obtain generalized convolution formulas for the quark distributions in the proton in terms of hadronic splitting functions and quark distributions in the hadronic configurations, and from these derive model-independent relations for the leading nonanalytic behavior of their moments. Within the limits of parameters of the Pauli-Villars regulators derived from inclusive hyperon production, we find that the polarized strange quark distribution is rather small and mostly negative.

hep-ph↗

arXiv2020

Octet and decuplet baryon self-energies in relativistic SU(3) chiral effective theory

The self-energies of the full set of flavor SU(3) octet and decuplet baryons are computed within a relativistic chiral effective theory framework. The leading nonanalytic chiral behavior is derived for the octet and decuplet masses, and a finite-range regularization consistent with Lorentz and gauge invariance is applied to account for the finite size of the baryons. Using a four-dimensional dipole form factor, the relative importance of various meson-baryon loop contributions to the self-energies is studied numerically as a function of the dipole range parameter and meson mass, and comparison is made between the relativistic results and earlier approximations within the heavy baryon limit.

hep-ph↗

arXiv2020

Chiral anomaly and the pion properties in the light-front quark model

We explore the link between the chiral symmetry of QCD and the numerical results of the light-front quark model, analyzing both the two-point and three-point functions of the pion. Including the axial-vector coupling as well as the pseudoscalar coupling in the light-front quark model, we discuss the implication of the chiral anomaly in describing the pion decay constant, the pion-photon transition form factor and the electromagnetic form factor of the pion. In constraining the model parameters, we find that the chiral anomaly plays a critical role and the analysis of $F_{πγ}(Q^2)$ in timelike region is important. Our results indicate that the constituent quark picture is effective for the low and high $Q^2$ ranges implementing the quark mass evolution effect as $Q^2$ grows.

hep-ph↗

arXiv2019

Pion off-shell electromagnetic form factors: data extraction and model analysis

We investigate the pion electromagnetic half off-shell form factors, which parametrize the matrix element of the charged pion electromagnetic current with one leg off-mass-shell and the other leg on-mass-shell, using an exactly solvable manifestly covariant model of a $(3+1)$ dimensional fermion field theory. The model provides a 3D imaging of the two off-shell pion form factors $F_1$ and $F_2$ as a function of $(Q^2,t)$, which are related to each other satisfying the Ward-Takahashi identity. The normalization of the renormalized charge form factor $F_1$ is fixed by $F_1(Q^2=0, t=m^2_π)=1$ while the other form factor $F_2$ vanishes, i.e. $F_2(Q^2, t=m^2_π)=0$ for any value of $Q^2$ due to the time-reversal invariance of the strong interaction. We define the new form factor $g(Q^2,t)=F_2(Q^2,t)/(t-m^2_π)$ and find that $g(Q^2,t)$ can be measurable in the on-mass-shell limit. In particular, $g(Q^2=0, t=m^2_π)$ is related with the pion charge radius. We also compare our form factors with the data extracted from the pion electroproduction reaction for both the off-shell region ($t<0$) and the on-shell limit ($t \rightarrow m_π^2$).

hep-ph↗

arXiv2019

Twist-2 Pseudoscalar and Vector Meson Distribution Amplitudes in Light-Front Quark Model with Exponential-type Confining Potential

We study the twist-2 distribution amplitudes (DAs) and the decay constants of pseudoscalar light ($π$, $K$) and heavy ($D$, $D_s$, $B$, $B_s$) mesons as well as the longitudinally and transversely polarized vector light ($ρ$, $K^*$) and heavy ($D^*$, $D_s^*$, $B^*$, $B_s^*$) mesons in the light-front quark model with the Coulomb plus exponential-type confining potential $V_{\rm {exp}} = a + b e^{αr}$ in addition to the hyperfine interaction. We first compute the mass spectra of ground state pseudoscalar and vector light and heavy mesons and fix the model parameters necessary for the analysis, applying the variational principle with the trial wave function up to the first three lowest order harmonic oscillator (HO) wave functions $Φ(x, \textbf{k}_\bot) = \sum_{n=1}^{3} c_n ϕ_{nS}$. We then obtain the numerical results for the corresponding decay constants of light and heavy mesons. We estimate the DAs, analyze their variation as a function of momentum fraction and compute the first six $ξ$-moments of the $B$ and $D$ mesons as well. We compare our results with the available experimental data as well as with the other theoretical model predictions.

hep-ph↗

arXiv2019

Parton distributions from nonlocal chiral SU(3) effective theory: Flavor asymmetries

Using recently derived results for one-loop hadronic splitting functions from a nonlocal implementation of chiral effective theory, we study the contributions from pseudoscalar meson loops to flavor asymmetries in the proton. Constraining the parameters of the regulating functions by inclusive production of $n$, $Δ^{++}$, $Λ$ and $Σ^{*+}$ baryons in $pp$ collisions, we compute the shape of the light antiquark asymmetry $\bar{d}-\bar{u}$ in the proton and the strange asymmetry $s-\bar{s}$ in the nucleon sea. With these constraints, the magnitude of the $\bar{d}-\bar{u}$ asymmetry is found to be compatible with that extracted from the Fermilab E866 Drell-Yan measurement, with no indication of a sign change at large values of $x$, and an integrated value in the range $\langle \bar d-\bar u \rangle \approx 0.09-0.17$. The $s-\bar s$ asymmetry is predicted to be positive at $x > 0$, with compensating negative contributions at $x=0$, and an integrated $x$-weighted moment in the range $\langle x (s-\bar s) \rangle \approx (0.9-2.5) \times 10^{-3}$.

hep-ph↗