arXiv subjects

Xingbo Zhao

Publications and source records attributed to Xingbo Zhao.

At least 37 records · Page 2Linked to original sources

arXiv2025

Basis light-front quantization approach to $Λ$ and $Λ_c$ and their isospin triplet baryons

We obtain the masses, the electromagnetic properties, and the parton distribution functions (PDFs) of $Λ$, $Λ_c$, and their isospin triplet baryons, i.e, $Σ^0$, $Σ^+$, $Σ^-$ and $Σ_c^0$, $Σ_c^+$, $Σ_c^{++}$ from a light-front effective Hamiltonian in the leading Fock sector in the basis light-front quantization framework. The light-front wave functions of these baryons are given by the eigenstates of the effective Hamiltonian consisting of a three-dimensional confinement potential and a one-gluon exchange interaction with fixed coupling. The masses of these baryons in our approach are in the experimental range while isospin-dependent mass differences are too small. Meanwhile, the electromagnetic properties are in agreement with the available experimental data, the lattice QCD simulations, and the other theoretical calculations. We also present the gluon and the sea quark PDFs, which we generate dynamically from the QCD evolution of the valence quark distributions.

hep-ph↗

arXiv2025

Dynamical gluon effects in the three-dimensional structure of pion

We investigate the internal structure of the pion, including the contributions from one dynamical gluon, using the basis light-front quantization (BLFQ) approach. By solving a light-front QCD Hamiltonian with a three-dimensional confining potential, we obtain the light-front wavefunctions (LFWFs) for both the quark-antiquark and quark-antiquark-gluon Fock sectors. These wavefunctions are then employed to compute the unpolarized generalized parton distributions (GPDs) and the transverse-momentum-dependent parton distributions (TMDs) of valence quarks and gluons. We also extract the transverse spatial distributions, providing the squared radii of quark and gluon densities in the impact-parameter space. This work contributes toward a three-dimensional understanding of the pion's internal structure in both momentum and coordinate space.

hep-ph↗

arXiv2025

Structure of lightest nuclei in the visible Universe

The simplest atomic nucleus, deuteron, provides key insights into the strong nuclear interactions among quarks and gluons that shape the visible universe. We present the first attempt to calculate the internal structure of the deuteron by incorporating hidden-color degrees of freedom, modeling it as an effective mixture of singlet-singlet and octet-octet color clusters beyond the traditional proton-neutron picture. By employing the separation of variables for the light-front two-cluster bound-state equation, we explore how these hidden color correlations shape both its spin and electromagnetic structure. We incorporate the transverse and longitudinal dynamics by two Schrödinger-like equations, namely the light-front holography and the 't Hooft equation, respectively. Our predictions of the electromagnetic form factors and structure functions, including tensor-polarized function, align well with experimental data, offering insights into the partonic structure of the deuteron. Its tensor property could pave the way for a new era in spin physics, guiding future experimental investigations.

hep-ph↗

arXiv2025

Double parton distributions of the proton from basis light-front quantization

Within the basis light-front quantization framework, we systematically investigate the unpolarized and longitudinally polarized double parton distributions (DPDs) of quarks inside the proton. We utilize the light-front wave functions of the proton derived in the valence sector from a Hamiltonian quantized on the light-front. The interaction terms of the Hamiltonian consist of a one-gluon exchange interaction at fixed coupling and a three-dimensional confinement potential. Our current analysis yields significant correlations of the quarks' longitudinal momenta with their transverse separation. We also demonstrate that our calculations do not support the commonly used $x-\vec{k}_\perp$ factorization of the DPDs in $x$ and $k_\perp$. Our results are qualitatively consistent with those of other phenomenological models.

hep-ph↗

arXiv2025

Proton Gravitational Structure and Mass Decomposition on the Light Front

Gravitational form factors (GFFs) of hadrons encode essential information about the internal distributions of mass, spin, pressure, and shear among their quark and gluon constituents. We compute the quark and gluon GFFs of the proton using a fully relativistic, nonperturbative framework based on a light-front quantized Hamiltonian with quantum chromodynamics (QCD) input. This allows us to quantify the impact of a dynamical gluon on the proton's mechanical properties, such as pressure and shear distributions. Our predictions agree well with recent lattice QCD results and experimental extractions. We also determine the proton's mass and mechanical radii and address the long-standing puzzle of its mass decomposition. At the scale $μ^2 = 4~\mathrm{GeV}^2$, we find that quark energy, gluon field energy, the quark condensate, and the QCD trace anomaly contribute $31.5\%$, $34.7\%$, $11.3\%$, and $22.5\%$, respectively, which are consistent with lattice QCD findings.

hep-ph↗

arXiv2025

Gluonic contributions to the pion parton distribution functions

We investigate the role of a dynamical gluon in the pion within the Basis Light-Front Quantization (BLFQ) framework and compare it with the solution of the Minkowski space Bethe-Salpeter equation (BSE), focusing on contributions beyond the valence sector. We develop a framework to compute the quark-antiquark-gluon component of the pion, starting from its valence light-front wave function. Additionally, the quark and gluon parton distribution functions (PDFs) are derived by considering this higher Fock component in the pion state. The proposed operator, which acts on the valence state to produce the quark-antiquark-gluon component of the pion, is tested against results from BLFQ for its contribution to the quark and gluon PDFs, as well as with results from the BSE. In the BLFQ framework, we identify the effect of dynamical chiral symmetry breaking on the pion structure through the enhancement of the spin-flip matrix element. This enhancement is captured in the $|q\bar{q}g\rangle$ component of the light-front wave function and the associated gluon PDF. We explicitly demonstrate an enhancement of the low-$x$ contribution in the quark PDF, which is associated with the large spin-flip matrix element, which also drives the $π-ρ$ mass splitting. The proposed framework also enables an exploration of the effect of the dressed gluon mass for a given valence state at the pion scale. We show that when the gluon mass vanishes, departing from the constituent gluon picture, it has a significant impact on the gluon PDF.

hep-ph↗

arXiv2025

Basis light-front quantization approach to deuteron

We obtain the deuteron's wave functions as eigenstates of the light-front quantum chromodynamics (QCD) Hamiltonian using a fully relativistic and nonperturbative approach based on light-front quantization, without an explicit confining potential. These eigenstates include six-quark and six-quark--one-gluon components. The deuteron wave function consists of both a singlet-singlet color state and additional hidden color states arising from non-trivial color rearrangements. Our results reveal that while the singlet-singlet state is present, the hidden color states collectively dominate, contributing a larger probability to the deuteron wave function. This highlights the significant role of hidden color components in the QCD description of nuclear structure. Using these wave functions, we investigate the deuteron's electromagnetic properties.

hep-ph↗

arXiv2025

Gravitational form factor $D$ of charmonium from shear stress

Based on our recent analysis of the hadronic matrix element of the stress-energy tensor in covariant light front dynamics, we extract the charmonium gravitational form factor $D(Q^2)$ from shear stress $T^{12}$. This is in contrast to our recent work using the (light-front) energy density $T^{+-}$. Indeed, by comparing these two currents, we identify terms that are responsible for the violation of the current conservation. Numerical results based on basis light-front quantization show that the violation effects are small and the $D$-term extracted from the two currents are close to each other, hence validating our previous work using $T^{+-}$.

hep-ph↗

arXiv2025

Scattering and gluon emission of physical quarks in a SU(3) colored field

We study the scattering of the gluon-dressed physical quarks, defined as the eigenstates of the vacuum QCD Hamiltonian, off a colored medium. We solve the wavefunction of the physical quark state by diagonalizing the QCD Hamiltonian in vacuum in a $\ket{q}+\ket{qg}$ Fock space, with implementing the sector-dependent mass renormalization scheme. We then perform numerical simulations of the real-time quantum state evolution of the initially dressed quark state at various medium densities. The results are compared with those of an initially bare or off-shell quark states. With the obtained light-front wavefunction of the evolved state, we extract the quark jet transverse momentum broadening, the quenching parameter, the cross section, the gluon emission rate, and the evolution of the invariant mass. The scenario considered is relevant for high energy scattering processes, where the quark originates from far outside the color field describing the scattering target. This investigation on dressed quarks complements our earlier studies of the single quark scattering in the $\ket{q}$ Fock space, and of the bare quark scattering in the $\ket{q}+\ket{qg}$ Fock space, providing a novel systematic description of quark scattering process using a non-perturbative formalism.

hep-ph↗

arXiv2025

Color structure of deuteron on the light front

We investigate the color structure of the deuteron by solving the light-front QCD Hamiltonian for its six-quark and six-quark-one-gluon components using basis light-front quantization. In this framework, the deuteron wavefunction consists of a singlet-singlet color state as well as additional hidden color states arising from non-trivial color rearrangements. Our analysis shows that while the singlet-singlet state is present, the hidden color states collectively dominate, contributing a larger probability to the deuteron wavefunction. These findings provide new insights into the role of hidden color components in the QCD description of nuclear structure.

hep-ph↗

arXiv2025

Basis light-front quantization: Advancing a first principles approach for the nucleon

We present our recent progress in applying the basis light-front quantization approach to investigate the nucleon's structure. We solve its wave functions from the eigenstates of the light-front QCD Hamiltonian using a fully relativistic, nonperturbative approach without an explicit confining potential. These eigenstates are determined for the three-quark, three-quark-gluon, and three-quark-quark-antiquark Fock representations, making them suitable for low-resolution probes. From these wave functions, we compute the nucleon's quark and gluon matter densities, as well as its helicity and transversity distributions, showing qualitative consistency with experimental data. We also determine the quark and gluon helicity contributions to the proton spin and the tensor charges. The resulting light-front wave functions represent a significant step toward a unified description of hadron distribution functions in both longitudinal and transverse momentum space.

hep-ph↗

arXiv2025

Basis light-front quantization for the $Λ_b$ and $Σ_b$ baryons

Within the basis light-front quantization framework, we compute the masses and light-front wave functions of the $Λ_b$ baryon and its isospin triplet counterparts $Σ_b^+$, $Σ_b^0$, and $Σ_b^-$ using a light-front effective Hamiltonian in the leading Fock sector. These wave functions are obtained as eigenstates of the effective Hamiltonian, which incorporates the one-gluon exchange interaction with fixed coupling and a three-dimensional confinement potential. With the quark masses and the couplings as adjustable parameters, the computed masses are set within the experimental range. The resulting predictions for their electromagnetic properties align well with other theoretical calculations. Additionally, the parton distribution functions (PDFs) of these baryons are obtained for the first time, with gluon and sea quark distributions dynamically generated through QCD evolution of the valence quark PDFs.

hep-ph↗

arXiv2025

Transverse structure of the proton beyond leading twist: A light-front Hamiltonian approach

Within the Basis Light-Front Quantization framework, we systematically investigate the subleading twist (twist-3) transverse-momentum-dependent parton distribution functions (TMDs) of the proton beyond the Wandzura-Wilczek (WW) approximation. The subleading twist TMDs are not independent and can be decomposed into twist-2 and genuine twist-3 terms from the equations of motion. The latter involves quark-quark-gluon correlations and contains interferences between two light-front Fock sectors, $|qqq\rangle$ and $|qqqg\rangle$, which are usually neglected in the WW approximation.

hep-ph↗

arXiv2025

Gluon skewed generalized parton distributions of proton from a light-front Hamiltonian approach

We calculate all leading-twist gluon generalized parton distributions (GPDs) inside the proton at nonzero skewness using the basis light-front quantization framework. The proton's light-front wave functions are derived from a light-front quantized Hamiltonian incorporating Quantum Chromodynamics inputs. Our results show that the qualitative behaviors of the GPDs are consistent with those from other theoretical calculations. Additionally, we analyze the GPDs in the boost-invariant longitudinal coordinate, $σ=\frac{1}{2} b^- P^+$, which serves as the Fourier conjugate of the skewness. The GPDs in $σ$-space exhibit diffraction patterns, reminiscent of optical wave diffraction.

hep-ph↗

arXiv2025

Sub-barrier d+$^{208}$Pb scattering and sensitivity to nucleon-nucleon interactions

We employ the non-perturbative time-dependent basis function (tBF) approach to solve for the sub-Coulomb barrier scattering of the deuteron projectile on the $^{208}$Pb target. Specifically, we treat the target as a source of a strong external Coulomb field that induces higher-order effects in electric-dipole excitations of the deuteron projectile including the population of states not accessible through direct electric-dipole transitions from the ground state of the deuteron. We calculate the electric-dipole polarizability of the deuteron and elastic scattering observables for comparison with experimental data. With no adjustable parameters, the tBF approach provides good agreement with experimentally available differential cross-section ratios. The dependence of these measured quantities on nucleon-nucleon interactions is investigated. We also investigate the detailed scattering dynamics and identify characteristics of coherent and incoherent processes.

nucl-th↗

arXiv2025

Strange mesons with one dynamical gluon: A light-front approach

We obtain the mass spectra of strange mesons using a light-front quantized Hamiltonian with Quantum Chromodynamics (QCD) input, incorporating quark-antiquark and quark-antiquark-gluon Fock components, along with a three-dimensional confinement. We work within the basis light-front quantization framework. The resulting eigenvectors can simultaneously describe the kaon's electromagnetic form factor, decay constant, distribution amplitude, and quark and gluon distribution functions under QCD scale evolution. Using the obtained kaon parton distribution functions (PDFs), supplemented by established nuclear PDFs, we also predict the kaon-nucleus-induced Drell-Yan cross section, which is expected to be measured soon by COMPASS++/AMBER at CERN.

hep-ph↗

arXiv2024

Quark and gluon entanglement in the proton based on a light-front Hamiltonian

Given that the wave function of a proton can be derived relativistically and nonperturbatively from a light-front quantized Hamiltonian, investigating the quantum correlation between quarks and gluons offers a novel perspective on the internal structure of partons within a proton. In this work, we address this topic by computing the spin and longitudinal momentum entanglement of each parton inside the proton. The utilized wave functions are generated using Basis Light-front Quantization (BLFQ), incorporating both the valence quarks and one dynamical gluon Fock sectors, $\left|qqq\right\rangle$ and $\left|qqq\right\rangle +\left|qqqg\right\rangle$. Our calculations indicate that the dynamical gluon significantly enhances entanglement among the proton's partons. Additionally, we examine the spin entanglement of quarks and gluons at fixed values of longitudinal momentum fraction, revealing that the presence of a gluon may amplify the informational exchanges between quarks. Finally, these findings suggest the potential for experimental verification of the entanglement between partons by measuring parton helicity distributions in the proton.

hep-ph↗

arXiv2024

Flavor asymmetry from the non-perturbative nucleon sea

We demonstrate, in the context of a scalar version of the chiral effective field theory, that the multi-sea quark contribution to the nucleon is significant and highly non-trivial in sharp contrast to the prediction of perturbation theory. The non-perturbative calculation is performed in the Fock sector dependent renormalization scheme on the light front, in which the non-perturbative renormalization is incorporated. The calculation suggests that a fully non-perturbative calculation of the chiral EFT is needed to obtain a robust result to be compared with the recent experimental measurement of flavor asymmetry in the proton.

hep-ph↗