arXiv subjects

Xingbo Zhao

Publications and source records attributed to Xingbo Zhao.

At least 55 records · Page 3Linked to original sources

arXiv2024

Efficient and precise quantum simulation of ultra-relativistic quark-nucleus scattering

We present an efficient and precise framework to quantum simulate the dynamics of the ultra-relativistic quark-nucleus scattering. This framework employs the eigenbasis of the asymptotic scattering system and implements a compact scheme for encoding this basis upon lattice discretization. It exploits the operator structure of the light-front Hamiltonian of the scattering system, which enables the Hamiltonian input that utilizes the quantum Fourier transform for efficiency. Our framework simulates the scattering by the efficient and precise algorithm of the truncated Taylor series. The qubit cost of our framework scales logarithmically with the Hilbert space dimension of the scattering system. The gate cost has optimal scaling with the simulation error and near optimal scaling with the simulation time. These scalings make our framework advantageous for large-scale dynamics simulations on future fault-tolerant quantum computers. We demonstrate our framework with a simple scattering problem and benchmark the results with those from the Trotter algorithm and the classical calculations, where good agreement between the results is found. Our framework can be generalized to simulate the dynamics of various scattering problems in quantum chromodynamics.

quant-ph↗

arXiv2024

Towards a first principles light-front Hamiltonian for the nucleon

We solve the nucleon's wave functions from the eigenstates of the light-front quantum chromodynamics Hamiltonian for the first time, using a fully relativistic and nonperturbative approach based on light-front quantization, 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 this, we calculate the nucleon's quark and gluon matter densities, helicity, and transversity distributions, which show qualitative consistency with experimental extractions. We also compute the contributions of quark and gluon helicity to the proton spin and the tensor charges. The obtained light-front wave functions represent a significant advancement towards a unified description of various hadron distribution functions in both longitudinal and transverse momentum space.

hep-ph↗

arXiv2024

Chiral-odd gluon generalized parton distributions in the proton: A light-front quantization approach

Within the basis light-front quantization (BLFQ) framework, we evaluate the gluon chiral-odd generalized parton distributions (GPDs) inside the proton at zero skewness. We employ the light-front wave functions of the proton obtained from a light-front quantized Hamiltonian with quantum chromodynamics input using BLFQ. Our investigation encompasses both the valence Fock sector with three constituent quarks and an additional sector containing three quarks and a dynamical gluon. We analyze the gluon GPDs in the momentum space as well as in the transverse position space. We further present the gluon's generalized form factors derived from the Mellin moments of its chiral-odd GPDs. Using the proton transverse spin sum rule, we also present the $x$-dependence of the angular momentum carried by the polarized gluon and determine the relative contributions of quarks and the gluon to the transversity asymmetry.

hep-ph↗

arXiv2024

Stress out of charmonia

We investigate the gravitational form factors of charmonium. Our method is based on a Hamiltonian formalism on the light front known as basis light-front quantization. The charmonium mass spectrum and light-front wave functions were obtained from diagonalizing an effective Hamiltonian that incorporates confinement from holographic QCD and one-gluon exchange interaction from light-front QCD. We proposed a quantum many-body approach to construct the hadronic matrix elements of the energy momentum tensor $T^{++}$ and $T^{+-}$, which are used to extract the gravitational form factors $A(Q^2)$ and $D(Q^2)$. The obtained form factors satisfy the known constraints, e.g. von Laue condition. From these quantities, we also extract the energy, pressure and light-front energy distributions of the system. We find that hadrons are multi-layer systems.

hep-ph↗

arXiv2024

Pion to photon transition form factor: Beyond valence quarks

We investigate the singly virtual transition form factor (TFF) for the $π^0\toγ^*γ$ process in the space-like region using the hard-scattering formalism within the Basis Light-Front Quantization (BLFQ) framework. This form factor is expressed in terms of the perturbatively calculable hard-scattering amplitudes (HSAs) and the light-front wave functions (LFWFs) of the pion. We obtain the pion LFWFs by diagonalizing the light-front QCD Hamiltonian, which is determined for its constituent quark-antiquark and quark-antiquark-gluon Fock sectors with a three-dimensional confinement. We employ the HSAs up to next-to-leading order (NLO) in the quark-antiquark Fock sector and leading order (LO) in the quark-antiquark-gluon Fock sector. The NLO correction to the TFF in the quark-antiquark Fock sector is of the same order as the LO contribution to the TFF in the quark-antiquark-gluon Fock sector. We find that while the quark-antiquark-gluon Fock sector has minimal effect in the large momentum transfer ($Q^2$) region, it has a noteworthy impact in the low-$Q^2$ region. Our results show that, after accounting for both Fock sectors, the TFF within the BLFQ framework aligns well with existing experimental data, particularly in the low $Q^2$ region.

hep-ph↗

arXiv2024

The Connection between the Stochastic Schrödinger Equation and Boltzmann Equation

The heavy quarks present in the quark-gluon plasma (QGP) can act as a probe of relativistic heavy ion collisions as they retain the memory of their interaction history. In a previous study, a stochastic Schrödinger equation (SSE) has been applied to describe the transport process of heavy quarks, where an external field with random phases is used to simulate the thermal medium. In this work, we study the connection between the SSE and the Boltzmann equation (BE) approach in the Keldysh Green's function formalism. By comparing the Green's function of the heavy quark from the SSE and the Keldysh Green's functions leading to the Boltzmann equation, we demonstrate that the SSE is consistent with the Boltzmann equation in the weak coupling limit. We subsequently confirm their consistency through numerical calculations.

nucl-th↗

arXiv2024

Energy momentum tensor on and off the light cone: exposition with scalar Yukawa theory

We compute the gravitational form factors $A_i$, $D_i$ and $\bar c_i$ of the scalar Yukawa theory using both the light-cone and covariant perturbation theory at the one-loop level. The light-cone formalism provides a potential approach to access these form factors beyond the perturbative regime. However, unlike the covariant formulation, the Poincaré symmetry on the light cone is not manifest. In this work, we use perturbation theory as a benchmark to extract the gravitational form factors from the light-front energy-momentum tensor. By comparing results on and off the light cone, we identify $T^{++}, T^{+a}, T^{+-}, T^{12}$ as the "good currents" that are properly renormalized and can be used to extract the gravitational form factors.

hep-ph↗

arXiv2024

Electron form factors in Basis Light-front Quantization

In this paper, we evaluate the electromagnetic and gravitational form factors as well as the corresponding generalized parton distributions of the electron using the Basis Light-front Quantization approach to QED. We compare our results with those from light-front perturbation theory. We adopt a novel basis with its scale depending on the constituents' longitudinal momentum fraction. We show that this basis improves convergence of the form factors with increasing basis dimension, compared to that calculated in the original basis with fixed scale. These results both validate the BLFQ approach and provide guidance for its efficient implementation in solving light-front Hamiltonian mass eigenstates for more complex systems in QED and QCD.

hep-ph↗

arXiv2024

Gravitational Form Factors and Mechanical Properties of Quarks in Protons: A Basis Light-Front Quantization Approach

We compute the gravitational form factors (GFFs) and study their applications for the description of the mechanical properties such as the pressure, shear force distributions, and the mechanical radius of the proton from its light-front wave functions (LFWFs) based on basis light-front quantization (BLFQ). The LFWFs of the proton are given by the lowest eigenvector of a light-front effective Hamiltonian that incorporates a three-dimensional confining potential and a one-gluon exchange interaction with fixed coupling between the constituent quarks solved in the valence Fock sector. We find acceptable agreement between our BLFQ computations and the lattice QCD for the GFFs. Our $D$-term form factor also agrees well with the extracted data from the deeply virtual Compton scattering experiments at Jefferson Lab, and the results of different phenomenological models. The distributions of pressures and shear forces are similar to those from different models.

hep-ph↗

arXiv2024

Transverse-momentum-dependent gluon distributions of proton within basis light-front quantization

Gluon transverse-momentum dependent distributions (TMDs) are very important for revealing the internal structure of the proton. They correspond to a variety of experiments and are among the major tasks of the future electron-ion colliders. In this paper, we calculate the T-even gluon TMDs at the leading twist within the Basis Light-front Quantization framework. We employ the light-front wave functions of the proton obtained from a light-front quantized Hamiltonian with Quantum Chromodynamics input determined for its valence Fock sector with three constituent quarks and an additional Fock sector, encompassing three quarks and a dynamical gluon, with a three-dimensional confinement. After obtaining the numerical results we investigate the properties of gluon TMDs by checking whether they satisfy the Mulders-Rodrigues inequalities and investigate the correlations between transverse and longitudinal degrees of freedom. With their connection to unintegrated gluon distributions in mind, we further investigate the limiting behaviours of gluon TMDs in the small-$x$ and large-$x$ regions.

hep-ph↗

arXiv2024

Skewed generalized parton distributions of proton from basis light-front quantization

We obtain all the leading-twist quark generalized parton distributions (GPDs) inside the proton at nonzero skewness within the basis light-front quantization framework. We employ the light-front wave functions of the proton from a light-front quantized Hamiltonian in the valence Fock sector consisting of a three-dimensional confinement potential and a one-gluon exchange interaction with fixed coupling. We find that the qualitative behaviors of our GPDs are similar to those of other theoretical calculations. We further examine the GPDs within the boost-invariant longitudinal coordinate, $σ=\frac{1}{2} b^- P^+$, which is identified as the Fourier conjugate of the skewness. The GPDs in the $σ$-space show diffraction patterns, which are akin to the diffractive scattering of a wave in optics.

hep-ph↗

arXiv2024

Spatial imaging of proton via leading-twist non-skewed GPDs with basis light-front quantization

The internal image of the proton is unveiled by examining the generalized parton distributions (GPDs) at zero skewness, within the basis light-front quantized environment. Several distributions emerge when a quark is sampled with different currents depending upon the helicity arrangements of the active quark and the proton target. We investigate six of the eight leading-twist proton GPDs of the valence quarks, the helicity conserving distributions $(H, E, \tilde{H})$ and the helicity non-conserving $(H_T,E_T,\tilde{H}_T)$ distributions at skewness set to zero ($ζ=0$). We consider purely transverse momentum transfer and, hence, obtain results describe only the proton's two-dimensional structure in the transverse plane. We present the Mellin moments of these distribution functions, where the first moment produces a form factor and the second Mellin moments help extract the information on partonic contributions to the hadronic angular momentum. We compare our results for the Mellin moments with those from lattice QCD and other approaches where available. We also present the GPDs in transverse position space.

hep-ph↗

arXiv2024

Quark and gluon distributions in $ρ$-meson from basis light-front quantization

We solve for the $ρ$-meson's wave functions from a light-front QCD Hamiltonian determined for its constituent quark-antiquark and quark-antiquark-gluon Fock components, with a three-dimensional confinement using basis light-front quantization. From this, we obtain the leading-twist valence quark's parton distribution functions and transverse momentum-dependent parton distributions inside the $ρ$-meson. These results are qualitatively consistent with those of other models. We also demonstrate the important effects of a dynamical gluon on the $ρ$-meson's gluon densities, helicity, transversity, and tensor polarized distributions.

hep-ph↗

arXiv2023

Generalized parton distributions of gluon in proton: a light-front quantization approach

We solve for the gluon generalized parton distributions (GPDs) inside the proton, focusing specifically on leading twist chiral-even GPDs. We obtain and employ the light-front wavefunctions (LFWFs) of the proton from a light-front quantized Hamiltonian with Quantum Chromodynamics input using basis light-front quantization (BLFQ). Our investigation incorporates the valence Fock sector with three constituent quarks and an additional Fock sector, encompassing three quarks and a dynamical gluon. We examine the GPDs within impact parameter space and evaluate the $x$-dependence of the transverse square radius. We find that the transverse size of the gluon at lower-$x$ is larger than that of the quark, while it exhibits opposite behavior at large-$x$. Using the proton spin sum rule, we also determine the relative contributions of quarks and the gluon to the total angular momentum of the proton.

hep-ph↗

arXiv2023

On the momentum broadening of in-medium jet evolution using a light-front Hamiltonian approach

We have developed a non-perturbative light-front Hamiltonian formalism to simulate the real-time evolution of a quark state in a SU(3) colored medium, with a series of works. In this proceeding article, we focus on the transverse momentum broadening of an in-medium quark jet. We perform the numerical simulation of the quark jet evolution in the $\ket{q}+\ket{qg}$ Fock space at various medium densities. By analyzing the resulting jet light-front wavefunction, we extract the gluon emission rate and the non-eikonal quenching parameter. Additionally, we provide the analytical derivation of the eikonal expectation value of the quark-gluon state's transverse momentum for any color configuration and arbitrary spatial distribution. This study can help understand jet momentum broadening beyond the eikonal limit.

hep-ph↗

arXiv2023

On the momentum broadening of in-medium jet evolution using a light-front Hamiltonian approach

Following the non-perturbative light-front Hamiltonian formalism developed in our preceding work [Phys.Rev.D 104 (2021) 5, 056014], we investigate the momentum broadening of a quark jet inside a SU(3) colored medium. We perform the numerical simulation of the real-time jet evolution in Fock spaces of a single quark, a quark-gluon state, and coupled quark- and quark-gluon states at various jet momenta $p^+$ and medium densities. With the obtained jet light-front wavefunction, we extract the jet transverse momentum distribution, the quenching parameter, and the gluon emission rate. We analyze the dependence of momentum broadening on $p^+$, medium density, color configuration, spatial correlation, and medium-induced gluon emission. For comparison, we also derive analytically the expectation value of the transverse momentum of a quark-gluon state in any color configuration and in an arbitrary spatial distribution in the eikonal limit. This work can help understand jet momentum broadening in the non-eikonal regime.

hep-ph↗

arXiv2023

Transverse momentum structure of strange and charmed baryons: a light-front Hamiltonian approach

Under the basis light-front quantization framework, we investigate the leading-twist transverse-momentum-dependent parton distribution functions (TMDs) for $Λ$ and $Λ_c$ baryons, the spin-1/2 composite systems consisting of two light quarks ($u$ and $d$) and a $s/c$ quark. We evaluate the TMDs using the overlaps of the light-front wave functions in the leading Fock sector, which are obtained by solving the light-front eigenvalue equation. We also study the spin densities of quarks in momentum space for various polarizations. In the same model, we compare the TMDs of the strange and charmed baryons and the proton by reviewing their spin structures in the quark model and the probabilistic interpretations of their TMDs.

hep-ph↗

arXiv2023

Transverse structure of the pion beyond leading twist with basis light-front quantization

We investigate the twist-$3$ transverse-momentum-dependent parton distribution functions (TMDs) of the pion with basis light-front quantization. The twist-3 TMDs are not independent and can be decomposed into twist-$2$ and genuine twist-$3$ terms from the equations of motion (EOM). We compute the TMDs from the resulting light-front wave functions obtained by diagonalizing the light-front QCD Hamiltonian, determined for pion's constituent quark-antiquark and quark-antiquark-gluon Fock sectors, with three-dimensional confinement. We also obtain the twist-3 parton distribution functions (PDFs) and show that they preserve the sum rule, which affirms the robustness of our approach. This is the first time that theoretical predictions are made for subleading twist structures of the pion containing interference terms between two light-front Fock sectors.

hep-ph↗