arXiv subjects

Zhi Hu

Publications and source records attributed to Zhi Hu.

At least 19 recordsLinked to original sources

arXiv2026

Exclusive $J/\psi$ photoproduction in photon-proton diffractive scattering: A light-front Hamiltonian approach

We investigate the cross-section for exclusive $J/\psi$ production in photon-proton diffractive scattering within the Basis Light-Front Quantization (BLFQ) framework. The leading-order contribution to this process is well approximated by the charge conjugation-even two-gluon (``pomeron") exchange mechanism in the dipole model, which factorizes the total amplitude into the dipole scattering amplitude and the convolution of the $J/\psi$ and photon light-front wave functions (LFWFs). We express the dipole scattering amplitude as the matrix element of gluon field operators inserted between proton states, with the element being sensitive to the proton LFWFs and the Bjorken scaling variable, $x$. The proton and $J/\psi$ LFWFs are obtained by diagonalizing their respective light-front Hamiltonians within the BLFQ approach, while the virtual photon LFWFs are employed from perturbative QCD. Our results provide initial conditions for the Balitsky-Kovchegov (BK) equation, which can be used to probe the proton structure at smaller Bjorken scales. This work offers valuable theoretical insights for future electron-ion collider experiments.

hep-ph↗

arXiv2026

Study on the systematic effects on $b \to c$ inclusive semileptonic decays

We discuss the calculation of the inclusive semileptonic decay for the process $B_s \to X_c \, l \nu_l$ using lattice QCD. This calculation could be decisive in understanding the long-standing tension between inclusive and exclusive determinations of the CKM matrix element, $|V_{cb}|$. In this talk, we investigate the main sources of systematic uncertainty in these decays, including the impact of Jacobi smearing at the source and sink, variations in source-sink separation, and the intrinsic uncertainties of the inclusive reconstruction method itself. In addition, we explain how we can restrict the reconstruction of the inclusive decay rate to just the excited-state contributions. This is achieved by treating the ground-state contributions as an exclusive decay with well-controlled conventional techniques. Systematic effects from the reconstruction then only affect excited-state contributions. Where these are sub-dominant, a suppression of systematic effects is expected. We show results based on Chebyshev reconstruction, which are part of a larger effort towards a first phenomenologically relevant computation of the inclusive decay rate in the continuum and infinite-volume limits.

hep-lat↗

arXiv2026

Inclusive semileptonic $D_s\to X_s\ell\bar\nu$ decays from lattice QCD: continuum and chiral extrapolation

We present results for the inclusive semileptonic $D_s \to X_s \ell\bar\nu$ decay rate from lattice QCD. Chiral and continuum extrapolations are performed using gauge ensembles generated with 2+1 flavours of M\"obius domain-wall fermions. Systematic errors are fully addressed including those from the integral over all possible final states. Our results are in agreement with currently available experimental data, with an error at the few-percent level.

hep-lat↗

arXiv2026

Heavy mesons with dynamical gluon on the light front

We investigate the structure of charmonium, bottomonium, and $\rm B_c$ meson systems within the Basis Light-Front Quantization (BLFQ) approach, including both the quark-antiquark ($|q\bar{q}\rangle$) and quark-antiquark-gluon ($|q\bar{q}g\rangle$) Fock sectors. Our input light-front Hamiltonian incorporates a confining potential inspired by light-front holography, as well as the quark-gluon interaction from Quantum Chromodynamics. By adjusting model parameters to reproduce the mass spectra for low-lying states, we obtain the light-front wave functions for the heavy meson states. Based on these wave functions, we calculate electromagnetic form factors, decay constants, parton distribution amplitudes (PDAs), and parton distribution functions (PDFs) of the quarks and gluons in the heavy mesons. Our results for the charge radii and decay constants reasonably agree with experimental data and other theoretical approaches. The PDAs are consistent with the predictions from the earlier BLFQ calculations with an effective one-gluon exchange interaction. Furthermore, we present the first predictions within the BLFQ framework for the gluon PDFs in heavy mesons based on the light-front wave function in the $|q\bar{q}g\rangle$ sector.

hep-ph↗

arXiv2026

Inclusive and exclusive semileptonic decays of heavy mesons on the lattice

We report the recent progress from our group in extracting observables of both inclusive and exclusive semileptonic heavy-meson decays directly from lattice QCD four-point correlators. On the inclusive side, we illustrate how to estimate the systematic uncertainties from omitted higher-order terms and non-zero smearing of the kernel approximation, building on two important features of the Chebyshev expansion. On the exclusive side, we perform BCL parameterizations of the pseudoscalar to pseudoscalar form factors and compare the fitted coefficients with those from earlier results by HPQCD. We also perform a HQET-based parameterization of the P-wave form factors to shed new light on the 1/2-vs-3/2 puzzle. This work constitutes a step toward a unified lattice treatment of inclusive and exclusive semileptonic decays, relevant for the Vcb puzzle. In this study, we use lattice ensembles from the RBC/UKQCD collaboration for numerical investigations. Future developments from our group will focus on the control of other systematic effects for inclusive decays and investigations of other techniques with reduced statistical errors to extract exclusive contributions from lattice four-point correlators.

hep-lat↗

arXiv2025

Deformation theory of parabolic representation pairs

In this paper, we introduce the notions of parabolic representation pairs and the parabolic representation pair variety. We investigate the deformation theory of parabolic representation pairs. The Zariski tangent space and the tangent quadratic cone of the parabolic representation pair variety are described. By the Riemann--Hilbert--Deligne correspondence, we pro-represent the analytic germs of parabolic representation pair variety by functors related to certain groupoids of parabolic logarithmic flat bundles. Under suitable assumptions, we prove that the differential graded Lie algebra (DGLA) controlling the deformation of a parabolic logarithmic flat bundle is partially formal. This leads to the quadraticity of the subvariety of parabolic representation pair variety, which consists of parabolic representation pairs with fixed eigenvalues of monodromies, at certain generic points. Finally, we construct the moduli space of weighted parabolic representation pairs, and, by means of quiver representation theory, we establish the Kobayashi--Hitchin-type theorem for polystable parabolic representation pairs.

math.AG↗

arXiv2025

Inclusive semileptonic decays from lattice QCD: analysis of systematic effects

Lattice QCD calculations of inclusive semileptonic decay rates involve new types of systematic effects, such as truncation errors in the estimation of energy integrals, or finite-volume effects for multi-body final states. We investigate them for the lattice data of $D_s \to X_s \ell\nu$ decays, obtained using M\"obius domain-wall fermions. Separating the ground-state and excited-state contributions results in better control over these systematic effects. With the Chebyshev polynomial approximation, the truncation error is under control, while the finite-volume effects are estimated using a model to describe two-body final states.

hep-lat↗

arXiv2025

Basis light-front quantization for the $\Lambda_b$ and $\Sigma_b$ baryons

Within the basis light-front quantization framework, we compute the masses and light-front wave functions of the $\Lambda_b$ baryon and its isospin triplet counterparts $\Sigma_b^+$, $\Sigma_b^0$, and $\Sigma_b^-$ 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

Study on the $P$-wave form factors contributing to $ B_s $ to $D_s$ inclusive semileptonic decays from lattice simulations

We present a pilot study on extracting the form factors of the semileptonic decay of a $ B_s $ meson to the $P$-wave $ D_s^{**} $ states from $B_s$ four-point correlators. With their inclusive nature, four-point correlators include contributions from all possible final states. From the extracted $ P $-wave form factors, we obtain numerical results for the corresponding Isgur-Wise form factors. The results suggest significant contributions from radial excitations to the Uraltsev sum rule at zero-recoil. In this pilot study, a coarse lattice of $ 24^3\times 64 $ with lattice spacing of $0.11\,\mathrm{fm}$ is used for the analysis.

hep-lat↗

arXiv2024

Systematic effects in the lattice calculation of inclusive semileptonic decays

We report on the calculation of the inclusive semileptonic decay of the $D_s$ meson on the lattice. We simulate the $D_s \rightarrow X_s\ell\nu_\ell$ process with M\"obius domain-wall charm and strange quarks, whose masses are approximately tuned to their physical values. Our simulations cover the whole kinematical region. The focus of this work is to present updates on our strategies towards estimating the systematic uncertainties in the determination of the inclusive decay rate. We specifically focus on the systematic errors due to the choice of our approximation strategy and finite-volume effects.

hep-lat↗

arXiv2024

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↗

arXiv2024

Parahoric reduction theory of formal connections (or Higgs fields)

In this paper, we establish the parahoric reduction theory of formal connections (or Higgs fields) on a formal principal bundle with parahoric structures, which generalizes Babbitt-Varadarajan's result for the case without parahoric structures [5] and Boalch's result for the case of regular singularity [9]. As applications, we prove the equivalence between extrinsic definition and intrinsic definition of regular singularity and provide a criterion of relative regularity for formal connections, and also demonstrate a parahoric version of Frenkel-Zhu's Borel reduction theorem of formal connections [23].

math.AG↗

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

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

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↗

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

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

We solve for the $\rho$-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 $\rho$-meson. These results are qualitatively consistent with those of other models. We also demonstrate the important effects of a dynamical gluon on the $\rho$-meson's gluon densities, helicity, transversity, and tensor polarized distributions.

hep-ph↗

arXiv2023

Twist-3 Generalized Parton Distribution for the Proton from Basis Light-Front Quantization

We investigate the twist-3 generalized parton distributions (GPDs) for the valence quarks of the proton within the basis light-front quantization (BLFQ) framework. We first solve for the mass spectra and light-front waved functions (LFWFs) in the leading Fock sector using an effective Hamiltonian. Using the LFWFs we then calculate the twist-3 GPDs via the overlap representation. By taking the forward limit, we also get the twist-3 parton distribution functions (PDFs), and discuss their properties. Our prediction for the twist-3 scalar PDF agrees well with the CLAS experimental extractions.

hep-th↗