For a proton in the infinite momentum frame, its wave function contains a zero-momentum part (light-front zero-modes) originated from the modification of the QCD vacuum in the presence of the valence quarks, exhibiting a light-front long-range order in the quantum state. This ``non-travelling'' component of the proton contributes to its fundamental properties, including the mass and spin, as well as the naive-time-reversal-odd correlations between transverse momentum and spin. The large momentum effective theory (LaMET) provides a theoretical approach to study the physical properties of the proton's zero-mode ``condensate'' through lattice simulations.
We extend the recently developed formalism to extract light-front quark charge densities from nucleon form factor data to the deformations of these quark charge densities when applying an external electric field. We show that the resulting induced polarizations can be extracted from proton generalized polarizabilities. The available data for the generalized electric polarizabilitiy of the proton yield a pronounced structure in its induced polarization at large transverse distances, which will be pinned down by forthcoming high precision virtual Compton scattering experiments.
The holographic light-front QCD framework provides a unified nonperturbative description of the hadron mass spectrum, form factors and quark distributions. In this article we extend holographic QCD in order to describe the gluonic distribution in both the proton and pion from the coupling of the metric fluctuations induced by the spin-two Pomeron with the energy momentum tensor in anti--de Sitter space, together with constraints imposed by the Veneziano model{\color{blue},} without additional free parameters. The gluonic and quark distributions are shown to have significantly different effecti…
We present model predictions of Collins asymmetries for proton in the SIDIS process for $π^+$ and $π^-$ channels. We use a recently proposed light-front quark-diquark model for proton with the light-front wave functions predicted in soft-wall AdS/QCD. The model predictions are compared with the HERMES and COMPASS data.
We obtain the electromagnetic form factors, the axial form factor, and the parton distribution functions of the proton from the eigenstates of a light-front effective Hamiltonian in the leading Fock representation suitable for low-momentum scale applications. The electromagnetic and the axial form factors are found to be in agreement with the available experimental data. The unpolarized, the helicity, and the transversity valence quark distributions, after QCD evolution, are consistent with the global QCD analyses. The tensor charge also agree the experimental data, while the axial charge is s…
We obtain the gluon parton distribution functions (PDFs) in the proton within the extended light-front holographic QCD framework, where the proton couples with the spin-two Pomeron in Anti-de Sitter space, together with constraints imposed by the Veneziano model. The gluon helicity asymmetry, after satisfying the perturbative QCD constraints at small and large longitudinal momentum regions, agrees with existing experimental measurements. The polarized gluon distribution is consistent with global analyses. We predict the gluon helicity contribution to the proton spin, $ΔG=0.221^{+0.056}_{-0.044…
We present the parton distribution functions (PDFs) for un- polarised, longitudinally polarized and transversely polarized quarks in a proton using the light-front quark diquark model. We also present the scale evolution of PDFs and calculate axial charge and tecsor charge for $u$ and $d$ quarks at a scale of experimental findings.
Dynamical gluon effects in proton transversity and off-forward parton distributions from a light-front Hamiltonian approach
Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；University of Chinese Academy of Sciences（中国科学院大学）；Iowa State University（爱荷华州立大学）
We present all the leading twist T-even TMDs in the light-front quark diquark model(LFQDM) and study the relations among them. The model contains both the scalar and vector diquarks with the light front wave functions modeled from the soft-wall AdS/QCD prediction. The $x-p^2_\perp$ factorization used in phenomenological extraction for TMDs is observed in this model. We present the results for the quark densities and the transverse shape of proton. The shape of the transversely polarized proton is shown to be non-spherical for nonzero transverse momentum. The scale evolution of both integrated …
We employ an effective Hamiltonian that includes the transverse and longitudinal confinement and the one-gluon exchange interaction with fixed coupling constant. By solving the eigenvalue equation in basis light-front quantization (BLFQ), we generate the light-front wavefunctions (LFWFs) for the nucleon in the valence quark Fock space. Fitting the model parameters, we obtain high-quality descriptions of electromagnetic form factors and radius for proton while the results deviate somewhat from experimental data for neutron.
We present a study of the chiral-odd generalized parton distributions for $u$ and $d$ quarks in a proton using the light front wave functions of the scalar quark-diquark model for nucleon constructed from the soft-wall AdS/QCD correspondence. We obtain the GPDs in terms of overlaps of the LFWFs. Numerical results for chiral-odd GPDs in momentum as well as transverse position spaces considering both zero and nonzero skewness($ζ$) are presented. For nonzero skewness, the GPDs are also evaluated in longitudinal position space.
We study the unpolarized and the helicity dependent generalized parton distributions (GPDs) for the valence quarks of the proton in both momentum space and position space within the basis light-front quantization (BLFQ) framework. The GPDs for the valence quarks are computed from the eigenvectors of a light-front effective Hamiltonian in the valence Fock sector consisting of a three-dimensional confinement potential and a one-gluon exchange interaction with fixed coupling. Employing these GPDs, we obtain the spatial distributions of quark angular momentum inside the proton. In our BLFQ approac…
We present a recent calculation of the gravitational form factors (GFFs) of proton using the light-front quark-diquark model constructed by the soft-wall AdS/QCD. The four GFFs $~A(Q^2)$ , $B(Q^2)$ , $C(Q^2)$ and $\bar{C}(Q^2)$ are calculated in this model. We also show the pressure and shear distributions of quarks inside the proton. The GFFs, $A(Q^2)$ and $B(Q^2)$ are found to be consistent with the lattice QCD, while the qualitative behavior of the $D$-term form factor is in agreement with the extracted data from the deeply virtual Compton scattering (DVCS) experiments at JLab, the lattice …
We apply a dynamical three-constituent quark light-front model to study the proton. The dynamics is based on the notion of a diquark (bound or virtual) as the dominant interaction channel, which paramaterizes a contact interaction between the quarks in order to build the three-body Faddeev Bethe-Salpeter equations for the valence state, and we focus on the totally symmetric part of the wave function. The Dirac electromagnetic form factor is used to fix the model parameters, and the valence wave function is obtained. From that we investigate its Ioffe-time image, non-polarized longitudinal and …
We investigate the Wigner distributions and generalized transverse momentum-dependent distributions (GTMDs) for $u$ and $d$ quarks in the proton by using light-front quark-diquark model. We consider the contribution of scalar and axial-vector diquark having spin-0 and spin-1 respectively. We take different polarization configurations of quark and proton to calculate the Wigner distributions. The Wigner distributions are studied in the impact-parameter space, momentum space and mixed space for $u$ and $d$ quarks in the proton. We also study the relation of GTMDs with longitudinal momentum fract…
Double parton distribution functions (dPDF) represent a tool to explore the 3D proton structure. They can be measured in high energy proton-proton and proton nucleus collisions and encode information on how partons inside a proton are correlated among each other. dPFDs are studied here in the valence quark region, by means of a constituent quark model, where two particle correlations are present without any additional prescription. This framework allows to understand the dynamical origin of the correlations and to clarify which, among the features of the results, are model independent. Use wil…
The projection onto the Light-Front of a Minkowski space Faddeev-Bethe-Salpeter equation model truncated at the valence level is applied to study the proton structure with constituent quarks. The dynamics of the model has built-in: (i) a bound diquark brought by a contact interaction, and (ii) the separation by Λ_QCD of the infrared and ultraviolet interaction regions. The model parameters are fine tuned to reproduce the proton Dirac electromagnetic form factor and mass. From that, the non-polarized longitudinal and transverse momentum distributions were computed. The results for the evolved n…
Double parton distribution functions (dPDF), accessible in high energy proton-proton and proton nucleus collisions, encode information on how partons inside a proton are correlated among each other and could represent a tool to explore the 3D proton structure. In recent papers, double parton correlations have been studied in the valence quark region, by means of constituent quark models. This framework allows to understand clearly the dynamical origin of the correlations and to establish which, among the features of the results, are model independent. Recent relevant results, obtained in a rel…
We obtain the gravitational form factors (GFFs) and investigate their applications for the description of the mechanical properties, i.e., the distributions of pressures, shear forces inside proton, and the mechanical radius, in a light-front quark-diquark model constructed by the soft-wall AdS/QCD. The GFFs, $A(Q^2)$ and $B(Q^2)$ are found to be consistent with the lattice QCD, while the qualitative behavior of the $D$-term form factor is in agreement with the extracted data from the deeply virtual Compton scattering (DVCS) experiments at JLab, the lattice QCD, and the predictions of differen…
Exclusive $J/ψ$ photoproduction in photon-proton diffractive scattering: A light-front Hamiltonian approach
Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；School of Nuclear Science and Technology, University of Chinese Academy of Sciences（中国科学院大学核科学与技术学院）；CAS Key Laboratory of High Precision Nuclear Spectroscopy, Institute of Modern Physics, Chinese Academy of Sciences（中国科学院高精度核谱学重点实验室，中国科学院近代物理研究所）；High Energy Accelerator Research Organization (KEK)（高能加速器研究机构（KEK））
We obtain the leading twist T-odd quark transverse momentum dependent parton distribution functions (TMDs) of the proton, namely the Sivers function, $f_{1T}^{\perp q}(x,p_\perp^2)$, and the Boer-Mulders function, $h_1^{\perp q}(x,p_\perp^2)$, in a light-front quark-diquark model constructed with the wave functions predicted by the soft-wall AdS/QCD. The gluon rescattering is crucial to predict a nonzero T-odd TMDs. We study the utility of a nonperturbative $SU(3)$ gluon rescattering kernel going beyond the usual approximation of perturbative $U(1)$ gluons. The spin asymmetries in semi-inclusi…
Double parton distribution functions (dPDFs) represent a tool to explore the 3D partonic structure of the proton. They can be measured in high energy proton-proton and proton nucleus collisions and encode information on how partons inside a proton are correlated among each other. dPFDs are studied here in the valence region by means of a constituent quark model scenario within the relativistic Light Front approach, where two particle correlations are present without any additional prescription. Furthermore, a study of the QCD evolution at high energy scale, of the model results, has been compl…
Double parton scattering, occurring in high energy hadron-hadron collisions, e.g. at the LHC, is usually investigated through model dependent analyses of the so called effective cross section $σ_{eff}$. We present a dynamic approach to this fundamental quantity making use of a Light-Front model treatment. Within such a framework $σ_{eff}$ is initially evaluated at low energy scale using the model and then, through QCD evolution, at high energy scale to reach the experimental conditions. Our numerical outcomes are consistent with the present experimental analyses of data in kinematical region w…
We obtain the leading-twist valence quark transverse-momentum-dependent parton distribution functions (TMD PDFs) for the proton within the basis light-front quantization (BLFQ) framework. Our results are consistent with lattice QCD calculations and our previous results for the collinear limit. We also obtain consistency with the Soffer-type bounds. Within our approach, we find that six T-even TMDs in the leading twist are all independent of each other, and previously found model-dependent relations do not hold. This is a promising sign that our results are representative of future, more extens…
An explicit evaluation of the double parton distribution functions (dPDFs), within a relativistic Light-Front approach to constituent quark models, is presented. dPDFs encode information on the correlations between two partons inside a target and represent the non-perturbative QCD ingredient for the description of double parton scattering in proton-proton collisions, a crucial issue in the search of new Physics at the LHC. Valence dPDFs are evaluated at the low scale of the model and the perturbative scale of the experiments is reached by means of QCD evolution. The present results show that t…
Dynamical gluon effects in twist-3 generalized parton distributions of the proton
Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；School of Nuclear Science and Technology, University of Chinese Academy of Sciences（中国科学院大学核科学与技术学院）
We utilize a light-front relativistic quark model to predict the 3q core contribution to the electroexcitation of nucleon resonances of the [70,1-] multiplet on the proton and neutron at Q2 < 5GeV2. The investigation is stimulated in large degree by expected progress in the studies of the electroexcitation of nucleon resonances in the third resonance region in the CLAS experiment. For the resonances N(1520)3/2-, N(1535)1/2-, and N(1675)5/2-, experimental data on electroexcitation amplitudes on the proton are available in a wide range of Q2. This allowed us to quantify the expected meson-baryon…
Transverse force tomography inside a proton from Basis Light-front Quantization
Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；School of Nuclear Science and Technology, University of Chinese Academy of Sciences（中国科学技术大学核科学与技术学院）
Spin entanglement signatures of proton from a light-front Hamiltonian
Beijing Academy of Quantum Information Sciences（北京量子信息科学研究院）；Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；Department of Physics and Astronomy, Iowa State University（爱荷华州立大学物理与天文系）；School of Nuclear Science and Technology, University of Chinese Academy of Sciences（中国科学院大学核科学与技术学院）
The gravitational form factors which are obtained from the matrix elements of the energy-momentum tensor provide us information about internal distributions of mass, energy, pressure and shear. The Druck term is the least understood among all the gravitational form factors. In a light front quark-diquark model of proton, we investigate the Druck form factor. Using Abel transformation, we evaluate the 3D distribution in the Breit frame from the 2D light front distributions. The results are compared with other models and lattice predictions.
In this work we report on using light-front dynamics to describe generalized parton distributions, which are correlation functions encountered in virtual Compton scattering at large momentum transfer. This two photon process requires pair annihilation contributions which are subtle to handle in light-front dynamics. We are careful to derive such contributions in the light-front Bethe-Salpeter formalism. This derivation highlights the connection to the Fock space picture as well as provides a toy model for generalized parton distributions.Ultimately we use light-front dynamics to build a phenom…
We present a quark-diquark model for the nucleons where the light front wave functions are constructed from the soft-wall AdS/QCD prediction. The model is consistent with quark counting rule and Drell-Yan-West relation. The model reproduces the scale evolution of unpolarized PDF of proton for a wide range of energy scale. Helicity and transversity distributions for the proton predicted in this model agree with phenomenological fits. The axial and tensor charges are also shown to agree with the experimental data. The model can be used to evaluate distributions like GPDS, TMDs etc. and their sca…
Near-threshold heavy quarkonium photoproduction in a light-front spectator model
Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；School of Nuclear Science and Technology, University of Chinese Academy of Sciences（中国科学院大学核科学与技术学院）；CAS Key Laboratory of High Precision Nuclear Spectroscopy, Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所高精度核谱学重点实验室）；Department of Physics, Indian Institute of Technology Kanpur（坎普尔印度理工学院物理系）；University of Science and Technology of China（中国科学技术大学）
