Light-front Quark-diquark Model Research Articles

Exploring twist-4 chiral-even GPDs in the light-front quark-diquark model

In this work, we delve into the realm of quantum chromodynamics (QCD) by calculating twist-4 chiral-even generalized parton distributions (GPDs), within the context of the light-front quark-diquark model (LFQDM), focusing specifically on the intriguing case of zero skewness. To shed light on the behavior of twist-4 chiral-even GPDs, we present comprehensive two-dimensional (2-D) and 3-dimensional (3-D) plots, mapping their dependence on the longitudinal momentum fraction (x) and the momentum transfer (t). Furthermore, our research looks into the profound connection between twist-4 chiral-even GPDs and other distribution functions (DFs), including parton distribution functions (PDFs), transverse momentum-dependent parton distributions (TMDs) and generalized transverse-momentum dependent parton distributions (GTMDs). Additionally, our investigation extends to the exploration of related higher twist form factors (FFs), which play a pivotal role in elucidating the internal structure of hadrons. To provide significant insights into the partons spatial distribution, we have also yielded impact parameter GPD plots.

Electromagnetic form factors for nucleons in short-range correlations

Recent experimental studies have led to the suggestion that short-range correlations may be a major contributor to the nuclear EMC effect. This hypothesis requires that the structure function for nucleons involved in short-range correlations should be heavily suppressed compared to that of a free nucleon. Based on calculations performed within an AdS/QCD motivated, light-front quark-diquark model, we find that this large suppression of the nucleon structure function leads to a strong suppression of the nucleon elastic form factors.

Sub-leading twist transverse momentum dependent parton distributions in the light-front quark-diquark model

In this study, the T-even sub-leading twist transverse momentum dependent distributions (TMDs) of proton in the light-front quark-diquark model (LFQDM) have been investigated. We have derived the overlap form of the light-front wave functions (LFWFs) for the sub-leading twist proton TMDs by detangling the un-integrated quark-quark correlator for the semi-inclusive deep inelastic scattering (SIDIS). We have obtained the explicit expressions of TMDs for both the cases of the diquark being a scalar or a vector and analyzed their relationships with leading twist TMDs within the same model. Average transverse momenta and average square transverse momenta for the TMDs have been tabulated and compared with the results from the light-front bag model and the light-front constituent quark model (LFCQM). In addition to this, we have also compared our results for the PDF e(x) with the recent CLAS collaboration results.Transverse momentum dependent parton distributions of proton; T-even sub-leading twist TMDs; light-front quark-diquark model.

Sivers and Boer-Mulders TMDs of the proton in a light-front quark-diquark model

We obtain the leading twist T-odd quark transverse momentum-dependent parton distribution functions (TMDs) of the proton, namely, the Sivers function ${f}_{1T}^{\ensuremath{\perp}q}(x,{p}_{\ensuremath{\perp}}^{2})$ and the Boer-Mulders function ${h}_{1}^{\ensuremath{\perp}q}(x,{p}_{\ensuremath{\perp}}^{2})$, 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 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-inclusive deep inelastic scattering (SIDIS) associated with these T-odd TMDs are found to be consistent with HERMES and COMPASS data. We further predict the Sivers asymmetries of pion production in the SIDIS process in the kinematical region of the Electron-Ion Collider (EIC) and the EIC in China. We also evaluate the generalized Sivers and Boer-Mulders shifts and compare them with the available lattice QCD simulations.

Twist-4 T-even proton TMDs in the light-front quark–diquark model

We have dealt with the twist-4 T-even transverse momentum dependent parton distributions (TMDs) for the case of proton in the light-front quark–diquark model (LFQDM). By decoding the unintegrated quark–quark correlator for the semi-inclusive deep inelastic scattering (SIDIS), we have specifically obtained the overlap form for the unpolarized [Formula: see text], longitudinally polarized [Formula: see text] and transversely polarized ([Formula: see text] and [Formula: see text]) proton TMDs. We have provided the explicit expressions for both the cases of the diquark being a scalar or a vector. Average transverse momenta and the average square transverse momenta for the TMDs have been calculated and the results have been tabulated with corresponding leading twist TMDs. In addition, the value of average transverse momentum and average square transverse momentum for TMD [Formula: see text] has been compared with the available light-front constituent quark model (LFCQM) results. From TMDs, we have also obtained and discussed the transverse momentum-dependent parton distribution functions (TMDPDFs). The model relations of the twist-4 T-even TMDs with the available leading twist T-even TMDs have also been obtained.

Gravitational form factors and mechanical properties of the proton: Connections between distributions in 2D and 3D

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 a 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.

Proton gravitational form factors in a light-front quark-diquark model

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[1]. The four GFFs ~A(Q^2)A(Q2) , B(Q^2)B(Q2) , C(Q^2)C(Q2) and \bar{C}(Q^2)C‾(Q2) are calculated in this model. We also show the pressure and shear distributions of quarks inside the proton. The GFFs, A(Q^2)A(Q2) and B(Q^2)B(Q2) are found to be consistent with the lattice QCD, while the qualitative behavior of the DD-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 different phenomenological models.

Proton gravitational form factors and mechanical properties in a light-front quark-diquark model

We present our recent calculation of the gravitational form factors (GFFs) of proton using the light-front quark-diquark model constructed by the soft-wall AdS/QCD. We extract the four quark GFFs by calculating the matrix elements of the symmetric energy momentum tensor. Using the D-term we calculate the pressure and shear distributions of quarks inside the proton in the impact parameter space. The GFFs, A(Q2) and B(Q2) 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 different phenomenological models.

Leading twist GTMDs at nonzero skewness and Wigner distributions in boost-invariant longitudinal position space

We investigate the leading twist quark generalized transverse momentum distributions (GTMDs) at nonzero skewness in a light-front quark-diquark model for the nucleon motivated by soft-wall AdS/QCD. The boost-invariant longitudinal coordinate, $\sigma=\frac{1}{2} b^- P^+$, is identified as the Fourier conjugate of the skewness. The Fourier transform of the GTMDs with respect to the skewness variable $\xi$ can be employed to provide the Wigner distributions in the boost-invariant longitudinal position space $\sigma$, the coordinate conjugate to light-front time, $\tau=t+z/c$. The Wigner distributions in the longitudinal position space exhibit diffraction patterns, which are analogous to the diffractive scattering of a wave in optics.

Relations between generalized parton distributions and transverse momentum dependent parton distributions

We investigate the relations between transverse momentum dependent parton distributions (TMDs) and generalized parton distributions (GPDs) in a light-front quark-diquark model motivated by soft-wall AdS/QCD. Many relations are found to have similar structure in different models. It is found that a relation between the Sivers function and the GPD ${E}_{q}$ can be obtained in this model in terms of a lensing function. The quark orbital angular momentum is calculated and the results are compared with the results in other similar models. Implications of the results are discussed. Relations among different TMDs in the model are also presented.

Gravitational form factors and mechanical properties of proton in a light-front quark-diquark model

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 different phenomenological models. The pressure and shear force distributions are also consistent with the results of different models.

Sivers and Boer–Mulders GTMDs in light-front holographic quark–diquark model

We calculate the time reversal odd (T-odd) generalized transverse momentum dependent parton distributions (GTMDs) $F^o_{1,2}$ and $H^o_{1,1}$ in a light-front quark-diquark model based on ADS/QCD. In the limit of zero momentum transfer, these reduce to the Sivers and Boer-Mulders TMDs respectively. We have incorporated both scalar and axial vector diquarks in the model and obtained an overlap representation of the GTMDs using the light-front wave functions (LFWFs). Contribution from the final state interaction is incorporated at the level of one gluon exchange as a phase factor in the LFWF. We show that the final state interaction term can be factored out in this model and this part is the same for both GTMDs. We also present the corresponding Wigner distributions.

Wigner distributions and GTMDs in a proton using light-front quark–diquark model

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 fraction carried by the active quark x for different values of ζ (skewness) which is defined as the longitudinal momentum transferred to the proton. Further, we study the GTMDs in the relation with x for zero skewness (ζ=0) at different values of quark transverse momentum p⊥ as well as at different values of total momentum transferred to the proton Δ⊥.

Leading Twist TMDs in a Light-Front Quark–Diquark Model for Proton

We present $$\mathbf{p}_{\perp }$$ variation (fixed x) of the leading-twist T-even transverse momentum dependent parton distributions (TMDs) of a proton in a light-front quark–diquark model at $$\mu ^2=2.4$$ and $$20~\hbox {GeV}^2$$ . The quark densities for unpolarized and transversely polarized proton are also presented. We observe a Soffer bound for TMDs in this model.

Azimuthal Spin Asymmetries in SIDIS

We have presented the results for the single and double spin asymmetries in semi-inclusive deep inelastic scatterings for proton in a light front quark–diquark model. The asymmetries are found to satisfy certain inequalities. The model wavefunctions are modified to generate complex phase which is essential to produce asymmetries with Sivers and Boer-Mulders functions. The model predictions for Collins, Sivers and Boer-Mulders asymmetries are found to be consistent with data.

Sivers and cos2ϕ asymmetries in semi-inclusive deep inelastic scattering in light-front holographic model

The spin asymmetries in SIDIS associated with $T$-odd TMDs are presented in a light-front quark-diquark model of a proton. To incorporate the effects of the final-state interaction, the light front wave functions are modified to have a phase factor which is essential to have Sivers or Boer-Mulders functions. The Sivers and Boer-Mulder asymmetries are compared with HERMES and COMPASS data.

Model predictions for azimuthal spin asymmetries for HERMES and COMPASS kinematics

We have presented the results for the single and double spin asymmetries in semi-inclusive deep inelastic scatterings for proton in a light front quark-diquark model. The asymmetries generated by the T-even TMDs are discussed here. The model predictions are found to agree with the available data. We also present our model predictions for the Collins asymmetry for the future electron-ion collider experiments.

Gravitational form factors and angular momentum densities in light-front quark-diquark model

We investigate the gravitational form factors (GFFs) and the longitudinal momentum densities ($p^+$ densities) for proton in a light-front quark-diquark model. The light-front wave functions are constructed from the soft-wall AdS/QCD prediction. The contributions from both the scalar and the axial vector diquarks are considered here. The results are compared with the consequences of a parametrization of nucleon generalized parton distributions (GPDs) in the light of recent MRST measurements of parton distribution functions (PDFs) and a soft-wall AdS/QCD model. The spatial distribution of angular momentum for up and down quarks inside the nucleon has been presented. At the density level, we illustrate different definitions of angular momentum explicitly for an up and down quark in the light-front quark-diquark model inspired by AdS/QCD.

Unpolarized and polarized densities based on a light-front quark–diquark model

In this paper, we calculate the proton and neutron unpolarized and transversely polarized densities. We use the light-front wave function (LFWF), which at an initial scale is constrained by the soft-wall anti-de Sitter (AdS) QCD model, for calculating the Dirac and Pauli form factors which transverse densities are in terms of these form factors. Also, we use these form factors for calculating the flavor separated results for the proton and neutron electromagnetic form factors and calculate u and d quark unpolarized and transversely polarized densities. Finally, we compare our results with other previous parametrizations.

Quark Wigner distributions and spin-spin correlations

We investigate the Wigner distributions for $u$ and $d$ quarks in a light-front quark-diquark model of a proton to unravel the spatial and spin structure. The light-front wave functions are modeled from the soft-wall AdS/QCD prediction. We consider the contributions from both the scalar and the axial vector diquarks. The Wigner distributions for unpolarized, longitudinally polarized, and transversely polarized protons are presented in the transverse momentum plane as well as in the transverse impact parameter plane. The Wigner distributions satisfy a Soffer-bound-type inequality. We also evaluate all the leading twist GTMDs and show their scale evolution. The spin-spin correlations between the quark and the proton are investigated