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Register a new userProton gravitational form factors in a light-front quark-diquark model
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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 QCD, and the predictions of different phenomenological models.
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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.
The gravitational form factors are related to the matrix elements of the energy-momentum tensor $T^{mu u}$. Using the light front wave functions of the scalar quark-diquark model for nucleon predicted by the soft-wall AdS/QCD, we calculate the flavor dependent $A(Q^2)$, $B(Q^2)$ and $bar{C}(Q^2)$ form factors. We also present all the matrix element of the energy-momentum tensor in a transversely polarized state. Further, we evaluate the matrix element of Pauli-Lubanski operator in this model and show that the intrinsic spin sum rule involves the form factor $bar{C}$. The longitudinal momentum densities in the transverse impact parameter space are also discussed for both unpolarized and transversely polarized nucleons.
Using the light front wave functions for the nucleons in a quark model in AdS/QCD, we calculate the nucleon electromagnetic form factors. The flavor decompositions of the nucleon form factors are calculated from the GPDs in this model. We show that the nucleon form factors and their flavor decompositions calculated in AdS/QCD are in agreement with experimental data.
The light-front quark model analysis of the meson-photon transition form factor $F_{Pgamma} (Q^2)$ amenable both for the spacelike region ($Q^2 >0$) and the timelike region ($Q^2 <0$) provides a systematic twist expansion of $Q^2 F_{Pgamma} (Q^2)$ for the high $|Q^2|$ region. Investigating $F_{Pgamma} (Q^2) (P = eta_c,eta_b)$ for the entire kinematic regions of $Q^2$, we examine the twist-2 and twist-3 distribution amplitudes of $(eta_c,eta_b)$ mesons in the light-front quark model and quantify their contributions to $Q^2 F_{(eta_c,eta_b)gamma}(Q^2)$. Our numerical results for the normalized transition form factor $F_{(eta_c,eta_b)gamma}(Q^2)/F_{(eta_c,eta_b)gamma}(0)$ and the decay width $Gamma_{(eta_c,eta_b)togammagamma}$ are compared with the available data checking the sensitivity of our model to the variation of the constituent quark masses.
We report our investigation on the doubly virtual TFFs $F_{{rm P}gamma^*}(Q^2_1,Q^2_2)$ for the ${rm P}togamma^*(q_1)gamma^*(q_2) ;({rm P}=pi^0,eta,eta)$ transitions using the light-front quark model (LFQM). Performing a LF calculation in the exactly solvable manifestly covariant Bethe-Salpeter (BS) model as the first illustration, we used $q^+_1=0$ frame and found that both LF and manifestly covariant calculations produce exactly the same results for $F_{{rm P}gamma^*}(Q^2_1,Q^2_2)$. This confirms the absence of the LF zero mode in the doubly virtual TFFs. We then mapped this covariant BS model to the standard LFQM using the more phenomenologically accessible Gaussian wave function provided by the LFQM analysis of meson mass spectra. For the numerical analyses of $F_{{rm P}gamma^*}(Q^2_1,Q^2_2)$, we compared our LFQM results with the available experimental data and the perturbative QCD (pQCD) and the vector meson dominance (VMD) model predictions. As $(Q^2_1, Q^2_2)toinfty$, our LFQM result for doubly virtual TFF is consistent with the pQCD prediction, i.e. $F_{{rm P}gamma^*}(Q^2_1, Q^2_2)sim 1/(Q^2_1 + Q^2_2)$, while it differs far from the result of VMD model which behaves $F^{rm VMD}_{{rm P}gamma^*}(Q^2_1, Q^2_2)sim 1/(Q^2_1 Q^2_2)$. Our LFQM prediction for $F_{etagamma^*}(Q^2_1,Q^2_2)$ shows an agreement with the very recent experimental data obtained from the BaBar collaboration for the ranges of $2< Q^2_1, Q^2_1 <60$ GeV$^2$.
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