Diquark formation across a short-range nucleon-nucleon pair is proposed as the underlying QCD physics of short-range correlations (SRC) in nuclei. SRC pairs have been proposed as the cause of distorted quark behavior in nuclei; experimentally observed quark momentum distribution distortions termed the EMC effect. The strong spatial overlap of SRC pairs brings nucleon constituents within range of inter-nucleon QCD potentials and any bonds formed - such as the diquark bond - affects their distributions. In this SRC model, diquarks form in the $\rm 3_C \otimes 3_C \rightarrow \bar{3}_C$ channel of $\rm SU(3)_C$ acting on valence quarks from highly overlapping nucleon wavefunctions. The most energetically favorable diquark is a valence $u$ quark from one nucleon with a valence $d$ quark from the other in a spin-0 state bound together via continual single gluon exchange and an attractive quantum chromodynamics short-range potential. Formation of a new scalar isospin-singlet $[ud]$ diquark across a NN pair is proposed as the primary QCD-level theoretical foundation for SRC models of distorted structure functions in $\rm A\geq 3$ nuclei. Contributions from the higher mass spin-1 isospin triplet states $(ud)$, $(uu)$ and $(dd)$ are possible, with the spin-1 $(ud)$ diquark proposed as a higher mass but viable structure function distortion mechanism for the spin-1 ground state deuteron. Predictions are made for lepton scattering experiments on $\rm ^3H$ and $\rm ^3He$ nuclear targets, with implications for the coefficients of the 3-valence quark Fock states in the nucleon wavefunction.
Recent developments in understanding the influence of the nucleus on deep-inelastic structure functions, the EMC effect, are reviewed. A new data base which expresses ratios of structure functions in terms of the Bjorken variable $x_A=AQ^2/(2M_A q_0)$ is presented. Information about two-nucleon short-range correlations from experiments is also discussed and the remarkable linear relation between short-range correlations and teh EMC effect is reviewed. A convolution model that relates the underlying source of the EMC effect to modification of either the mean-field nucleons or the short-range co…
We determine nuclear structure functions and quark distributions for $^7$Li, $^{11}$B, $^{15}$N and $^{27}$Al. For the nucleon bound state we solve the covariant quark-diquark equations in a confining Nambu--Jona-Lasinio model, which yields excellent results for the free nucleon structure functions. The nucleus is described using a relativistic shell model, including mean scalar and vector fields that couple to the quarks in the nucleon. The nuclear structure functions are then obtained as a convolution of the structure function of the bound nucleon with the light-cone nucleon distributions. W…
The deep inelastic scattering of leptons off nuclei is considered within the the Bethe-Salpeter formalism. It is shown that nuclear short-range structure can be expressed in terms of the nucleon structure functions and four-dimensional Fermi motion of the nucleons. The four-dimensional Fermi motion broadens the bound nucleon localization area, what lead to the observation of the nucleon structure change in nuclei -- EMC effect. The $\rm ^4He$ to deuteron structure functions ratio is found in good agreement with experimental data. It is shown that the pattern of the ratio is defined by dynamica…
The Chiral Quark-Soliton model of the nucleon contains a mechanism for an attractive interaction between nucleons. This, along with the exchange of vector mesons between nucleons, is used to compute the saturation properties of infinite nuclear matter. This provides a new way to asses the effects of the nuclear medium on a nucleon that includes valence and sea quarks. We show that the model simultaneously describes the nuclear EMC effect and the related Drell-Yan experiments.
We study the parton distribution of nucleon and nuclear EMC effect in a statistical model. We find when we choose the parameters appropriately, the predictions given by pure statistical laws can fit the experimental data well in most range of $x$, this reveal statistical law play an important role in the parton distribution of nucleon.
We present our results for a flavor-dependent EMC effect based on the nIMParton nuclear PDFs, in which the $x$-dependence is described with a nucleon swelling model. The nuclear correction from nucleon swelling is considered through a modification of the initial valence quark distributions instead of a dynamical rescaling. To probe the flavor-dependence of the model, the experimental observables are calculated applying nIMParton nuclear modifications for various experiments: parity-violating deep inelastic scattering on nuclear target, pion-induced Drell-Yan, and W-boson production in proton-n…
The deep inelastic scattering cross section for scattering from bound nucleons differs from that of free nucleons.This phenomena, first discovered 30 years ago, is known as the EMC effect and is still not fully understood. Recent analysis of world data showed that the strength of the EMC effect is linearly correlated with the relative amount of Two-Nucleon Short Range Correlated pairs (2N-SRC) in nuclei. The latter are pairs of nucleons whose wave functions overlap, giving them large relative momentum and low center of mass momentum, where high and low is relative to the Fermi momentum of the …
In this paper, we examine the hypothesis that the nuclear EMC effect comes merely from the N-N SRC pairs inside the nucleus and that the properties of N-N SRC pair are universal among the various nuclei, using the conventional $x$-rescaling model for the EMC effect. With the previously determined effective mass of the short-range correlated nucleon and the number of N-N SRC pairs estimated, we calculate the EMC effect of various nuclei within the $x$-rescaling approach. From our calculations, the nuclear EMC effect due to the mass deficits of the SRC nucleons is not enough to reproduce the obs…
The break-up of the deuteron during deeply-virtual Compton scattering, gamma* d --> gamma(*) n p, is explored. In the effective field theory describing nucleon dynamics at momenta below the pion mass, the EMC effect results from four-nucleon interactions with the twist-2 operators, appropriate for describing forward, and near-forward, matrix elements in the two-nucleon system. We point out that the break-up of the deuteron to low-energy final states during deeply-virtual Compton scattering is a process with which to explore strong-interaction physics closely related to that responsible for the…
Recent data for the slope of the EMC-ratio in the intermediate $x$-region for {\em light} nuclei, with $3 \leq A \leq 12$, have the potential to shed new light on the origin of the EMC effect. Here we study the role of nuclear binding using the scaling variable ${\tilde y}$, best suited to take into account this effect, and the understanding of the average nucleon removal energies, $\bar{E}$, provided by state-of-the-art calculations based on nuclear many body theory. We find an excellent correlation between the new EMC data at $x \sim 0.5$ and $\bar{E}$ for nuclei with $A$ from 3 to $\infty$,…
Gamow-Teller transitions in nuclei tell us that the nucleon's axial charge $g_A^{(3)}$ is quenched in large nuclei by about 20%. This result tells us that the spin structure of the nucleon is modified in nuclei and disfavours models of the medium dependence of parton structure based only on nucleon short range correlations in nuclei. For polarized photoproduction the Gerasimov-Drell-Hearn integral is expected to be strongly enhanced in medium.
We develop a rather simple, formally covariant quark-diquark model of the nucleon. The nucleon is treated as a bound state of a constituent quark and a diquark interacting via a quark exchange. We include both scalar and axial-vector diquarks. The underlying Bethe-Salpeter equation is transformed into a pair of coupled Salpeter equations. The electromagnetic form factors of the nucleon are calculated in the Mandelstam formalism. We obtain a very good description of all electromagnetic form factors for momentum transfers up to -3 (GeV/c)^2.
In a model where constituent quarks and diquarks interact through quark exchange the Bethe-Salpeter equation in ladder approximation for the nucleon is solved. Quark and diquark confinement is effectively parametrized by choosing appropriately modified propagators. The coupling to external currents is implemented via nontrivial vertex functions for quarks and diquarks to ensure gauge invariance at the constituent level. Nucleon matrix elements are evaluated in a generalised impulse approximation, and electromagnetic, pionic and axial form factors are calculated.
The nucleon axial vector form factor is investigated in a light-cone quark spectator diquark model, in which Melosh rotations are applied to both the quark and vector diquark. It is found that this model gives a very good description of available experimental data and the results have very little dependence on the parameters of the model. The relation between the nucleon axial constant and the anomalous magnetic moment of nucleons is also discussed.
We develop a formally covariant quark-diquark model of the nucleon. The nucleon is treated as a bound state of a constituent quark and a diquark interacting via a quark exchange. We include both scalar and axial-vector diquarks. The underlying Bethe-Salpeter equation is transformed into a pair of coupled Salpeter equations. The space- and timelike electromagnetic form factors of the nucleon are calculated in the Mandelstam formalism for squared momentum transfers up to 3 (GeV/c)^2 above threshold. The model is applied also to the Delta(3/2).
In the covariant quark-diquark model the effective Bethe-Salpeter (BS) equations for the nucleon and the $Δ$ are solved including scalar {\em and axialvector} diquark correlations. Their quark substructure is effectively taken into account in both, the interaction kernel of the BS equations and the currents employed to calculate nucleon observables. Electromagnetic current conservation is maintained. The electric form factors of proton and neutron match the data. Their magnetic moments improve considerably by including axialvector diquarks and photon induced scalar-axialvector transitions. The…
We argue that precise measurements of charge and magnetic radii can meaningfully constrain diquark models of the nucleon. We construct properly symmetrized, nonrelativistic three-quark wave functions that interpolate between the limits of a pointlike diquark pair and no diquark correlation. We find that good fits to the data can be obtained for a wide range of diquark sizes, provided that the diquark wave functions are close to those that reduce to a purely scalar state in the pointlike limit. A modest improvement in the experimental uncertainties will render a fit to the charge radii a more t…
We present a simple covariant constituent diquark-quark model for the nucleon. The nucleon is assumed to be composed of a scalar diquark and a quark which interact via a quark exchange. Starting from the Bethe-Salpeter equation, the instantaneous approximation leads to a diquark-quark Salpeter equation. In the Mandelstam formalism, the electromagnetic form factors of the nucleon are calculated for momentum transfers up to $q^2 = - 3 \; (\mbox{GeV/c})^2$. A remarkable description of the experimental data is obtained. Especially, the model gives nearly the right values for the proton and (negati…
The EMC effect in deuterium and helium-3 is studied using a convolution formalism that allows isolating the impact of high-momentum nucleons in short-ranged correlated (SRC) pairs. We assume that the modification of the structure function of bound nucleons is given by a universal (i.e. nucleus independent) function of their virtuality, and find that the effect of such modifications is dominated by nucleons in SRC pairs. This SRC-dominance of nucleon modifications is observed despite the fact that the bulk of the nuclear inelastic scattering cross-section comes from interacting with low-momentu…
Starting from a covariant relativistic formalism which uses nucleon and pion propagators in a nuclear medium, we revise the traditional effects of Fermi motion, binding and mesonic corrections to the EMC effect. The calculations are done in a very accurate way, using precise nucleon spectral functions and meson self-energies and a good reproduction of the EMC data is obtained outside the shadowing region which is not explored.
Double parton scattering off nuclei and the double-EMC effect
Università degli Studi di Perugia（佩鲁贾大学）；INFN Sezione di Perugia（意大利国家核物理研究所佩鲁贾分部）；Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；Université de Liège（列日大学）；Università di Roma Tor Vergata（罗马第二大学）；INFN Sezione di Roma Tor Vergata（意大利国家核物理研究所罗马第二大学分部）；Istituto Nazionale di Fisica Nucleare Sezione di Perugia（意大利国家核物理研究所佩鲁贾分部）
A light front formalism for deep inelastic lepton scattering from finite nuclei is developed. In particular, the nucleon plus momentum distribution and a finite system analog of the Hugenholtz-van Hove theorem are presented. Using a relativistic mean field model, numerical results for the plus momentum distribution and ratio of bound to free nucleon structure functions for Oxygen, Calcium and Lead are given. We show that we can incorporate light front physics with excellent accuracy while using easily computed equal time wavefunctions. Assuming nucleon structure is not modified in-medium we fi…
We report progress on the development of Perturbative Integral Representation Ansätze to compute the nucleon Faddeev Wave function, using an explicit quark-diquark picture. Our formalism is able to handle non-pointlike diquark and to mimic the strong, dynamical correlations observed when solving the Faddeev Equation. We then project the wave function in order to compute the leading-twist Parton Distribution Amplitude.
We study the instabilities of quark matter in the framework of a generalized Nambu--Jona-Lasinio model, in order to explore possible competition between three-quark clustering to form nucleons and diquark formation leading to color superconductivity. Nucleon and $Δ$ solutions are obtained for the relativistic Faddeev equation at finite density and their binding energies are compared with those for the scalar and axial-vector diquarks found from the Bethe-Salpeter equation. In a model with interactions in both scalar and axial diquark channels, bound nucleons exist up to nuclear matter density.…
We briefly describe our relativistic quark-diquark model, developed within the framework of point form dynamics, which is the relativistic extension of the interacting quark-diquark model. In order to do that we have to show the main properties and quantum numbers of the effective degree of freedom of constituent diquark. Our results for the nonstrange baryon spectrum and for the nucleon electromagnetic form factors are discussed.
In the 35 years since the European Muon Collaboration announced the astonishing result that the valence structure of a nucleus was very different from that of a free nucleon, many explanations have been suggested. The first of the two most promising explanations is based upon the different effects of the strong Lorentz scalar and vector mean fields known to exist in a nucleus on the internal structure of the nucleon-like clusters which occupy shell model states. The second links the effect to the modification of the structure of nucleons involved in short-range correlations, which are far off …
It is widely discussed in the literature that the wave function of the nucleon bound in a nucleus is modified due to the interaction with the surrounding medium. We argue that the modification should strongly depend on the momentum of the nucleon. We study such an effect in the case of the point-like configuration component of the wave function of a nucleon bound in a nucleus A, considering the case of arbitrary final state of the spectator A-1 system. We show that for non relativistic values of the nucleon momentum, the momentum dependence of the nucleon deformation appears to follow from rat…
We investigate the gluonic structure of nuclei within a mean-field model of nuclear structure based upon the modification of the structure of a bound nucleon, with the nucleon described by the Nambu--Jona-Lasinio model. This approach has been shown to reproduce the European Muon Collaboration (EMC) effect, involving the ratio of the spin-independent structure functions of a heavier nucleus to that of the deuteron. It also predicts a significant nuclear modification for the spin structure functions, known as the polarized EMC effect. Here we report sizeable nuclear modifications of the gluon di…
We study the nucleon and diquarks in a non-local Nambu-Jona-Lasinio model. For certain parameters the model exhibits quark confinement, in the form of a propagator without real poles. After truncation of the two-body channels to the scalar and axial-vector diquarks, a relativistic Faddeev equation for nucleon bound states is solved in the covariant diquark-quark picture. The dependence of the nucleon mass on diquark masses is studied in detail. We find parameters that lead to a simultaneous reasonable description of pions and nucleons. Both the diquarks contribute attractively to the nucleon m…
We present a phenomenological unpolarized Parton Distribution Functions for diquarks based on a soft-wall light front AdS/QCD quark-diquark nucleon model. From a probed model consistent with the Drewll-Yan-West relation and quark counting rule, we have performed a fit of some free parameters using known phenomenological quark PDF data. The model considers the entire set of possible diquarks within the nucleon valence, in the present work we focus on the spin-0 $ud_0$, spin-1 $ud_1$ and spin-1 $uu_1$ diquarks into the valence of protons. The diquark PDFs obtained are able to used in proton-prot…
Nucleon form factors are calculated on q^2 in [0,3] GeV^2 using an Ansatz for the nucleon's Fadde'ev amplitude motivated by quark-diquark solutions of the relativistic Fadde'ev equation. Only the scalar diquark is retained, and it and the quark are confined. A good description of the data requires a nonpointlike diquark correlation with an electromagnetic radius of 0.8 r_pi. The composite, nonpointlike nature of the diquark is crucial. It provides for diquark-breakup terms that are of greater importance than the diquark photon absorption contribution.
Nuclear structure functions and EMC effect in a relativistic deuteron
University of Science and Technology of China（中国科学技术大学）；Lebedev Physical Institute（列别捷夫物理研究所）；Anhui Center for Fundamental Sciences in Theoretical Physics（安徽理论物理基础科学中心）
We demonstrate that measurement of tagged structure functions of the deuteron in (e,e'N) semi-inclusive reactions can discriminate between different hypotheses on the origin of the nuclear EMC effect. By choosing extreme backward kinematics for the spectator nucleon to minimize effects from the deuteron wave function and final state interactions, one can isolate the modifications in the structure of the bound nucleon within the impulse approximation. The same reaction can be used to extract the large-x neutron to proton structure function ratio.
Nucleon form factors are calculated in a relativistic diquark--quark picture based on the Nambu--Jona-Lasinio model. The nucleon wave function is obtained in a static approximation to the quark exchange interaction between the valence quark and the diquark. We evaluate the valence quark and $0^+$--diquark contribution to the nucleon electromagnetic and weak currents. We find reasonable electric charge radii, magnetic moments as in the additive diquark model, and $g_A \approx 1$. We discuss the dependence on the model parameters.
Quark light cone momentum distributions in nuclear matter and the structure function of a bound nucleon are investigated in the framework of the Nambu-Jona-Lasinio model. This framework describes the nucleon as a relativistic quark-diquark state, and the nuclear matter equation of state by using the mean field approximation. The scalar and vector mean fields in the nuclear medium couple to the quarks in the nucleon and their effect on the spin independent nuclear structure function is investigated in detail. Special emphasis is placed on the important effect of the vector mean field and on a f…
We discuss the electromagnetic form factors, axial form factors, and structure functions of a bound nucleon in the quark-meson coupling (QMC) model. Free space nucleon form factors are calculated using the improved cloudy bag model (ICBM). After describing finite nuclei and nuclear matter in the quark-based QMC model, we compute the in-medium modification of the bound nucleon form factors in the same framework. Finally, limits on the medium modification of the bound nucleon $F_2$ structure function are obtained using the calculated in-medium electromagnetic form factors and local quark-hadron …
The nucleon structure functions are studied with a special emphasis on diquark correlations inside the nucleon. Assuming a phenomenological diquark-quark model of the nucleon at the low energy hadronic scale, we calculate the leading twist contributions to the nucleon structure functions. We take the Nambu and Jona-Lasinio model for the calculation of the quark distributions in the diquarks, and use the convolution method for the diquark scattering process. The resulting quark distributions are evolved to the experimental momentum scale using the perturbative QCD. We discuss the flavor depende…
A description of the nucleon and Roper resonance in a quark-diquark approach is presented. We show that two states with the quantum number of the nucleon can appear in the ground state of the spatial configuration, when there are two types of diquarks: scalar-isoscalar and axial-vector-isovector diquarks. The mass difference between the two states is generated by the mass difference between the two diquarks, which is due to the spin-spin interaction between the two quarks in the diquarks. The two states are then identified with the nucleon and Roper resonance.
A model for elastic scattering of nucleons (and anti-nucleons) based on the quark-diquark representation of the nucleon with springy Pomeron, providing increased real part of the scattering amplitude, is developed. The model predictions are compared with experimental data for the differential elastic cross-sections of nucleons in the energy range from few GeV up to 7 TeV using available databases.
We investigate the electric form factors of the nucleon and Roper resonance using a quark-diquark model. We find that the charge radii of the nucleon and Roper resonance are almost the same in size.
Applying exact QCD sum rules for the baryon charge and energy-momentum we demonstrate that if nucleons are the only degrees of freedom of nuclear wave function, the structure function of a nucleus would be the additive sum of the nucleon distributions at the same Bjorken x = AQ^2/2(p_Aq)< 0.5 up to very small Fermi motion corrections if x>0.05. Thus the difference of the EMC ratio from one reveals the presence of non-nucleonic degrees of freedom in nuclei. Using exact QCD sum rules we show that the ratio R_A(x_p,Q^2) used in experimental studies, where x_p = Q^2/2q_0 m_p deviates from one even…
We study the structure of the nuclear force by using a path-integral hadronization approach in a chiral quark-diquark model. After the construction of the chiral quark-diquark model, we hadronize it to obtain a meson-baryon Lagrangian. The effective meson-baryon Lagrangian incorporates chiral symmetry and the composite description of the mesons and baryons. Using the effective meson-baryon Lagrangian we investigate the structure of the nuclear force in the simple case of neglecting the axial-vector diquark. It is shown that the meson-baryon Lagrangian contains two kinds of the nuclear force; t…
We study the ground and first excited states of nucleons in a chiral quark-diquark model. We include two quark-diquark channels of the scalar-isoscalar and axial-vector-isovector types for the nucleon states. The diquark correlation violating the spin-flavor SU(4)$_{SF}$ symmetry allows to treat the two quark-diquark channels independently. Hence the two states appear as the superpositions of the two quark-diquark channels; one is the nucleon and the other is a state which does not appear in the SU(4)$_{SF}$ quark models. With a reasonable choice of model parameters, the mass of the excited st…
Spin-dependent and spin-independent quark light-cone momentum distributions and structure functions are calculated for the nucleon. We utilize a modified Nambu-Jona-Lasinio model in which confinement is simulated by eliminating unphysical thresholds for nucleon decay into quarks. The nucleon bound state is obtained by solving the Faddeev equation in the quark-diquark approximation, where both scalar and axial-vector diquark channels are included. We find excellent agreement between our model results and empirical data.
The mass of the nucleon is studied in a chiral quark-diquark model. Both scalar and axial-vector diquarks are taken into account for the construction of the nucleon state. After the hadronization procedure to obtain an effective meson-baryon Lagrangian, the quark-diquark self-energy is calculated in order to generate the baryon kinetic term as well as the mass of the nucleon. It turns out that both the scalar and axial-vector parts of the self-energy are attractive for the mass of the nucleon. We investigate the range of parameters that can reproduce the mass of the nucleon.
We investigate the electromagnetic form factors of nucleons within a simple relativistic quark spectator-diquark model using the light-cone formalism. Melosh rotations are applied to both quark and vector diquark. It is shown that the difference between vector and scalar spectator diquarks reproduces the right electric form factor of neutrons, and both the form factors $G_E(Q^2)$ and $G_M(Q^2)$ of the proton and neutron agree with experimental data well up to $Q^2=2 ~\rm{GeV}^2$ in this simple model.
We study electromagnetic properties of the nucleon and Roper resonance in a chiral quark-diquark model including two kinds of diquarks needed to describe the nucleon: scalar and axial-vector diquarks. The nucleon and Roper resonance are described as superpositions of two quark-diquark bound states of a quark and a scalar diquark and of a quark and an axial-vector diquark. Electromagnetic form factors of the nucleon and Roper resonance are obtained from one-loop diagrams where the quark and diquarks are coupled by a photon. We include the effects of intrinsic properties of the diquarks: the int…
The description of baryons as fully relativistic bound states of quark and glue reduces to an effective Bethe-Salpeter equation with quark-exchange interaction when irreducible 3-quark interactions are neglected and separable 2-quark (diquark) correlations are assumed. This covariant quark-diquark model of baryons is studied with the inclusion of the quark substructure of the diquark correlations. In order to maintain electromagnetic current conservation it is then necessary to go beyond the impulse approximation. A conserved current is obtained by including the coupling of the photon to the e…
In the diquark-quark model of the nucleon including scalar and axialvector diquarks we compare solutions of the ladder Bethe-Salpeter equation in the instantaneous Salpeter approximation and in the fully covariant (i.e. four-dimensional) treatment. We obtain that the binding energy is severly underestimated in the Salpeter approximation. For the electromagnetic form factors of the nucleon we find that in both approaches the overall shapes of the respective form factors are reasonably similar up to $Q^2 \approx 0.4$ GeV^2. However, the magnetic moments differ substantially as well as results fo…
A covariant, composite scalar diquark, Fadde'ev amplitude model for the nucleon is used to calculate pseudoscalar, isoscalar- and isovector-vector, axial-vector and scalar nucleon form factors. The last yields the nucleon sigma-term and on-shell sigma-nucleon coupling. The calculated form factors are soft, and the couplings are generally in good agreement with experiment and other determinations. Elements in the dressed-quark-axial-vector vertex that are not constrained by the Ward-Takahashi identity contribute ~20% to the magnitude of g_A. The calculation of the nucleon sigma-term elucidates …
The semi-inclusive deep inelastic scattering of electrons off the deuteron ($^2H \equiv D$) and $^3He$ with detection of slow protons and deuterons, respectively, i.e. the processes $D(e,e'p)X$ and $^3He(e,e'D)X$, are calculated within the spectator mechanism, taking into account the final state interaction of the hadronizing quark with the detected protons and deuterons, respectively. It is shown that by a proper choice of the kinematics the origin of the EMC effect and the details of the interaction between the hadronizing quark and the nuclear medium can be investigated at a level which can…
This work is devoted to the study of diquark correlations inside the nucleon. We analyze some matrix elements which encode information about the non-perturbative forces, in different color anti-triplet diquark channels. We suggest a lattice calculation to check the quark-diquark picture and clarify the role of instanton-mediated interactions. We study in detail the physical properties of the 0+ diquark, using the Random Instanton Liquid Model. We find that instanton forces are sufficiently strong to form a diquark bound-state, with a mass of ~500 MeV, which is compatible with earlier estimates…
We investigate the generalized form factors of the nucleon in a light-cone spectator-diquark model. Compared to the form factors, the generalized form factors contain some more information of the structure of the nucleon. In our calculation, both the scalar and the axial-vector spectator-diquark are taken into account. As a relation between the spin in the instant form and that in the light-cone form, the Melosh-Wigner rotation effect is included for both the quark and the axial-vector diquark. We also provide numerical results from our model calculations, and the results are comparable with t…
We present calculation of influence caused by nucleon Fermi motion on the parton distributions in nuclei. Our approach is based on the model where momenta of valence partons have some primordial distribution inside the hadron at rest, which is either provided by a statistical considerations or calculated using spherically symmetric Gaussian distribution with a width derived from the Heisenberg uncertainty relation. The sea parton contribution emerges from the similar Gaussian distribution with a width dictated by the presence of virtual pions in hadron. We show that the influence of Fermi moti…
We introduce diquarks as separable correlations in the two-quark Green's function to facilitate the description of baryons as relativistic three-quark bound states. These states then emerge as solutions of Bethe-Salpeter equations for quarks and diquarks that interact via quark exchange. Approximating quark and diquark propagators by the corresponding free ones, we calculate nucleon static properties and form factors. For the description of production processes off the nucleon, we consider various dressing functions for the propagators to remove unphysical thresholds. Results for kaon photopro…
