Proton structure functions in an infinite resonance O(4, 2) model

The proton electromagnetic inelastic structure functions have been explicitly evaluated in a noncompact O(4, 2) model for the spectrum of hadronic states, using the Barut-Corrigan-Kleinert infinite component wave equation. The resulting structure functions exhibit nontrivial scaling behavior in the Bjorken limit and give qualitative agreement with observation. They also satisfy exactly the Callan-Gross relation.     

Statistical model for the structure functions of the nucleon

The deep-inelastic structure functions of the nucleon are calculated in a statistical model considering the nucleon to be composed of a gas of quarks and gluons. Several differences with the standard parton-model approach are pointed out. To zeroth order in perturbative QCD, the model is worked out completely. A fit to the large-x part of the structure functions requires a temperature of about 40–50 MeV for the quarks and gluons and a chemical potential around 200 MeV.     

Quark sea structure functions of the nucleon in a statistical model

Within a statistical model of linear confined quarks we obtain the flavor asymmetry and corresponding structure function of the nucleon. The model parameters are fixed by the experimental available data. The temperature parameter is adjusted by the Gottfried sum rule violation and the chemical potentials by the corresponding up (u) and down (d) quark normalizations in the nucleon. The light antiquark and quark distributions in the proton, given by d̄/ū, d/u and d̄-ū, as well as the neutron to proton ratio of the structure functions, extracted from the experimental data, are well fitted by the model. As the quark-confining strengths should be flavor dependent, a mechanism is introduced in the model to adjust the corresponding distribution, in order to improve the comparison obtained for the sea-quark asymmetries in the nucleon with the available experimental analysis. PACS  11.30.Hv; 14.20.Dh; 12.39.Ki; 12.40.Ee; 11.55.Hx     

Model for the nucleon structure function F2(x,Q2)

A particular j-plane singularity, leading to long-range effects in hadron scattering, is attributed to hard constituent quark interactions. A definite prediction for the nucleon structure function, including scaling violations consistent with QCD. is obtained, which is confronted with the available data.     

Unpolarized structure functions and the parton distributions for nucleon in an independent quark model

Considering the nucleon as consisting entirely of its valence quarks confined independently in a scalar-vector harmonic potential; unpolarized structure functions F ₁(x, μ ²) and F ₂(x, μ ²) are derived in the Bjorken limit under certain simplifying assumptions; from which valence quark distribution functions u _v(x, μ ²) and d _v(x, μ ²) are appropriately extracted satisfying the normalization constraints. QCD-evolution of these input distributions from a model scale of μ ²=0.07 GeV² to a higher Q ² scale of Q ₀ ² =15 GeV² yields xu _v(x, Q ₀ ² ) and xd _v(x, Q ₀ ² ) in good agreement with experimental data. The gluon and sea-quark distributions such as G(x, Q ₀ ² ) and q _s(x, Q ₀ ² ) are dynamically generated with a reasonable qualitative agreement with the available data; using the leading order renormalization group equations with appropriate valence-quark distributions as the input.     

The (spin) structure of the nucleon

A selection of new data obtained by the HERMES experiment at DESY is presented, which provides new insight into the QCD structure of the nucleon. Using polarized lepton beams and polarized targets, the spin-dependent structure function g ₁(x) has been determined for ¹ H, ² H and ³ He. By also observing one of the produced hadrons it has been possible to extract the polarization distribution of individual quark flavours in the nucleon as well. Further information on nucleon structure has been obtained by observing (almost) exclusive reactions, which can be interpreted in terms of the recently introduced generalized parton distributions (GPDs). As an example of such data measurements of both the beam-spin and beam-charge asymmetries resulting from deeply virtual Compton scattering (DVCS) are presented. By embedding the deep-inelastic scattering process in the nuclear environment additional information can be obtained on nucleon structure and some QCD effects. The potential of this technique is illustrated by showing new results on tagged structure functions and hadronization in nuclei.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.60.Hb Total and inclusive cross-sections (including deep-inelastic processes) - 13.88. + e Polarization in interactions and scattering - 14.20.Dh Protons and neutrons - 24.85. + p Quarks, gluons, and QCD in nuclei and nuclear processesG. van der Steenhoven: For the HERMES Collaboration     

过渡金属(Ni)掺杂ZnV2O4的第一性原理计算

采用基于密度泛函理论下的MS软件模拟了过渡金属Ni掺杂ZnV₂O₄前后的能带结构、态密度以及光学性质.结果表明：ZnV₂O₄具有间接的光学跃迁且能带间隙为0.355 eV,Ni掺杂后能带间隙增加为0.785 eV,且带隙类型不变,引入的Ni-3d轨道电子对ZnV₂O₄的价带和导带组成提供了较大贡献.光学性质结果表明ZnV₂O₄为一种低介电材料,在可见光区的吸收系数和折射率较低,主要表现为紫外吸收.掺杂Ni后,在可见光区的吸收特性和光电导率均增大,有效改善了ZnV₂O₄在可见光区的光电性能.     

Diquark contributions to the nucleon deep inelastic structure functions

The contributions of diquarks to the nucleon structure functions are discussed in the framework of the parton model and in the most general case of both vector and scalar diquarks inside unpolarized and polarized nucleons. The vector diquark anomalous magnetic moment and the scalar-vector and vector-scalar diquark transitions are also taken into account. The properties of the diquarks and of their form factors, required in order for the resulting scaling violations to be compatible with the observed ones, are discussed.     

An investigation of the phase structure of the two-dimensional O(2) and O(4) symmetric nonlinear sigma-models

We investigate the phase structure of the two-dimensional O(2) and O(4) lattice σ-models by means of a Monte Carlo simulation using Binder's phenomenological renormalization group. For the O(2) model the transition temperature β_c⁻¹ is estimated and the expected line of critical points is found. For the O(4) model no signal of a phase transition is found in the range of couplings considered. This is in contradiction to a recent claim that the O(4) model has a critical point at finite β.     

Chiral-odd transversity spin structure function h1(x) of the nucleon in a constituent quark model

We study the chiral-odd transversity spin-dependent quark distribution function h₁(x) of the nucleon in a constituent quark model. The twist-2 structure functions, f₁(x), g₁(x) and h₁(x) are calculated within the diquark spectator approximation. Whereas an inequality f₁(x) > h₁(x) > g₁(x) holds with the interaction between quark and diquark being scalar, the axial-vector effective quark-diquark interaction, which contributes to the d-quark distribution, does not lead to such a simple relation. We find that h₁(x) for the d-quark becomes somewhat smaller than g₁^d(x), when we fix the model parameter to reproduce known other structure functions. We also include corrections due to the non-trivial structure of the constituent quark, which is modeled by the Goldstone boson dressing. This improves agreements of f₁(x) and g₁(x) with experiments, and brings further reduction of h₁^d(x) distribution. Consequences for semi-inclusive experiments are also discussed.