Light cone and vector meson dominance in photo-and electroproduction

By using the formalism of mass dispersion relations and light cone dominance for large masses, relations are derived between photoproduction and deep inelastic electroproduction. In addition large deviations from VDM are derived for ?^o electroproduction in the deep inelastic region; these results compare quite well with recent experimental information.     

Range,light-cone dominance and scaling at low Q2 in electroproduction

The analysis of light cone singularities is used to connect the y · P, or range, dependence of the current correlation function with the Q² dependence of the inelastic electroproduction structure functions. We study for what regions of the Q², ν plane and for what y · P dependence the leading light-cone singularity dominates contributions from less singular terms with the same y · P dependence. When the leading singularity can be shown to dominate for a particular region of Q² and ν, we study whether this implies scaling for νW₂ in that kinematic region. It is shown that a division of the current correlation function into short and long range contributions is fundamentally ambiguous and not related to scaling at low Q². Short range terms which are shown to be light-cone dominated for all Q² so long as ν → ∞, are found but are shown not to scale at low Q² and to be indistinguishable from corrections to long range terms which produce the leading Regge behavior. We show that leading Regge terms may receive contributions far away from the light cone for small virtual photon mass, but that light-cone dominance and scaling are recovered when the photon mass is taken very large.     

On violation of Feynman scaling law in the framework of dual parton model

The violation of scaling in the central- and fragmentation regions for nucleon-antinucleon collision is studied in the framework of the dual parton model. The results of calculations are compared with data. The formulae for the preasymptotic behavior of inclusive spectra in the central region are obtained. It is shown that the analytical form of the preasymptotic behavior is determined by the shape of the momentum distribution functions atx=0. The comparison with the corresponding results of the quark-gluon string model is given. Some problems concerning the calculation of the momentum distribution functions are considered.     

Dynamical coupled-channels model of meson photo- and electroproduction in the nucleon resonance region

A dynamical approach of the meson production reaction for extracting nucleon resonance parameters has been developed. We report on the γN Δ form factors extracted from the recent pion electroproduction data and the coupled-channels model of πN scattering up to W ≤ 2 GeV. An analysis of the resonance poles extracted using the speed-plot and time-delay methods is briefly discussed. Correspondence: T. Sato, Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan     

Regularisation of theP→γγ vertex in the vector meson dominance model

The problem of the PCAC anomaly in the decaysP→γγ (P≡ pseudoscalar meson) is essentially one of regularisation. The constraints deriving there-from, together with similar ones from gauge invariance, typical of a spin 1/2 field theory, are used to define a vector meson dominance approximation for the corresponding amplitudes. The approximation is in this sense dual to the quark model and does indeed reconstruct the high energy quark model behaviour of the amplitudes in the Bjorken-Johnson-Low (BJL) limit. There are interesting new relations for vector meson (V) coupling constants in the decaysV→Pγ and for the PCAC anomaly itself.     

New form of vector meson dominance and the dependence on the vector meson mass squared

We propose a new form of VMD which relates the reactions πN → VN and γN → πN. Our form fits the experimental results within errors. As our restriction is strong enough, we can discuss the k_μ² dependence. Unexpectedly the k_μ² dependence is larger and this suggest the necessity of generalized vector dominance.     

Some consequences of the quark parton model in inclusive electroproduction

Consequences of the quark parton model proposed by Feynman for inclusive electroproduction are studies. We show that the SLAC experiment γ_v+p(n) → h^±+anything which distinguishes the outcoming hdrons by their charges only gives the possibility to check sum rules with fractional quark quantum numbers, to determine the charge of the proton quark (neutron quark) and to measure the valence distribution function directly. We predict the multiplicity difference for the charged hadrons as the function of q² which agrees well with the experimental data published recently.     

Unitarity constraints and role of geometrical effects in deep-inelastic scattering and vector meson electroproduction

Deep-inelastic scattering at low x and elastic vector meson electroproduction are analyzed on the basis of the s-channel unitarity extended to off-shell particle scattering. It appeared that the role of unitarity is important, but contrary to the case of on-shell scattering it does not rule out a power-like behavior of the total cross sections. We discuss the behavior of the total cross section of virtual photon–proton scattering in the geometrical approach and obtain the result that the exponent of the power-like energy dependence of is related to the constituent quark interaction radius. The mass effects and energy dependence of vector meson electroproduction are discussed along with the angular distributions at large momentum transfers in these processes. Received: 10 September 2001 / Published online: 7 December 2001     

Dual parton model and the photoproduction of pseudoscalar and vector mesons in the high energy region

On the basis of the dynamical dual model of strong interactions followed from the parton model of hadrons as discussed in an earlier paper, we study here the photo-production of pseudoscalar and vector mesons in the high energy region. To incorporate the concept of duality, it is taken that any two spin $\text{1}\text{2}$ pointlike constituents (partons) can form a π-meson cluster in the structure of a nucleon and the basic interaction involved in MB scattering is the interaction of the incident meson with the π meson in the structure of the nucleon. In this scheme, the amplitudes for the photoproduction of mesons such as γN → Nπ, γN → N?, and γN → Nω in the high energy region can be related with the amplitudes for the process γπ → ππ, γπ → π?, and γπ → πω, respectively. To calculate the amplitudes for the relevant process we also consider a factor corresponding to the structural rearrangement of partons involved in duality diagrams. To obtain the cross sections, we take into account the photon-vector meson analogy, though the naive form of the vector dominance model (VDM) has not been considered here. From a knowledge of the coupling constants $\text{γ?}{}^2\text{4π}$, $\text{γω}{}^2\text{?π}$, , and we obtain the differential cross sections which are in excellent agreement with experimental results. Also we obtain a good fit for the scattering process γN → Nπ at backward angles. For the vector meson production processes, we have contributions from the diffraction mechanism also apart from the amplitudes considered here. In the region where the contribution from the diffraction part is negligible, we obtain the relation

which is in nice agreement with experiments. Finally, it is shown that, though the vector meson dominance is not considered here, the universality of the vector meson coupling with hadrons follows directly from the present model.     

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.     

Scaling violation,the Callan Gross relation,and color excitation in electroproduction

The Callan-Gross relation is shown to be consistent with MIT-SLAC data for $\text{σ}{}_{\mathrm{<mtext>L</mtext>}}\text{(Q}{}^2\text{)}\text{σ}{}_{\mathrm{<mtext>T</mtext>}}\text{(Q}{}^2\text{)}$ for x ? 0.33 in deep inelastic eN scattering, despite the fact that these data are taken in the large Q² region where F₁ and F₂ individually exhibit scaling violation. Comparison is made with asymptotic freedom predictions, and color excitation is proposed to explain large values of $\text{σ}{}_{\mathrm{<mtext>L</mtext>}}\text{σ}{}_{\mathrm{<mtext>T</mtext>}}$ at small x.     

Double Q^2-rescaling model and the nuclear effect of the parton distribution functions

In order to overcome the shortcoming of nonconservation of nuclear momentum existing in the original -rescaling model (ORM) and avoid introducing nuclear shadowing factor, we proposed a double -rescaling model (DRM) for the parton distributions of the bound nucleon. Using the experimental data of lepton-nucleus deep inelastic scattering (DIS) and the condition of the nuclear momentum conservation, the -rescaling parameters of various partons for Sn, Fe, Ca and C nuclei are determined. The rescaling parameters of valence quark distributions are larger than unity and gradually increase with atomic number A, on the contrary, the rescaling parameters of sea quark distributions and gluon distributions are smaller than unity, and slowly decrease with A. By using this model, the experimental data of the DIS process, the nuclear Drell-Yan process and ph otoproduction process are consistently and quite satisfactorily explained. Received: 18 August 1997 / Published online: 20 February 1998     

Thermal states of the vector meson model in two dimensions

We compute the KMS states for the vector meson model in two-dimensional space-time. We also consider their limit to those of the Thirring model.     

Hadron production at supercolliders in the two component dual parton model and the smallx behaviour of the structure functions

Models which contain a semihard component sensitively depend on the smallx region of the structure functions. Within the framework of a two component dual parton model the effect of recently proposed steeper structure functions is investigated. Drastic changes which appear in the bare scattering amplitudes get significantly reduced by unitarization. For presently available energies the semihard component seems still too small to allow for clear cut conclusions about the correctness of the various proposed structure functions. However, the predictions for SSC or LHC energies depend on the choice of the structure function quite decisively, resulting in a substantial uncertainty in the extrapolations. The uncertainty is reduced to a less worrisome level if the consideration is restricted to the strongly shadowed parton distribution.