493 research outputs found
Off-diagonal generalized vector dominance in DIS and QCD
We review the generalized vector dominance (GVD) approach to DIS at small
values of the scaling variable, x. In particular, we concentrate on a recent
formulation of GVD that explicitly incorporates the configuration of the
gamma^* -> q qbar transition and a QCD-inspired ansatz for the (qqbar)p
scattering amplitude. The destructive interference, originally introduced in
off-diagonal GVD is traced back to the generic strcuture of two-gluon exchange.
Asymptotically, the transverse photoabsorption cross section behaves as (ln
Q^2)/Q^2, implying a logarithmic violation of scaling for F_2, while the
longitudinal-to-transverse ratio decreases as 1/\ln Q^2. We also briefly
comment on vector-meson production.Comment: 21 pages latex, 12 postscript files for figures, talk given at the
XXI School of Theoretical Physics, Ustron, Poland, September 199
Log(1/x) Gluon Distribution and Structure Functions in the Loop-Loop Correlation Model
We consider the interaction of the partonic fluctuation of a scalar
``photon'' with an external color field to calculate the leading and
next-to-leading order gluon distribution of the proton following the work done
by Dosch-Hebecker-Metz-Pirner. We relate these gluon distributions to the short
and long distance behavior of the cross section of an adjoint dipole scattering
off a proton. The leading order result is a constant while the next-to-leading
order result shows a ln(1/x) enhancement at small x. To get numerical results
for the gluon distributions at the initial scale Q^2_0=1.8 GeV^2, we compute
the adjoint dipole-proton cross section in the loop-loop correlation model.
Quark distributions at the same initial scale are parametrized according to
Regge theory. We evolve quark and gluon distributions to higher Q^2 values
using the DGLAP equation and compute charm and proton structure functions in
the small-x region for different Q^2 values.Comment: 13 pages, 10 figures,revised version,references added, typos
corrected, to be published in Eur. Phys. Journal
Vacuum Expectation Value of a Wegner-Wilson Loop near the Light Cone
Vacuum expectation values for one Wegner-Wilson loop representing a moving
quark-antiquark pair are calculated in four-dimensional Euclidean and Minkowski
space-time. The calculation uses gluon field strength correlators with
perturbative gluon exchange and non-perturbative correlations from the
stochastic vacuum model. The expectation value of a Wegner-Wilson loop forming
a hyperbolic angle in Minkowski space-time is connected by an analytical
continuation to the expectation value of the Wegner-Wilson loop in Euclidean
four-space. The obtained result shows how confinement enters into the
light-cone Hamiltonian for valence quarks independently of the chosen model.Comment: 12 pages, 2 figures, sections 2 and 3 shortened, more details added
in section
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