Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Diffractive Exclusive Photon Production in DIS at HERA   We demonstrate that perturbative QCD allows one to calculate the absolute
cross section of diffractive exclusive production of photons at large $Q^2$ at
HERA, while the aligned jet model allows one to estimate the cross section for
intermediate $Q^2 \sim 2 GeV^2$.
  Furthermore, we find that the imaginary part of the amplitude for the
production of real photons is larger than the imaginary part of the
corresponding DIS amplitude by about a factor of 2, leading to the prediction
of a significant counting rate for the current generation of experiments at
HERA. We also find a large azimuthal angle asymmetry in $ep$ scattering for
HERA kinematics which allows one to directly measure the real part of the DVCS
amplitude and hence the nondiagonal parton distributions.

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The categories of this paper are: comp-gas
21
The categories of this paper are: adap-org
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The categories of this paper are: q-alg
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The categories of this paper are: bayes-an
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The categories of this paper are: alg-geom
6
The categories of this paper are: astro-ph
16
The categories of this paper are: stat
34
The categories of this paper are: chem-ph
29
The categories of this paper are: funct-an
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The categories of this paper are: quant-ph
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The categories of this paper are: hep-th
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The categories of this paper are: dg-ga
5
The categories of this paper are: gr-qc
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The categories of this paper are: chao-dyn
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The categories of this paper are: cmp-lg
31
The categories of this paper are: ao-sci