Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Two-photon exchange in elastic electron-proton scattering : QCD
  factorization approach   We estimate the two-photon exchange contribution to elastic electron-proton
scattering at large momentum transfer $Q^2$. It is shown that the leading
two-photon exchange amplitude behaves as $1/Q^4$ relative to the one-photon
amplitude, and can be expressed in a model independent way in terms of the
leading twist nucleon distribution amplitudes. Using several models for the
nucleon distribution amplitudes, we provide estimates for existing data and for
ongoing experiments.

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The categories of this paper are: astro-ph
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The categories of this paper are: cond-mat
35
The categories of this paper are: mtrl-th
22
The categories of this paper are: chao-dyn
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The categories of this paper are: ao-sci
25
The categories of this paper are: patt-sol
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The categories of this paper are: quant-ph
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The categories of this paper are: q-bio
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The categories of this paper are: hep-lat
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The categories of this paper are: adap-org
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The categories of this paper are: cs
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The categories of this paper are: physics
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The categories of this paper are: chem-ph
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The categories of this paper are: q-fin
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The categories of this paper are: math-ph
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The categories of this paper are: bayes-an