Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: GZK Photons in the Minimal Ultra High Energy Cosmic Rays Model   In a recently proposed model the cosmic rays spectrum at energies above
10^{18} eV can be fitted with a minimal number of unknown parameters assuming
that the extragalactic cosmic rays are only protons with a power law source
spectrum ~E^{-alpha} and alpha~2.6.
  Within this minimal model, after fitting the observed HiRes spectrum with
four parameters (proton injection spectrum power law index and maximum energy,
minimum distance to sources and evolution parameter) we compute the flux of
ultra-high energy photons due to photon-pion production, the GZK photons, for
several radio background models and average extragalactic magnetic fields with
amplitude between 10^{-11} G and 10^{-9} G. We find the photon fraction to be
between 10^{-4} and 10^{-3} in cosmic rays at energies above 10^{19} eV. These
small fluxes could only be detected in future experiments like Auger North plus
South and EUSO.

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The categories of this paper are: q-alg
4
The categories of this paper are: cond-mat
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The categories of this paper are: chem-ph
15
The categories of this paper are: nucl-ex
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The categories of this paper are: dg-ga
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The categories of this paper are: nlin
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The categories of this paper are: q-fin
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The categories of this paper are: stat
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The categories of this paper are: eess
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The categories of this paper are: cmp-lg
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The categories of this paper are: acc-phys
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The categories of this paper are: adap-org
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The categories of this paper are: quant-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: alg-geom
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The categories of this paper are: gr-qc