Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Orthopositronium Decay Spectrum using NRQED   The photon spectrum in orthopositronium to 3 gamma decay is computed using
effective field theory methods. For energetic photons, the spectrum agrees with
the Ore-Powell result, but deviates from it when the photon energy is
comparable to the positronium binding energy. The decay spectrum in this region
depends on a positronium structure function, which is computed in this paper.
At still lower energies the photon spectrum is dominated by the parapositronium
resonance contribution. Our results are compatible with Low's theorem on soft
photon emission.

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The categories of this paper are: bayes-an
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The categories of this paper are: cmp-lg
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The categories of this paper are: supr-con
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The categories of this paper are: patt-sol
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The categories of this paper are: cs
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The categories of this paper are: alg-geom
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The categories of this paper are: eess
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The categories of this paper are: econ
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The categories of this paper are: hep-ex
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-th
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The categories of this paper are: astro-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-bio
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The categories of this paper are: solv-int