Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Hard Nonlogarithmic Corrections of Order $m\alpha^7$ to Hyperfine
  Splitting in Positronium   We consider hard three-loop nonlogarithmic corrections of order $m\alpha^7$
to hyperfine splitting in positronium. All these contributions are generated by
the graphs with photon and/or electron loop radiative insertions in the
two-photon exchange diagrams. We calculate contributions of six gauge invariant
sets of diagrams. The total result for all these diagrams is $\Delta
E=-1.2917(1)m\alpha^7/\pi^3=-5.672$ kHz.

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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: acc-phys
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The categories of this paper are: chem-ph
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The categories of this paper are: astro-ph
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The categories of this paper are: funct-an
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The categories of this paper are: math
1
The categories of this paper are: cs
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The categories of this paper are: q-alg
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The categories of this paper are: supr-con
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The categories of this paper are: cmp-lg
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The categories of this paper are: ao-sci
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The categories of this paper are: nucl-ex
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The categories of this paper are: gr-qc
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The categories of this paper are: dg-ga
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The categories of this paper are: q-bio