Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Three-Body Collective Excitations in the Superconducting Phase of
  $MgB_2$   It is shown that coherent behavior of Cooper's pairs and electrons in the
two-band superconductors $MgB_2$ is possible as a result of a strong
two-phonon-electron coupling. The spin-$\frac 12$ triples with zero angular
momentum are made up of three spin-$\frac 12$ fermions with charge $\emph{e}$.
They are gapped Fermi excitations with gap induced by the gaps of the single
fermions. Their contribution to the thermodynamics of the $MgB_2$
superconductors is considered.

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The categories of this paper are: adap-org
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The categories of this paper are: eess
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The categories of this paper are: comp-gas
34
The categories of this paper are: chem-ph
2
The categories of this paper are: math
13
The categories of this paper are: quant-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-th
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The categories of this paper are: mtrl-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: nlin
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The categories of this paper are: bayes-an
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The categories of this paper are: econ
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The categories of this paper are: stat
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The categories of this paper are: atom-ph