Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Generalization of the Hartree-Fock-Bogoliubov theory: one and two
  quasiparticle excitations   We present a generalization of the Hartree-Fock Bogoliubov (HFB) theory in
which the coupling between one and two quasi-particles is taken into
account.This is done by writing the excitation operators as linear combinations
of one and two HFB quasi-particles. The excitation energies and the
quasi-particle amplitudes are given by generalized Bogoliubov equations. The
excitation spectrum has two branches. The first one is a discrete branch which
is gapless and has a phonon character at large wave-length and, contrarily to
HFB, is always stable. This branch is detached from a continuum branch whose
threshold, at fixed total momentum, coincides with the two quasi-particle
threshold of the HFB theory. The gap between these two branches at P=0 is equal
to two times the HFB gap, which then provides for the relevant energy scale. We
also give numerical results for a specific case.

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The categories of this paper are: astro-ph
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The categories of this paper are: physics
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The categories of this paper are: hep-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: q-bio
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: quant-ph
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The categories of this paper are: econ
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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: atom-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: gr-qc
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The categories of this paper are: patt-sol