Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Correlation energy of the pairing Hamiltonian   We study the correlation energy associated with the pair fluctuations in BCS
theory. We use a schematic two-level pairing model and discuss the behavior of
the correlation energy across shell closures, including the even-odd
differences. It is shown that the random phase approximation (RPA) to the
ground state energy reproduces the exact solutions quite well both in the
normal fluid and in the superfluid phases. In marked contrast, other methods to
improve the BCS energies such as Lipkin-Nogami method, only work when the
strength of a pairing interaction is large. We thus conclude that the RPA
approach is better for a systematic theory of nuclear binding energies.

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The categories of this paper are: cond-mat
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The categories of this paper are: acc-phys
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The categories of this paper are: cs
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The categories of this paper are: stat
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The categories of this paper are: gr-qc
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The categories of this paper are: quant-ph
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The categories of this paper are: physics
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The categories of this paper are: hep-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: math
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-ph
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The categories of this paper are: q-fin
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The categories of this paper are: chao-dyn
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The categories of this paper are: funct-an
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The categories of this paper are: nucl-ex