Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Scalar O(N) Model at Finite Temperature -- 2PI Effective Potential in
  Different Approximations   We calculate the two-particle irreducible (2PI) effective potential of the
O(N) linear sigma model in 1+1 dimensions. The approximations we use are the
next-to-leading order of a 1/N expansion (for arbitrary N) and a kind of
"resummed loop approximation" for N=1. We show that the effective potential of
the 1/N expansion is convex for N=4 and N=10 whereas it is not for the "loop"
expansion and the case N=1 of the 1/N expansion.

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The categories of this paper are: supr-con
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The categories of this paper are: quant-ph
4
The categories of this paper are: cond-mat
5
The categories of this paper are: gr-qc
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The categories of this paper are: eess
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The categories of this paper are: stat
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The categories of this paper are: acc-phys
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The categories of this paper are: q-fin
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The categories of this paper are: hep-ex
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The categories of this paper are: alg-geom
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The categories of this paper are: funct-an
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The categories of this paper are: dg-ga
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The categories of this paper are: chem-ph
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The categories of this paper are: adap-org
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The categories of this paper are: solv-int
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The categories of this paper are: hep-th