Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Large N planar or bare vertex approximation and critical behavior of a
  SU(N) invariant four-fermion model in 2+1 dimensions   A four-fermion model in 2+1 dimensions describing N Dirac fermions
interacting via SU(N) invariant N^2-1 four-fermion interactions is solved in
the leading order of the 1/N expansion. The 1/N expansion corresponds to 't
Hoofts topological 1/N expansion in which planar Feynman diagrams prevail. For
the symmetric phase of this model, it is argued that the planar expansion
corresponds to the ladder approximation. A truncated set of Schwinger-Dyson
equations for the fermion propagator and composite boson propagator
representing the relevant planar diagrams is solved analytically. The critical
four-fermion coupling and various critical exponents are determined as
functions of N. The universality class of this model turns out to be quite
distinct from the Gross-Neveu model in the large N limit.

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The categories of this paper are: atom-ph
3
The categories of this paper are: physics
16
The categories of this paper are: stat
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The categories of this paper are: solv-int
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The categories of this paper are: supr-con
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The categories of this paper are: bayes-an
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The categories of this paper are: alg-geom
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The categories of this paper are: mtrl-th
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The categories of this paper are: econ
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The categories of this paper are: acc-phys
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The categories of this paper are: nucl-th
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The categories of this paper are: q-bio
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The categories of this paper are: patt-sol
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The categories of this paper are: q-fin
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The categories of this paper are: nucl-ex
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The categories of this paper are: eess