Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Towards analytic description of a transition from weak to strong
  coupling regime in correlated electron systems. I. Systematic diagrammatic
  theory with two-particle Green functions   We analyze behavior of correlated electrons described by Hubbard-like models
at intermediate and strong coupling. We show that with increasing interaction a
pole in a generic two-particle Green function is approached. The pole signals
metal-insulator transition at half filling and gives rise to a new vanishing
``Kondo'' scale causing breakdown of weak-coupling perturbation theory. To
describe the critical behavior at the metal-insulator transition a novel,
self-consistent diagrammatic technique with two-particle Green functions is
developed. The theory is based on the linked-cluster expansion for the
thermodynamic potential with electron-electron interaction as propagator.
Parquet diagrams with a generating functional are derived. Numerical
instabilities due to the metal-insulator transition are demonstrated on
simplifications of the parquet algebra with ring and ladder series only. A
stable numerical solution in the critical region is reached by factorization of
singular terms via a low-frequency expansion in the vertex function. We stress
the necessity for dynamical vertex renormalizations, missing in the simple
approximations, in order to describe the critical, strong-coupling behavior
correctly. We propose a simplification of the full parquet approximation by
keeping only most divergent terms in the asymptotic strong-coupling region. A
qualitatively new, feasible approximation suitable for the description of a
transition from weak to strong coupling is obtained.

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The categories of this paper are: plasm-ph
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The categories of this paper are: funct-an
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The categories of this paper are: nucl-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-ph
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The categories of this paper are: physics
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The categories of this paper are: gr-qc
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The categories of this paper are: alg-geom
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The categories of this paper are: q-alg
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The categories of this paper are: stat
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The categories of this paper are: hep-lat
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The categories of this paper are: patt-sol
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The categories of this paper are: supr-con
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The categories of this paper are: adap-org
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-ex