Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A pedagogical derivation of dynamical susceptibilities   Dynamical two-particle susceptibilites are important for a wide range of
different experiments in condensed-matter physics and beyond. Nevertheless,
most textbooks avoid describing how to derive such response functions, perhaps
because they are viewed as too complex. In the literature, most derivations
work with generalized susceptibilities, which are more general, but require an
even higher layer of complexity. In this work, we show a more direct derivation
in the context of model Hamiltonians which can be mapped directly onto an
impurity model. We also present an alternative derivation for the irreducible
vertex in the context of the Falicov-Kimball model.

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The categories of this paper are: nlin
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The categories of this paper are: q-alg
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The categories of this paper are: funct-an
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The categories of this paper are: eess
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The categories of this paper are: math-ph
5
The categories of this paper are: gr-qc
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The categories of this paper are: comp-gas
35
The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-lat
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The categories of this paper are: chem-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: econ
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The categories of this paper are: adap-org
2
The categories of this paper are: math
24
The categories of this paper are: dg-ga