Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Integrability conditions of quasi-Newtonian cosmologies in modified
  gravity   We investigate the integrability conditions of a class of shear-free
perfect-fluid cosmological models within the framework of anisotropic fluid
sources, applying our results to f(R) dark energy models. Generalising earlier
general relativistic results for time-like geodesics, we extend the potential
and acceleration terms of the quasi-Newtonian formulation of integrable dust
cosmological models about a linearized Friedmann-Lemaitre-Robertson-Walker
background and derive the equations that describe their dynamical evolutions.
We show that in general, models with an anisotropic fluid source are not
consistent, but because of the particular form the anisotropic stress takes in
f(R) gravity, the general integrability conditions, in this case, are
satisfied.

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The categories of this paper are: physics
8
The categories of this paper are: hep-ex
16
The categories of this paper are: stat
18
The categories of this paper are: econ
34
The categories of this paper are: chem-ph
35
The categories of this paper are: mtrl-th
32
The categories of this paper are: atom-ph
25
The categories of this paper are: patt-sol
30
The categories of this paper are: q-alg
37
The categories of this paper are: supr-con
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The categories of this paper are: quant-ph
14
The categories of this paper are: math-ph
26
The categories of this paper are: bayes-an
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The categories of this paper are: cond-mat
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The categories of this paper are: hep-ph
12
The categories of this paper are: nucl-th