Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Scalar perturbations in cosmological $f(R)$ models: the cosmic screening
  approach   We investigate cosmological perturbations for nonlinear $f(R)$ models within
the cosmic screening approach. Matter is considered both in the form of a set
of discrete point-like massive bodies and in the form of a continuous
pressureless perfect fluid. We perform full relativistic analysis of the
first-order theory of scalar perturbations for arbitrary nonlinear $f(R)$
models and demonstrate that scalar potentials $\Phi(t,\mathbf{r})$ and
$\Psi(t,\mathbf{r})$ are determined by a system of only two master equations.
Our equations are applicable at all spatial scales as long as the approximation
$\delta R/\bar R \ll 1$ (which is usually assumed in studies devoted to
cosmological perturbations in $f(R)$ models) works.

36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg
21
The categories of this paper are: adap-org
28
The categories of this paper are: alg-geom
18
The categories of this paper are: econ
25
The categories of this paper are: patt-sol
10
The categories of this paper are: q-bio
33
The categories of this paper are: plasm-ph
26
The categories of this paper are: bayes-an
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The categories of this paper are: acc-phys
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The categories of this paper are: eess
14
The categories of this paper are: math-ph
27
The categories of this paper are: comp-gas
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The categories of this paper are: stat
22
The categories of this paper are: chao-dyn
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The categories of this paper are: dg-ga