Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Background cosmological dynamics in $f(R)$ gravity and observational
  constraints   In this paper, we carry out a study of viable cosmological models in
$f(R)$-gravity at the background level. We use observable parameters like
$\Omega$ and $\gamma$ to form autonomous system of equations and show that the
models under consideration exhibit two different regimes in their time
evolution, namely, a phantom phase followed by a quintessence like behavior. We
employ statefinder parameters to emphasize a characteristic discriminative
signature of these models.

1
The categories of this paper are: cs
31
The categories of this paper are: ao-sci
19
The categories of this paper are: eess
21
The categories of this paper are: adap-org
16
The categories of this paper are: stat
10
The categories of this paper are: q-bio
23
The categories of this paper are: solv-int
18
The categories of this paper are: econ
29
The categories of this paper are: funct-an
36
The categories of this paper are: cmp-lg
13
The categories of this paper are: quant-ph
17
The categories of this paper are: q-fin
27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin