Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Neutron Stars in f(R)-Gravity and Its Extension with a Scalar Axion
  Field   We present a brief review of general results about non-rotating neutron stars
in simple R-square gravity and its extension with a scalar axion field.
Modified Einstein equations are presented for metrics in isotropical
coordinates. The mass-radius relation, mass profile and dependence of mass from
central density on various equations of state are given in comparison to
general relativity.

12
The categories of this paper are: nucl-th
29
The categories of this paper are: funct-an
21
The categories of this paper are: adap-org
30
The categories of this paper are: q-alg
19
The categories of this paper are: eess
37
The categories of this paper are: supr-con
36
The categories of this paper are: cmp-lg
33
The categories of this paper are: plasm-ph
34
The categories of this paper are: chem-ph
20
The categories of this paper are: acc-phys
22
The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph
1
The categories of this paper are: cs
7
The categories of this paper are: hep-th
25
The categories of this paper are: patt-sol
24
The categories of this paper are: dg-ga