Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Second Order perturbation Theory: A covariant approach involving a
  barotropic equation of state   We present a covariant and gauge invariant formalism suited to the study of
second-order effects associated with higher order tensor perturbations. The
analytical method we have developed enables us to characterize pure
second-order tensor perturbations about FLRW model having different kinds of
equations of state. Our analysis of the radiation case suggests that it may be
feasible to examine the CMB polarization arising from higher order
perturbations.

22
The categories of this paper are: chao-dyn
25
The categories of this paper are: patt-sol
28
The categories of this paper are: alg-geom
2
The categories of this paper are: math
17
The categories of this paper are: q-fin
7
The categories of this paper are: hep-th
11
The categories of this paper are: hep-lat
13
The categories of this paper are: quant-ph
9
The categories of this paper are: nlin
36
The categories of this paper are: cmp-lg
37
The categories of this paper are: supr-con
30
The categories of this paper are: q-alg
31
The categories of this paper are: ao-sci
16
The categories of this paper are: stat
10
The categories of this paper are: q-bio
3
The categories of this paper are: physics