Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gauge-invariant Formulation of the Second-order Cosmological
  Perturbations   Gauge invariant treatments of the second order cosmological perturbation in a
four dimensional homogeneous isotropic universe filled with the perfect fluid
are completely formulated without any gauge fixing. We derive all components of
the Einstein equations in the case where the first order vector and tensor
modes are negligible. These equations imply that the tensor and the vector mode
of the second order metric perturbations may be generated by the scalar-scalar
mode coupling of the linear order perturbations as the result of the non-linear
effects of the Einstein equations.

8
The categories of this paper are: hep-ex
12
The categories of this paper are: nucl-th
18
The categories of this paper are: econ
31
The categories of this paper are: ao-sci
25
The categories of this paper are: patt-sol
35
The categories of this paper are: mtrl-th
34
The categories of this paper are: chem-ph
23
The categories of this paper are: solv-int
37
The categories of this paper are: supr-con
20
The categories of this paper are: acc-phys
30
The categories of this paper are: q-alg
28
The categories of this paper are: alg-geom
27
The categories of this paper are: comp-gas
1
The categories of this paper are: cs
4
The categories of this paper are: cond-mat
10
The categories of this paper are: q-bio