Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: The cosmological backreaction: gauge (in)dependence, observers and
  scalars
22
The categories of this paper are: chao-dyn
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
0
The categories of this paper are: hep-ph
21
The categories of this paper are: adap-org
2
The categories of this paper are: math
28
The categories of this paper are: alg-geom
11
The categories of this paper are: hep-lat
4
The categories of this paper are: cond-mat
23
The categories of this paper are: solv-int
19
The categories of this paper are: eess
36
The categories of this paper are: cmp-lg
14
The categories of this paper are: math-ph
13
The categories of this paper are: quant-ph
3
The categories of this paper are: physics
34
The categories of this paper are: chem-ph