Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Modeling Background Radiation in Isotropic Cosmologies   Using explicit perturbations of isotropic cosmological models which describe
simple gravitational waves, an isotropic tensor having the algebraic symmetries
of the Bel-Robinson tensor is derived as a model of cosmic background
gravitational radiation and this is used to provide an answer to the question:
in what sense can an energy-momentum-stress tensor similar to that describing
the cosmic microwave background radiation (neglecting anisotropies) be
associated with an isotropic background of gravitational radiation?

17
The categories of this paper are: q-fin
9
The categories of this paper are: nlin
7
The categories of this paper are: hep-th
36
The categories of this paper are: cmp-lg
28
The categories of this paper are: alg-geom
29
The categories of this paper are: funct-an
26
The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
27
The categories of this paper are: comp-gas
13
The categories of this paper are: quant-ph
8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org
12
The categories of this paper are: nucl-th
19
The categories of this paper are: eess
33
The categories of this paper are: plasm-ph