Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Rainbow universe   The formalism of rainbow gravity is studied in a cosmological setting. We
consider the very early universe which is radiation dominated. A novel
treatment in our paper is to look for an ``averaged'' cosmological metric
probed by radiation particles themselves. Taking their cosmological evolution
into account, we derive the modified Friedmann-Robertson-Walker(FRW) equations
which is a generalization of the solution presented by Magueijo and Smolin.
Based on this phenomenological cosmological model we argue that the spacetime
curvature has an upper bound such that the cosmological singularity is absent.
These modified $FRW$ equations can be treated as effective equations in the
semi-classical framework of quantum gravity and its analogy with the one
recently proposed in loop quantum cosmology is also discussed.

4
The categories of this paper are: cond-mat
1
The categories of this paper are: cs
20
The categories of this paper are: acc-phys
34
The categories of this paper are: chem-ph
26
The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con
23
The categories of this paper are: solv-int
8
The categories of this paper are: hep-ex
33
The categories of this paper are: plasm-ph
11
The categories of this paper are: hep-lat
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
9
The categories of this paper are: nlin
22
The categories of this paper are: chao-dyn
28
The categories of this paper are: alg-geom
31
The categories of this paper are: ao-sci