Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quantum gravity in the very early universe   General relativity describes the gravitational field geometrically and in a
self-interacting way because it couples to all forms of energy, including its
own. Both features make finding a quantum theory difficult, yet it is important
in the high-energy regime of the very early universe. This review article
introduces some of the results for the quantum nature of space-time which
indicate that there is a discrete, atomic picture not just for matter but also
for space and time. At high energy scales, such deviations from the continuum
affect the propagation of matter, the expansion of the universe, and perhaps
even the form of symmetries such as Lorentz or CP transformations. All these
effects may leave traces detectable by sensitive measurements, as pointed out
here by examples.

27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex
8
The categories of this paper are: hep-ex
1
The categories of this paper are: cs
21
The categories of this paper are: adap-org
3
The categories of this paper are: physics
32
The categories of this paper are: atom-ph
0
The categories of this paper are: hep-ph
13
The categories of this paper are: quant-ph
11
The categories of this paper are: hep-lat
25
The categories of this paper are: patt-sol
16
The categories of this paper are: stat
2
The categories of this paper are: math
35
The categories of this paper are: mtrl-th
17
The categories of this paper are: q-fin
33
The categories of this paper are: plasm-ph