Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gravitational particle production in bouncing cosmologies   It is argued that the Universe reheating in bouncing cosmologies could be
explained via gravitational particle production, as due to a sudden phase
transition in the contracting regime. To this end, it is shown that
gravitational production of massive particles conformally coupled with gravity
in a matter-ekpyrotic bouncing Universe, where the sudden phase transition
occurs in the contracting regime, yields a reheating temperature which is in
good agreement with cosmological observations.

2
The categories of this paper are: math
18
The categories of this paper are: econ
7
The categories of this paper are: hep-th
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics
32
The categories of this paper are: atom-ph
11
The categories of this paper are: hep-lat
34
The categories of this paper are: chem-ph
20
The categories of this paper are: acc-phys
16
The categories of this paper are: stat
28
The categories of this paper are: alg-geom
21
The categories of this paper are: adap-org
19
The categories of this paper are: eess
26
The categories of this paper are: bayes-an
24
The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat