Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Primordial Gravitational Waves Induced by Magnetic Fields in an
  Ekpyrotic Scenario   Both inflationary and ekpyrotic scenarios can account for the origin of the
large scale structure of the universe. It is often said that detecting
primordial gravitational waves is the key to distinguish both scenarios. We
show that this is not true if the gauge kinetic function is present in the
ekpyrotic scenario. In fact, primordial gravitational waves sourced by the
gauge field can be produced in an ekpyrotic universe. We also study scalar
fluctuations sourced by the gauge field and show that it is negligible compared
to primordial gravitational waves. This comes from the fact that the fast roll
condition holds in ekpyrotic models.

36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg
3
The categories of this paper are: physics
35
The categories of this paper are: mtrl-th
14
The categories of this paper are: math-ph
27
The categories of this paper are: comp-gas
19
The categories of this paper are: eess
8
The categories of this paper are: hep-ex
1
The categories of this paper are: cs
37
The categories of this paper are: supr-con
9
The categories of this paper are: nlin
29
The categories of this paper are: funct-an
24
The categories of this paper are: dg-ga
15
The categories of this paper are: nucl-ex
16
The categories of this paper are: stat
4
The categories of this paper are: cond-mat