Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the No-Boundary Proposal for Ekpyrotic and Cyclic Cosmologies   The no-boundary proposal provides a compelling theory for the initial
conditions of our universe. We study the implications of such initial
conditions for ekpyrotic and cyclic cosmologies. These cosmologies allow for
the existence of a new type of "ekpyrotic instanton", which describes the
creation of a universe in the ekpyrotic contraction phase. Remarkably, we find
that the ekpyrotic attractor can explain how the universe became classical. In
a cyclic context, in addition to the ekpyrotic instantons there exist de
Sitter-like instantons describing the emergence of the universe in the dark
energy phase. Our results show that typically the ekpyrotic instantons yield a
higher probability. In fact, in a potential energy landscape allowing both
inflationary and cyclic cosmologies, the no-boundary proposal implies that the
probability for ekpyrotic and cyclic initial conditions is vastly higher than
that for inflationary ones.

25
The categories of this paper are: patt-sol
33
The categories of this paper are: plasm-ph
21
The categories of this paper are: adap-org
29
The categories of this paper are: funct-an
10
The categories of this paper are: q-bio
18
The categories of this paper are: econ
12
The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn
36
The categories of this paper are: cmp-lg
13
The categories of this paper are: quant-ph
35
The categories of this paper are: mtrl-th
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics
24
The categories of this paper are: dg-ga
0
The categories of this paper are: hep-ph
8
The categories of this paper are: hep-ex