Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Topological defects: A problem for cyclic universes?   We study the behaviour of cosmic string networks in contracting universes,
and discuss some of their possible consequences. We note that there is a
fundamental time asymmetry between defect network evolution for an expanding
universe and a contracting universe. A string network with negligible loop
production and small-scale structure will asymptotically behave during the
collapse phase as a radiation fluid. In realistic networks these two effects
are important, making this solution only approximate. We derive new scaling
solutions describing this effect, and test them against high-resolution
numerical simulations. A string network in a contracting universe, together
with the gravitational radiation background it has generated, can significantly
affect the dynamics of the universe both locally and globally. The network can
be an important source of radiation, entropy and inhomogeneity. We discuss the
possible implications of these findings for bouncing and cyclic cosmological
models.

24
The categories of this paper are: dg-ga
30
The categories of this paper are: q-alg
14
The categories of this paper are: math-ph
16
The categories of this paper are: stat
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
25
The categories of this paper are: patt-sol
31
The categories of this paper are: ao-sci
29
The categories of this paper are: funct-an
1
The categories of this paper are: cs
18
The categories of this paper are: econ
11
The categories of this paper are: hep-lat
26
The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con
21
The categories of this paper are: adap-org
28
The categories of this paper are: alg-geom