Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the evolution of universes in quadratic theories of gravity   We use a dynamical systems approach to investigate Bianchi type I and II
universes in quadratic theories of gravity. Due to the complicated nature of
the equations of motion we focus on the stability of exact solutions and find
that there exists an isotropic FRW universe acting as a past attractor. This
may indicate that there is an isotropisation mechanism at early times for these
kind of theories. We also discuss the Kasner universes, elucidate the
associated centre manifold structure, and show that there exists a set of
non-zero measure which has the Kasner solutions as a past attractor. Regarding
the late-time behaviour, the stability shows a dependence of the parameters of
the theory. We give the conditions under which the de Sitter solution is stable
and also show that for certain values of the parameters there is a possible
late-time behaviour with phantom-like behaviour. New types of anisotropic
inflationary behaviour are found which do not have counterparts in general
relativity.

11
The categories of this paper are: hep-lat
12
The categories of this paper are: nucl-th
27
The categories of this paper are: comp-gas
32
The categories of this paper are: atom-ph
9
The categories of this paper are: nlin
13
The categories of this paper are: quant-ph
15
The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
22
The categories of this paper are: chao-dyn
19
The categories of this paper are: eess
37
The categories of this paper are: supr-con
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
4
The categories of this paper are: cond-mat
34
The categories of this paper are: chem-ph
31
The categories of this paper are: ao-sci