Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Evolution of the Universe with Flat Extra Dimensions   Evolution of a universe with homogeneous extra dimensions is studied with the
benefit of a well-chosen parameter space that provides a systematic, useful,
and convenient way for analysis. In this model we find a natural evolution
pattern that entails not only stable extra dimensions in the
radiation-dominated era, thereby preserving essential predictions in the
standard cosmology, but also the present accelerating expansion while
satisfying the limit on the variation of Newtonian gravitational constant. In
this natural evolution pattern the extra dimensions tend to be stabilized
automatically without resorting to artificial mechanisms in both the
radiation-dominated and the matter-dominated era, as a wonderful feature for
building models with extra dimensions. In addition, the naturalness of this
evolution pattern that guarantees the late-time accelerating expansion of a
matter-dominated universe presents a solution to the coincidence problem: why
the accelerating phase starts at the present epoch. The feasibility of this
evolution pattern for describing our universe is discussed.

25
The categories of this paper are: patt-sol
20
The categories of this paper are: acc-phys
14
The categories of this paper are: math-ph
5
The categories of this paper are: gr-qc
9
The categories of this paper are: nlin
13
The categories of this paper are: quant-ph
4
The categories of this paper are: cond-mat
32
The categories of this paper are: atom-ph
11
The categories of this paper are: hep-lat
31
The categories of this paper are: ao-sci
33
The categories of this paper are: plasm-ph
2
The categories of this paper are: math
18
The categories of this paper are: econ
16
The categories of this paper are: stat
28
The categories of this paper are: alg-geom
8
The categories of this paper are: hep-ex