Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Purely kinetic k-essence as unified dark matter   We examine k-essence models in which the Lagrangian p is a function only of
the derivatives of a scalar field phi and does not depend explicity on phi. The
evolution of phi for an arbitrary functional form for p can be given in terms
of an exact analytic solution. For quite general conditions on the functional
form of p, such models can evolve to a state characterized by a density scaling
with the scale factor as rho = rho_0 + rho_1(a/a_0)^{-3}, but with a sound
speed c_s^2 << 1 at all times. Such models can serve as a unified model for
dark matter and dark energy, while avoiding the problems of the generalized
Chaplygin gas models, which are due to a non-negligible sound speed in these
models. A dark energy component with c_s << 1 serves to suppress cosmic
microwave background fluctuations on large angular scales.

11
The categories of this paper are: hep-lat
12
The categories of this paper are: nucl-th
26
The categories of this paper are: bayes-an
1
The categories of this paper are: cs
13
The categories of this paper are: quant-ph
16
The categories of this paper are: stat
25
The categories of this paper are: patt-sol
2
The categories of this paper are: math
35
The categories of this paper are: mtrl-th
31
The categories of this paper are: ao-sci
21
The categories of this paper are: adap-org
18
The categories of this paper are: econ
4
The categories of this paper are: cond-mat
34
The categories of this paper are: chem-ph
32
The categories of this paper are: atom-ph
15
The categories of this paper are: nucl-ex