Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Dust of Dark Energy   We introduce a novel class of field theories where energy always flows along
timelike geodesics, mimicking in that respect dust, yet which possess non-zero
pressure. This theory comprises two scalar fields, one of which is a Lagrange
multiplier enforcing a constraint between the other's field value and
derivative. We show that this system possesses no wave-like modes but retains a
single dynamical degree of freedom. Thus, the sound speed is always identically
zero on all backgrounds. In particular, cosmological perturbations reproduce
the standard behaviour for hydrodynamics with vanishing sound speed. Using all
these properties we propose a model unifying Dark Matter and Dark Energy in a
single degree of freedom. In a certain limit this model exactly reproduces the
evolution history of Lambda-CDM, while deviations away from the standard
expansion history produce a potentially measurable difference in the evolution
of structure.

22
The categories of this paper are: chao-dyn
32
The categories of this paper are: atom-ph
30
The categories of this paper are: q-alg
13
The categories of this paper are: quant-ph
26
The categories of this paper are: bayes-an
27
The categories of this paper are: comp-gas
28
The categories of this paper are: alg-geom
4
The categories of this paper are: cond-mat
15
The categories of this paper are: nucl-ex
1
The categories of this paper are: cs
0
The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con
18
The categories of this paper are: econ
29
The categories of this paper are: funct-an
16
The categories of this paper are: stat
14
The categories of this paper are: math-ph