15 research outputs found
Isocurvature modes and Baryon Acoustic Oscillations
The measurement of Baryonic Acoustic Oscillations from galaxy surveys is well
known to be a robust and powerful tool to constrain dark energy. This method
relies on the knowledge of the size of the acoustic horizon at radiation drag
derived from Cosmic Microwave Background Anisotropy measurements. In this paper
we quantify the effect of non-standard initial conditions in the form of an
isocurvature component on the determination of dark energy parameters from
future BAO surveys. In particular, if there is an isocurvature component (at a
level still allowed by present data) but it is ignored in the CMB analysis, the
sound horizon and cosmological parameters determination is biased, and, as a
consequence, future surveys may incorrectly suggest deviations from a
cosmological constant. In order to recover an unbiased determination of the
sound horizon and dark energy parameters, a component of isocurvature
perturbations must be included in the model when analyzing CMB data.
Fortunately, doing so does not increase parameter errors significantly.Comment: 23 pages, 3 figure
The Distinguishability of Interacting Dark Energy from Modified Gravity
We study the observational viability of coupled quintessence models with
their expansion and growth histories matched to modified gravity cosmologies.
We find that for a Dvali-Gabadadze-Porrati model which has been fitted to
observations, the matched interacting dark energy models are observationally
disfavoured. We also study the distinguishability of interacting dark energy
models matched to scalar-tensor theory cosmologies and show that it is not
always possible to find a physical interacting dark energy model which shares
their expansion and growth histories.Comment: 8 pages, 5 figure
A Model for Dark Energy decay
We discuss a model of non perturbative decay of dark energy into hot and cold
dark matter. This model provides a mechanism from the field theory to realize
the energy transfer from dark energy into dark matter, which is the requirement
to alleviate the coincidence problem. The advantage of the model is the fact
that we accommodate a mean life compatible with the age of the universe. We
also argue that supersymmetry is a natural set up, though not essential.Comment: 5 pages to be published in Physics Letters
Hidden vector dark matter
We show that dark matter could be made of massive gauge bosons whose
stability doesn't require to impose by hand any discrete or global symmetry.
Stability of gauge bosons can be guaranteed by the custodial symmetry
associated to the gauge symmetry and particle content of the model. The
particle content we consider to this end is based on a hidden sector made of a
vector multiplet associated to a non-abelian gauge group and of a scalar
multiplet charged under this gauge group. The hidden sector interacts with the
Standard Model particles through the Higgs portal quartic scalar interaction in
such a way that the gauge bosons behave as thermal WIMPS. This can lead easily
to the observed dark matter relic density in agreement with the other various
constraints, and can be tested experimentally in a large fraction of the
parameter space. In this model the dark matter direct detection rate and the
annihilation cross section can decouple if the Higgs portal interaction is
weak.Comment: 13 pages, 7 figures, JHEP published version (2009) + update of
section 7 (reference to arXiv:0912.4496
Coupled dark matter-dark energy in light of near Universe observations
Cosmological analysis based on currently available observations are unable to
rule out a sizeable coupling among the dark energy and dark matter fluids. We
explore a variety of coupled dark matter-dark energy models, which satisfy
cosmic microwave background constraints, in light of low redshift and near
universe observations. We illustrate the phenomenology of different classes of
dark coupling models, paying particular attention in distinguishing between
effects that appear only on the expansion history and those that appear in the
growth of structure. We find that while a broad class of dark coupling models
are effectively models where general relativity (GR) is modified --and thus can
be probed by a combination of tests for the expansion history and the growth of
structure--, there is a class of dark coupling models where gravity is still
GR, but the growth of perturbations is, in principle modified. While this
effect is small in the specific models we have considered, one should bear in
mind that an inconsistency between reconstructed expansion history and growth
may not uniquely indicate deviations from GR. Our low redshift constraints
arise from cosmic velocities, redshift space distortions and dark matter
abundance in galaxy voids. We find that current data constrain the
dimensionless coupling to be |xi|<0.2, but prospects from forthcoming data are
for a significant improvement. Future, precise measurements of the Hubble
constant, combined with high-precision constraints on the growth of structure,
could provide the key to rule out dark coupling models which survive other
tests. We shall exploit as well weak equivalence principle violation arguments,
which have the potential to highly disfavour a broad family of coupled models.Comment: 34 pages, 6 figures; changes to match published versio
Running coupling: Does the coupling between dark energy and dark matter change sign during the cosmological evolution?
In this paper we put forward a running coupling scenario for describing the
interaction between dark energy and dark matter. The dark sector interaction in
our scenario is free of the assumption that the interaction term is
proportional to the Hubble expansion rate and the energy densities of dark
sectors. We only use a time-variable coupling (with the scale factor
of the universe) to characterize the interaction . We propose a
parametrization form for the running coupling in which the
early-time coupling is given by a constant , while today the coupling is
given by another constant, . For investigating the feature of the running
coupling, we employ three dark energy models, namely, the cosmological constant
model (), the constant model (), and the time-dependent
model (). We constrain the models with the current
observational data, including the type Ia supernova, the baryon acoustic
oscillation, the cosmic microwave background, the Hubble expansion rate, and
the X-ray gas mass fraction data. The fitting results indicate that a
time-varying vacuum scenario is favored, in which the coupling crosses
the noninteracting line () during the cosmological evolution and the sign
changes from negative to positive. The crossing of the noninteracting line
happens at around , and the crossing behavior is favored at about
1 confidence level. Our work implies that we should pay more attention
to the time-varying vacuum model and seriously consider the phenomenological
construction of a sign-changeable or oscillatory interaction between dark
sectors.Comment: 8 pages, 5 figures; refs added; to appear in EPJ
Entropy-corrected new agegraphic dark energy in Horava-Lifshitz cosmology
We study the entropy-corrected version of the new agegraphic dark energy
(NADE) model and dark matter in a spatially non-flat Universe and in the
framework of Ho\v{r}ava-Lifshitz cosmology. For the two cases containing
noninteracting and interacting entropy-corrected NADE (ECNADE) models, we
derive the exact differential equation that determines the evolution of the
ECNADE density parameter. Also the deceleration parameter is obtained.
Furthermore, using a parametrization of the equation of state parameter of the
ECNADE model as , we obtain both
and . We find that in the presence of interaction, the
equation of state parameter of this model can cross the phantom
divide line which is compatible with the observation.Comment: 20 pages, 2 figures, to appear in 'Astrophysics and Space Science