341,351 research outputs found
Comment on "Constraining the smoothness parameter and dark energy using observational H(z) data"
In this Comment we discuss a recent analysis by Yu et al. [RAA 11, 125
(2011)] about constraints on the smoothness parameter and dark energy
models using observational data. It is argued here that their procedure
is conceptually inconsistent with the basic assumptions underlying the adopted
Dyer-Roeder approach. In order to properly quantify the influence of the
data on the smoothness parameter, a -test involving a sample
of SNe Ia and data in the context of a flat CDM model is
reanalyzed. This result is confronted with an earlier approach discussed by
Santos et al. (2008) without data. In the () plane, it
is found that such parameters are now restricted on the intervals and within 95.4% confidence
level (2), and, therefore, fully compatible with the homogeneous case.
The basic conclusion is that a joint analysis involving data can
indirectly improve our knowledge about the influence of the inhomogeneities.
However, this happens only because the data provide tighter constraints
on the matter density parameter .Comment: 3 pages, 1 figure, submitted to Research in Astronomy and
Astrophysic
Constraining dark energy with Hubble parameter measurements: an analysis including future redshift-drift observations
Dark energy affects the Hubble expansion rate (namely, the expansion history)
by an integral over . However, the usual observables are the
luminosity distances or the angular diameter distances, which measure the
distance-redshift relation. Actually, dark energy affects the distances (and
the growth factor) by a further integration over functions of . Thus, the
direct measurements of the Hubble parameter at different redshifts are
of great importance for constraining the properties of dark energy. In this
paper, we show how the typical dark energy models, for example, the
CDM, CDM, CPL, and holographic dark energy (HDE) models, can be
constrained by the current direct measurements of (31 data in total,
covering the redshift range of ). In fact, the future
redshift-drift observations (also referred to as the Sandage-Loeb test) can
also directly measure at higher redshifts, covering the range of . We thus discuss what role the redshift-drift observations can play in
constraining dark energy with the Hubble parameter measurements. We show that
the constraints on dark energy can be improved greatly with the data
from only a 10-year observation of redshift drift.Comment: 20 pages, 5 figures; final version published in EPJ
Interacting Energy Components and Observational Data
In this note, we extend our previous work [Phys. Lett. B 644, 7 (2007),
astro-ph/0609597], and compare eleven interacting dark energy models with
different couplings to the observational data. However, none of these
models is better than the simplest CDM model. This implies that either
more exotic couplings are needed in the cosmological models with interaction
between dark energy and dust matter, or {\em there is no interaction at all}.
We consider that this result is disadvantageous to the interacting dark energy
models studied extensively in the literature.Comment: 15 pages, 5 figures, 3 tables, Latex2e; v2: references added; v3:
discussions added, Phys. Lett. B in press; v4: published versio
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