939 research outputs found
Power of Observational Hubble Parameter Data: a Figure of Merit Exploration
We use simulated Hubble parameter data in the redshift range 0 \leq z \leq 2
to explore the role and power of observational H(z) data in constraining
cosmological parameters of the {\Lambda}CDM model. The error model of the
simulated data is empirically constructed from available measurements and
scales linearly as z increases. By comparing the median figures of merit
calculated from simulated datasets with that of current type Ia supernova data,
we find that as many as 64 further independent measurements of H(z) are needed
to match the parameter constraining power of SNIa. If the error of H(z) could
be lowered to 3%, the same number of future measurements would be needed, but
then the redshift coverage would only be required to reach z = 1. We also show
that accurate measurements of the Hubble constant H_0 can be used as priors to
increase the H(z) data's figure of merit.Comment: 8 pages, 1 table, 8 figures. v2: version accepted by Ap
Constraints on the Dark Side of the Universe and Observational Hubble Parameter Data
This paper is a review on the observational Hubble parameter data that have
gained increasing attention in recent years for their illuminating power on the
dark side of the universe --- the dark matter, dark energy, and the dark age.
Currently, there are two major methods of independent observational H(z)
measurement, which we summarize as the "differential age method" and the
"radial BAO size method". Starting with fundamental cosmological notions such
as the spacetime coordinates in an expanding universe, we present the basic
principles behind the two methods. We further review the two methods in greater
detail, including the source of errors. We show how the observational H(z) data
presents itself as a useful tool in the study of cosmological models and
parameter constraint, and we also discuss several issues associated with their
applications. Finally, we point the reader to a future prospect of upcoming
observation programs that will lead to some major improvements in the quality
of observational H(z) data.Comment: 20 pages, 6 figures, and 1 table, uses REVTeX 4.1. Review article,
accepted by Advances in Astronom
Cosmological constraints on holographic dark energy models under the energy conditions
We study the holographic and agegraphic dark energy models without
interaction using the latest observational Hubble parameter data (OHD), the
Union2.1 compilation of type Ia supernovae (SNIa), and the energy conditions.
Scenarios of dark energy are distinguished by the cut-off of cosmic age,
conformal time, and event horizon. The best-fit value of matter density for the
three scenarios almost steadily located at by the joint
constraint. For the agegraphic models, they can be recovered to the standard
cosmological model when the constant which presents the fraction of dark
energy approaches to infinity. Absence of upper limit of by the joint
constraint demonstrates the recovery possibility. Using the fitted result, we
also reconstruct the current equation of state of dark energy at different
scenarios, respectively. Employing the model criteria
, we find that conformal time model is the worst,
but they can not be distinguished clearly. Comparing with the observational
constraints, we find that SEC is fulfilled at redshift with confidence level. We also find that NEC gives a meaningful
constraint for the event horizon cut-off model, especially compared with OHD
only. We note that the energy condition maybe could play an important role in
the interacting models because of different degeneracy between and
constant .Comment: 8 pages, 4 figures, accepted for publication in PR
Numerical Strategies of Computing the Luminosity Distance
We propose two efficient numerical methods of evaluating the luminosity
distance in the spatially flat {\Lambda}CDM universe. The first method is based
on the Carlson symmetric form of elliptic integrals, which is highly accurate
and can replace numerical quadratures. The second method, using a modified
version of Hermite interpolation, is less accurate but involves only basic
numerical operations and can be easily implemented. We compare our methods with
other numerical approximation schemes and explore their respective features and
limitations. Possible extensions of these methods to other cosmological models
are also discussed.Comment: 4 pages, 2 figures. v2: A minor error in the last equation has been
corrected (conclusions are not affected). v3: Accepted by MNRA
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