2,425 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

### Distinguishing between inhomogeneous model and $\Lambda\textrm{CDM}$ model with the cosmic age method

Cosmological observables could be used to construct cosmological models,
however, a fixed number of observables limited on the light cone is not enough
to uniquely determine a certain model. A reconstructed spherically symmetric,
inhomogeneous model that share the same angular-diameter-distance-redshift
relationship $d_A(z)$ and Hubble parameter $H(z)$ besides $\Lambda\textrm{CDM}$
model (which we call LTB-$\Lambda\textrm{CDM}$ model in this paper), may
provide another solution. Cosmic age, which is off the light cone, could be
employed to distinguish these two models. We derive the formulae for age
calculation with origin conditions. From the data given by 9-year WMAP
measurement, we compute the likelihood of the parameters in these two models
respectively by using the Distance Prior method and do likelihood analysis by
generating Monte Carlo Markov Chain for the purpose of breaking the degeneracy
of $\Omega_m$ and $H_0$ (the parameters that we use for calculation). The
results yield to be: $t_{\Lambda\textrm{CDM}} =13.76 \pm 0.09 ~\rm Gyr$,
$t_{\rm {LTB}-\Lambda\textrm{CDM}} =11.38 \pm 0.15 ~\rm Gyr$, both in $1\sigma$
agreement with the constraint of cosmic age given by metal-deficient stars. The
cosmic age method that is set in this paper enables us to distinguish between
the inhomogeneous model and $\Lambda\textrm{CDM}$ model.Comment: 10 pages, 2 figures, accepted by Physics Letters B. arXiv admin note:
text overlap with arXiv:0911.3852 by other author

### Statefinder diagnostic for the modified polytropic Cardassian universe

We apply the Statefinder diagnostic to the Modified Polytropic Cardassian
Universe in this work. We find that the Statefinder diagnostic is quite
effective to distinguish Cardassian models from a series of other cosmological
models. The $s-r$ plane is used to classify the Modified Polytropic Cardassian
models into six cases. The evolutionary trajectories in the $s-r$ plane for the
cases with different $n$ and $\beta$ reveal different evolutionary properties
of the universe. In addition, we combine the observational $H(z)$ data, the
Cosmic Microwave Background (CMB) data and the Baryonic Acoustic Oscillation
(BAO) data to make a joint analysis. We find that \textbf{Case 2} can be
excluded at the 68.3% confidence level and any case is consistent with the
observations at the 95.4% confidence level.Comment: Comments: Final version for publication in Physical Review D [minor
revision to match the appear version] Journal-ref: Physical Review D 75,
083515 (2007

### 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

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