Puxun Wu

The dynamical behavior of

Recently, a new model obtained from generalizing teleparallel gravity, named f(T) theory, is proposed to explain the present cosmic accelerating expansion with no need of dark energy. In this Letter, we analyze the dynamical property of this theory. For a concrete power law model, we obtain that the dynamical system has a stable de Sitter phase along with an unstable radiation dominated phase and an unstable matter dominated one. We show that the Universe can evolve from a radiation dominated era to a matter dominated one, and finally enter an exponential expansion phase.

f(T)

Abstract In this Letter, by reconstructing the Om diagnostic and the deceleration parameter q from the latest Union2 Type Ia Supernova sample with and without the systematic error along with the baryon acoustic oscillation (BAO) and the cosmic microwave background (CMB), we study the cosmic expanding history, using the Chevallier–Polarski–Linder (CPL) parametrization. We obtain that Union2 + BAO favor an expansion with a decreasing of the acceleration at z 0.3 . However, once the CMB data is added in the analysis, the cosmic acceleration is found to be still increasing, indicating a tension between low redshift data and high redshift. In order to reduce this tension significantly, two different methods are considered and thus two different subsamples of Union2 are selected. We then find that two different subsamples + BAO + CMB give completely different results on the cosmic expanding history when the systematic error is ignored, with one suggesting a decreasing cosmic acceleration, the other just the opposite, although both of them alone with BAO support that the cosmic acceleration is slowing down. However, once the systematic error is considered, two different subsamples of Union2 along with BAO and CMB all favor an increasing of the present cosmic acceleration. Therefore a clear-cut answer on whether the cosmic acceleration is slowing down calls for more consistent data and more reliable methods to analyze them.

theory

Abstract The stability of the Einstein static universe against the homogeneous scalar perturbations in f ( T ) gravity is analyzed. Both the spatial closed and open universes are considered. We find that the stable Einstein static solutions exist in both cases. Considering a concrete f ( T ) model and assuming that the cosmic energy has a constant equation of state w , we obtain that, in the closed case, w 1 / 3 is required. Thus, f ( T ) theory gives a larger region of w than that in general relativity ( − 1 w − 1 / 3 ) to have the stable Einstein static solution. For the open universe, f ( T ) theory allows the stable Einstein static solution, although this kind of solution is forbidden in general relativity. Thus, a modification of gravity can play a crucial role in stabilizing the Einstein static solution.

Examining the cosmic acceleration with the latest Union2 supernova data

We investigate the implications for some nonstandard cosmological models using data from the first three years of the Supernova Legacy Survey (SNLS3), assuming a spatially flat universe. A comparison between the constraints from the SNLS3 and those from other SN Ia samples, such as the ESSENCE, Union2, SDSS-II, and Constitution samples, is given and the effects of different light-curve fitters are considered. We find that analyzing SNe Ia with SALT2 or SALT or SiFTO can give consistent results and the tensions between different data sets and different light-curve fitters are obvious for fewer-free-parameters models. At the same time, we also study the constraints from SNLS3 along with data from the cosmic microwave background and the baryonic acoustic oscillations (CMB/BAO), and the latest Hubble parameter versus redshift (H(z)). Using model selection criteria such as χ2/dof, goodness of fit, Akaike information criterion, and Bayesian information criterion, we find that, among all the cosmological models considered here (ΛCDM, constant w, varying w, Dvali-Gabadadze-Porrati (DGP), modified polytropic Cardassian, and the generalized Chaplygin gas), the flat DGP is favored by SNLS3 alone. However, when additional CMB/BAO or H(z) constraints are included, this is no longer the case, and the flat ΛCDM becomes preferred.

The Stability of the Einstein static state in

In this paper, we quantify the ability of a future measurement of the Sandage-Loeb test signal from the Cosmic-Dynamic-Experiment-like spectrograph to constrain some popular modified gravity theories including DGP brane-world scenario,

f(T)

f(R)

gravity

modified gravity and

Testing Nonstandard Cosmological Models with SNLS3 Supernova Data and Other Cosmological Probes

f(T)

Probing modified gravity theories with the Sandage-Loeb test

gravity theory. We find that the Sandage-Loeb test measurements are able to break degeneracies between model parameters markedly and thus greatly improve cosmological constraints for all concerned modified gravity theories when combined with the latest observations of CMB--shift parameter. However, they yield almost the same degeneracy directions between model parameters as that from the distance ratio data derived from the latest observations of the cosmic microwave background and baryonic acoustic oscillations (CMB/BAO). Moreover, for the

A consistent test of the distance–duality relation with galaxy clusters and Type Ia Supernovae

f(R)