Revisiting Cardassian model and cosmic constraint
- PDF / 597,438 Bytes
- 6 Pages / 595.276 x 790.866 pts Page_size
- 70 Downloads / 145 Views
Regular Article - Theoretical Physics
Revisiting Cardassian model and cosmic constraint Lixin Xua Institute of Theoretical Physics, School of Physics & Optoelectronic Technology, Dalian University of Technology, Dalian 116024, P.R. China College of Advanced Science & Technology, Dalian University of Technology, Dalian 116024, P.R. China
Received: 28 May 2012 / Revised: 29 July 2012 / Published online: 31 August 2012 © Springer-Verlag / Società Italiana di Fisica 2012
Abstract In this paper, we revisit the Cardassian model in which the radiation energy component is included. It is important for the early epoch when the radiation cannot be neglected because the equation of state (EoS) of the effective dark energy becomes time variable. Therefore, it is not equivalent to the quintessence model with a constant EoS anymore. This situation was almost overlooked in the literature. By using the recent released Union2 557 of type Ia supernovae (SN Ia), the baryon acoustic oscillation (BAO) from Sloan Digital Sky Survey and the WiggleZ data points, the full information of cosmic microwave background (CMB) measurement given by the seven-year Wilkinson Microwave Anisotropy Probe observation, we constrain the Cardassian model via the Markov Chain Monte Carlo (MCMC) method. A tight constraint is obtained: n = −0.0479+0.0730+0.142 −0.0732−0.148 in 1, 2σ regions. The deviation of the Cardassian model from quintessence model is shown in CMB anisotropic power spectra at high l’s parts due to the evolution of EoS. But it is about the order of 0.1/% which cannot be discriminated by current data sets. The Cardassian model is consistent with current cosmic observational data sets.
1 Introduction Since the discovery of current accelerated expansion of our Universe [1, 2], a flood of models have been designed to explain this late time accelerated expansion phase. For the reviews, please see [3–9]. In the phenomenological perspective, the accelerated expansion of our Universe can be realized through modifying the form of Friedmann equation via the introduction of an extra exotic energy component, dubbed dark energy, which has negative pressure, or by some possible modifications of gravity theory, say f (R) and a e-mail:
[email protected]
brane models etc. As a result, the conventional Friedmann equation can be modified into the form of H 2 = f (ρ),
(1)
where f (ρ) is a function of energy density ρ which may include dark matter and extra energy components, and H is the Hubble parameter. The Cardassian model firstly proposed by Freese and Lewis [10], where the Friedmann equation was modified into the form of H2 =
8πG ρ + Aρ n 3
(2)
to explain the current accelerated expansion of our Universe. Here ρ can be composed of conventional matter, i.e, cold dark matter, baryons and radiation. For the origin of the ρ n term, one can find several explanations [11–15]. It can mimic the brane model which include a power law term due to the embedding of our universe into a five dimensional bulk. The late time accelerated expansion of our Univers
Data Loading...
