Revisiting Cardassian Model and Cosmic Constraint

TL;DR

This study revisits the Cardassian cosmological model including radiation, constrains its parameters using recent observational data, and finds it consistent with current measurements, with minimal deviation from quintessence models.

Contribution

It provides the first comprehensive constraint on the Cardassian model with radiation included using multiple cosmological data sets.

Findings

The parameter n is tightly constrained around -0.048.

Deviations from quintessence are too small to be detected with current data.

The model remains consistent with observational data.

Abstract

In this paper, we revisit the Cardassian model in which the radiation energy component is included. It is important for 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: $n= -0.0479_{- 0.0732- 0.148}^{+ 0.0730+ 0.142}$ in $1,2\sigma$ regions. The deviation of 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.