Which cosmological model - with dark energy or modified FRW dynamics?

Recent measurements of distant type Ia supernovae (SNIa), as well as other observations, indicate that our universe is in an accelerating phase of expansion. In principle, there are two alternative explanations for such an acceleration (there is also a possibility that the acceleration can be driven by inhomogenities in cosmological models). The first approach postulates an unknown form of energy violating the strong energy condition, while the second postulates some modification of FRW dynamics. Both approaches agree well with present-day observations which results in the difficulty of choosing the model. We use the Akaike (AIC) and Bayesian (BIC) information criteria of model selection to overcome this degeneracy and to determine a model with a set of parameters which gives the most preferred fit to the SNIa data. We consider five representative evolutionary scenarios in each of the groups. Among the dark energy proposals are the Lambda CDM model, the CDM model with phantom field, CDM model with topological defect, a model with the Chaplygin gas, and a model with a linear dynamical equation of state parameter. As alternative prototype scenarios we consider: the brane world Dvali-Gabadadze-Porrati scenario, brane models in Randall-Sundrum scenario, Cardassian models with dust matter and radiation, a bouncing model with the cosmological constant and metric-affine gravity (MAG) inspired cosmological models. Applying the model selection criteria, we show that both AIC and BIC indicate that additional contributions arising from non-standard FRW dynamics are not necessary to explain SNIa. Adopting the model selection information criteria, we show that the AIC indicates the flat phantom model while BIC indicates both flat phantom and flat ACDM models. (c) 2005 Elsevier B.V. All rights reserved.