Constraining Van der Waals quintessence with observations

Abstract

We discuss an alternative approach to quintessence, modifying the usual equation of stateof the cosmological fluid in order to see whether going further than the approximation ofperfect fluid allows one to better reproduce the available data. We consider a cosmologicalmodel comprising only two fluids, namely baryons (modelled as dust) and darkmatter with a Van der Waals equation of state. First, the general features of themodel are presented and then the evolution of the energy density, the Hubbleparameter and the scale factor are determined showing that it is possible to obtainaccelerated expansion by suitably choosing the model parameters. We use thedata on the dimensionless coordinate distances to type Ia supernovae and distantradio galaxies to see whether Van der Waals quintessence is viable for explainingdark energy and for constraining its parameters. We then compare the modelpredictions with the estimated age of the universe and the position of the first threepeaks of the anisotropy spectrum of the cosmic microwave background radiation.