Constraining Van der Waals quintessence with observations

We discuss an alternative approach to quintessence, modifying the usual equation of state of the cosmological fluid in order to see whether going further than the approximation of perfect fluid allows one to better reproduce the available data. We consider a cosmological model comprising only two fluids, namely baryons (modelled as dust) and dark matter with a Van der Waals equation of state. First, the general features of the model are presented and then the evolution of the energy density, the Hubble parameter and the scale factor are determined showing that it is possible to obtain accelerated expansion by suitably choosing the model parameters. We use the data on the dimensionless coordinate distances to type Ia supernovae and distant radio galaxies to see whether Van der Waals quintessence is viable for explaining dark energy and for constraining its parameters. We then compare the model predictions with the estimated age of the universe and the position of the first three peaks of the anisotropy spectrum of the cosmic microwave background radiation. © 2005 IOP Publishing Ltd.