The generalized Chaplygin gas ( GCG ) model allows for an unified description of the cosmologically recent accelerated expansion of the Universe and of the evolution of energy density perturbations .
This dark energy - dark matter unification is achieved through a rather exotic background fluid whose equation of state is given by p = - A / \rho ^ { \alpha } , where A is a positive constant .
Observational constraints arising from bounds on the locations of the first few peaks and troughs of the Cosmic Microwave Background Radiation ( CMBR ) power spectrum from recent WMAP and BOOMERanG experiments are consistent with the model for \alpha \mathrel { \hbox to 0.0 pt { \lower 4.0 pt \hbox { $ \sim$ } } \raise 1.0 pt \hbox { $ < $ } % } 0.6 assuming that 0 < \alpha \leq 1 .
Most recent Type-Ia Supernova data indicates however , that the range \alpha > 1 must be considered .