  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 $\alpha \lsim 0.6$ assuming that $0 < \alpha \le 1$. Most recent
Type-Ia Supernova data indicates however, that the range $\alpha > 1 $ must be
considered.

Astrophysics