New Constraints On The Dark Energy Equation of State
  We combine recent measurements of Cosmic Microwave Background Anisotropies,
Supernovae luminosity distances and Baryonic Acoustic Oscillations to derive
constraints on the dark energy equation of state w in the redshift range 0<z<2,
using a principal components approach. We find no significant deviations from
the expectations of a cosmological constant. However, combining the datasets we
find slight indication for w<-1 at low redshift, thus highlighting how these
datasets prefer a non-constant w. Nevertheless the cosmological constant is
still in agreement with these observations, while we find that some classes of
alternative models may be in tension with the inferred w(z) behaviour.
