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 data sets, we find a slight indication for w<-1 at low redshift, thus highlighting how these data sets prefer a nonconstant 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) behavior. © 2013 American Physical Society.