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.

• Received 19 March 2013

DOI:https://doi.org/10.1103/PhysRevD.88.043515