Consistency tests for the cosmological constant

We propose consistency tests for the cosmological constant which provide a direct observational signal if Λ is wrong, regardless of the densities of matter and curvature. As an example of its utility, our flat case test can warn of a small transition of the equation of state w(z) from w(z)=-1 of 20% from SNAP (Supernova Acceleration Probe) quality data at 4-σ, even when direct reconstruction techniques see virtually no evidence for deviation from Λ. It is shown to successfully rule out a wide range of non-Λ dark energy models with no reliance on knowledge of Ωm using SNAP quality data and a large range for using 105 supernovae as forecasted for the Large Synoptic Survey Telescope. © 2008 The American Physical Society.