We apply a parameterization-independent approach to fitting the dark energy equation-of-state ( EOS ) .
Utilizing the latest type Ia supernova data , combined with results from the cosmic microwave background and baryon acoustic oscillations , we find that the dark energy is consistent with a cosmological constant .
We establish independent estimates of the evolution of the dark energy EOS by diagonalizing the covariance matrix .
We find three independent constraints , which taken together imply that the equation of state is more negative than -0.2 at the 68 % confidence level in the redshift range 0 < z < 1.8 , independent of the flat universe assumption .
Our estimates argue against previous claims of dark energy “ metamorphosis , ” where the EOS was found to be strongly varying at low redshifts .
Our results are inconsistent with extreme models of dynamical dark energy , both in the form of “ freezing ” models where the dark energy EOS begins with a value greater than -0.2 at z > 1.2 and rolls to a value of -1 today , and “ thawing ” models where the EOS is near -1 at high redshifts , but rapidly evolves to values greater than -0.85 at z < 0.2 .
Finally , we propose a parameterization-independent figure-of-merit , to help assess the ability of future surveys to constrain dark energy .
While previous figures-of-merit presume specific dark energy parameterizations , we suggest a binning approach to evaluate dark energy constraints with a minimum number of assumptions .