Narrowing constraints with type Ia supernovae: converging on a cosmological constant
Abstract
We apply a parameterizationindependent approach to fitting the dark energy equationofstate (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 parameterizationindependent figure of merit (FOM), to help assess the ability of future surveys to constrain dark energy. While the more common FOM presumes a specific dark energy parameterization with two parameters, we suggest a binning approach to evaluate dark energy constraints with a minimum number of assumptions.
 Publication:

Journal of Cosmology and Astroparticle Physics
 Pub Date:
 September 2007
 DOI:
 10.1088/14757516/2007/09/004
 arXiv:
 arXiv:0706.3730
 Bibcode:
 2007JCAP...09..004S
 Keywords:

 Astrophysics;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Theory
 EPrint:
 16 pages, 6 figures, submitted to JCAP