What can be learned about dark energy evolution?

¹ Institut d'Astrophysique Spatiale (IAS), Univ. Paris-Sud, CNRS, Bâtiment 121, 91405 Orsay, France e-mail: marian.douspis@ias.u-psud.fr
² Laboratoire d'Annecy-le-Vieux de Physique des Particules, UMR 5814 CNRS, 9 chemin de Bellevue, BP 110, 74941 Annecy-le-Vieux Cedex, France e-mail: zolnierowski@lapp.in2p3.fr
³ LATT, Université de Toulouse, CNRS, 14 avenue É. Belin, 31400 Toulouse, France e-mail: alain.blanchard@ast.obs-mip.fr
⁴ CNRS, UMR 7095, Institut d'Astrophysique de Paris, 75014 Paris, France; Université Pierre et Marie Curie-Paris 6, UMR 7095, 75014 Paris, France e-mail: riazuelo@iap.fr

Received: 22 February 2006
Accepted: 22 April 2008

Abstract

We examine constraints obtained from SNIa surveys on a two parameter model of dark energy in which the equation of state undergoes a transition over a period significantly shorter than the Hubble time. We find that a transition between and (the first value being somewhat arbitrary) is allowed at redshifts as low as 0.1, despite the fact that data extend beyond . Surveys with the precision anticipated for space experiments should allow only slight improvement on this constraint, as a transition occurring at a redshift as low as ~0.17 could still remain undistinguishable from a standard cosmological constant. The addition of a prior on the matter density only modestly improves the constraints. Even deep space experiments would still fail to identify a rapid transition at a redshift above 0.5. These results illustrate that a Hubble diagram of distant SNIa alone will not reveal the actual nature of dark energy at a redshift above 0.2 and that only the local dynamics of the quintessence field can be inferred from a SNIa Hubble diagram. Combinations, however, seem to be very efficient: we found that the combination of present day CMB data and SNIa already excludes a transition at redshifts below 0.8.