Constraints on dark energy evolution
  We investigate a class of dark energy models in which the equation of state
undergoes a rapid transition and for which the Hubble SN Ia diagram is known to
be poorly discriminant. Interestingly enough, we find that transitions at high
redshift can lead to distortion in the correlation function of dark matter at
lower redshift. We therefore use a combination of the SN Ia Hubble diagram,
Cosmic Microwave Background data and power spectrum from the Sloan Digital Sky
Survey Luminous Red Galaxies (SDSS LRG) to constrain the redshift of a possible
transition. We find that the fundamental cosmological parameters are well
constrained independently of the presence of a transition. Acceptable
transitions from an equation of state close to $w = 0$ to a value close to -1
are strongly rejected at redshifts much higher than those for which Large Scale
Structure and SN Ia data are available: the transition redshift can be rejected
up to a value as high as 10. We conclude that no preference for a transition
appears from present-day data.
