This paper looks at the power of future Lensing+CMB+SNIa observations in distinguishing between DGP braneworld cosmologies and a quintessence cosmology with smoothly varying equation of state.
The draft is a summary of brute force Fisher matrix analyses, which show that w(z) reconstructed from (SNIa+CMB) and (Lensing+CMB) can be siginificantly discrepant, if we have an underlying DGP braneworld cosmology.
The problem is that, even if such discrepancy is observed, it could also be interpreted as a sign of more bells and whistles in the dark energy model (less smooth w(z), variable speed of sound, etc.).
Here is my prejudice: The sheer abundance of dark energy models makes ruling them out next to impossible, which is probably similar to the case for inflation.
[astroph/0507184] Is Cosmic Acceleration a Symptom of the Breakdown of General Relativity?
Authors:  Mustapha Ishak, Amol Upadhye, David N. Spergel (Princeton University) 
Abstract:  If general relativity is the correct theory of physics on large scales, then there is a differential equation that relates the Hubble expansion function, inferred from measurements of angular diameter distance and luminosity distance, to the growth rate of large scale structure. Deviations from this consistency relationship could be the signature of the breakdown of general relativity on cosmological scales. As an example, we consider a universe described by a recently proposed 5dimensional modified gravity theory. We demonstrate that this leads to an inconsistency within the dark energy parameter space. We propose a procedure to detect this signature of modified gravity theory using different combinations of cosmological probes. 
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 Joined: December 17 2004
 Affiliation: Perimeter Institute/ University of Waterloo
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