Don't Doubt Accuracy Of Cosmological Constant Yet

Previous empirical tests of the "standard model of cosmology", sometimes called the six parameter lamda CDM model, have found that a simple "cosmological constant" of general relativity is sufficient to fully describe observed dark energy effects in astronomy observations.  A pre-print released a week ago argues that it sees a two standard deviation variation from that prediction in one subset of data.  The abstract of the paper states:

The cosmological fit to 313 SNe Ia (112 PS1 SNe Ia + 201 low-z SNe Ia), using only SNe and assuming a constant dark energy equation of state and flatness, yields w = -1.015^{+0.319}_{-0.201}(Stat)+{0.164}_{-0.122}(Sys). When combined with BAO+CMB(Planck)+H0, the analysis yields Omega_M = 0.277^{+0.010}_{-0.012} and w = -1.186^{+0.076}_{-0.065} including all identified systematics, as spelled out in the companion paper by Scolnic et al. (2013a).

The value of w is inconsistent with the cosmological constant value of -1 at the 2.4 sigma level. This tension has been seen in other high-z SN surveys and endures after removing either the BAO or the H0 constraint. If we include WMAP9 CMB constraints instead of those from Planck, we find w = -1.142^{+0.076}_{-0.087}, which diminishes the discord to <2 data-blogger-escaped-b="" data-blogger-escaped-sigma.="">We cannot conclude whether the tension with flat CDM is a feature of dark energy, new physics, or a combination of chance and systematic errors.

The full Pan-STARRS1 supernova sample will be 3 times as large as this initial sample, which should provide more conclusive results.

But, as Motl explains, there are sound theoretical reasons to doubt that the deviation observed is more than a statistical fluke because if the universe had the properties claimed (a w constant more negative than -1), this would lead to a variety of implications that appear non-physical, particularly in light of the modest statistical significance of the result. For instance, it would imply a speed of sound greater than the speed of light in some instances. Sean Carroll is co-author of a paper that at least admits the possibility as one not to be dismissed out of hand