KiDS-450: Testing extensions to the standard cosmological model [CEA]

Since I’ve just attended a seminar in Cardiff by Catherine Heymans on exactly this work, I couldn’t resist reblogging the arXiver entry for this paper which appeared on arXiv a couple of days ago.

The key finding is that the weak lensing analysis of KIDS data (which is mainly to the distribution of matter at low redshift) does seem to be discrepant with the predictions of the standard cosmological model established by Planck (which is sensitive mainly to high-redshift fluctuations).

Could this discrepancy be interpreted as evidence of something going on beyond the standard cosmology? Read the paper to explore some possibilities!


We test extensions to the standard cosmological model with weak gravitational lensing tomography using 450 deg$^2$ of imaging data from the Kilo Degree Survey (KiDS). In these extended cosmologies, which include massive neutrinos, nonzero curvature, evolving dark energy, modified gravity, and running of the scalar spectral index, we also examine the discordance between KiDS and cosmic microwave background measurements from Planck. The discordance between the two datasets is largely unaffected by a more conservative treatment of the lensing systematics and the removal of angular scales most sensitive to nonlinear physics. The only extended cosmology that simultaneously alleviates the discordance with Planck and is at least moderately favored by the data includes evolving dark energy with a time-dependent equation of state (in the form of the $w_0-w_a$ parameterization). In this model, the respective $S_8 = sigma_8 sqrt{Omega_{rm m}/0.3}$ constraints agree at the $1sigma$ level, and there is `substantial concordance’ between…

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10 Responses to “KiDS-450: Testing extensions to the standard cosmological model [CEA]”

  1. Peter what is your take on Oxford’s group latest analysis of the SN data?

    • Is there an accepted version of the paper publicly available?

      • I’ve just glanced over it, but looking at their figure 2, I don’t see much difference. Yes, one can rule out all non-accelerating universes at three sigma or so, but these are all of really low density. Of course, there is always the question what a particular test shows and what it show combined with other tests (“cosmic data fusion” as Sarah likes to say). On the face of it, their figure 2 looks like very good evidence for the concordance model. More interestingly, a negative lambda is still allowed at 3 sigma. Is this region just not in the figure (if so, why), or did they have a prior that lambda cannot be negative?

        Even if one doubts the supernova data, even if one ignores them completely, then the concordance model is still essentially the same. These days, the CMB alone can give us the concordance model with much smaller uncertainties than just the supernova data. In fact, what is really interesting is that, although the contours are broad, the best-fit values using just the supernova data are almost dead on the concordance model. (I note that the authors of the Nature paper, like most authors, a) assume a completely homogeneous universe and b) don’t even mention this explicitly. As I show in the link above, one can turn this around and, assuming the concordance model, use the supernova data to tell us something about the clustering properties of dark matter.)

      • I have also shown that not only do the supernova data indicate a universe very homogeneous, even down to the scale of a supernova beam (which is probably the thinnest object every studied by science), but even each beam is probably a fair sample of the universe, not just when one averages over all beams (or all the sky, which is not necessarily the same).

      • Thanks, Peter. I am also curious to hear your take on Stacy’s paper on radial acceleration relation in rotationally supported galaxy and related responses and counter-responses to that paper.

      • telescoper Says:

        I haven’t seen that one.

  2., in particular Fig 3 and equation 4. Do you have a trivial explanation of why the total acceleration is a simple parametric equation of only the baryonic acceleration, especially if most spiral galaxies are dark matter dominated? (arxiv trackback links to some press releases about this paper)
    This paper already has 2 citations claiming that it can be explained using feedback processes, including 1 rebuttal. I would be very curious on your take on this.

  3. […] The central values of DES and Planck values are different, but the discrepancy is only marginal. Compare this with a an equivalent diagram from a paper I discussed last year. […]

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