I'm very sorry. As I wrote last week, we just hosted a conference here in Helsinki. I wanted to cover it as the conference happened and I just didn't have the combination of time and mental energy to do so. I won't be covering it in any detail retrospectively either because I need to get on with research. Nevertheless, this blog is slightly more than a hobby for me, it is also slightly ideological, so I will try to work out how to do it all better next time and try again then (this will be the annual theoretical cosmology conference "COSMO" in early September).
Here's a summary of some of the more interesting aspects that I'll quickly write up, starting with some closure concerning the topic I was halfway through in my last post...
David Lyth, the curvaton and the power asymmetry
|David Lyth receiving the Hoyle Medal. David's the one in the photo who doesn't already have two medals. From this photo it seems that the guy on the left is graciously donating one of his many medals to David. I got this image from Lancaster University.|
Where I left my last post I was describing David Lyth's talk about explaining the possible asymmetry in the amplitude of fluctuations on the sky (as seen through the temperature of the CMB). It's a small effect, the sky is almost symmetric; but it could be a real effect, the sky might be slightly asymmetric.
The possible asymmetry was seen before Planck and one candidate explanation involves quite large super-horizon fluctuations in some of the properties of the universe. "Super-horizon" here means fluctuations whose characteristic scale is bigger than the currently observable universe, i.e they are outside of our observable horizon. Such a fluctuation would be seen by us, within the observable universe as a smooth gradient in the fluctuating observable. Put simply, the idea is to have a smooth gradient in the amplitude of the measured temperature anisotropies. This would quite naturally result in a bigger amplitude in one direction, than another.
It seems that simple inflation can't achieve this without making the fluctuations in the universe significantly non-Gaussian. However, the curvaton can do it (according to David and a paper he is working on). Quite nicely, there is a relationship that David discussed that occurs between the amplitude of the asymmetry and the amount of deviation from a Gaussian distribution one would expect in both an inflation model and a curvaton model. For inflation, the deviation is too big, but for the curvaton it is small but not insignificant. This is nice because, according to David, if this asymmetry is real and the curvaton is responsible for it, then the fluctuations will be measurably non-Gaussian.
This means we can either rule this mechanism out as the cause of the apparent asymmetry, or even better, get evidence supporting it and thus supporting both the curvaton model and the real-ness of the asymmetry. So, watch this space...