Update Sep 22nd: a Planck paper on polarization is out, suggesting dust could explain the BICEP2 signal – or just 1/2 of it – but lacking the resolution to settle anything. A joint Planck-BICEP2 paper should be out in November but it seems predetermined that they only want to impose an upper bound on \(r\) so it won't be too strong or interesting, either.It's generally expected that the Planck collaboration should present their new results on the CMB polarization data within days, weeks, or a month. Will they be capable of confirming the BICEP2 discovery – or refute it by convincing data?
Ten days ago, Planck published a paper on dust modelling:
Perhaps more interestingly, Wesley Colley and Richard Gott released their preprint
Genus Topology and Cross-Correlation of BICEP2 and Planck 353 GHz B-Modes: Further Evidence Favoring Gravity Wave Detectionthat seems to claim that the data are powerful enough to confirm some influence of the dust yet defend the notion that the primordial gravitational waves have to represent a big part of the BICEP2 observation, too.
What did they do? Well, they took some new publicly available maps by Planck – those at the frequency 353 GHz (wavelength 849 microns). Recall that the claimed BICEP2 discovery appeared at the frequency 150 GHz (wavelength 2 millimeters).
They assume, hopefully for good reasons, that the dust's contribution to the data should be pretty much the same for these two frequencies, up to an overall normalization. Planck sees a lot of radiation at 353 GHz – if all of it were due to dust, the amount of dust would be enough to account for the whole BICEP2 signal.
However, if this were the case, the signals in the BICEP2 patch of the sky at these two frequencies would have to be almost perfectly correlated with each other. Instead, Colley and Gott see the correlation coefficient to be\[
15\% \pm 4\%
\] (does someone understand why the \(\rm\LaTeX\) percent sign has a tilde connecting the upper circle with the slash?) which is "significantly" (four-sigma) different from zero but it is still decidedly smaller than 100 percent. The fact that this correlation is much smaller than 100% implies that most of the BICEP2 signal is uncorrelated to what is classified as dust by the Planck maps or, almost equivalently, that most of the observations at 353 GHz in the BICEP2 region is due to noise, not dust.
When they quantify all this logic, they conclude that about one-half of the BICEP2 signal is due to dust and the remaining one-half has to be due to the primordial gravitational waves; that's why their preferred \(r\), the tensor-to-scalar ratio, drops from BICEP2's most ambitious \(r=0.2\) to \(r=0.11\pm 0.04\), a value very nicely compatible with chaotic inflation. The values "one-half" aren't known quite accurately but with the error margins they seem to work with, they still seem to see that the value \(r=0\) – i.e. non-discovery of the primordial gravitational waves – may be excluded at the 2.5-sigma level.
"Engineers with a diploma" vs "The Big Bang Theory"