Friday, February 5, 2016

Quick Update on BB Modes in CMB

This is just a quick update.
I found an arxiv manuscript by a researcher who was one of the many co-authors on that joint BICEP/Planck paper last year. (H.U. Nørgaard - Nielsen)
He has taken the Planck 2015 Polarization maps (U&Q) and he has tried to remove the dust foreground in order to obtain EE and BB power spectra. Note that the Planck Collaboration has yet to publish yet official BB power spectra (except between l =2 and l= 30.)

The plot below from his manuscript is a plot of his determination of the CMB's BB Power spectra (red) and models for the lensing B-modes plus primordial B-modes (blue) as a function of the tensor-to-scalar ratio (r =T/S.)


What we can see is (a) there is large error in the data, which is due to the low sensitivity of Planck to BB modes, and (b) there is likely a spike around l = 225, which corresponds to the location of the first peak in the TT data. As such, it would be interesting to see what H.U. Nørgaard - Nielsen obtains for the correlation spectra for TB. (The TB power spectra is not in the manuscript.)

(c) There's no way (using only these results) to make a meaningful constrain on the tensor-to-scalar ratio, or even the lensing B-modes.

As such, we will have to wait for BICEP3 and CLASS results before we can make any real constraints on the tensor-to-scalar ratio. (Luckily, BICEP3 and CLASS will be able to improve their constraints on r =T/S by using Planck estimates for dust and for lensing B-modes.)

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