The Planck experiment looks to be "in tension" (e.g. it conflicts) with BICEP2's results: Planck has previously reported an upper bound $r<0.11$ for the parameter that BICEP2 reports at 0.20 (see for example, http://arxiv.org/abs/1303.5082). Planck is expected to publish new results this
21 Sep 2014 update: Planck has now published their galactic dust measurement results.
The situation to date:
- BICEP2 assessed (via indirect means) that polarized emissions from galactic dust ("foregrounds") constituted at most a small fraction of the signal they observed at 150 GHZ in the multipole region $l=30-150$, so that all (or at least most) of the signal was cosmological in origin and therefore Nobel-worthy evidence for inflation. (The larger the foreground, the lower the value of the tensor-to-scalar ratio $r$; BICEP2's reported $r=0.20$ corresponds to no foreground.)
- However, Planck's new results put the level of those foreground signals substantially higher than BICEP2's estimates. (Planck's result is not a direct measurement at BICEP2's 150GHz frequency, where Planck cannot match BICEP2's sensitivity, but a calibrated extrapolation from 353 GHz data, where the dust signal is much stronger.) In fact, it is possible that Planck's foreground accounts for all of BICEP2's observations, which would mean that BICEP2 detected no cosmological signal at all.
- Currently, Planck and BICEP2 are jointly analyzing their combined data sets to determine how much, if any, of BICEP2's signal can be attributed to cosmological inflation. The results of their joint analysis are expected by year end 2014.
31 Jan 2015 update:
The joint Planck-BICEP2 analysis is now complete, with the paper available here. The result: BICEP's claim of detecting primordial B-mode polarization at a level of $r = 0.16-0.20$ is withdrawn, and replaced by a 95%-confidence upper bound $r<0.12$, which is almost exactly the same as Planck's upper bound $r<0.11$ before BICEP2 reported last year.