Challenges continue for BICEP2 gravitational wave inflation signal

Nature : In March the BICEP2 team announced it had found a polarization signal in the cosmic microwave background radiation that it attributed to primordial gravitational waves. However, the finding was soon challenged by Raphael Flauger of New York University, who argued that the researchers did not properly account for microwaves from galactic dust. Now Flauger, with David Spergel and Colin Hill, both of Princeton University, have posted a paper on arXiv that presents specific numbers to clarify their argument. They claim that instead of BICEP2′s calculation that 3.5% to 5% of the polarization came from dust, the actual value is between 8% and 15%, enough to eliminate the signal. Separately, Uroš Seljak and Michael Mortonson of the University of California, Berkeley, argue that the distribution and variation of the intensity of microwaves from galactic dust eliminate the evidence of gravitational waves. They also argue that the BICEP2 team, in analyzing the signal found at 150 GHz, failed to correctly consider the effects of small-scale gravitational lensing, which reduces the strength of the detected signal so that it falls well below the claimed level of significance.