Tuesday, March 18, 2014

[1403.4596] Suppressing the impact of a high tensor-to-scalar ratio on the temperature anisotropies

[1403.4596] Suppressing the impact of a high tensor-to-scalar ratio on the temperature anisotropies:

The BICEP2 collaboration has reported a strong B mode signal in the CMB polarization, which is well fit by a tensor-to-scalar ratio of r ~ 0.2. This is greater than the upper limit r < 0.11 obtained from the temperature anisotropies under the assumption of a constant scalar spectral index n_s. This discrepancy can be reduced once the statistical error and the contamination from polarized dust are accounted for. If however a large value for r will be confirmed, it will need to be reconciled with the temperature anisotropies data. The most advocated explanation involves a variation of n_s with scales that has a magnitude significantly greater than the generic slow roll predictions. We instead study the possibility that the large scale temperature anisotropies are not enhanced because (1) of a suppression of the scalar power at large scales, or (2) of an anti-correlation between tensor and scalar modes. The first possibility can be achieved for instance by a sudden change of the speed of the inflaton; the second possibility requires breaking of Lorentz invariance, and it also leads to violation of statistical isotropy in the temperature data, which is (i) of O (10%) or less, and (ii) present only at large scales. Interestingly, violation of statistical isotropy with these two properties appears to be present both in the WMAP and Planck data.

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