Tensors, BICEP2 results, prior dependence, and dust

Marina Cortês, Andrew R. Liddle, David Parkinson
2015 Physical Review D  
We investigate the prior dependence on the inferred spectrum of primordial tensor perturbations, in light of recent results from BICEP2 and taking into account a possible dust contribution to polarized anisotropies. We highlight an optimized parameterization of the tensor power spectrum, and adoption of a logarithmic prior on its amplitude A_T, leading to results that transform more evenly under change of pivot scale. In the absence of foregrounds the tension between the results of BICEP2 and
more » ... anck drives the tensor spectral index n_T to be blue-tilted in a joint analysis, which would be in contradiction to the standard inflation prediction (n_T<0). When foregrounds are accounted for, the BICEP2 results no longer require non-standard inflationary parameter regions. We present limits on primordial A_T and n_T, adopting foreground scenarios put forward by Mortonson & Seljak and motivated by Planck 353 GHz observations, and assess what dust contribution leaves a detectable cosmological signal. We find that if there is sufficient dust for the signal to be compatible with standard inflation, then the primordial signal is too weak to be robustly detected by BICEP2 if Planck+WMAP upper limits from temperature and E-mode polarization are correct.
doi:10.1103/physrevd.92.063511 fatcat:vpwilrwptzg7vbq44wzo7rxini