2014/05/06 by Benjamin Audren, Daniel G. Figueroa, Audren, Benjamin +3 · 1 citation
Physics and Astronomy · #Advanced Frequency and Time Standards #Atomic and Subatomic Physics Research #Cold Atom Physics and Bose-Einstein Condensates #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #astro-ph.CO
paper · pdf · doi:10.48550/arxiv.1405.1390
Brief note (2 pages, 2 figures), just to clarify certain aspects about the comparison between the BICEP2 and Planck results
arxiv created 2014/05/06 · openalex publication_date 2014/05/06 · arxiv updated 2014/05/07 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The apparent discrepancy between the value of the tensor-to-scalar ratio reported by the BICEP2 collaboration, r = 0.20+0.07-0.05 at 68% CL, and the Planck upper limit, r < 0.11 at 95% CL, has attracted a great deal of attention. In this short note, we show that this discrepancy is mainly due to an `apples to oranges' comparison. The result reported by BICEP2 was measured at a pivot scale k_* = 0.05 Mpc-1, assuming nt = 0, whereas the Planck limit was provided at k_* = 0.002 Mpc-1, assuming the slow-roll consistency relation nt = -r/8. One should obviously compare the BICEP2 and Planck results under the same circumstances. By imposing nt = 0, the Planck constraint at k_* = 0.05 Mpc-1 becomes r < 0.135 at 95% CL, which can be compared directly with the BICEP2 result. Once a plausible dust contribution to the BICEP2 signal is taken into account (DDM2 model), r is reduced to r = 0.16+0.06-0.05 and the discrepancy becomes of order 1.3σ only.