Journal
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
Volume -, Issue 8, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/1475-7516/2014/08/053
Keywords
gravitational waves and CMBR polarization; cosmological parameters from CMBR; CMBR polarisation; inflation
Funding
- NeSI's collaborator institutions and through the Ministry of Business, Innovation Sz Employment's Research Infrastructure programme
- NSF [PHY-11-59224]
- Division Of Physics
- Direct For Mathematical & Physical Scien [1159224] Funding Source: National Science Foundation
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An inflationary gravitational wave background consistent with BICEP2 is difficult to reconcile with a simple power-law spectrum of primordial scalar perturbations. Tensor modes contribute to the temperature anisotropies at multipoles with l less than or similar to 100, and this effect together with a prior on the form of the scalar perturbations was the source of previous bounds on the tensor-to-scalar ratio. We compute Bayesian evidence for combined fits to BICEP2 and Planck for three nontrivial primordial spectra: a) a running spectral index, b) a cutoff at fixed wavenumber, and c) a spectrum described by a linear spline with a single internal knot. We find no evidence for a cutoff, weak evidence for a running index, and significant evidence for a broken spectrum. Taken at face-value, the BICEP2 results require two new inflationary parameters in order to describe both the broken scale invariance in the perturbation spectrum and the observed tensor-to-scalar ratio. Alternatively, this tension may be resolved by additional data and more detailed analyses.
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