The Knotted Sky II: Does BICEP2 require a nontrivial primordial power spectrum? - INSPIRE

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The Knotted Sky II: Does BICEP2 require a nontrivial primordial power spectrum?

Mar 24, 2014

14 pages

Published in:

JCAP 08 (2014) 053

Published: 2014

e-Print:

1403.5922 [astro-ph.CO]

DOI:

10.1088/1475-7516/2014/08/053

View in:

ADS Abstract Service

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Abstract: (IOP)

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 llesssim 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.

Note:

14 pages, 5 figures, 4 tables; v2: references added, discussion updated, matches published version

gravitational waves and CMBR polarization
cosmological parameters from CMBR
CMBR polarisation
inflation
perturbation: spectrum
power spectrum: primordial
perturbation: scalar
gravitational radiation: background
temperature: anisotropy
inflation

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