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arXiv · 1403.5922

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

Kevork N. Abazajian·Grigor Aslanyan·Richard Easther·Layne C. Price
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Abstract

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 $l\lesssim 100$, 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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Kevork N. Abazajian, Grigor Aslanyan, Richard Easther, Layne C. Price. 2014-08-26. The Knotted Sky II: Does BICEP2 require a nontrivial primordial power spectrum?. https://doi.org/10.1088/1475-7516%2F2014%2F08%2F053

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