English

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

Cosmology and Nongalactic Astrophysics 2014-08-28 v2 High Energy Physics - Phenomenology High Energy Physics - Theory

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 l100l\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.

Keywords

Cite

@article{arxiv.1403.5922,
  title  = {The Knotted Sky II: Does BICEP2 require a nontrivial primordial power spectrum?},
  author = {Kevork N. Abazajian and Grigor Aslanyan and Richard Easther and Layne C. Price},
  journal= {arXiv preprint arXiv:1403.5922},
  year   = {2014}
}

Comments

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