Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Knotted Sky II: Does BICEP2 require a nontrivial primordial power
  spectrum?   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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The categories of this paper are: cond-mat
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The categories of this paper are: plasm-ph
37
The categories of this paper are: supr-con
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The categories of this paper are: math
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The categories of this paper are: bayes-an
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The categories of this paper are: q-fin
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The categories of this paper are: comp-gas
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The categories of this paper are: cmp-lg
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The categories of this paper are: gr-qc
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The categories of this paper are: stat
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The categories of this paper are: quant-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: adap-org
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The categories of this paper are: funct-an
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The categories of this paper are: ao-sci