The Shape of the Primordial Power Spectrum: A Last Stand Before Planck

TL;DR

This paper reconstructs the primordial power spectrum using current data, finding no significant deviations from a power law and highlighting the importance of future data for more definitive conclusions.

Contribution

It provides a minimally-parametric analysis of the primordial power spectrum without strong priors, emphasizing the need for better data to confirm theoretical assumptions.

Findings

No evidence for departure from a power law spectrum

Scale-invariant spectrum is disfavored but less so with minimal priors

Current data insufficient to strongly constrain the spectrum shape

Abstract

We present a minimally-parametric reconstruction of the primordial power spectrum using the most recent cosmic microwave background and large scale structure data sets. Our goal is to constrain the shape of the power spectrum while simultaneously avoiding strong theoretical priors and over-fitting of the data. We find no evidence for any departure from a power law spectral index. We also find that an exact scale-invariant power spectrum is disfavored by the data, but this conclusion is weaker than the corresponding result assuming a theoretically-motivated power law spectral index prior. The reconstruction shows that better data are crucial to justify the adoption of such a strong theoretical prior observationally. These results can be used to determine the robustness of our present knowledge when compared with forthcoming precision data from Planck.