Primordial gravity wave fossils and their use in testing inflation

TL;DR

It is found that the Square Kilometer Array will not be competitive with current cosmic microwave background constraints on primordial gravity waves from inflation, however, a more futuristic experiment could provide the highest ultimate to tensor modes and possibly even measure the tensor spectral index.

Abstract

A new effect is described by which primordial gravity waves leave a permanent signature in the large scale structure of the Universe. The effect occurs at second order in perturbation theory and is sensitive to the order in which perturbations on different scales are generated. We derive general forecasts for the detectability of the effect with future experiments, and consider observations of the pre-reionization gas through the 21 cm line. It is found that the Square Kilometre Array will not be competitive with current cosmic microwave background constraints on primordial gravity waves from inflation. However, a more futuristic experiment could, through this effect, provide the highest ultimate sensitivity to tensor modes and possibly even measure the tensor spectral index. It is thus a potentially quantitative probe of the inflationary paradigm.

Figures (1)

• Figure 1: Primordial tensor power spectrum obeying the consistency relation for $r=0.1$. The solid line is the tensor power spectrum. Error bars represent the reconstruction uncertainty on the binned power spectrum for a perfect experiment, surveying $200\,(\textrm{Gpc}/h)^3$ and resolving scalar modes down to $k_{max}=168h/\textrm{Mpc}$. The dashed, nearly vertical, line is the reconstruction noise power. The non-zero slope of the solid line is the deviation from scale-free.