Model selection forecasts for the spectral index from the Planck satellite

Abstract

The recent WMAP3 results have placed measurements of the spectral index ${n}_{\mathrm{S}}$ in an interesting position. While parameter estimation techniques indicate that the Harrison--Zel'dovich spectrum ${n}_{\mathrm{S}}=1$ is strongly excluded (in the absence of tensor perturbations), Bayesian model selection techniques reveal that the case against ${n}_{\mathrm{S}}=1$ is not yet conclusive. In this paper, we forecast the ability of the Planck satellite mission to use Bayesian model selection to convincingly exclude (or favor) the Harrison--Zel'dovich model.