Reconstruction of the primordial power spectrum from CMB data

Measuring the deviation from scale invariance of the primordial power spectrum is a critical test of inflation. In this paper we reconstruct the shape of the primordial power spectrum of curvature perturbations from the cosmic microwave background data, including the 7-year Wilkinson Microwave Anisotropy Probe data and the Atacama Cosmology Telescope 148 GHz data, by using a binning method of a cubic spline interpolation in log-log space. We find that the power-law spectrum is preferred by the data and that the Harrison-Zel'dovich spectrum is disfavored at 95% confidence level. These conclusions hold with and without allowing for tensor modes, however the simpler model without tensors is preferred by the data. We do not find evidence for a feature in the primordial power spectrum — in full agreement with generic predictions from cosmological inflation.