Discovery-HET cosmology journal club by Paul Hunt – University of Copenhagen

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Discovery-HET cosmology journal club by Paul Hunt

When and where: Monday 30th, 11.00 (sharp!) in Fb6
Title: Reconstructing the primordial spectrum of density fluctuations
Speaker: Paul Hunt (Warsaw)
Detailed knowledge of the primordial power spectrum (PPS) of curvature perturbations is essential both in order to elucidate the physical mechanism (inflation?) which generated it, and for estimating the parameters of the assumed cosmological model from CMB and LSS data. Hence it ought to be extracted from such data in a model-independent manner, however this is difficult because relevant cosmological observables are given in general by a convolution of the PPS with some smoothing kernel. The deconvolution problem is ill-conditioned so a regularisation scheme must be employed to control error propagation. We apply `Tikhonov regularisation' to data from WMAP, other ground-based small angular scale CMB experiments, and the Sloan Digital Sky Survey. The reconstructed PPS is not scale-free but has an infrared cutoff at k <= 5 X 10^{-4} Mpc^{-1} (due to the low CMB quadrupole), and several features with ~2 sigma significance at k/Mpc^{-1} = 0.0013-0.0023, 0.0362-0.0402 and 0.051-0.056, reflecting the WMAP `glitches'. To test whether these are indeed real will require more accurate data, such as from the Planck satellite and new ground-based experiments.