Cosmological Parameters 2006

Recent measurements of the cosmic microwave background radiation (CMB), particularly when combined with other datasets, have revolutionised our knowledge of the values of the basic cosmological parameters. Here we summarize the state of play at the end of 2006, focusing on the combination of CMB measurements with the power spectrum of galaxy clustering. We compare the constraints derived from the extant CMB data circa 2005 and the final 2dFGRS galaxy power spectrum, with the results obtained when the WMAP 1-year data is replaced by the 3-year measurements (hereafter WMAP1 and WMAP3). Remarkably, the picture has changed relatively little with the arrival of WMAP3, though some aspects have been brought into much sharper focus. One notable example of this is the index of primordial scalar fluctuations, n_s. Prior to WMAP3, Sanchez et al. (2006) found that the scale invariant value of n_s = 1 was excluded at the 95% level. With WMAP3, this becomes a 3sigma result, with implications for models of inflation. We find some disagreement between the constraints on certain parameters when the 2dFGRS P(k) is replaced by the SDSS measurement. This suggests that more work is needed to understand the relation between the clustering of different types of galaxies and the linear perturbation theory prediction for the power spectrum of matter fluctuations.