Yin-Zhe Ma (UBC Physics & Astronomy)
Event Date and Time:
Mon, 2012-02-13 16:00 - 17:15
In this talk, I will test concordance cosmology on three different cosmic scales. (1) On the super-horizon scale, Copi et al. (2009) argued that the lack of large angular correlations of the CMB temperature field provides strong evidence against the standard, statistically isotropic, LCDM (Lambda Cold Dark Matter) cosmology. I will argue that the ad-hoc discrepancy is due to the sub-optimal estimator of the low-l multipoles, and 'a posteriori' statistics, which exaggerate the statistical significance. (2) The LCDM model also predicts the existence of primordial gravitational waves, for which B-mode polarisation will be a powerful tool to distinguish different models of the early Universe. (3) On Galactic scales, Watkins et al. (2008) show that the very large bulk flow prefers a very large density fluctuation, which seems to contradict the LCDM model. I provide a physical explanation for this big bulk flow, based on the assumption that the CMB frame does not coincide with matter rest frame, resulting in a "tilted Universe". We show that a tilted Universe could well explain the bulk flow phenomenon and more importantly, the constraints for this tilted Universe can lead to a constraint on the number of e-folds of inflation. In addition, the cosmic Mach Number from peculiar velocity catalogue data may provide a powerful test of the growth of structure.