Cosmological Implications of the CMB Large-scale Structure

TL;DR

This paper examines large-scale anomalies in the CMB, such as low power and alignments, comparing their probabilities in LCDM and R_h=ct cosmologies, and finds the latter explains these features more naturally.

Contribution

It introduces the R_h=ct universe as an alternative cosmological model that better accounts for certain CMB anomalies without invoking cosmic variance.

Findings

In LCDM, anomalies have very low probabilities (~0.005%).

In R_h=ct, anomalies are more probable (~7-10%).

The maximum fluctuation size at recombination explains the differences.

Abstract

WMAP and Planck may have uncovered several anomalies in the full CMB sky that could indicate possible new physics driving the growth of density fluctuations in the early Universe. These include an unusually low power at the largest scales and an apparent alignment of the quadrupole and octopole moments. In LCDM, the quadrupole and octopole moments should be statistically independent. These low probability features may simply be due to posterior selections from many such possible effects. If this is not the case, however, their combined statistical significance would be equal to the product of their individual significances. Ignoring the biasing due to posterior selection, the missing large-angle correlations would have a probability as low as ~0.1% and the low-l multipole alignment would be unlikely at the ~4.9% level; under the least favourable conditions, their simultaneous observation in the context of the standard model could then be likely at only the ~0.005% level. In this paper, we explore the possibility that these features are indeed anomalous, and show that the corresponding probability of CMB multipole alignment in the R_h=ct Universe would then be ~7-10%, depending on the number of large-scale Sachs-Wolfe induced fluctuations. Since the low power at the largest spatial scales is reproduced in this cosmology without the need to invoke cosmic variance, the overall likelihood of observing both of these features in the CMB is > 7%, much more likely than in LCDM. The key physical ingredient responsible for this difference is the existence in the former of a maximum fluctuation size at the time of recombination, which is absent in the latter because of inflation.