Constraints on the topology of the Universe derived from the 7-year WMAP CMB data and prospects of constraining the topology using CMB polarisation maps

TL;DR

This study uses 7-year WMAP data to constrain the Universe's topology by searching for matched circles in CMB temperature maps, demonstrating that polarisation maps from future experiments could further improve these constraints.

Contribution

It provides new constraints on the Universe's topology using WMAP data and highlights the potential of CMB polarisation maps for future topological studies.

Findings

Universes with large matched circles (>10°) are ruled out.

Lower bound on the fundamental domain size is approximately 27.9 Gpc.

Polarisation maps are promising for constraining topology with upcoming CMB data.

Abstract

We impose constraints on the topology of the Universe determined from a search for matched circles in the cosmic microwave background (CMB) temperature anisotropy patterns of the 7-year WMAP data. We pay special attention to the sensitivity of the method to residual foreground contamination of the sky maps. A search for pairs of matched back-to-back circles in the higher resolution WMAP W-band map allows tighter constraints to be imposed on topology. Our results rule out universes with topologies that predict pairs of such circles with radii larger than approximately 10 degrees. This places a lower bound on the size of the fundamental domain for a flat universe of about 27.9 Gpc. We study also the possibility for constraining the topology of the Universe by means of the matched circles statistic applied to polarised CMB anisotropy maps. The advantages of using the CMB polarisation maps in studies of the topology over simply analysing the temperature data as has been done to-date are clearly demonstrated. It is found that the noise levels of both Planck and next generation CMB experiments data are no longer prohibitive and should be low enough to enable the use of the polarisation maps for such studies.