Constraints on the topology of the Universe derived from the 7-year WMAP data

TL;DR

This paper uses 7-year WMAP data to constrain the Universe's topology by searching for matched circles in the CMB, establishing a lower bound on the size of the fundamental domain and ruling out certain topologies.

Contribution

It introduces a refined analysis method that accounts for foreground contamination, providing tighter constraints on the Universe's topology using WMAP data.

Findings

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

The lower bound on the fundamental domain size is approximately 27.9 Gpc.

The observable Universe's diameter is close to the detection limit of the method.

Abstract

We impose constraints on the topology of the Universe determined from a search for matched circles in the 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, and show that for a full sky estimate of the CMB signal (the ILC map) such residuals introduce a non-negligible effect on the statistics of matched circles. In order to reduce this effect, we perform the analysis on maps for which the most contaminated regions have been removed. 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 \alpha_min \approx 10 degrees. This places a lower bound on the size of the fundamental domain for a flat universe of about 27.9 Gpc. This bound is close to the upper limit on the size of Universe possible to detect by the method of matched circles, i.e. the diameter of the observable Universe is 28.3 Gpc.