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
  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.
