Cosmic Microwave Background in Closed Multiply Connected Universes
  We have investigated the cosmic microwave background (CMB) anisotropy in closed multiply connected universes   (flat and hyperbolic) with low matter density. We show that the COBE constraints on these low matter density models with non-trivial topology are less stringent since a large amount of CMB anisotropy on large angular scales can be produced due to the decay of the gravitational potential at late time. 
Kaiki Taro Inoue