Global monopoles can change Universe's topology
  If the Universe undergoes a phase transition, at which global monopoles are created or destroyed, topology of its spatial sections can change. More specifically, by making use of Myers' theorem, we show that, after a transition in which global monopoles form, spatial sections of a spatially flat Universe become finite and closed. This implies that global monopoles can change topology of Universe's spatial sections (from infinite and open to finite and closed). We emphasize that global monopoles cannot alter topology of the space-time manifold. 
Anja Marunovic and Tomislav Prokopec
gr-qc astro-ph.CO hep-th