Defect formation from defect--anti-defect annihilations
  We show that when a topological defect with extended world-volume annihilates with an anti-defect, there arise topological defects with dimensions less than those of the original defects by one. Domain wall annihilations create vortices while monopole-string annihilations result in instantons. We find that twisted domain wall rings are vortices, whereas twisted monopole rings are instantons. 
Muneto Nitta
hep-th astro-ph.HE hep-ph