Homotopy classification of cosmological defects
= Homotopy classification of cosmological defects
{title2=$\pi_0:\text{walls},\ \pi_1:\text{strings},\ \pi_2:\text{monopoles}$}
Disconnected vacuum components support walls, noncontractible vacuum loops support line defects, and nontrivial vacuum two-spheres support monopoles in three spatial dimensions. Allowed <topology> does not alone predict the number formed or their subsequent survival.