The fate of primordial magnetic monopoles

Unified gauge theories, in which the SU (2)_L and U (1)_Y subgroups do not have non-trivial intersections, possess an in-built mechanism for a complete extinction of the primordial magnetic monopoles. The potential conflict with the standard hot big bang cosmology is therefore avoided in such theories. The usual gauge theories, based on SU (5), SO (10) and E₆ do not have this property.