They generically occur in theories in which the U(1) group of electromagnetism is embedded in a larger non-Abelian group
They generically occur in theories in which the U(1) group of electromagnetism is embedded in a larger non-Abelian group G. The 't Hooft - Polyakov "hedgehog" solution is an example in an SU(2) theory equipped with a Higgs field. Better known is the Dirac string example, which predicts that the existence of one would lead to the quantization of electric charge, but the third of Maxwell's equations claims that they don't exist. FTP, what are these hypothetical particles possessing an isolated elementary magnetic charge?
They generically occur in theories in which the U(1) group of electromagnetism is embedded in a larger non-Abelian group
magnetic monopole