## Decay of magnetic fields in Kaluza-Klein theory

Magnetic fields in five-dimensional Kaluza-Klein theory compactified on a circle correspond to ``twisted`` identifications of five-dimensional Minkowski space. We show that a five-dimensional generalization of the Kerr solution can be analytically continued to construct an instanton that gives rise to two possible decay modes of a magnetic field. One decay mode is the generalization of the ``bubble decay`` of the Kaluza-Klein vacuum described by Witten. The other decay mode, rarer for weak fields, corresponds in four dimensions to the creation of monopole-antimonopole pairs. An instanton for the latter process is already known and is given by the analytic continuation ofmore »