DECAY OF MAGNETIC-FIELDS IN KALUZA-KLEIN THEORY

Magnetic fields in five-dimensional Kaluza-Klein theory compactified o n a circle correspond to ''twisted'' identifications of five-dimension al Minkowski space. We show that a five-dimensional generalization of the Kerr solution can be analytically continued to construct an instan ton that gives rise to two possible decay modes of a magnetic field. O ne decay mode is the generalization of the ''bubble decay'' of the Kal uza-Klein vacuum described by Witten. The other decay mode, rarer for weak fields, corresponds in four dimensions to the creation of monopol e-antimonopole pairs. An instanton for the latter process is already k nown and is given by the analytic continuation of the Kaluza-Klein Ern st metric, which we show is identical to the five-dimensional Kerr sol ution. We use this fact to illuminate further properties of the decay process. It appears that fundamental fermions can eliminate the bubble decay of the magnetic field, while allowing the pair production of Ka luza-Klein monopoles.