KALUZA-KLEIN MONOPOLES AND GAUGED SIGMA-MODELS

We propose an effective action for the eleven-dimensional (bosonic) Ka luza-Klein monopole solution. The construction of the action requires that the background fields admit an Abelian isometry group. The corres ponding sigma-model is gauged with respect to this isometry. The gauge d sigma-model is the source for the monopole solution. A direct (doubl e) dimensional reduction of the action leads to the effective action o f a 10-dimensional D-6-brane (IIA Kaluza-Klein monopole), We also show that the effective action of the 10-dimensional heterotic Kaluza-Klei n monopole (which is a truncation of the IIA monopole action) is T-dua l to the effective action of the solitonic 5-brane. We briefly discuss the kappa-symmetric extension of our proposal and the possible role o f gauged sigma-models in connection with the conjectured M-theory 9-br ane. (C) 1997 Elsevier Science B.V.