S-DUALITY AND DYONIC P-BRANE SOLUTIONS IN TYPE-II STRING THEORY

We show how a solitonic ''magnetically'' charged p-brane solution of a given supergravity theory, with the magnetic charge carried by an ant isymmetric tensor gauge field, can be generalized to a dyonic solution . We discuss the cases of ten-dimensional and eleven-dimensional super gravity in more detail and a new dyonic five-brane solution in ten dim ensions is given. Unlike the purely electrically or magnetically charg ed five-brane solution the dyonic five-brane contains nonzero Ramond-R amond fields and is, therefore, an intrinsically type II solution. The solution preserves half of the type II spacetime supersymmetries. It is obtained by applying a solution-generating SL(2,R) X SL(2,R) S dual ity transformation to the purely magnetically charged five-brane solut ion. One of the SL(2,R) duality transformations is basically an extens ion to the type II case of the six-dimensional Z(2) string-string dual ity. We also present an action underlying the type IIB supergravity th eory.