Superembedding approach and S-duality: a unified description of superstring and super-D1-brane

It is proved that a basic superembedding equation for the 2-dimensional worldsheet superspace Sigma (2\8+8) embedded into D = 10 type W superspace M(10\16+16) provides a universal, S-duality invariant description of a fundamental superstring and super-D1-brane. We work out generalized action principle, obtain superfield equations of motion for both these objects and find how the S-duality transformations relate the superfield equations of superstring and super-D1-brane. The superembedding of 6-dimensional worldsheet superspace Sigma (6\16) into the D = 10 type IIB superspace M(10\16+16),ill probably provide a similar universal description for the set of type IIB super-NS5-brane, super-D5-brane and a Kaluza-Klein monopole (super-KK5-brane). (C) 2001 Elsevier Science B.V. All rights reserved.