Generating branes via sigma models

Starting with the D-dimensional Einstein-dilaton-antisymmetric form equations and assuming a block-diagonal form of a metric we derive a (D-d)-dimensional sigma model with the target space SL(d,R)/SO(d) x SL(2,R)/SO(2) x R or its noncompact form. Various solution-generating techniques are applied to reproduce some known and to construct some new p-brane solutions. It is shown that the p-brane Harrison transformation belonging to the SL(2,R) subgroup generates black p-branes from the seed Schwarzschild solution. A flux-brane generalizing the Bonnor-Melvin-Gibbons-Maeda solution is constructed as well as a nonlinear superposition of the flux-brane and a spherical black hole. A new simple way to endow branes with additional internal structure such as plane waves is suggested. Applying the harmonic maps technique we generate new solutions with a nontrivial shell structure in the transverse space ("matrioshka" p-branes). Bonnor-type symmetry relating the four-dimensional vacuum SL(2,R) to the corresponding sector of the above global symmetry group is used to construct a new magnetic six-brane with a dipole moment in the ten-dimensional type IIA theory. A similar sigma model is constructed for the intersecting branes. it is shown that the intersection rules have a simple geometric interpretation as conditions ensuring the symmetric space property of the target space. The null-geodesic method is used to find intersecting "matrioshka" p-branes in type ITA supergravity. [S0556-2821(98)03120-8].