Type IIA D-branes, K-theory and matrix theory

Abstract

We show that all supersymmetric Type IIA D-branes can be constructed as bound states of a certain number of unstable non-supersymmetric Type IIA D9-branes. This string-theoretical construction demonstrates that D-brane charges in Type IIA theory on spacetime manifold X are classified by the higher K-theory group K _1 (X), as suggested recently by Witten. In particular, the system of N DO-branes can be obtained, for any iV, in terms of sixteen Type IIA D9-branes. This suggests that the dynamics of Matrix theory is contained in the physics of magnetic vortices on the worldvolume of sixteen unstable D9-branes, described at low energies by a 7(16) gauge theory.