Electric-Magnetic Duality and the Brane Spectrum of M Theory

Poincare duality in ten dimensions implies the existence of a scalar field strength, the magnetic dual of the ten-form field strength of the massive type IIA string theory. In this paper we summarize the evidence for the existence of point sources of the associated Dirichlet (-2)brane charge, from four independent perspectives: (i) the massive IIA supergravity Lagrangian and algebraic jade relations for the spectrum of pbrane tensions, (ii) a soliton solution of the massive IIA supergravity, and of M theory, exhibiting a point source of magnetic D(-2)brane charge, (iii) analysis of the global symmetry algebra of the massive type IIA supergravity theory, and, (iv) the worldsheet computation of the tension of a D(-2)brane in type I' string theory with boundary state description. We point out that the concrete worldsheet evidence for a Dpbrane spectrum with precisely twelve elements, -2 <= p <= 9, in the type II string theories can be understood as a simple consequence of Poincare duality for the associated field strengths in eleven dimensions. Further, since the (-1)form potential is simply the generator of spacetime translations in any dimension, we find, remarkably, that the full spectrum of Dirichlet pform potentials in higher dimensions, 0 <= d <= 11, can be inferred by the dimensional uplifting of a single, Poincare self-dual, (-1)form potential in zero dimensions.