Particles in String Theory
MSc Thesis, Dept. of Physics, University of Amsterdam, 1997. [Full text (pdf)]
A low energy effective action is derived for a single D-particle. We find that at open string tree level, it behaves like a free particle with mass ~ 1/gc. A system of many D-particles is described by a Yang-Mills action after dimensional reduction to 0+1 dimensions. Physically, the degrees of freedom are the relative positions of the particles, and a set of harmonic oscillators corresponding to strings that may stretch between them. Upon compactification, the quantum mechanics of many D-particles turns out to be equivalent to Yang-Mills theory on a single multiply wound D-string, a fact that is known as T-duality.
Scattering of two D-particles is considered. It is found that supersymmetry is essential, since purely bosonic D-particles are confined by a potential that grows linearly with the distance between them. In the supersymmetric theory, D-particle scattering is found to contain broad resonances, which offers evidence for the existence of bound states of N D-particles, as needed for the conjectured equivalence of M-theory and D-particle quantum mechanics.
A short general introduction to string theory, and to the way D-branes appear in it, is included.