Boundary deformation theory and moduli spaces of D-branes

Boundary conformal field theory is the suitable framework for a microscopic treatment of D-branes in arbitrary CFT backgrounds. In this work, we devel op boundary deformation theory in order to study the changes of boundary co nditions generated by marginal boundary fields. The deformation parameters may be regarded as continuous moduli of D-branes. We identify a large class of boundary fields which are shown to be truly marginal, and we derive clo sed formulas describing the associated deformations to all orders in pertur bation theory. This allows us to study the global topology properties of th e moduli space rather than local aspects only. As an example, we analyse in detail the moduli space of c = 1 theories, which displays various stringy phenomena. (C) 1999 Elsevier Science B.V.