Spectra of D-branes and Ext groups

Abstract:
It is studied topological properties of the D-brane resolution of three-dimensional orbifold singularities, give s sheaf-theoretic description of D-branes and check that description by noting that Ext groups between the sheaves modelling the D-branes, do in fact correctly count open string states. It is proposed the correspondence between open string states and the spectrum of states of IIB supergravity on AdS-space.