Boundary States of D-branes in AdS_3 Based on Discrete Series

摘要

We study D-branes in the Lorentzian AdS_3 background from the viewpoint ofboundary states, emphasizing the role of open-closed duality in string theory.Employing the world sheet with Lorentzian signature, we construct the Cardystates with the discrete series. We show that they are compatible with (1)unitarity and normalizability, and (2) the spectral flow symmetry, in the openstring spectrum. We also discuss their brane interpretation. We further showthat in the case of superstrings on AdS_3 x S^3 x T^4, our Cardy states yieldan infinite number of physical BPS states in the open string channel, on whichthe spectral flows act consistently.