Boundary States in the Open String Channel and CFT near a Corner

We generalize the idea of boundary states to the open string channel. Theydescribe emission and absorption of open strings in the presence ofintersecting D-branes. We construct the explicit oscillator representation forthe free boson and fermionic ghost. The inner product of such states describesa disk amplitude of rectangular shape and possesses modular covariance with anontrivial conformal weight. We compare the result obtained here with thoseobtained using two different methods, one employing the path integral formalismand one employing the conformal anomaly. We find that all these methods giveconsistent results. In our method, we must be careful in our treatment of thesingularity of the CFT near the corners. Specifically, we derive the correctionto the conformal weight of the primary field inserted at the corner, and itgives the modular weight of the rectangle amplitude. We also carry out explicitcomputations of the correlation functions.Comment: 23 pages, 4 figures, PTPTeX, v2 references added and some equations improved, v3 style macro has been changed. BRST analysis adde