Mathematics Colloquia and Seminars

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Exact results for the BPS index are known for a class of BPS dyons in type II string theory compactified on a six dimensional torus. In this work we set up the problem of counting the same BPS states in a duality frame consisting of only D branes. We explicitly count the number of states for a few small charges. For lowest possible charges we find agreement with the result obtained in other duality frames. Furthermore, we find that after factoring out the supermultiplet structure, each of these states carry zero angular momentum. This is in agreement with the prediction obtained from a representation of these states as supersymmetric black holes. It would be tempting to conjecture that even for higher charges all microstates carry zero angular momentum in this duality frame. To check this, we consider some other small charges and again get only zero angular momentum states. However for these charges our results seem to differ from the existing results by small amounts. We examine possible sources of this discrepancy.