Index saddle for the D1-D5-P black string

by Shanmugapriya Prakasam (ICTS-TIFR, Bengaluru)

Thursday 17 Sept 2026, 14:30 → 15:30 Europe/Rome

For a large class of black holes, the explanation of the macroscopic entropy has been successfully given via a microscopic count over a set of states. The central object of interest in these computations is the supersymmetric index. Recent results found the true gravitational saddles that contribute to the macroscopic index of certain asymptotically AdS and also to asymptotically flat black holes. The saddles in asymptotically flat space are rotating, supersymmetric and non-extremal black hole solutions that exhibit the new attractor mechanism in four dimensions. In this talk, we will first demonstrate how to uplift a 4D new attractor saddle to a known 5D black hole index saddle. Black string saddles were recently constructed in five dimensions by uplifting 4D black hole index saddles and applying a novel decoupling limit. Motivated by this work, we further extend this program by constructing a 6D black string index saddle by uplifting the known 5D black hole index saddle. An appropriately engineered decoupling limit allows us to zoom into the $AdS_3 \times S^3$ near horizon region and construct the BTZ $\times S^3$ index saddle.