Appears in collection : Physical Mathematics : Celebration of Albert Schwarz’s 70 Years in Science

Donaldson-Thomas invariants are the mathematical incarnation of BPS indices counting black hole micro-states in string compactifications. They are notoriously difficult to compute, and subject to wall-crossing phenomena. String dualities predict that generating series of DT invariants counting D4-D2-D0 black holes should have modular (or more generally mock modular) behavior. For one-parameter CY threefolds such as the quintic, one may compute the first few terms in the generating series using vanishing theorems and wall-crossing formulae,and find a unique modular completion. This in turn allows to predict new Gopakumar-Vafa invariants, and determine the topological string amplitude to higher genus than hitherto possible. Based on work in collaboration with Sergey Alexandrov, Soheyla Feyzbakhsh, Albrecht Klemm and Thorsten Schimmanek.