Counting sheaves by counting curves

Contact: Prof. D. Huybrechts.

DT invariants count stable bundles and sheaves on a Calabi-Yau 3-fold X. The generalised DT invariants of Joyce-Song count semistable bundles and sheaves on X. I will describe work with Soheyla Feyzbakhsh showing these generalised DT invariants in any rank r can be written in terms of rank 1 invariants counting ideal sheaves of curves in X. By the MNOP conjecture the latter invariants are determined by the Gromov-Witten invariants of X. Along the way we also show all these invariants are determined by rank 0 invariants counting sheaves supported on surfaces in X. These invariants are predicted by S-duality to be governed by (vector-valued, mock) modular forms.