##### Department of Mathematics,

University of California San Diego

****************************

### Math 208 - Algebraic Geometry Seminar

## Michail Savvas

#### UCSD

## Generalized Donaldson-Thomas Invariants via Kirwan Blowups

##### Abstract:

Donaldson-Thomas (abbreviated as DT) theory is a sheaf theoretic technique of enumerating curves on a Calabi-Yau threefold. Classical DT invariants give a virtual count of Gieseker stable sheaves provided that no strictly semistable sheaves exist. This assumption was later lifted by the work of Joyce and Song who defined generalized DT invariants using Hall algebras and the Behrend function, their method being motivic in nature. In this talk, we will present a new approach towards generalized DT theory, obtaining an invariant as the degree of a virtual cycle inside a Deligne-Mumford stack. The main components are an adaptation of Kirwanâ€™s partial desingularization procedure and recent results on the structure of moduli of sheaves on Calabi-Yau threefolds. Based on joint work with Young-Hoon Kiem and Jun Li.

Host: James McKernan

### September 28, 2018

### 2:00 PM

### AP&M 5829

****************************