Group stacks in geometry
Two talks by Behrang Noohi at the CRCG Workshop - Higher Structures in Topology and Geometry III, June 4-5 2009.
As higher analogues of group schemes, group stacks arise in several contexts in geometry. E.g., symmetries of stacks, structure group stacks of higher principal bundles, stacky abelianization of reductive groups (Deligne), and so on. Working with group stacks is, however, considerably more difficult than working with group schemes, especially when one needs to do explicit calculations. In these talks we introduce some general techniques for dealing with this problem. We discuss applications to 'group actions on stacks' and to 'classification of forms of stacks over a field'.
Notes of the talks taken by Christoph Wockel.