Columbia Mathematics Department Colloquium


On the geometry of ├ętale gerbes


Hsian-Hua Tseng

Ohio State University



A G-gerbe over a base B is roughly speaking a fiber bundle whose fibers are the classifying orbifold BG of the group G. Gerbes occur naturally in the theory of orbifolds. For example every orbifold with nontrivial generic stabilizers is a gerbe over another orbifold. Gerbes are also very important in other subjects, such as the theory of non-abelian cohomology. It is conjectured by physicists that for finite groups G the geometry of a G-gerbe is equivalent to the geometry of a disconnected space with a U(1)-twist. The purpose of this talk is to explain what this conjecture means, and why one should believe this conjecture. Much of this is joint work with Xiang Tang of Washington University in St. Louis.


Wednesday, October 12th, 5:00 - 6:00 p.m.
Mathematics 520
Tea will be served at 4:30 p.m.