We are running a seminar on differentiable stacks from the middle of February to the end of March/beginning of April, consisting of 6 lectures. The aim of this seminar is to first understand stacks in an abstract categorical sense and then relate this back to the concrete setting of Lie groupoids up to Morita equivalence. The key point of the seminar will be to understand the three definitions of a stack as given on Wikipedia. In addition, we will focus on why these three definitions are equivalent and we will make the theory more concrete using plenty of examples. A preliminary overview of the intended topics and a tentative schedule are given below. The seminar will probably be livestreamed and recorded. If you would be interested in giving a talk at the seminar, feel free to contact Douwe (d.hoekstra [at] uu.nl) or Jaime (j.pedregalpastor [at] uu.nl).

Intended topics

  1. Stacks of triangles [AS, Chapter 1]
  2. Categorical prerequisites [W, TMS, DSG, PASLG]
  3. Abstract definitions of a stack [W, TMS, DSG, PASLG]
  4. Lie groupoids up to Morita equivalence as stacks [TMS, DSG, LGDS, PASLG]
  5. Morphisms of stacks in the Lie groupoid picture [TMS, DSG, LGDS, PASLG]
  6. Optional: C*-algebras or some other topic.

References

Talks