Institut für Mathematik


Modul:   MAT770  Oberseminar: Algebraische Geometrie

Searching for the impossible Azumaya algebra

Vortrag von Dr. Siddharth Mathur

Sprecher eingeladen von: Prof. Dr. Andrew Kresch

Datum: 25.04.22  Zeit: 13.15 - 14.45  Raum: Y27H25

In two 1968 seminars, Grothendieck used the framework of etale cohomology to extend the definition of the Brauer group to all schemes. Over a field, the objects admit a well-known algebro-geometric description: they are represented by $\mathbb{P}^n$-bundles (equivalently: Azumaya Algebras). Despite the utility and success of Grothendieck's definition, an important foundational aspect remains open: is every cohomological Brauer class over a scheme represented by a $\mathbb{P}^n$-bundle? It is not even known if smooth proper threefolds over the complex numbers have enough Azumaya algebras!

In this talk, I will outline a strategy to construct a Brauer class that cannot be represented by an Azumaya algebra. Although the candidate is algebraic, the method will leave the category of schemes and use formal-analytic line bundles to create Brauer classes. I will then explain a strange criterion for the existence of a corresponding Azumaya Algebra. At the end, I will reveal the unexpected conclusion of the experiment.

To attend remotely: