Christian Schnell : Group actions and freeness

Posted by Eamon Quinlan-Gallego , part of the Algebraic Geometry Seminar.

At

March 18, 2026, 3 p.m.

In

712 SEO

Abstract

My talk is about group actions on projective varieties. Every algebraic group G over the complex numbers is an extension of an abelian variety A by a linear algebraic group L (Chevalley's theorem). The main result is that if G acts algebraically on a projective variety X, then the cohomology of X is "free" over the cohomology of A. The precise statement involves Hopf algebras and comodules. This is joint work with Mark de Cataldo and Yoonjoo Kim.