# Representation theory II

This page contains the information about the course **V4A4 Representation Theory II**, taught by Prof. Dr. Catharina Stroppel.

This course will give an introduction into some aspects of geometric representation theory. We will start by studying flag varieties and Grassmannians. Important hereby are in particular the Schubert cells which are the cells in some affine cellular decomposition of these varieties. Moreover we will spend some time on describing these varieties as varieties with a torus action. Then the connection to cohomology theories will be made.

We will introduce the socalled Bott-Samelson varieties, which are certain resolutions of singularities arising in this context. We will study them from a combinatorial, representation theoretic and geometric point of view. These varieties (in connection with Soergel bimodules) turned out to be extremely useful in proving and disproving long-outstanding conjectures in representation theory. The second part will most likely introduce equivariant cohomology and explain the important localisation theorem.

The motto throughout the course will be that we want to use geometry to do representation theory.

**Prerequisites** Basic knowledge on algebraic varieties and projective spaces, some familiarity with representation theory. The material from courses like Algebra I and Algebra II are assumed to be known. Basic knowledge in Lie theory (like in Humphreys book) helps for the applications.

## Lectures

To be determined.

## Tutorials

To be determined.

## Exercise sheets

To be added.

## Exam

To be determined.

## References

Andersen: Introduction to Equivariant cohomology in algebraic geometry, arXiv:1112.1421

Chriss–Ginzburg: Representation Theory and Complex geometry

Fulton: Young tableaux

Lakshmibai–Brown: Flag varieties: An interplay of geometry, combinatorics and representation theory