A Cluster tilting module for a representation-infinite block of a group algebra

Abstract

Let $G=SL(2,5)$ be the special linear group of $2\times 2$-matrices with coefficients in the field with $5$ elements. We show that the principal block over a splitting field $K$ of characteristic two of the group algebra $KG$ has a $3$-cluster tilting module. This gives the first example of a representation-infinite block of a group algebra having a cluster tilting module and answers a question by Erdmann and Holm.