A topological approach to induction theorems in Springer theory

We give a self-contained account of a construction due to Rossmann, which lifts Springer's action of a Weyl group on the cohomology of a Springer fiber to an action on its homotopy type. We use this construction to produce a generalization of an ``induction theorem'' of Alvis and Lusztig, which relates the Springer representations attached to a reductive group to those attached to a Levi subgroup. Our generalization applies to more general centralizers and to representations of Weyl groups on mod $p$ cohomology.