Localization of modules for a semisimple Lie algebra in prime characteristic (with an Appendix by R. Bezrukavnikov and S. Riche: Computation for sl(3))

Abstract

We show that, on the level of derived categories, representations of the Lie algebra of a semisimple algebraic group over a field of finite characteristic with a given (generalized) regular central character are the same as coherent sheaves on the formal neighborhood of the corresponding (generalized) Springer fiber.

The first step is to observe that the derived functor of global sections provides an equivalence between the derived category of $\mathcal{D}$-modules (with no divided powers) on the flag variety and the appropriate derived category of modules over the corresponding Lie algebra. Thus the “derived” version of the Beilinson-Bernstein localization theorem holds in sufficiently large positive characteristic. Next, one finds that for any smooth variety this algebra of differential operators is an Azumaya algebra on the cotangent bundle. In the case of the flag variety it splits on Springer fibers, and this allows us to pass from $\mathcal{D}$-modules to coherent sheaves. The argument also generalizes to twisted $\mathcal{D}$-modules. As an application we prove Lusztig’s conjecture on the number of irreducible modules with a fixed central character. We also give a formula for behavior of dimension of a module under translation functors and reprove the Kac-Weisfeiler conjecture.

The sequel to this paper [BMR2] treats singular infinitesimal characters.

Authors

Simon Riche

Université Pierre et Marie Curie
Institut de Mathématiques de Jussieu (UMR 7586 du CNRS)
75013 Paris
France

Ivan Mirković

Department of Mathematics
University of Massachusetts
Amherst, MA 01003
United States

Dmitriy Rumynin

Mathematics Institute
University of Warwick
Coventry CV4 7AL
United Kingdom

Roman Bezrukavnikov

Department of Mathematics
Massachusetts Institute of Technology
Cambridge MA 02139
United States