Set-up for classical Springer Correspondence:
G = reductive group (usually assumed to be semisimple of adjoint type) over mathbbC, with Borel subgroup and
maximal torus BsupsetT, Weyl group W=NG(T)/T.
Fix a unipotent uinG with component group A(u)=CG(u)/CG(u)circ.
mathcalB=G/B (flag variety), containing Springer fiber mathcalBu
= fixed points under u, d=dimmathcalBu (= half codimension
of class of u in unipotent variety)
Then WtimesA(u) acts on cohomology (ell-adic or classical)
H∗(mathcalBu) with top cohomology in degree 2d.
(Springer) Each irreducible representation of W occurs, for some pair
(u,phi) with u unipotent andphi an irreducible character of A(u), as an isotypic component of the WtimesA(u) representation
on the top cohomology. Here all pairs (u,1) occur.
Assume A(u)neq1 (possible except in type A).
(1) Must some pair (u,phi) with phineq1 occur?
(2) Is the representation of A(u) on H∗(mathcalBu)
always a permutation permutation?
The answers to both questions seem to be yes, but I don't know
any uniform approach using Springer theory. For example,
(1) can be checked using case-by-case study of simple
types, but is there a general reason for it? For (2) there is
a sophisticated indirect argument using work of Bezrukavnikov,
Mirkovic, Rumynin. All of this ties in naturally with some
unsolved problems about representations of related Lie algebras
in characteristic p.
No comments:
Post a Comment