International Mathematics Research Notices Advance Access published online on September 23, 2009
International Mathematics Research Notices, doi:10.1093/imrn/rnp145
Actions of the Derived Group of a Maximal Unipotent Subgroup on G-Varieties
Independent University of Moscow, Bolshoi Vlasevskii per. 11, 119002 Moscow, Russia
Correspondence: Correspondence to be sent to: panyush{at}mccme.ru
Let U be a maximal unipotent subgroup of a connected semisimple group G and U' the derived group of U. We study actions of U' on affine G-varieties. First, we consider the algebra of U' invariants on G/ U. We prove that
is a polynomial algebra of Krull dimension 2r, where r = rk(G). A related result is that, for any simple finite-dimensional G-module V,
is a cyclic U/ U'-module. Second, we study "symmetries" of Poincare series for U'-invariants on affine conical G-varieties. The results we obtain are very similar to those for the algebras of U-invariants. Third, we obtain a classification of simple G-modules V with polynomial algebras of U'-invariants (for G simple).