Two results on equations of nilpotent orbits

Abstract

We prove two results on the defining ideals of certain varieties of matrices. Let us fix two positive integers r, e. Let M(r) be the set of r x r matrices over a field K. We consider the closed subscheme of the nilpotent variety of M(r) over K defined by the conditions char_A(T)=T^r, A^e=0. We prove that when the characteristic of K is zero this scheme is reduced. Also for e=2 we prove that this scheme is reduced over a field K of arbitrary characteristic. These results were motivated by the questions of G. Pappas and M. Rapoport (compare their paper ''Local models in the ramified case I. The EL-case", math.AG/0006222) and give answers to some of their conjectures.