Algebra publication

Title

Invariants under tori of rings of differential operators and related topics.

Author(s)

I.M. Musson, M. Van den Bergh.

Year

1995

Abstract

If $G$ is a reductive algebraic group acting rationally on a smooth affine variety $X$ then it is generally believed that $D(X)^G$ has properties very similar to those of enveloping algebras of semisimple Lie algebras. In this paper we show that this is indeed the case when $G$ is a torus and $X=k^r\times (k^*)^s$. We give a precise description of the primitive ideals in $D(X)^G$ and we study in detail the ring theoretical and homological properties of the minimal primitive quotients of $D(X)^G$. The latter are of the form $D(X)^G/(\g-\chi(\g))$ where $\g=\Lie(G)$, $\chi\in \g^\ast$ and $\g-\chi(\g)$ is the set of all $v-\chi(v)$ with $v\in \g$. They occur as rings of twisted differential operators on toric varieties. As a side result we prove that if $G$ is a torus acting rationally on a smooth affine variety then $D(X\quot G)$ is a simple ring.

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