On Chevalley-Shephard-Todd's theorem in positive characteristic

Abstract

Let $G$ be a finite group acting linearly on the vector space $V$ over a field of arbitrary characteristic. The action is called coregular if the invariant ring is generated by algebraically independent homogeneous invariants and the direct summand property holds if there is a surjective $k[V{]}^G$-linear map $\pi :k[V]\to k[V{]}^G$. The following Chevalley-Shephard-Todd type theorem is proved. Suppose $V$ is an irreducible $kG$-representation, then the action is coregular if and only if $G$ is generated by pseudo-reflections and the direct summand property holds.

14 pages