Rationality of normal forms of isotropy strata of a representation of a compact Lie group

Abstract: In this article we study the isotropy stratification of a linear representation $V$ of a compact Lie group $G$. We prove that the closed isotropy strata are real algebraic manifolds and that for each isotropy subgroup $H$, every rational invariant of the induced representation $(V<sup>{H},N(H))$ can be obtained as the restriction of a global invariant of $(V,G)$, where $N(H)$ is the normalizer of $H$ and $V<sup>{H}$ is the fixed point set of $H$.