The symmetric invariants of centralizers and Slodowy grading II (1604.01274v2)
Abstract: Let $\mathfrak{g}$ be a finite-dimensional simple Lie algebra of rank $\ell$ over an algebraically closed field $\Bbbk$ of characteristic zero, and let $(e,h,f)$ be an $\mathfrak{sl}2$-triple of g. Denote by $\mathfrak{g}{e}$ the centralizer of $e$ in $\mathfrak{g}$ and by ${\rm S}(\mathfrak{g}{e}){\mathfrak{g}{e}}$ the algebra of symmetric invariants of $\mathfrak{g}{e}$. We say that $e$ is good if the nullvariety of some $\ell$ homogenous elements of ${\rm S}(\mathfrak{g}{e}){\mathfrak{g}{e}}$ in $(\mathfrak{g}{e}){*}$ has codimension $\ell$. If $e$ is good then ${\rm S}(\mathfrak{g}{e}){\mathfrak{g}{e}}$ is a polynomial algebra. In this paper, we prove that the converse of the main result of arXiv:1309.6993 is true. Namely, we prove that $e$ is good if and only if for some homogenous generating sequence $q_1,\ldots,q\ell$, the initial homogenous components of their restrictions to $e+\mathfrak{g}{f}$ are algebraically independent over $\Bbbk$.