The index of a Lie algebra, the centraliser of a nilpotent element, and the normaliser of the centraliser

On symmetric invariants of centralisers in reductive Lie algebras

Let $g_e$ be the centraliser of a nilpotent element $e$ in a finite dimensional simple Lie algebra $g$ of rank $l$ over an algebraically closed field of characteristic 0. We investigate the algebra $S(g_e)^{g_e}$ of symmetric invariants of $g_e$ and prove that if $g$ is of type $A$ or $C$, then $S(g_e)^{g_e}$ is always a graded polynomial algebra in $l$ variables. We show that this continues to hold for some nilpotent elements in the Lie algebras of other types. In type $A$ we prove that $S(g_e)^{g_e}$ is freely generated by a regular sequence in $S(g_e)$ and describe the tangent cone at $e$ t…

二阶幂零元中心化子在旗簇中的轨道闭包：A、B、D 型的正规性与消解

Orbit closures in flag varieties for the centralizer of an order-two nilpotent element : normality and resolutions for types A, B, D

本文研究 A、B、D 型约化群中二阶幂零元中心化子在旗簇内的轨道闭包，证明其正规性、特定条件下的 Cohen–Macaulay 性与有理奇点，并构造涉及 Schubert 簇的双有理有理消解。