Surjectivity of Engel Maps over trace zero matrices in ${\mathrm{M}}_2(\mathcal{O})$

Abstract

The surjectivity of various noncommutative polynomials has been studied extensively on Lie algebras over fields of different characteristics. In this article, we study the surjectivity of Engel Maps over trace zero matrices in ${\mathrm{M}}_2(\mathcal{O})$, where $\mathcal{O}$ is a local principal ideal ring complete with respect to its maximal ideal and has a residue field $k$ of characteristic $\ne 2$. We show that the image of $(m+1)$-th Engel map induced by the Engel polynomial $e_{m+1}(x,y)=[\cdots [[x,\underset{m+1\text{ times}}{\underbrace{y],y],\dots ,y]}}$ over ${\mathrm{M}}_2(\mathcal{O})$ can be determined by the image of the corresponding Engel map over ${\mathrm{M}}_2(k)$, for $m\ge 1$. Moreover, we prove that the $(m+1)$-th Engel map on ${\mathfrak{sl}}_2^{\circ }(\mathcal{O})=\left\{A\in {\mathrm{M}}_2(\mathcal{O})\mid \mathrm{tr}(A)=0\right\}$ is surjective if and only if the corresponding Engel map on ${\mathfrak{sl}}_2(k)$ is surjective. Under some mild condition on the residue field $k$, our results shows that every $g\in {\mathfrak{sl}}_2^{\circ }(\mathcal{O})$ can be expressed as $g=e_{m+1}(h_1,h_2)$ for $m\ge 1$, where both $h_1,h_2$ are in ${\mathfrak{sl}}_2^{\circ }(\mathcal{O})$.

Version 2, 14 pages, Comments are welcome