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On the automorphism group of a toral variety (2211.16584v2)
Published 29 Nov 2022 in math.AG
Abstract: Let $\mathbb{K}$ be an algebraically closed field of characteristic zero. An affine algebraic variety $X$ over $\mathbb{K}$ is toral if it is isomorphic to a closed subvariety of a torus $(\mathbb{K}*)d$. We study the group $\mathrm{Aut}(X)$ of regular automorpshims of a toral variety $X$. We prove that if $T$ is a maximal torus in $\mathrm{Aut}(X)$, then $X$ is a direct product $Y\times T$, where $Y$ is a toral variety with a trivial maximal torus in the automorphism group. We show that knowing $\mathrm{Aut}(Y)$, one can compute $\mathrm{Aut}(X)$. In the case when the rank of the group $\mathbb{K}[Y]/\mathbb{K}^$ is $\dim Y + 1$, the group $\mathrm{Aut}(Y)$ can be described explicitly.