Automorphism groups of non-normal affine toric surfaces

Abstract

We investigate the automorphism groups of non-normal affine toric surfaces. While the connected component of the automorphism group of a normal toric surface is always generated by the acting torus and root subgroups, we prove that this fails for non-normal surfaces in general. Specifically, we show that the property holds if the singular locus contains a one-dimensional torus orbit, but can fail if the singular locus is an isolated point. To illustrate this, we construct an explicit non-normal affine toric surface in $\mathbb{A}^4$ whose connected component of the identity is strictly larger than the subgroup generated by the torus and root automorphisms of the surface.