Gale duality and homogeneous toric varieties

Abstract

A non-degenerate toric variety $X$ is called $S$-homogeneous if the subgroup of the automorphism group $\text{Aut}(X)$ generated by root subgroups acts on $X$ transitively. We prove that maximal $S$-homogeneous toric varieties are in bijection with pairs $(P,\mathcal{A})$, where $P$ is an abelian group and $\mathcal{A}$ is a finite collection of elements in $P$ such that $\mathcal{A}$ generates the group $P$ and for every $a\in\mathcal{A}$ the element $a$ is contained in the semigroup generated by $\mathcal{A}\setminus\{a\}$. We show that any non-degenerate homogeneous toric variety is a big open toric subset of a maximal $S$-homogeneous toric variety. In particular, every homogeneous toric variety is quasiprojective. We conjecture that any non-degenerate homogeneous toric variety is $S$-homogeneous.