Cohomological support varieties for monomial ideals

Abstract

Let $R$ be a local or positively graded ring with a regular presentation $R\cong Q/I$ where $I$ is a monomial ideal generated by $n$ elements on a regular sequence. In Briggs-Grifo-Pollitz (2025), the authors classify the cohomological support varieties ${\mathcal{V}}_R(R)$ for $n⩽5$. In this paper we extend their results to classify the varieties that can occur as ${\mathcal{V}}_R(R)$ for $n=6$. Moreover, we provide two families of rings, one realizing cohomological support varieties of unbounded codimension, the other realizing an unbounded number of components. Finally, we answer a question of Gintz (2026) about the varieties that occur as ${\mathcal{V}}_R(R)$ where $I$ is given by the edge ideal of a cycle.

32 pages. Comments welcome