Asymptotic regularity of invariant chains of edge ideals

Abstract

We study chains of nonzero edge ideals that are invariant under the action of the monoid \({{\,\textrm{Inc}\,}}\) of increasing functions on the positive integers. We prove that the sequence of Castelnuovo–Mumford regularity of ideals in such a chain is eventually constant with limit either 2 or 3, and we determine explicitly when the constancy behavior sets in. This provides further evidence to a conjecture on the asymptotic linearity of the regularity of \({{\,\textrm{Inc}\,}}\)-invariant chains of homogeneous ideals. The proofs reveal unexpected combinatorial properties of \({{\,\textrm{Inc}\,}}\)-invariant chains of edge ideals.