A stable version of Harbourne's Conjecture and the containment problem for space monomial curves

Abstract

The symbolic powers $I^{(n)}$ of a radical ideal $I$ in a polynomial ring consist of the functions that vanish up to order $n$ in the variety defined by $I$. These do not necessarily coincide with the ordinary algebraic powers $I^n$, but it is natural to compare the two notions. The containment problem consists of determining the values of $n$ and $m$ for which $I^{(n)} \subseteq I^m$ holds. When $I$ is an ideal of height $2$ in a regular ring, $I^{(3)} \subseteq I^2$ may fail, but we show that this containment does hold for the defining ideal of the space monomial curve $(t^a, t^b, t^c)$. More generally, given a radical ideal $I$ of big height $h$, while the containment $I^{(hn-h+1)} \subseteq I^n$ conjectured by Harbourne does not necessarily hold for all $n$, we give sufficient conditions to guarantee such containments for $n \gg 0$.