Symbolic Blowup algebras and invariants of certain monomial curves in an affine space

TL;DR

This paper characterizes the symbolic powers of certain monomial curve ideals, proves the Cohen-Macaulayness of their symbolic blowup algebras, and computes invariants for the case when the dimension is three.

Contribution

It provides explicit descriptions of symbolic powers for a class of monomial curves and establishes Cohen-Macaulayness of their symbolic blowup algebras, answering a question by S. Goto.

Findings

Symbolic powers are explicitly described for all n ≥ 1.

Symbolic blowup algebras are Cohen-Macaulay.

For d=3, computed resurgence, Waldschmidt constant, and Castelnuovo-Mumford regularity.

Abstract

Let $d \geq 2$ and $m\geq 1$ be integers such that $\gcd (d,m)=1.$ Let ${\mathfrak p}$ be the defining ideal of the monomial curve in ${\mathbb A}_{ \Bbbk{k}}^d$ parametrized by $(t^{n_1}, \ldots, t^{n_d})$ where $n_i = d + (i-1)m$ for all $i = 1, \ldots, d$. In this paper, we describe the symbolic powers ${\mathfrak p}^{(n)} $ for all $n \geq 1$. As a consequence we show that the symbolic blowup algebras ${\mathcal R}_s{({\mathfrak p})}$ and $G_{s}({\mathfrak p}) $ are Cohen-Macaulay. This gives a positive answer to a question posed by S.~Goto in \cite{goto}. We also discuss when these blowup algebras are Gorenstein. Moreover, for $d=3$, considering ${\mathfrak p}$ as a weighted homogeneous ideal, we compute the resurgence, the Waldschmidt constant and the Castelnuovo-Mumford regularity of ${\mathfrak p}^{(n)}$ for all $n \geq 1$. The techniques of this paper for computing ${\mathfrak p}^{(n)}$ are new and we hope that these will be useful to study the symbolic powers of other prime ideals.