The weak Lefschetz property of Gorenstein algebras of codimension three associated to the Ap\'ery sets

TL;DR

This paper investigates the weak Lefschetz property of Gorenstein algebras associated with Apéry sets of symmetric numerical semigroups, providing new cases where the property holds, thus contributing to the conjecture for codimension three algebras.

Contribution

It proves the weak Lefschetz property for specific classes of Gorenstein algebras related to Apéry sets, expanding known cases beyond complete intersections.

Findings

Weak Lefschetz property holds for certain parameter ranges.

Identifies cases where the property is guaranteed, including small values of generators.

Supports the conjecture that all such algebras have the weak Lefschetz property.

Abstract

It has been conjectured that {\it all} graded Artinian Gorenstein algebras of codimension three have the weak Lefschetz property over a field of characteristic zero. In this paper, we study the weak Lefschetz property of associated graded algebras $A$ of the Ap\'ery set of $M$-pure symmetric numerical semigroups generated by four natural numbers. In 2010, Bryant proved that these algebras are graded Artinian Gorenstein algebras of codimension three. In a recent article, Guerrieri showed that if $A$ is not a complete intersection, then $A$ is of form $A=R/I$ with $R=K[x,y,z]$ and \begin{align*} I=(x^a, y^b-x^{b-\gamma} z^\gamma, z^c, x^{a-b+\gamma}y^{b-\beta}, y^{b-\beta}z^{c-\gamma}), \end{align*} where $ 1\leq \beta\leq b-1,\; \max\{1, b-a+1 \}\leq \gamma\leq \min \{b-1,c-1\}$ and $a\geq c\geq 2$. We prove that $A$ has the weak Lefschetz property in the following cases: (a) $ \max\{1,b-a+c-1\}\leq \beta\leq b-1$ and $\gamma\geq \lfloor\frac{\beta-a+b+c-2}{2}\rfloor$; (b) $ a\leq 2b-c$ and $| a-b| +c-1\leq \beta\leq b-1$; (c) one of $a,b,c$ is at most five.