Complete Intersections of Quadrics and the Weak Lefschetz Property

Abstract

We consider artinian algebras $A=\mathbb{C}[x_0,\dots ,x_m]/I$, with $I$ generated by a regular sequence of homogeneous forms of the same degree $d\ge 2$. We show that the multiplication by a general linear form from $A_{d-1}$ to $A_d$ is injective. We prove that the Weak Lefschetz Property holds for artinian complete intersection algebras as above, with $d=2$ and $m\le 4$. Apparently, this was previously known only for $m\le 3$. Although we are proposing only very limited progress towards the WLP conjecture for complete intersections, we hope that the methods of the present article can illustrate some geometrical aspects of the general problem.

Some improvements in the statement and the proof of Lemma 7. Case 1 in the proof of Theorem 1 provided with a new and more complete argument. Other minor improvements in the exposition