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On \(a\)-fold products ideals of hyperplane arrangements. (English) Zbl 1542.13010

Let \(\mathbb K\) be a field of characteristic zero and let \(R = \mathbb K[x_1,\dots,x_k]\). Let \(\Sigma = \{ \ell_1,\dots,\ell_s\}\), where \(\ell_1,\dots,\ell_s\) are linear forms in \(R\), and we allow the possibility that some are proportional. Let \(s = |\Sigma|\). Define the ideal generated by \(a\)-fold products of \(\Sigma\) to be \(I_a(\Sigma) = \langle \ell_{i_1} \cdots \ell_{i_a} \ | \ 1 \leq i_1 < \dots < i_a \leq s \rangle\). We make the convention that \(I_0(\Sigma) = R\) and \(I_b(\Sigma) = 0\) for all \(b > s\). A conjecture of the author with Tohǎneanu and Xie states that the ideals generated by \(a\)-fold products of linear forms are of fiber type. Those authors proved it in the case of line arrangements in \(\mathbb P^2\) when \(a = |\Sigma |-2\). This conjecture was also verified by Garrousian, Simis and Tohǎneanu when \(\Sigma\) defines a hyperplane arrangement \(\mathcal A\) and \(a = |\mathcal A | - 1\). In this paper the author proves this conjecture in the case where \(\Sigma\) defines a hyperplane arrangement, \(\mathcal A\), in \(\mathbb P^{k-1}\) (so the linear forms are not proportional), with the additional assumption \(|\mathcal A | - a \geq k\). In this paper the author also proves a conjecture of Mantero, Miranda-Neto and Nagel on symbolic powers of ideals in the special case where the ideals are generated by \((|\mathcal A|-1)\)-fold products of linear forms and \(\mathcal A\) is a generic hyperplane arrangement.

MSC:

13D02 Syzygies, resolutions, complexes and commutative rings
14N20 Configurations and arrangements of linear subspaces
52C35 Arrangements of points, flats, hyperplanes (aspects of discrete geometry)
13A30 Associated graded rings of ideals (Rees ring, form ring), analytic spread and related topics
14Q99 Computational aspects in algebraic geometry

Software:

Macaulay2
Full Text: DOI

References:

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