Modified Segre conjecture for fat points in arbitrary position

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Fix integers d≥2d\ge 2 and n>2n>2. Let S⊆PnS\subseteq {\mathbb P}^n be a finite collection of ss points, fix integers m1,…,msm_1,\dots,m_s, and set

Z:=∑i=1smipi.Z:=\sum_{i=1}^s m_i p_i.

Let w⁡(Z)\operatorname{w}(Z) be the total weight of ZZ, and for a linear subspace L⊆PnL\subseteq {\mathbb P}^n let w⁡L(Z)\operatorname{w}_L(Z) be the sum of the multiplicities of the points lying in LL. Modified Segre conjecture. Then h1(IZ(d))=0h^1(\mathcal I_Z(d))=0 if all the following conditions hold: w⁡(Z)≤nd+1\operatorname{w}(Z)\le nd+1; w⁡L(Z)≤d+1\operatorname{w}_L(Z)\le d+1 for each line L⊆PnL\subseteq {\mathbb P}^n; and, for every integer r=2,…,n−1r=2,\dots,n-1 and every rr-dimensional linear subspace L⊆PnL\subseteq {\mathbb P}^n, w⁡L(Z)≤rd+2\operatorname{w}_L(Z)\le rd+2, with the additional assumption h1(L,IZ∩L(d))=0h^1(L,\mathcal I_{Z\cap L}(d))=0 whenever w⁡L(Z)=rd+2\operatorname{w}_L(Z)=rd+2. This conjecture modifies Segre's conjecture for points in arbitrary position by imposing weight conditions on linear subspaces and a boundary cohomology condition. The supplied text presents examples and evidence but no resolution, so the conjecture remains open.

References

Primary source

Edoardo Ballico, Olivia Dumitrescu and Elisa Postinghel, “On Segre's bound for fat points in P^n”, arXiv:1504.05151 (2015).

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