Finiteness conjecture for Picard rank jumps in Lefschetz pencils

Let YP1\mathcal{Y}\to\mathbb{P}^1 be a Lefschetz pencil of degree-dd surfaces in P3\mathbb{P}^3, and let Ys\mathcal{Y}_s denote its fiber over sP1(C)s\in\mathbb{P}^1(\mathbb{C}). Assume d5d\geq 5.

Picard-rank finiteness conjecture. The Picard number of Ys\mathcal{Y}_s is greater than or equal to 22 for at most finitely many values of sP1(C)s\in\mathbb{P}^1(\mathbb{C}).

This is a special conjectural case involving zero-dimensional components and is described as beyond the authors' current understanding. It concerns finiteness of fibers with an extra Picard class in a Lefschetz pencil.

Sources & referencesView supporting material

Primary source

Gregorio Baldi, Bruno Klingler and Emmanuel Ullmo, “Non-density of the exceptional components of the Noether-Lefschetz locus”, arXiv:2312.11246 (2024).

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