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2. Algebraic, Complex and Differential Geometry and Topology

Families of curves on cones that give rise to components of the Hilbert scheme of curves

Hristo Iliev
Institute of Mathematics and Informatics of the Bulgarian Academy of Sciences, Sofia, Bulgaria

Abstract:

In the present report we consider curves on a cone that pass through its vertex and are also triple covers of the base of the cone that is is a general smooth curve of genus $\gamma$ and degree $e$ in $\mathbb{P}^{e-\gamma}$.

Using the free resolution of the ideal of such a curve found by Catalisano and Gimigliano, as well as a technique involving very flat families introduced by Ciliberto, we show that the deformations of such curves remain on cones over a deformation of the base curve.

This allows us to prove that for every $\gamma \geq 3$ and $e \geq 4\gamma + 5$ there exists a non-reduced component $\mathcal{H}$ of the Hilbert scheme $\mathcal{I}_{3e+1, 3e + 3\gamma, e-\gamma+1}$ of smooth curves of genus $3e + 3\gamma$ and degree $3e+1$ in $\mathbb{P}^{e-\gamma+1}$. We show that $\dim T_{[X]} \mathcal{H} = \dim \mathcal{H} + 1 = (e - \gamma + 1)^2 + 7e + 5$ for a general point $[X] \in \mathcal{H}$.

The reported results are based on arXiv:2302.08707 [math.AG]. The last develops an approach of the same authors aimed at constructing non-reduced components of the Hilbert scheme of curves in projective spaces of high dimension introduced in arXiv:2208.12470 [math.AG].