Optimal Degenerations of K-unstable Fano threefolds

Minghao Miao; Linsheng Wang

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arXiv · 2401.13999

Optimal Degenerations of K-unstable Fano threefolds

Minghao Miao·Linsheng Wang

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Abstract

We explicitly determine the optimal degenerations of Fano threefolds $X$ in family No 2.23 of Mori-Mukai's list as predicted by the Hamilton-Tian conjecture. More precisely, we find a special degeneration $(\mathcal{X}, \xi_0)$ of $X$ such that $(\mathcal{X}_0, \xi_0)$ is weighted K-polystable, which is equivalent to $(\mathcal{X}_0, \xi_0)$ admitting a K\"ahler-Ricci soliton (KRS) by \cite{HL23} and \cite{BLXZ23}. Furthermore, we study the moduli spaces of $(\mathcal{X}_0, \xi_0)$. The $\mathbf{H}$-invariant of $X$ divides the natural parameter space into two strata, which leads to different moduli spaces of KRS Fano varieties. We show that one of them is isomorphic to the GIT-moduli space of biconic curves $C\subseteq \mathbb{P}^1\times \mathbb{P}^1$, and the other one is a single point.

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Minghao Miao, Linsheng Wang. 2024-01-25. Optimal Degenerations of K-unstable Fano threefolds. https://arxiv.org/abs/2401.13999

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