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Explicit bound for singularities on toric fibrations

Author:
Bingyi Chen
Keyword:
Mathematics, Algebraic Geometry, Algebraic Geometry (math.AG)
journal:
--
date:
2023-11-01 16:00:00
Abstract
It was conjectured by McKernan and Shokurov that for any Fano contraction $f:X \to Z$ of relative dimension $r$ with $X$ being $\epsilon$-lc, there is a positive $\delta$ depending only on $r,\epsilon$ such that $Z$ is $\delta$-lc and the multiplicity of the fiber of $f$ over a codimension one point of $Z$ is bounded above by $1/\delta$. Recently, this conjecture was confirmed by Birkar. In this paper, we give an explicit value for $\delta$ in terms of $\epsilon,r$ in the toric case, which belongs to $O(\epsilon^{2^r})$ as $\epsilon \to 0$. When $r=2$, the order $O(\epsilon^4)$ is optimal by an example given by Alexeev and Borisov.
PDF: Explicit bound for singularities on toric fibrations.pdf
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