The degree of irrationality of most abelian surfaces is 4

Olivier Martin

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arXiv · 1911.00296

The degree of irrationality of most abelian surfaces is 4

Olivier Martin

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Abstract

The degree of irrationality of a smooth projective variety $X$ is the minimal degree of a dominant rational map $X\dashrightarrow \mathbb{P}^{\dim X}$. We show that if an abelian surface $A$ over $\mathbb{C}$ is such that the image of the intersection pairing $\text{Sym}^2NS(A)\to \mathbb{Z}$ does not contain $12$, then it has degree of irrationality $4$. In particular, a very general $(1,d)$-polarized abelian surface has degree of irrationality $4$ provided that $d\nmid 6$. This answers two questions of Yoshihara by providing the first examples of abelian surfaces with degree of irrationality greater than $3$ and showing that the degree of irrationality is not isogeny-invariant for abelian surfaces.

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Olivier Martin. 2019-11-01. The degree of irrationality of most abelian surfaces is 4. https://arxiv.org/abs/1911.00296

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