Abstract

Let $C$ be a hyperelliptic curve $y^2 = f(x)$ over a discretely valued field $K$. The $p$-adic distances between the roots of $f(x)$ can be described by a completely combinatorial object known as the cluster picture. We show that the cluster picture of $C$, along with the leading coefficient of $f$ and the action of $\mathrm{Gal}(\bar{K}/K)$ on the roots of $f$, completely determines the combinatorics of the special fibre of the minimal strict normal crossings model of $C$. In particular, we give an explicit description of the special fibre in terms of this data.

Highlights

  • Let C be a hyperelliptic curve y2 = f (x) over a discretely valued field K

  • Using cluster pictures we will calculate a combinatorial description of the minimal SNC model X of C/K: a model whose singularities on the special fibre Xk are normal crossings, and where blowing down any exceptional component of Xk would result in a worse singularity

  • The minimal SNC model of a hyperelliptic curve has a rather straightforward description: it consists of a central component with some tails whose multiplicities can be explicitly described using the results of Section 3.2

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Summary

Notation

For the convenience of the reader, the following two tables collate the general notation and terminology which we use throughout the paper. Whenever a component in a figure is drawn in bold it is a central component. In any figure describing the special fibre of a model numbers indicate multiplicities, except those preceded by g, which indicate the genus of a component.

Background — cluster pictures
Background — models
Chains of rational curves
Quotients of models
Semistable models
Background — models of curves via Newton polytopes
Newton polytopes
Calculating a model
Sloped chains
The automorphism and its orbits
Relation to Newton polytopes
The curve Cs
Calculating linking chains
The Newton polytope
Structure of the SNC model
Small distances
Main theorems
Orbits
The special fibre of the minimal SNC model
A more explicit description
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