Abstract
We show that the metric structure of morphisms f:Y→X between quasi-smooth compact Berkovich curves over an algebraically closed field admits a finite combinatorial description. In particular, for a large enough skeleton Γ=(ΓY,ΓX) of f, the sets Nf,≥n of points of Y of multiplicity at least n in the fiber are radial around ΓY with the radius changing piecewise monomially along ΓY. In this case, for any interval l=[z,y]⊂Y connecting a point z of type 1 to the skeleton, the restriction f|l gives rise to a profile piecewise monomial function φy:[0,1]→[0,1] that depends only on the type 2 point y∈ΓY. In particular, the metric structure of f is determined by Γ and the family of the profile functions {φy} with y∈ΓY (2). We prove that this family is piecewise monomial in y and naturally extends to the whole Y. In addition, we extend the classical theory of higher ramification groups to arbitrary real-valued fields and show that φy coincides with the Herbrand function of H(y)/H(f(y)). This gives a curious geometric interpretation of the Herbrand function, which also applies to non-normal and even inseparable extensions.
Original language | American English |
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Pages (from-to) | 438-472 |
Number of pages | 35 |
Journal | Advances in Mathematics |
Volume | 317 |
DOIs | |
State | Published - 7 Sep 2017 |
Bibliographical note
Funding Information:This work was supported by the European Union Seventh Framework Programme (FP7/2007–2013) under grant agreement 268182.
Publisher Copyright:
© 2017 Elsevier Inc.
Keywords
- Berkovich curves
- Herbrand function
- Wild ramification