English

Degrees of points on varieties over Henselian fields

Algebraic Geometry 2023-06-16 v2 Number Theory

Abstract

Let W/KW/K be a nonempty scheme over the field of fractions of a Henselian local ring RR. A result of Gabber, Liu and Lorenzini shows that the GCD of the set of degrees of closed points on WW (which is called the index of W/KW/K) can be computed from data pertaining only to the special fiber of a proper regular model of WW over RR. We show that the entire set of degrees of closed points on WW can be computed from data pertaining only to the special fiber, provided the special fiber is a strict normal crossings divisor. As a consequence we obtain an algorithm to compute the degree set of any smooth curve over a Henselian field with finite or algebraically closed residue field. Using this we show that degree sets of curves over such fields can be dramatically different than degree sets of curves over finitely generated fields. For example, while the degree set of a curve over a finitely generated field contains all sufficiently large multiples of the index, there are curves over pp-adic fields with index 11 whose degree set excludes all integers that are coprime to 66.

Keywords

Cite

@article{arxiv.2306.01267,
  title  = {Degrees of points on varieties over Henselian fields},
  author = {Brendan Creutz and Bianca Viray},
  journal= {arXiv preprint arXiv:2306.01267},
  year   = {2023}
}

Comments

19 pages; added additional references for degree sets over Hilbertian fields