Enumerating pencils with moving ramification on curves

Author:

Lian Carl

Abstract

We consider the general problem of enumerating branched covers of the projective line from a fixed general curve subject to ramification conditions at possibly moving points. Our main computations are in genus 1; the theory of limit linear series allows one to reduce to this case. We first obtain a simple formula for a weighted count of pencils on a fixed elliptic curve E E , where base-points are allowed. We then deduce, using an inclusion-exclusion procedure, formulas for the numbers of maps E P 1 E\to \mathbb {P}^1 with moving ramification conditions. A striking consequence is the invariance of these counts under a certain involution. Our results generalize work of Harris, Logan, Osserman, and Farkas-Moschetti-Naranjo-Pirola.

Publisher

American Mathematical Society (AMS)

Subject

Geometry and Topology,Algebra and Number Theory

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1. ℤ/rℤ-equivariant covers of ℙ1 with moving ramification;Israel Journal of Mathematics;2022-11-17

2. LINEAR SERIES ON GENERAL CURVES WITH PRESCRIBED INCIDENCE CONDITIONS;Journal of the Institute of Mathematics of Jussieu;2022-06-06

3. Hyperelliptic odd coverings;Israel Journal of Mathematics;2022-05-02

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