English

Counting isomorphism classes of elliptic curves over $\mathbb{F}_q(t)$

Number Theory 2025-07-10 v1 Algebraic Geometry K-Theory and Homology

Abstract

We determine the precise number of isomorphism classes of elliptic curves over Fq(t)\mathbb{F}_q(t) with char(Fq)=3,2\text{char}(\mathbb{F}_q) = 3,2. The key idea is to obtain the exact unweighted number of rational points on the classifying stacks BQ12\mathcal{B} Q_{12}, BQ24\mathcal{B} Q_{24} and BZ\mathcal{B} Z, where Q12Q_{12} and Q24Q_{24} denote the dicyclic groups of orders 12 and 24, respectively, and ZZ denotes the non-reduced group scheme of order 2. This computation, inspired by the classical work of [de Jong] and performed via motivic height zeta functions of height moduli spaces constructed in [Bejleri-Park-Satriano], establishes a complete determination of the total number of isomorphism classes of rational points on M1,1\overline{\mathcal{M}}_{1,1} over any rational function field k(t)k(t) with perfect residue field char(k)0\text{char}(k) \ge 0.

Keywords

Cite

@article{arxiv.2507.06754,
  title  = {Counting isomorphism classes of elliptic curves over $\mathbb{F}_q(t)$},
  author = {Jun-Yong Park},
  journal= {arXiv preprint arXiv:2507.06754},
  year   = {2025}
}

Comments

13 pages; Comments very welcome!