English

Arithmetic exceptionality of Latt\`{e}s maps

Number Theory 2026-03-27 v1

Abstract

Let Fq\mathbb{F}_q denote a finite field of order qq. A rational function r(x)Q(x)r(x)\in \mathbb{Q}(x) is said to be arithmetically exceptional if it induces a permutation on P1(Fp)\mathbb{P}^1(\mathbb{F}_p) for infinitely many primes pp. Based on some computational results, Odaba\c{s} conjectured that for each kNk\in \mathbb{N}, the kk-th Latt\`{e}s map attached to an elliptic curve E/QE/\mathbb{Q} is arithmetically exceptional if and only if EE has no kk-torsion point whose xx-coordinate is rational. In this paper, we prove that this conjecture is true for any elliptic curve E/QE/\mathbb{Q} having complex multiplication by an imaginary quadratic field other than Q(11).\mathbb{Q}(\sqrt{-11}). On the other hand, we show that the conjecture becomes invalid if EE has CM by Q(11)\mathbb{Q}(\sqrt{-11}) and 6k6\mid k. Partial results for non-CM elliptic curves are also given.

Keywords

Cite

@article{arxiv.2603.25014,
  title  = {Arithmetic exceptionality of Latt\`{e}s maps},
  author = {Chatchawan Panraksa and Detchat Samart and Songpon Sriwongsa},
  journal= {arXiv preprint arXiv:2603.25014},
  year   = {2026}
}

Comments

22 pages

R2 v1 2026-07-01T11:38:28.201Z