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arXiv · 2603.06203

Rational Preperiodic Points of Quadratic Rational Maps over $\mathbb{Q}$ with Nonabelian Automorphism Groups

Hasan Bilgili·Mohammad Sadek
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Abstract

Let $f:\mathbb{P}^1\to\mathbb{P}^1$ be a quadratic rational map defined over the rational field $\mathbb{Q}$ with nonabelian automorphism group. We prove that no such map has a $\mathbb{Q}$-rational periodic point with exact period $N\ge 4$. We also give an explicit parametrization of such maps that have $\mathbb{Q}$-rational periodic points of period $1$, $2$, and $3$. In addition, we show that the number of $\mathbb{Q}$-rational preperiodic points of such a map $f$ cannot exceed $6$. As a result, we completely classify all portraits of $\mathbb{Q}$-rational preperiodic points for quadratic rational maps defined over $\mathbb{Q}$ with nonabelian automorphism showing that there are exactly $5$ such portraits.

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Hasan Bilgili, Mohammad Sadek. 2026-03-06. Rational Preperiodic Points of Quadratic Rational Maps over $\mathbb{Q}$ with Nonabelian Automorphism Groups. https://arxiv.org/abs/2603.06203

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