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Scarcity of finite orbits for rational functions over a number field

Volume 190 / 2019

Jung Kyu Canci, Sebastian Troncoso, Solomon Vishkautsan Acta Arithmetica 190 (2019), 221-237 MSC: Primary 37P05, 37P35; Secondary 11D45. DOI: 10.4064/aa180210-4-12 Published online: 28 June 2019


Let $\phi $ be an endomorphism of degree $d\geq {2}$ of the projective line, defined over a number field $K$. Let $S$ be a finite set of places of $K$, including the archimedean places, such that $\phi $ has good reduction outside $S$. The article presents two main results. The first result is a bound on the number of $K$-rational preperiodic points of $\phi $ in terms of the cardinality of $S$ and the degree $d$ of $\phi $. This bound is quadratic in $d$, which is a significant improvement to all previous bounds in terms of $d$. The second result is that if there is a $K$-rational periodic point of period at least 2, then there exists a bound on the number of $K$-rational preperiodic points of $\phi $ that is linear in $d$.


  • Jung Kyu CanciMathematisches Institut
    Universität Basel
    Spiegelgasse 1
    CH-4051 Basel, Switzerland
  • Sebastian TroncosoMathematics Department
    Birmingham-Southern College
    Box 549032
    900 Arkadelphia Road
    Birmingham, AL 35254, U.S.A.
  • Solomon VishkautsanDepartment of Mathematics
    Bayreuth University
    Universitätsstraße 30
    95447 Bayreuth, Germany

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