ATTRACTING CYCLES IN p-ADIC DYNAMICS AND HEIGHT BOUNDS FOR POST-CRITICALLY FINITE MAPS

A rational function φ(z) of degree d ≥ 2 with coefficients in an algebraically closed field is post-critically finite (PCF) if all of its critical points have finite forward orbit under iteration. We show that the collection of PCF rational functions is a set of bounded height in the moduli space of rational functions over the complex numbers, once the well-understood family known as flexible Lattès maps is excluded. As a consequence, there are only finitely many conjugacy classes of non-Lattès PCF rational maps of a given degree defined over any given number field. The key ingredient of the proof is a non-archimedean version of Fatou’s classical result that every attracting cycle of a rational function over C attracts a critical point.