Maps with No a Priori Bounds

Communications in Mathematical Physics. 2025. Vol. 406. Article 141.

Blokh A., Levin G., Oversteegen L., Timorin V.

The modulus of a polynomial-like (PL) map is an important invariant that controls distortion of the straightening map and, hence, geometry of the corresponding PL Julia set. Lower bounds on the modulus, called complex a priori bounds, are known in a great variety of contexts. For any rational function we complement this by an upper bound for moduli of PL maps in the satellite case that depends only on the relative period and the degree of the PL map. This rules out a priori bounds in the satellite case with unbounded relative periods. We also apply our tools to obtain lower bounds for hyperbolic lengths of geodesics in the infinitely renormalizable case, and to show that moduli of annuli must converge to 0 for a sequence of arbitrary renormalizations, under several conditions all of which are shown to be necessary.

Keywords: рациональные функции, rational maps, Renormalization, ренормализация, голоморфная динамика, polynomial-like map, полиномиально-подобное отображение, holomorphic dynamics

Publication based on the results of: Geometry of algebraic varieties, derived categories, motives, and metrics of special holonomy (2025)