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* Starred papers have appeared in the journal cited.

Hang Fu, Hongming Nie
Böttcher coordinates at wild superattracting fixed points

Let p be a prime number, let g(x)=xp2+pr+2xp2+1 with r∈ℤ≥0, and let ϕ(x)=x+O(x2) be the Böttcher coordinate satisfying ϕ(g(x))=ϕ(x)p2. Salerno and Silverman conjectured that the radius of convergence of ϕ−1(x) in ℂp is p−p−r/(p−1). In this article, we confirm that this conjecture is true by showing that it is a special case of our more general result.


Mikhail Lyubich, Jacob Mazor, Sabyasachi Mukherjee
Antiholomorphic correspondences and mating I: realization theorems

In this paper, we study the dynamics of a general class of antiholomorphic correspondences; i.e., multi-valued maps with antiholomorphic local branches, on the Riemann sphere. Such correspondences are closely related to a class of single-valued antiholomorphic maps in one complex variable; namely, Schwarz reflection maps of simply connected quadrature domains. Using this connection, we prove that matings of all parabolic antiholomorphic rational maps with connected Julia sets (of arbitrary degree) and antiholomorphic analogues of Hecke groups can be realized as such correspondences. We also draw the same conclusion when parabolic maps are replaced with critically non-recurrent antiholomorphic polynomials with connected Julia sets.

David Martí-Pete, Lasse Rempe, James Waterman
Bounded Fatou and Julia components of meromorphic functions

Abstract: We completely characterise the bounded sets that arise as components of the Fatou and Julia sets of meromorphic functions. On the one hand, we prove that a bounded domain is a Fatou component of some meromorphic function if and only if it is regular. On the other hand, we prove that a planar continuum is a Julia component of some meromorphic function if and only if it has empty interior. We do so by constructing meromorphic functions with wandering continua using approximation theory.


Dzmitry Dudko, Mikhail Hlushchanka, Dierk Schleicher
A canonical decomposition of postcritically finite rational maps and their maximal expanding quotients

We provide a natural canonical decomposition of postcritically finite rational maps with non-empty Fatou sets based on the topological structure of their Julia sets. The building blocks of this decomposition are maps where all Fatou components are Jordan disks with disjoint closures (Sierpiński maps), as well as those where any two Fatou components can be connected through a countable chain of Fatou components with common boundary points (crochet or Newton-like maps). We provide several alternative characterizations for our decomposition, as well as an algorithm for its effective computation. We also show that postcritically finite rational maps have dynamically natural quotients in which all crochet maps are collapsed to points, while all Sierpiński maps become small spheres; the quotient is a maximal expanding cactoid. The constructions work in the more general setup of Böttcher expanding maps, which are metric models of postcritically finite rational maps.


Russell Lodge, Yusheng Luo, Sabyasachi Mukherjee
On Deformation Space Analogies between Kleinian Reflection Groups and Antiholomorphic Rational Maps

In a previous paper, we constructed an explicit dynamical correspondence between certain Kleinian reflection groups and certain anti-holomorphic rational maps on the Riemann sphere. In this paper, we show that their deformation spaces share many striking similarities. We establish an analogue of Thurston's compactness theorem for critically fixed anti-rational maps. We also characterize how deformation spaces interact with each other and study the monodromy representations of the union of all deformation spaces.


Dzmitry Dudko, Mikhail Lyubich
Uniform a priori bounds for neutral renormalization

We prove uniform a priori bounds for Siegel disks of bounded type that give a uniform control of oscillations of their boundaries in all scales. As a consequence, we construct the Mother Hedgehog for any quadratic polynomial with a neutral periodic point.


Jan Kiwi, Hongming Nie
The basin of infinity of tame polynomials

Let ℂv be a characteristic zero algebraically closed field which is complete with respect to a non-Archimedean absolute value. We provide a necessary and sufficient condition for two tame polynomials in ℂv[z] of degree d≥2 to be analytically conjugate on their basin of infinity. In the space of monic centered polynomials, tame polynomials with all their critical points in the basin of infinity form the tame shift locus. We show that a tame map f∈ℂv[z] is in the closure of the tame shift locus if and only if the Fatou set of f coincides with the basin of infinity.



Hongming Nie
Nonarchimedean Lyapunov exponents of polynomials

Let K be an algebraically closed and complete nonarchimedean field with characteristic 0 and let f∈K[z] be a polynomial of degree d≥2. We study the Lyapunov exponent L(f,μ) of f with respect to an f-invariant and ergodic Radon probability measure μ on the Berkovich Julia set of f and the lower Lyapunov exponent L−f(f(c)) of f at a critical value f(c). Under an integrability assumption, we show L(f,μ) has a lower bound only depending on d and K. In particular, if f is tame and has no wandering nonclassical Julia points, then L(f,μ) is nonnegative; moreover, if in addition f possesses a unique Julia critical point c0, we show L−f(f(c0)) is also nonnegative.


Yusheng Luo, Insung Park
Polynomials with core entropy zero

This paper studies polynomials with core entropy zero. We give several characterizations of polynomials with core entropy zero. In particular, we show that a degree d post-critically finite polynomial f has core entropy zero if and only if f is in the degree d main molecule. The characterizations define several quantities which measure the complexities of polynomials with core entropy zero. We show that these measures are all comparable.


Shengyuan Zhao
Birational Kleinian groups

In this paper we initiate the study of birational Kleinian groups, i.e.\ groups of birational transformations of complex projective varieties acting in a free, properly discontinuous and cocompact way on an open set of the variety with respect to the usual topology. We obtain a classification in dimension two.