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Pascale Roesch

Publications and source records attributed to Pascale Roesch.

14 recordsLinked to original sources
arXiv2026

Biggest bounded type Siegel disks of monic polynomials include those that stick to all critical points

We prove that for all degree $d\geq 2$ and all bounded type irrational $\theta$, in the space of monic polynomials having a period $1$ Siegel disk $\Delta$ of rotation number $\theta$, the maximum locus of the conformal radius of $\Delta$ with respect to its fixed point contains polynomials having all critical points on the boundary of $\Delta$. We apply this to reduce a conjecture of Douady (optimality of the Bruno condition) to a weaker statement.

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arXiv2025

Some invariant classes for parabolic renormalization in the multicritical case

Parabolic renormalization associates to a holomorphic map f with a parabolic fixed point another holomorphic map with a parabolic fixed point. This procedure is essential for understanding the phenomenon of parabolic enrichment, which occurs when one perturbs f appropriately. Shishikura defined in [Shi98] (see also [LY14]) a class of maps that is stable under this parabolic renormalization operator. These maps have only one critical point in their immediate basins. We extend here this result to the more general classes of maps conjugated on their immediate basins to finite Blaschke products. For these classes, we introduce an analogue of Milnor's mapping schemes [Mil12] and describe the action of parabolic renormalization on the scheme. This shall be a starting point to the fine study of perturbation of these bigger classes of maps.

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arXiv2024

The Parabolic Mandelbrot Set

We solve the longstanding conjecture by Milnor (1993) concerning the connectedness locus $M_1$ of the family of quadratic rational maps tangent to the identity at $\infty$. We prove that this locus in homeomorphic to the Mandelbrot set $M$ and that the homeomorphism is unique, provided it identifies maps that are "hybridly" conjugate on their filled-in Julia set. Moreover this homeomorphism from $M$ to $M_1$ is nowhere Hölder on the boundary and so can not have even locally a quasi-conformal extension to complements.

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arXiv2024

Connected McMullen-like Julia sets in a Chebyshev-Halley Family

In this paper we study a one parameter family of rational maps obtained by applying the Chebyshev-Halley root finding algorithms. We show that the dynamics near parameters where the family presents some degeneracy might be understood from the point of view of singular perturbations. More precisely, we relate the dynamics of those maps with the one of the McMullen family $M_{\lambda}(z)=z^4 + \lambda /z^2$, using quasi-conformal surgery.

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arXiv2023

Rigidity of non-renormalizable Newton maps

Non-renormalizable Newton maps are rigid. More precisely, we prove that their Julia set carries no invariant line fields and that the topological conjugacy is equivalent to quasi-conformal conjugacy in this case.

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arXiv2018

Julia sets with a wandering branching point

According to the Thurston No Wandering Triangle Theorem, a branching point in a locally connected quadratic Julia set is either preperiodic or precritical. Blokh and Oversteegen proved that this theorem does not hold for higher degree Julia sets: there exist cubic polynomials whose Julia set is a locally connected dendrite with a branching point which is neither preperiodic nor precritical. In this article, we reprove this result, constructing such cubic polynomials as limits of cubic polynomials for which one critical point eventually maps to the other critical point which eventually maps to a repelling fixed point.

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arXiv2016

Moduli space of cubic Newton maps

In this article, we study the topology and bifurcations of the moduli space $\mathcal{M}_3$ of cubic Newton maps. It's a subspace of the moduli space of cubic rational maps, carrying the Riemann orbifold structure $(\mathbb{\widehat{C}}, (2,3,\infty))$. We prove two results: (1). The boundary of the unique unbounded hyperbolic component is a Jordan arc and the boundaries of all other hyperbolic components are Jordan curves. (2).The Head's angle map is surjective and monotone. The fibers of this map are characterized completely. The first result is a moduli space analogue of the first author's dynamical regularity theorem \cite{Ro08}. The second result confirms a conjecture of Tan Lei.

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arXiv2014

Newton maps as matings of cubic polynomials

In this paper we prove existence of matings between a large class of renormalizable cubic polynomials with one fixed critical point and another cubic polynomial having two fixed critical points. The resulting mating is a Newton map. Our result is the first part towards a conjecture by Tan Lei, stating that all (cubic) Newton maps can be described as matings or captures.

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arXiv2012

Hyperbolic components of McMullen maps

In this article, we study the hyperbolic components of McMullen maps. We show that the boundaries of all hyperbolic components are Jordan curves. This settles a problem posed by Devaney. As a consequence, we show that cusps are dense on the boundary of the unbounded hyperbolic component. This is a dynamical analogue of McMullen's theorem that cusps are dense on the Bers' boundary of Teichmüller space.

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arXiv2010

Carrots for dessert

Carrots for dessert is the title of a section of the paper `On polynomial-like mappings' by Douady and Hubbard. In that section the authors define a notion of dyadic carrot fields of the Mandelbrot set M and more generally for Mandelbrot like families. They remark that such carrots are small when the dyadic denominator is large, but they do not even try to prove a precise such statement. In this paper we formulate and prove a precise statement of asymptotic shrinking of dyadic Carrot-fields around M. The same proof carries readily over to show that the dyadic decorations of copies M' of the Mandelbrot set M inside M and inside the parabolic Mandelbrot set shrink to points when the denominator diverge to infinity.

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arXiv2007

Cubic polynomials with a parabolic point

We consider the family of cubic polynomials with a simple parabolic fixed point. We prove that the boundary of the immediate basin of attraction of the parabolic point is a Jordan curve and give a description of the dynamics.

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arXiv2006

Hyperbolic components of polynomials with a fixed critical point of maximal order

For the study of the 2-dimensional space of cubic polynomials, J. Milnor considers the complex 1-dimensional slice S_n of the cubic polynomials which have a super-attracting orbit of period n. He gives in [M4] a detailed conjectural picture of S_n. In this article, we prove these conjectures for S_1 and generalize these results in higher degrees. In particular, this gives a description of the closures of the hyperbolic components and of the Mandelbrot copies sitting in the connectedness locus. We prove that the closure of hyperbolic components is a Jordan curve, the points of which are characterized according to their dynamical behaviour. The global picture of the connectedness locus is a closed disk together with ``limbs'' sprouting off at the cusps of Mandelbrot copies and whose diameter tends to 0 (which corresponds to the Yoccoz inequality in the quadratic case). [[M4] J. Milnor - On cubic polynomials with periodic critical point, preprint (1991).]

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