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Arnaud Cheritat

Publications and source records attributed to Arnaud Cheritat.

10 recordsLinked to original sources
arXiv2019

Location of Siegel capture polynomials in parameter spaces

A cubic polynomial $f$ with a periodic Siegel disk containing an eventual image of a critical point is said to be a \emph{Siegel capture polynomial}. If the Siegel disk is invariant, we call $f$ a \emph{IS-capture polynomial} (or just an IS-capture; IS stands for Invariant Siegel). We study the location of IS-capture polynomials in the parameter space of all cubic polynomials and show that any IS-capture is on the boundary of a unique hyperbolic component determined by the rational lamination of the map. We also relate IS-captures to the cubic Principal Hyperbolic Domain and its closure (by definition, the \emph{cubic Principal Hyperbolic Domain} consists of cubic hyperbolic polynomials with Jordan curve Julia sets) and prove that, in the slice of cubic polynomials given by a fixed multiplier at one of the fixed points, the closure of the cubic principal hyperbolic domain might possibly only have bounded complementary domains $U$ such that (1) critical points of $f\in U$ are distinct and belong to $J(f)$, and (2) $J(f)$ has positive Lebesgue measure and carries an invariant line field.

math.DS↗
arXiv2008

Quadratic Julia Sets with Positive Area

We prove the existence of quadratic polynomials having a Julia set with positive Lebesgue measure in three cases: the presence of a Cremer fixed point, the presence of a Siegel disk, the presence of infinitely many (satellite) renormalizations.

math.DS↗
arXiv2006

A new proof of a conjecture of Yoccoz, Remarks, New results

We give a new proof of the following conjecture of Yoccoz: the sum of the logarithm of the conformal radius of fixed Siegel disks of monic quadratic polynomials and of the Brjuno function of their rotation number is bounded from above. In a former article we obtained a first proof based on the control of parabolic explosion. Here, we present a more elementary proof based on Yoccoz's initial methods. We then extend this result to some new families of polynomials such as unicritical ones. We also show that the conjecture does not hold for some other families of polynomials.

math.DS↗
arXiv2004

Ghys-like models providing trick for a class of simple maps

For quadratic polynomials with an indifferent fixed point with bounded type rotation number (they have a Siegel disk), much of what is known of their Julia set comes from the study of a quasiconformal model. The model is build from a Blaschke fraction, that we call a pre-model, and that is given by a formula. We give here a geometric construction of pre-model maps, that extends to some cases where no formula is known. More precisely, we are able to make this work for a class of entire maps, very specific but nonetheless spanning uncountably many equivalence classes (thus with probably no hope for a formula), and also in the case of the Lavaurs maps that arise in the parabolic implosion of quadratic polynomials.

math.DS↗
arXiv2004

The Brjuno function continuously estimates the size of quadratic Siegel disks

If alpha is an irrational number, we define Yoccoz's Brjuno function Phi by Phi(alpha)=sum_{n geq 0} alpha_0*alpha_1*...*alpha_{n-1}*log(1/alpha_n), where alpha_0 is the fractional part of alpha and alpha_{n+1} is the fractional part of 1/alpha_n. The numbers alpha such that Phi(alpha) e^{2i pi alpha}z+z^2 has an indifferent fixed point at the origin. If P_alpha is linearizable, we let r(alpha) be the conformal radius of the Siegel disk and we set r(alpha)=0 otherwise. Yoccoz proved that Phi(alpha)=infty if and only if r(alpha)=0 and that the restriction of alpha -> Phi(alpha)+log r(alpha) to the set of Brjuno numbers is bounded from below by a universal constant. We proved that it is also bounded from above by a universal constant. In fact, Marmi, Moussa and Yoccoz conjecture that this function extends to $R$ as a Hölder function of exponent 1/2. In this article, we prove that there is a continuous extension to $R$.

math.DS↗
arXiv2003

Quadratic Siegel Disks with Rough Boundaries

In the quadratic family (the set of polynomials of degree 2), Petersen and Zakeri proved the existence of Siegel disks whose boundaries are Jordan curves, but not quasicircles. In their examples, the critical point is contained in the curve. In the first part, we prove the existence of quadratic examples that do not contain the critical point. In the second part, using a more abstract point of view (suggested by Avila), we show that we can control quite precisely the degree of regularity of the boundary of the quadratic Siegel disks we create by perturbations. For instance there exists examples where the boundary is C^n but not C^{n+1}.

math.DS↗
arXiv2003

Cage de Faraday

We prove that the difference between 1 and the conformal radius at 0 of the universal covering of a big open subset U of the unit disk in the complex plane is comparable to the area of a union of triangles constucted from the complement of U. We apply this to corret a lemma in the thesis of the author. ----- Nous prouvons que la difference entre 1 et le rayon conforme en 0 du revetement universel d'un grand ouvert U du disque unite du plan complexe est comparable a l'aire d'une reunion de triangles construits a partir du complementaire de U. Nous appliquons cela a la correction d'un lemme de la these de l'auteur.

math.DS↗
arXiv2003

On the Size of Quadratic Siegel Disks: Part I

If $\a$ is an irrational number, we let $\{p_n/q_n\}_{n\geq 0}$, be the approximants given by its continued fraction expansion. The Bruno series $B(\a)$ is defined as $$B(\a)=\sum_{n\geq 0} \frac{\log q_{n+1}}{q_n}.$$ The quadratic polynomial $P_\a:z\mapsto e^{2iπ\a}z+z^2$ has an indifferent fixed point at the origin. If $P_\a$ is linearizable, we let $r(\a)$ be the conformal radius of the Siegel disk and we set $r(\a)=0$ otherwise. Yoccoz proved that if $B(\a)=\infty$, then $r(\a)=0$ and $P_\a$ is not linearizable. In this article, we present a different proof and we show that there exists a constant $C$ such that for all irrational number $\a$ with $B(\a)<\infty$, we have $$B(\a)+\log r(\a) < C.$$ Together with former results of Yoccoz (see \cite{y}), this proves the conjectured boundedness of $B(\a)+\log r(\a)$.

math.DS↗