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Henk Bruin

Publications and source records attributed to Henk Bruin.

66 records · Page 4Linked to original sources
arXiv2008

Existence and convergence properties of physical measures for certain dynamical systems with holes

We study two classes of dynamical systems with holes: expanding maps of the interval and Collet-Eckmann maps with singularities. In both cases, we prove that there is a natural absolutely continuous conditionally invariant measure $μ$ (a.c.c.i.m.) with the physical property that strictly positive Hölder continuous functions converge to the density of $μ$ under the renormalized dynamics of the system. In addition, we construct an invariant measure $ν$, supported on the Cantor set of points that never escape from the system, that is ergodic and enjoys exponential decay of correlations for Hölder observables. We show that $ν$ satisfies an equilibrium principle which implies that the escape rate formula, familiar to the thermodynamic formalism, holds outside the usual setting. In particular, it holds for Collet-Eckmann maps with holes, which are not uniformly hyperbolic and do not admit a finite Markov partition. We use a general framework of Young towers with holes and first prove results about the \accim and the invariant measure on the tower. Then we show how to transfer results to the original dynamical system. This approach can be expected to generalize to other dynamical systems than the two above classes.

math.DS↗
arXiv2008

Equilibrium states for potentials with $\supϕ- \infϕ< \htop(f)$

In the context of smooth interval maps, we study an inducing scheme approach to prove existence and uniqueness of equilibrium states for potentials $ϕ$ with he `bounded range' condition $\sup ϕ- \inf ϕ< \htop$, first used by Hofbauer and Keller. We compare our results to Hofbauer and Keller's use of Perron-Frobenius operators. We demonstrate that this `bounded range' condition on the potential is important even if the potential is Hölder continuous. We also prove analyticity of the pressure in this context.

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arXiv2008

Equilibrium states for interval maps: the potential $-t\log |Df|$

Let $f:I \to I$ be a $C^2$ multimodal interval map satisfying polynomial growth of the derivatives along critical orbits. We prove the existence and uniqueness of equilibrium states for the potential $ϕ_t:x\mapsto -t\log|Df(x)|$ for $t$ close to 1, and also that the pressure function $t \mapsto P(ϕ_t)$ is analytic on an appropriate interval near $t = 1$.

math.DS↗
arXiv2008

Admissibility of kneading sequences and structure of Hubbard trees for quadratic polynomials

Hubbard trees are invariant trees connecting the points of the critical orbits of postcritically finite polynomials. Douady and Hubbard \cite{Orsay} introduced these trees and showed that they encode the essential information of Julia sets in a combinatorial way. The itinerary of the critical orbit within the Hubbard tree is encoded by a (pre)periodic sequence on $\{\0,\1\}$ called \emph{kneading sequence}. We prove that the kneading sequence completely encodes the Hubbard tree and its dynamics, and we show how to reconstruct the tree and in particular its branch points (together with their periods, their relative posititions, their number of arms and their local dynamics) in terms of the kneading sequence alone. Every kneading sequence gives rise to an abstract Hubbard tree, but not every kneading sequence occurs in real dynamics or in complex dynamics. Milnor and Thurston \cite{MT} classified which kneading sequences occur in real dynamics; we do the same for complex dynamics in terms of a complex \emph{admissibility condition}. This complex admissibility condition fails if and only if the abstract Hubbard tree has a so-called \emph{evil} periodic branch point that is incompatible with local homeomorphic dynamics on the plane.

math.DS↗
arXiv2006

Complex maps without invariant densities

We consider complex polynomials $f(z) = z^\ell+c_1$ for $\ell \in 2\N$ and $c_1 \in \R$, and find some combinatorial types and values of $\ell$ such that there is no invariant probability measure equivalent to conformal measure on the Julia set. This holds for particular Fibonacci-like and Feigenbaum combinatorial types when $\ell$ sufficiently large and also for a class of `long-branched' maps of any critical order.

math.DS↗
arXiv2006

Markov extensions and lifting measures for complex polynomials

For polynomials $f$ on the complex plane with a dendrite Julia set we study invariant probability measures, obtained from a reference measure. To do this we follow Keller in constructing canonical Markov extensions. We discuss ``liftability'' of measures (both $f$-invariant and non-invariant) to the Markov extension, showing that invariant measures are liftable if and only if they have a positive Lyapunov exponent. We also show that $δ$-conformal measure is liftable if and only if the set of points with positive Lyapunov exponent has positive measure.

math.DS↗
arXiv2005

Livsic Regularity For Markov Systems

We prove measurable Livsic theorems for dynamical systems modelled by Markov Towers. Our regularity results apply to solutions of cohomological equations posed on Henon-like mappings and a wide variety of nonuniformly hyperbolic systems. We consider both Holder cocycles and cocycles with singularities of prescribed order.

math.DS↗
arXiv2002

Decay of correlations in one-dimensional dynamics

We consider multimodal C^3 interval maps f satisfying a summability condition on the derivatives D_n along the critical orbits which implies the existence of an absolutely continuous f -invariant probability measure mu. If f is non-renormalizable, mu is mixing and we show that the speed of mixing (decay of correlations) is strongly related to the rate of growth of the sequence D_n as n tends to infinity . We also give sufficient conditions for mu to satisfy the Central Limit Theorem. This applies for example to the quadratic Fibonacci map which is shown to have subexponential decay of correlations.

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arXiv2000

Return time statistics via inducing

We prove that return time statistics of a dynamical system do not change if one passes to an induced (i.e. first return) map. We apply this to show exponential return time statistics in i) smooth interval maps with nowhere-dense critical orbits and ii) certain interval maps with neutral fixed points. The method also applies to iii) certain quadratic maps of the complex plane.

math.DS↗
arXiv1994

Absorbing Cantor sets in dynamical systems: Fibonacci maps

In this paper we shall show that there exists a polynomial unimodal map f: [0,1] -> [0,1] which is 1) non-renormalizable(therefore for each x from a residual set, $ω(x)$ is equal to an interval), 2) for which $ω(c)$ is a Cantor set, and 3) for which $ω(x)=ω(c)$ for Lebesgue almost all x. So the topological and the metric attractor of such a map do not coincide. This gives the answer to a question posed by Milnor.

math.DS↗