Transience and thermodynamic formalism for infinitely branched interval maps

We study a one-parameter family of countably piecewise linear interval maps, which, although Markov, fail the `large image property'. This leads to conservative as well as dissipative behaviour for different maps in the family with respect to Lebesgue. We investigate the transition between these two types, and study the associated thermodynamic formalism, describing in detail the second order phase transitions (i.e. the pressure function is $C^1$ but not $C^2$ at the phase transition) that occur in transition to dissipativity. We also study the various natural definitions of pressure which arise here, computing these using elementary recurrence relations.Comment: Corrected the proof of the lower bound in Proposition 2 in the case $\lambda\leq 1/2

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.Comment: 26 pages, 5 figure

Topological invariance of the sign of the Lyapunov exponents in one-dimensional maps

We explore some properties of Lyapunov exponents of measures preserved by smooth maps of the interval, and study the behaviour of the Lyapunov exponents under topological conjugacy.Comment: 9 page

Wild attractors and thermodynamic formalism

Fibonacci unimodal maps can have a wild Cantor attractor, and hence be Lebesgue dissipative, depending on the order of the critical point. We present a one-parameter family $f_\lambda$ of countably piecewise linear unimodal Fibonacci maps in order to study the thermodynamic formalism of dynamics where dissipativity of Lebesgue (and conformal) measure is responsible for phase transitions. We show that for the potential $\phi_t = -t\log|f'_\lambda|$, there is a unique phase transition at some $t_1 \le 1$, and the pressure $P(\phi_t)$ is analytic (with unique equilibrium state) elsewhere. The pressure is majorised by a non-analytic $C^\infty$ curve (with all derivatives equal to 0 at $t_1 < 1$) at the emergence of a wild attractor, whereas the phase transition at $t_1 = 1$ can be of any finite order for those $\lambda$ for which $f_\lambda$ is Lebesgue conservative. We also obtain results on the existence of conformal measures and equilibrium states, as well as the hyperbolic dimension and the dimension of the basin of $\omega(c)$

The topological entropy of Banach spaces

We investigate some properties of (universal) Banach spaces of real functions in the context of topological entropy. Among other things, we show that any subspace of $C([0,1])$ which is isometrically isomorphic to $\ell_1$ contains a functions with infinite topological entropy. Also, for any $t \in [0, \infty]$, we construct a (one-dimensional) Banach space in which any nonzero function has topological entropy equal to $t$.Comment: The paper is going to appear at Journal of Difference Equations and Application