The talks take place on Tuesdays at 15h (BCN time, CET) at T2 (Universitat de Barcelona).

Coming talks

  • July 11, 2024, 15h
    Xavier Jarque
    (Universitat de Barcelona)
    Title: Old and new results in dynamical systems
    Abstract: I will talk about old results on interval dynamics and new results on holomorphic dynamics.

Past talks (2023/24)

  • May 14, 2024, 15h
    Lasse Rempe
    (The University of Liverpool)
    Title: Wandering dynamics of entire functions
    Abstract: Let f be a transcendental entire or meromorphic function. A compact set K is called wandering if any two forward iterates of K under f are disjoint from each other. In this talk, we discuss which wandering dynamics can be realised entire and meromorphic functions.

    I will begin by motivating the problem, and then present our main result, which states effectively that, for any sequence of compact sets and holomorphic maps between them, the behaviour of this sequence can be realised by the orbit of a wandering compactum of a transcendental meromorphic function. If each of the compact sets is full (that is, its complement in the plane is connected), then the function can be chosen to be entire.

    The results are proved using approximation theory. This is joint work with Vasiliki Evdoridou and David Martí-Pete.

  •  
  • May 7, 2024, 15h

    Jordi Canela (Universitat Jaume I)
    Title: Numerical analysis of parameter planes with several critical points
    Abstract:  When studying a family of rational maps depending on one parameter it is convenient to draw a parameter plane to better understand the dynamics of the maps. However, it may happen that such maps have several free critical points. In this talk we will discuss different options for drawing parameter planes in this situation and we will explain the advantatges and inconvenients of each option. We will focus on the drawing of parameter planes of polynomials and families of rational maps arising from root-finding algorithms.

  • April 30, 2024, 15h

    Xavier Jarque (Universitat de Barcelona)
    Title: Chaotic dynamics at the boundary of an attracting basin via non transversal intersections for a non global smooth diffeomorphism
    Abstract:   In this talk we study the existence of transversal homoclinic points for a family of smooth  maps in $\mathbb R^2$ with no global smooth inverse which come out as a truncated map governing the local dynamics of a critical period three cycle associated to the Secant map. Using Moser-Birkoff-Smale's Theorem, we show that the boundary of the basin of attraction of the origin of $T_d$ contains a Cantor-like invariant subset whose restricted dynamics is conjugated to the full shift of 2-symbols.

  • April 19, 2024, 15.30h

    Luka Boc Thaler (University of Ljubljana)
    Title: Dynamics of skew-products tangent to the identity
    Abstract:  We will look at the family maps  P_b(z,w) = (z + z^2, w + w^2 + bz^2) with b\in\mathbb{C}. We will see that already such simple family of maps exabits a rich variety of dynamical behaviors, in particular for certain values b>1/4 we get wandering domains. Also we will see that there infinitely many parameters b_n converging to ¼ , for which maps P_{b_n} are not topologically conjugate to each other. In particular this implies that the family P_b is not structuraly stable at b=1/4.

  • April 16, 2024, 15h

    This email address is being protected from spambots. You need JavaScript enabled to view it. (Universitat de Barcelona)
    Title: An approximation technique based on Hörmander’s solution to the dbar-equation (III)
    Abstract:  In this third talk, we will cover two applications of the technique. First, we will show how to use it to construct maps with fast escaping wandering domains. Second, we will discuss an approximate answer to Erdős's question about maximum modulus points.

  • April 9, 2024, 15h

    This email address is being protected from spambots. You need JavaScript enabled to view it. (Universitat de Barcelona)
    Title: An approximation technique based on Hörmander’s solution to the dbar-equation (II)
    Abstract:  In this series of talks, we aim to explore a technique, based on a theorem of Hörmander, to construct entire functions with prescribed features. In this first talk, we shall review some background material, present the main theorem, and provide an outline of the method.

  • April 2, 2024, 15h

    This email address is being protected from spambots. You need JavaScript enabled to view it. (Universitat de Barcelona)
    Title: An approximation technique based on Hörmander’s solution to the dbar-equation (I)
    Abstract:  In this series of talks, we aim to explore a technique, based on a theorem of Hörmander, to construct entire functions with prescribed features. In this first talk, we shall review some background material, present the main theorem, and provide an outline of the method.

  • March 19, 2024, 15h

    This email address is being protected from spambots. You need JavaScript enabled to view it. (Universitat de Barcelona)
    Title: Mixing and ergodicity for compositions of inner functions.
    Abstract: Thanks to the work of Aaronson, Doering and Mañé, Crazier, and many others, we know that the properties of an inner function and its dynamics in the unit disc are closely related to the dynamics of its boundary extension. If, however, we consider compositions of inner functions, i.e. non-autonomous dynamics in the unit disc, much less is known about its relation to the corresponding non-autonomous dynamical system on the unit circle given by composing the boundary extensions. In this talk, we will tackle this problem from the point of view of ergodicity. We will derive necessary and sufficient conditions for a composition of inner functions fixing the origin to be ergodic on the unit circle, construct examples and counterexamples, and discuss some consequences of ergodicity. Time allowing, we will also explore mixing of compositions of inner functions, strengthening a result of Pommerenke and discussing what the correct definition of mixing is in the non-autonomous context. This is joint work with Artur Nicolau.

  • March 12, 2024, 15h
    Núria Fagella (Universitat de Barcelona) 
    T
    itle: Grand orbit relations in wandering domains (II).
    Abstract: We consider dynamical systems generated by the iteration of a complex entire map with an essential singularity at infinity. We say that two points are in the same Grand Orbit, if they are eventually iterated to the same point, even if the number of iterates needed are different for each of them. Grand orbits induce and equivalent relation in the complex plane, where two points belong to the same class if they belong to the same Grand Orbit. 

    Motivated by the work of McMullen and Sullivan in 98 to to study the Teichmuller space of a rational map, we study the nature of Grand Orbit relations in stable components, specially in those specific for entire transcendental maps (Baker and wandering domains). We will show that all grand orbit relations are discrete or all are indiscrete, when considering connected components of the stable set minus the closure of marked points. We will also give an example of a wandering component, on which discrete and indiscrete grand orbits coexist, something that never occurs for stable components of rational maps.
    This talk is based in joint work with Christian Henriksen in '06 and '09, and in work in progress with Vasiliki Evdoridou, Lukas Geyer and Leticia Pardo.

  • March 5, 2024, 15:30
    Núria Fagella (Universitat de Barcelona) 
    T
    itle: Grand orbit relations in wandering domains (I).
    Abstract: We consider dynamical systems generated by the iteration of a complex entire map with an essential singularity at infinity. We say that two points are in the same Grand Orbit, if they are eventually iterated to the same point, even if the number of iterates needed are different for each of them. Grand orbits induce and equivalent relation in the complex plane, where two points belong to the same class if they belong to the same Grand Orbit. 

    Motivated by the work of McMullen and Sullivan in 98 to to study the Teichmuller space of a rational map, we study the nature of Grand Orbit relations in stable components, specially in those specific for entire transcendental maps (Baker and wandering domains). We will show that all grand orbit relations are discrete or all are indiscrete, when considering connected components of the stable set minus the closure of marked points. We will also give an example of a wandering component, on which discrete and indiscrete grand orbits coexist, something that never occurs for stable components of rational maps.
    This talk is based in joint work with Christian Henriksen in '06 and '09, and in work in progress with Vasiliki Evdoridou, Lukas Geyer and Leticia Pardo.

  • February 27, 2024, 15:30
    Leticia Pardo Simón (Universitat de Barcelona) 
    T
    itle:  Wandering domains with nearly bounded orbits.
    Abstract: In this talk, I will explain how to construct a bounded wandering domain with the property that, in a sense, we will make precise, nearly all of its forward iterates are contained within a bounded domain. This is based on joint work with D. Sixsmith.
  • February 8, 2024, 15:30
    Anna Miriam Benini (University of Parma) 
    T
    itle:  Entire maps with measures of maximal entropy whose support is the Julia set.
    Abstract: We will see how to obtain measures with infinite entropy for several classes of entire maps, whose support is all of the Julia set. This is joint work with Leandro Arosio, Han Peters, and John Erik Fornaess.
  • December 20, 2023, 9:30
    This email address is being protected from spambots. You need JavaScript enabled to view it.
    (Universitat de Barcelona)
    T
    itle: Local connectivity of boundaries of Fatou Components V
    Abstract: In the talk, I will re-prove the famous result of Roesch and Yin about local connectivity of boundaries of bounded Fatou components of polynomials (except Siegel). For this, I will present techniques of puzzles and generalized renormalizations (box mappings) and will show how to use these techniques to get the result. All necessary background will be provided.
  • December 14, 2023, 12:15
    This email address is being protected from spambots. You need JavaScript enabled to view it.
    (University College Dublin)
    T
    itle: Optimal constants for bounds on the Hausdorff dimension of some quadratic Julia sets. 
    Abstract: In recently published work, joint with J. Graczyk and N. Mihalache, we proved some asymptotic estimates for the Hausdorff dimension of quadratic Julia sets as one approaches the parameter -2 (the leftmost tip of the Mandelbrot set), inside a large subset of the real line: the dimension behaved  $\approx 1 + const.\sqrt{c+2}$. In the meantime, L. Jaksztas conjectured the value of the optimal constant.
    Combining techniques from thermodynamic formalism with a more refined inducing argument, we obtain a proof for the optimal constant. Moreover, we extend our lower bound estimates to a fat cusp of complex parameters. 
  • December 1, 2023, 14:00
    This email address is being protected from spambots. You need JavaScript enabled to view it.
    (Universitat de Barcelona)
    T
    itle: Local connectivity of boundaries of Fatou components IV
    Abstract: In the talk, I will re-prove the famous result of Roesch and Yin about local connectivity of boundaries of bounded Fatou components of polynomials (except Siegel). For this, I will present techniques of puzzles and generalized renormalizations (box mappings) and will show how to use these techniques to get the result. All necessary background will be provided.
  • November 24, 2023, 14:00
    This email address is being protected from spambots. You need JavaScript enabled to view it.
    (Universitat de Barcelona)
    T
    itle: Local connectivity of boundaries of Fatou components III
    Abstract: In the talk, I will re-prove the famous result of Roesch and Yin about local connectivity of boundaries of bounded Fatou components of polynomials (except Siegel). For this, I will present techniques of puzzles and generalized renormalizations (box mappings) and will show how to use these techniques to get the result. All necessary background will be provided.
  • November 16, 2023, 12:15
    This email address is being protected from spambots. You need JavaScript enabled to view it.
    (Universitat de Barcelona)
    T
    itle: Local connectivity of boundaries of Fatou components II
    Abstract: In the talk, I will re-prove the famous result of Roesch and Yin about local connectivity of boundaries of bounded Fatou components of polynomials (except Siegel). For this, I will present techniques of puzzles and generalized renormalizations (box mappings) and will show how to use these techniques to get the result. All necessary background will be provided.
  • November 10, 2023, 14:00
    This email address is being protected from spambots. You need JavaScript enabled to view it.
    (Universitat de Barcelona)
    T
    itle: Local connectivity of boundaries of Fatou components
    Abstract: In the talk, I will re-prove the famous result of Roesch and Yin about local connectivity of boundaries of bounded Fatou components of polynomials (except Siegel). For this, I will present techniques of puzzles and generalized renormalizations (box mappings) and will show how to use these techniques to get the result. All necessary background will be provided.
  • November 2, 2023, 12:15
    This email address is being protected from spambots. You need JavaScript enabled to view it. (University of Warsaw)
    T
    itle: Local connectivity of the boundary of a Fatou component 
    Abstract: In this talk, I will present my current work on local connectivity of the boundary of the Baker Domain of the function  $f(x)=z-\frac{1-e^z}{1-2e^z}$ ($N((e^z)(1-e^z))$).

  • October 26, 2023, 12:15
    Gustavo Rodrigues Ferreira (Centre de Recerca Matemàtica)
    T
    itle: Transcendental dynamics and wandering domains  III
    Abstract: In this three-part talk, we will discuss the internal dynamics of wandering domains of meromorphic functions. Focusing on the hyperbolic distance between pairs of orbits, we will show that every wandering of a meromorphic function locally resembles a wandering of an entire function.

  • October 19, 2023, 12:15
    Xavier Jarque (Universitat de Barcelona)
    T
    itle: Connectivity of the basins of attraction of fixed points for some root finding algorithms
    Abstract: We consider the connectivity of the immediate basins of attraction for different dynamical systems, basically inspired by root-finding algorithms, as the title already explains.


  • October 16, 2023, 12:00
    Kevin Pilgrim (Indiana University)
    T
    itle: Real bimodal quadratic rational maps: moduli space and entropy
    Abstract:
    Bruin-van Strien and Kozlovski showed that for multimodal self-maps $f$ of the unit interval, the function $f \mapsto h(f)$ sending $f$ to its topological entropy is monotone. K. Filom and I showed that for interval maps arising from real bimodal quadratic rational maps, this monotonicity fails. A key ingredient in our proof is an analysis of a family $f_{p/q}, p/q \in \mathbb{Q}/\mathbb{Z}$ of critically finite maps on which the dynamics on the postcritical set is conjugate to the rotation $x \mapsto x+p \bmod q$ on $\mathbb{Z}/q\mathbb{Z}$, where $x=0$ and $x=1$ correspond to the two critical points. The recent PhD thesis of S. Kang constructs a piecewise-linear (PL) copy of the well-known Farey tree whose vertices are expanding PL quotients of the $f_{p/q}$’s. This PL model, conjecturally, sheds light on the moduli space of the real quadratic bimodal family, and on the variation of entropy among such maps.

    (Joint work with K. Filom and S. Kang)

  • October 5, 2023, 12:15
    Oleg Ivrii (Tel Aviv University)
    T
    itle: Pesin theory and inner functions
    Abstract:
    An inner function is a holomorphic self-map of the unit disk which extends to a measure-theoretic dynamical system of the unit circle. Even though the forward dynamics of an inner function can be very wild, if its derivative belongs to the Nevanlinna class, then backward iteration is asymptotically linear along almost every inverse orbit. We give several applications.
    (This is joint work with Mariusz Urbański.)

  • September 28, 2023, 12:30
    Gustavo Rodrigues Ferreira (Centre de Recerca Matemàtica)
    T
    itle: Transcendental dynamics and wandering domains  II
    Abstract: In this three-part talk, we will discuss the internal dynamics of wandering domains of meromorphic functions. Focusing on the hyperbolic distance between pairs of orbits, we will show that every wandering of a meromorphic function locally resembles a wandering of an entire function.

  • September 21, 2023, 12:30
    Gustavo Rodrigues Ferreira (Centre de Recerca Matemàtica)
    T
    itle: Transcendental dynamics and wandering domains
    Abstract: In this three-part talk, we will discuss the internal dynamics of wandering domains of meromorphic functions. Focusing on the hyperbolic distance between pairs of orbits, we will show that every wandering of a meromorphic function locally resembles a wandering of an entire function.