Dynamics Day, 23 July - Stasi Room at 14:30

[ICTP Math Section]

Please see the revised schedule for today:

Maik Groger (14:30-14:55)
Sonja Štimac (15:05-15:30)
Jan Boronski (16:00-16:25)
Hamza Ounseli (16:35-17.00)

Best regards,

Micol

On 22/07/2026 16:39, ICTP Math Section wrote:
> *TOMORROW - 23 July, 14:30 - 17:00*
> *
> *
> *Stasi Room, ICTP Leonardo Building*
> *
> *
> *
> *
> *14:30 - 14:55 Hamza Ounesli, ICTP*
> /New manifolds supporting volume preserving homeomorphisms with 
> exponential decay of correlations/
> *Abstract: *Manifolds known to support volume preserving 
> homeomorphisms with exponential decay of correlation are all of the 
> form N x K where N is up to a cover a hyperbolic infranilmanifold and 
> K the unit tangent bundle of a manifold admitting a Riemannian metric 
> with strictly negative sectional curvature. D. Dolgpyat and Y. Pesin, 
> in the spirit of realization problems initiated by J. Von Neumann, 
> asked if there are manifolds not supporting exponentially mixing 
> systems with respect to a volume measure. Our main result, gives a 
> class of systems that can be defined on any manifold of dimension at 
> least 4 carrying a particular type of singular compact foliation, and 
> exhibit exponential mixing with respect to the volume. Our second 
> result building on the first result, shows that for any finitely 
> presented group G. There exists a closed 4-manifold whose fundamental 
> group is G and support the class of systems of the first result, this 
> proves there are no topological restrictions at the homotopy level for 
> existence of such systems.
>
> *15:05 - 15:30 Maik Gröger, Jagiellonian University*
> /Besicovitch vs. Weyl mean equicontinuity/
> *Abstract: *The notions of Besicovitch and Weyl mean equicontinuity 
> arise naturally in the study of systems with long-range order. In the 
> minimal setting, it is well known that both describe the same class of 
> actions: systems with discrete spectrum and continuous eigenfunctions. 
> In this talk, I will show that this equivalence fails in the context 
> of general actions by amenable but non-abelian groups, presenting 
> explicit counterexamples involving the group of orientation-preserving 
> homeomorphisms of the unit interval and the Lamplighter group. If time 
> permits, I will describe some of the new tools developed to analyze 
> these counterexamples.
> This is joint work with G. Fuhrmann and T. Hauser.
>
> *16:00 - 16:25 Sonja Štimac, University of Zagreb*
> /Classification of Hénon maps with strange attractors via the topology 
> of a stable manifold/
> *Abstract:* In an earlier work with Jan Boroński, we classified (up to 
> conjugacy) the Hénon maps with strange attractors using three 
> invariants we introduced: (a) kneading sequences, (b) pruned trees, 
> and (c) folding patterns of the unstable manifold of the hyperbolic 
> fixed point in the attractor. In this talk, I will present another 
> method for determining conjugacy classes of these maps, this time 
> based on the topology of the stable manifold of the hyperbolic fixed 
> point. We consider a region of dissipation for the Hénon map and study 
> the connected components of the stable manifold within this region. To 
> each such component, we assign a separation type and prove that two 
> Hénon maps are conjugate if and only if their corresponding components 
> share the same separation type. This is joint work with Jan Boroński.
>
> *
> *
> *16:35 - 17:00 Jan Boroński, Jagiellonian University*
> /Topologically mildly dissipative homeomorphisms and Wang-Young 
> Strange Attractors/
> *Abstract:* In this joint work with Sonja Štimac, we extend R.F. 
> Williams’ result on 1-dimensional hyperbolic attractors to the 
> non-uniformly hyperbolic setting, by showing that each Wang-Young 
> strange attractor in the plane is conjugate to the shift on the 
> inverse limit of a baobab (Peano continuum that contains at most one 
> Jordan curve), generalizing our earlier result on Hénon attractors. 
> More generally, the result holds on the core of the maximal attractor 
> of any mildly dissipative diffeomorphism (in the sense of Crovisier 
> and Pujals). We also generalize these results to the C0 setting, by 
> introducing the class of topologically mildly dissipative surface 
> homeomorphisms, providing a unified approach that covers many classes 
> of dissipative dynamical systems scattered in the literature. Our 
> purely topological conditions lead to a one-to-one correlation between 
> the sets of ergodic measures of the one-dimensional and 
> two-dimensional systems, as well as equality between the corresponding 
> measure-theoretic entropies.
>
> All are welcome to join.
>
> -- 
> Micol Stock
> Secretariat of the ICTP Math Section
>
> Abdus Salam International Centre for Theoretical Physics
> Strada Costiera 11
> 34151 Trieste
> Italy
>
> Tel.: (+39) 040 2240 4455

-- 
Micol Stock
Secretariat of the ICTP Math Section

Abdus Salam International Centre for Theoretical Physics
Strada Costiera 11
34151 Trieste
Italy

Tel.: (+39) 040 2240 4455