Dynamics Seminar 2021-2022

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The Dynamics seminar meets in room 901 of Van Vleck Hall on Mondays from 2:30pm - 3:20pm. To sign up for the mailing list send an email from your wisc.edu address to dynamics+join@g-groups.wisc.edu. For more information, contact Caglar Uyanik or Chenxi Wu.


Fall 2021

date speaker title host(s)
Sep. 13 Nate Fisher (UW Madison) "Boundaries, random walks, and nilpotent groups" local
Sep. 20 Caglar Uyanik (UW Madison) "Dynamics on currents and applications to free group automorphisms" local
Sep. 27 Michelle Chu (UIC) "Prescribed virtual torsion in the homology of 3-manifolds" caglar
Oct. 4 Osama Khalil (Utah) "Generalized Hecke Operators and Mahler’s Problem in Diophantine Approximation" caglar
Oct. 11 Theodore Weisman (UT Austin) "TBA" zimmer
Oct. 18 Grace Work (UW Madison) TBA local
Oct. 25 Chenxi Wu (UW Madison) TBA local
Nov. 1 Jack Burkart (UW Madison) TBA local
Nov. 8 Jayadev Athreya (UW Seattle) "Stable Random Fields, Patterson-Sullivan Measures, and Extremal Cocycle Growth" caglar and grace
Nov. 15 Funda Gültepe (U Toledo) "TBA" caglar
Nov. 22 Jonah Gaster (UW Milwaukee) "TBA" caglar
Nov. 29 Chloe Avery (U Chicago) "TBA" Dymarz
Dec. 6 Matt Clay (Arkansas) tbc "TBA" caglar


Nate Fisher (UW Madison)

Boundaries, random walks, and nilpotent groups

In this talk, we will discuss boundaries and random walks in the Heisenberg group. We will discuss a class of sub-Finsler metrics on the Heisenberg group which arise as the asymptotic cones of word metrics on the integer Heisenberg group and describe new results on the boundaries of these polygonal sub-Finsler metrics. After that, we will explore experimental work to examine the asymptotic behavior of random walks in this group. Parts of this work are joint with Sebastiano Nicolussi Golo.

Caglar Uyanik (UW Madison)

Dynamics on currents and applications to free group automorphisms

Currents are measure theoretic generalizations of conjugacy classes on free groups, and play an important role in various low-dimensional geometry questions. I will talk about the dynamics of certain "generic" elements of Out(F) on the space of currents, and explain how it reflects on the algebraic structure of the group.

Michelle Chu (UIC)

Prescribed virtual torsion in the homology of 3-manifolds

Hongbin Sun showed that a closed hyperbolic 3-manifold virtually contains any prescribed torsion subgroup as a direct factor in homology. In this talk we will discuss joint work with Daniel Groves generalizing Sun’s result to irreducible 3-manifolds which are not graph-manifolds.

Osama Khalil (Utah)

Generalized Hecke Operators and Mahler’s Problem in Diophantine Approximation

Khintchine's Theorem provides a zero-one law describing the approximability of typical points by rational points. In 1984, Mahler asked whether the same holds for Cantor’s middle thirds set. His question fits into a long studied line of research aiming at showing that Diophantine sets are highly random and are thus disjoint, in a suitable sense, from highly structured sets.

We will discuss the first complete analogue of Khintchine’s theorem for certain self-similar fractal measures, recently obtained in joint work with Manuel Luethi. The key ingredient in the proof is an effective equidistribution theorem for fractal measures on the space of unimodular lattices, generalizing a long history of similar results for smooth measures beginning with Sarnak’s work in the eighties. To prove the latter, we associate to such fractals certain p-adic Markov operators, reminiscent of the classical Hecke operators, and leverage their spectral properties. No background in homogeneous dynamics will be assumed.

Theodore Weisman (UT Austin)


Grace Work (UW Madison)


Chenxi Wu (UW Madison)


Jack Burkart (UW Madison)


Jayadev Athreya (UW Seattle)

Stable Random Fields, Patterson-Sullivan Measures, and Extremal Cocycle Growth

We study extreme values of group-indexed stable random fields for discrete groups G acting geometrically on spaces X in the following cases: (1) G acts freely, properly discontinuously by isometries on a CAT(-1) space X, (2) G is a lattice in a higher rank Lie group, acting on a symmetric space X, (3) G is the mapping class group of a surface acting on its Teichmuller space. The connection between extreme values and the geometric action is mediated by the action of the group G on its limit set equipped with the Patterson-Sullivan measure. Based on motivation from extreme value theory, we introduce an invariant of the action called extremal cocycle growth which measures the distortion of measures on the boundary in comparison to the movement of points in the space X and show that its non-vanishing is equivalent to finiteness of the Bowen-Margulis measure for the associated unit tangent bundle U(X/G) provided X/G has non-arithmetic length spectrum. This is joint work with Mahan MJ and Parthanil Roy.

Funda Gültepe (U Toledo)


Jonah Gaster (UWM)


Chloe Avery (U Chicago)


Matt Clay (Arkansas)


Archive of past Dynamics seminars

2020-2021 Dynamics_Seminar_2020-2021