The Geometry of Outer Space

Marseille  -  July 2013

Tentative Schedule


First Week


MondayTuesdayWednesdayThursdayFriday

July 1July 2July 3July 4July 5
9h-10hCoffee
Morning discussion
Coffee
Morning discussion
Coffee
Morning discussion
Coffee
Morning discussion
Coffee
Morning discussion
10h30-11h30Matt ClayBrian MannCamille HorbezRic WadeTeichmüller seminar
12h-14hLunchWorking LunchLunchWorking LunchLunch
14h30-15h30Free discussionFree discussionPierre ArnouxStefano FrancavigliaIvan Dynnikov
16hTeaTeaTeaTeaTea

Pierre Arnoux (Université d'Aix-Marseille) : informal discussion "Generalized substitutions and tilings for algebraists"

Matt Clay (University of Arkansas) : "Uniform hyperbolicity of the curve graph" (joint with S. Schleimer and K. Rafi)

Ivan A. Dynnikov (Moscow State University): "On typical leaves of a measured foliated 2-complex of thin type" (joint with A. Skripchenko)

Stefano Francaviglia (Bologne) : "Stretching factors and train-tracks for outer space of free groups / free products"
            We discuss how to compute the lipschitz distance between points of the outer space of either a free product or a free group, and how to construct train-track
representatives for irreducible automorphisms. This is a joint work with Y. Antolin and A. Martino.

Camille Horbez (Université de Rennes) : "The hyperbolicity of the sphere complex via surgery paths" (joint with A. Hilion)

Brian Mann (University of Utah) : "Hyperbolicity of the Cyclic splitting complex"

Ric Wade (University of Utah) : "Displacement functions on Outer space"


On Friday morning, participants of the program are invited to attend the Teichmüller seminar :
Tom Schmidt (Oregon State University) :  "Geodesic flow and natural extensions for continued fractions"
            Arnoux used Teichmueller flow to show that regular continued fractions arise as a factor of a cross section for the geodesic flow on the modular surface.
Luzzi and Marmi asked if also the alpha-continued fractions of Nakada can arise as a factor of a cross section.   With Arnoux, extending work with Kraaikamp and Steiner,  we showed that this is so.  Using these cross sections, with Fisher we gave a version of Moeckel's result on the  distribution of the numerators and denominators of the convergents arising from such continued fraction expansions.
            The talk will start with the basics,  and include quite a few figures.



Second Week


MondayTuesdayWednesdayThursdayFriday

July 8July 9July 10July 11July 12
9h-10hCoffee
Morning discussion
Coffee
Morning discussion
Coffee
Morning discussion
Coffee
Morning discussion
Coffee
Morning discussion
10h30-11h30Lee MosherHoward MasurMartin LustigDuc-Manh Nguyen
Kasra Rafi
12h-14hLunchWorking LunchLunchWorking LunchLunch
14h30-15h30Gilbert LevittKaren VogtmannChristopher LeiningerMladen BestvinaSaul Schleimer
16hTeaTeaTeaTeaTea


Mladen Bestvina (University of Utah) : "Large scale geometry of Outer space"

Christopher Leininger
(University of Illinois at Urbana-Champaign) : "Short geodesics in moduli space and a question for people from outer space"

Gilbert Levitt
(Université de Caen) : "Stabilizers of trees"

Martin Lustig (Université d'Aix-Marseille) : "The fibers of the Cannon-Thurston map for free group automorphisms"

Howard Masur (University of Chicago) : "Geometric rank in Teichmuller space and the mapping class group"
            We consider three spaces X: Teichmuller space with the Teichmuller metric, Teichmuller space with the Weil-Petersson metric and the mapping class group with the word metric. We define the topological rank of X to be the maximum number of disjoint essential subsurfaces. The geometric rank is the maximal n such that there is a quasi-isometry of R^n into X.
We show that the geometric and topological rank coincide. I will sketch some of the main ideas of the proof.
(joint with Alex Eskin, Kasra Rafi)

Lee Mosher (Rutgers University) : "Some hyperbolic complexes for subgroups of Out(F_n)"

Duc-Manh Nguyen (Université de Bordeaux 1) : "Cylinder deformations and GL(2,R)-orbit closures of translation surfaces in genus 3"
            The groundbreaking results of Eskin-Mirzakhani-Mohammadi on GL(2,R)-invariant submanifolds, together  with a result by Avila-Eskin-Moeller, have shed light on the properties that must be satisfied by GL(2,R)-orbit closures in moduli spaces of translation surfaces. Using these results, we show that an orbit closure in the hyperelliptic component of the stratum H(4) is either a closed or a dense subset of this component. The main tool of our approach is the study of deformations of surfaces admitting a cylinder decomposition in the horizontal direction. This is a joint work with Alex Wright (University of Chicago).

Kasra Rafi (University of Toronto)  : "Coarse geometry of Outer Space"

Saul Schleimer (Warwick Mathematics Institute) : "Curves in the Masur domain"
           Suppose that a is a simple closed curve in a surface S, and suppose that the curve complex distance between a and the "disk set" D(V) is at least three.  Then a lies in the Masur domain.  I'll define all of these things and sketch the proof, relying on the theory of "holes" for the disk set, which is joint work with Masur.  This answers a question of Juan Souto and, independently, Feng Luo.

Karen Vogtmann (Cornell University) : "Outer space for RAAGs"


Third week


MondayTuesdayWednesdayThursdayFriday

July 15July 16July 17July 18July 19
10h-10h30Coffee
Morning discussion 
Ensuès -
La Redonne

by

le train de la côte bleue
Coffee
Morning discussion
Coffee
Morning discussion
Coffee
Morning discussion
10h30-11h30Jing Tao
Mark Feighn

Moritz Rodenhausen
Informal talk
on
Hamenstädt
lines of minima

(Martin Lustig)
12h-14hWorking LunchLunchWorking LunchLunch
14h30-15h30Informal discussion
on
systems of partial isometries

SAGE introduction
Spencer DowdallAnia LenzhenInformal discussion
16hTeaTeaTeaTea



On Tuesday morning:
Meeting at 10h in the main hall of Saint-Charles train station,
close to the blue train ticket machines.




Spencer Dowdall
 (University of Illinois at Urbana-Champaign) :  "Dynamics for splittings of free-by-cyclic groups."
                The combined work of Thurston and Fried shows that the monodromies associated to the fibrations of a hyperbolic 3-manifold are intimately related in important topological, geometric, and dynamical ways. After reviewing this picture, I will describe recent results showing that similar relationships hold for the monodromies associated to splittings of a free-by-cyclic group. In particular, when the free-by-cyclic group is the mapping-torus group of a fully irreducible atoroidal automorphism of F_n, we will see that the monodromies of all nearby splittings are also fully irreducible and have similar stretch factors. This is joint work with I. Kapovich and C. Leininger.

Mark Feighn (Rutgers University) : ''Folding lines''

Ania Lenzhen (Université de Rennes) : ''Teichmüller rays''

Moritz Rodenhausen (University of Bonn) :  "Centralisers of polynomially growing automorphisms of free groups"

Jing Tao (University of Oklahoma) : ''Short curves in modular space''