Group Actions Seminar: Burillo, Tang

UPDATE: the talks are in Carslaw 451.

There will be a Group Actions Seminar at the University of Sydney on Wednesday 27
February.  The speakers will be José Burillo (Universitat Politècnica de Catalunya) and
Robert Tang (University of Warwick).  Titles and abstracts are below.  

The talks will be in either the Access Grid Room or 451, depending on viewer interest
from other universities.  I will update this news item before the first talk to let you
know the venue.  

As usual, we will have one talk before lunch and one afterwards, and we will be heading
to the pub some time after the second talk.  

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Date: Wednesday 27 February 

Time: 12 noon 

Location: Carslaw 451, University of Sydney 

Speaker: José Burillo (Universitat Politècnica de Catalunya) 

Title: Metric properties of Houghton’s groups 

Abstract: Houghton groups were defined in the 1960s, and provided examples of groups
which belong to class FP_n but not to class FP_{n+1}.  Recently these groups have been
studied from the modern geometric point of view.  I will present here some results
related to Houghton’s groups: find an estimate for their metric, find their automorphism
group and their commensurator group, proving that it is infinitely generated.  As it
embeds into the quasi-isometry group, this provides a large quantity of examples of
quasi-isometries of Houghton’s groups.  

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Date: Wednesday 27 February 

Time: 3pm 

Location: Carslaw 451, University of Sydney 

Speaker: Robert Tang (University of Warwick) 

Title: Projections and hulls in the curve graph

Abstract: The curve graph C(S) associated to a surface S is a graph whose
vertices are simple closed curves on S and whose edges are spanned by
pairs of disjoint curves. This provides a combinatorial means for
understanding the coarse geometry of mapping class groups,
Teichmueller space and hyperbolic 3-manifolds. After presenting some
basic definitions, I will describe a coarse analogue of a "convex
hull" for a finite set of vertices in C(S) using only intersection
number information. I then show how these results can be used to give
a combinatorial approximation for nearest point projection maps to
subgraphs of the curve graph which arise naturally from surface
covering maps.

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