Type: Seminar

Modified: Tue 19 Feb 2013 1031; Wed 20 Feb 2013 1607; Wed 27 Feb 2013 1038

Distribution: World

Expiry: 27 Feb 2013

CalTitle1: Group Actions Seminar: Burillo -- Metric properties of Houghton’s groups

Calendar2: 27 Feb 2013 1500-1600

CalLoc2: Carslaw 451

CalTitle2: Group Actions Seminar: Tang -- Projections and hulls in the curve graph

Auth: athomas@p615.pc (assumed)

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. ---------------------------------------------------------------------------- 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. ---------------------------------------------------------------- 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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