[Binghamton Geometry/Topology Seminar] (no subject)

[Ross Geoghegan]

                   BINGHAMTON GEOMETRY/TOPOLOGY SEMINAR


        TWO TALKS THIS WEEK -  NOTE UNUSUAL DAY AND TIME OF SECOND ONE                        
FIRST TALK:

   Date: Thursday May 3, 2007 

   Time:  2.50 pm

   Place: Library North 2205 followed by coffee/tea in the Anderson
          Reading Room.

   Speaker: Bruce Hughes (Vanderbilt University) 

   Title: Local similarities and the Haagerup property 

Abstract: 
I will introduce a new class of groups - finitely determined groups of
local similarities on a compact ultrametric space - and prove that they
have the Haagerup property (that is, they are a-T-menable in the sense
of Gromov). The class includes Thompson's groups, which have already been
shown to have the Haagerup property by Dan Farley, as well as many other
groups acting on boundaries of trees. The Haagerup property for a group
means that there is a proper, affine isometric action of the group on
some Hilbert space. Higson and Kasparov proved that such groups satisfy
the Connes-Baum conjecture.

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SECOND TALK:

     Date: Friday May 4, 2007

     Time:  4.30 pm

     Place: Library North 2205 following coffee/tea in the Anderson
          Reading Room.

     Speaker:  Jean-Francois Lafont (Ohio State University)

     Title: Ultralimit rigidity for locally symmetric spaces.

Abstract: 
Ultralimits provide a way to talk about the "large-scale geometry" of
metric spaces.  In the case of the universal cover of a closed Riemannian
manifold of non-positive curvature, I will explain how existence of
flats in the ultralimit imply existence of parallel Jacobi fields along
certain geodesics.  As an application, I will show the following rigidity
result: if such an ultralimit is isometric to the ultralimit of a higher
rank symmetric space of non-compact type, then the original closed
Riemannian manifold is itself isometric to a locally symmetric space.
This is work in progress with Stefano Francaviglia (UAB - Spain).

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NOTE:  The seminar has a webpage where the semester's program is listed:

http://math.binghamton.edu/MATH/dept/topsem/index.html

It can also be linked from the Department's Home Page.
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