# Geometry and Topology Online

## Term II, 2021-22

Please contact Saul Schleimer or Robert Kropholler if you would like to speak or to suggest a speaker.

While this page is the seminar's "main page", I will attempt to also maintain an up-to-date listing at researchseminars.org.

The seminar will run weekly, with one 30 minute talk, followed by a 20 minute discussion/Q&A. The talk starts five minutes after the hour. We will open and close the Zoom session on the hour. Note that no password is required; links to the zoom session for each talk are below.

 Thursday January 13, 15:05 (UK time). Kim Ruane (Tufts) Torsion-free groups acting geometrically on the product of two trees Abstract: Given a group acting geometrically on product of two trees, we know that one visual boundary is the topological join of two Cantor sets. We prove that these groups are "boundary rigid": any $\CAT(0)$ space on which the group acts has visual boundary homeomorphic to such a join. Since there is no hyperbolicity going on here, one cannot expect that the natural equivariant quasi-isometry between an arbitrary $\CAT(0)$ space and the product of two trees to extend to any sort of map on boundaries, thus the proof requires new techniques. The proof uses work of Ricks on recognising product splittings from the Tits boundary as well as work of Guralnik and Swenson on general dynamics of a $\CAT(0)$ group on both the visual and Tits boundary. This is (recent) joint work with Jankiewicz, Karrer, and Sathaye.

 Thursday January 20, 15:05 (UK time). TBA (TBA) TBA Abstract: TBA

 Thursday January 27, 15:05 (UK time). TBA (TBA) TBA Abstract: TBA

 Thursday February 3, 15:05 (UK time). TBA (TBA) TBA Abstract: TBA

 Thursday February 10, 15:05 (UK time). TBA (TBA) TBA Abstract: TBA

 Thursday February 17, 15:05 (UK time). TBA (TBA) TBA Abstract: TBA

 Thursday February 24, 15:05 (UK time). TBA (TBA) TBA Abstract: TBA

 Thursday March 3, 15:05 (UK time). TBA (TBA) TBA Abstract: TBA

 Thursday March 10, 15:05 (UK time). TBA (TBA) TBA Abstract: TBA

 Thursday March 17, 15:05 (UK time). TBA (TBA) TBA Abstract: TBA

Information on past talks. This line was last edited on Mon 25 Oct 2021 16:10:37 BST

Internet Access at Warwick:
Where possible, visitors should obtain an EDUROAM account from their own university to enable internet access whilst at Warwick.
If you need WiFi whilst at Warwick, click here for instructions (upon arrival at Warwick)
Registration:
You can register for any of the symposia or workshops online. To see which registrations are currently open and to submit a registration, please click here.
Contact:
Mathematics Research Centre
Zeeman Building
University of Warwick
Coventry CV4 7AL - UK
E-mail:
mrc@maths.warwick.ac.uk