Our seminar meets Tuesdays at 4:30 in JCC 502, and this semester is hybrid (in person talks are streamed on Zoom). You can subscribe to the GGTT mailing list at https://elist.tufts.edu/sympa/info/ggtt for details and announcements. The seminar organizers are Kim Ruane, Lorenzo Ruffoni and Genevieve Walsh.

Sep 13Corey Bregman (Southern Maine) – in personEmbedding spaces of split links
Abstract:  The homotopy type of the embedding space of a knot in R^3 or S^3 has been studied extensively, culminating in a complete description by Budney.  However, for links in R^3 much less is known. Brendle-Hatcher showed that the space of smooth embeddings of an n-component unlink in R^3 is homotopy equivalent to the space of round unlinks, i.e. where each component is a round circle lying in a plane.  In this talk we consider the embedding space of a split link with n sublinks, and show that the homotopy type of this embedding space depends only on that of the embeddings of a single sublink in a ball, together with a combinatorial object called the space of separating systems.  We use the space of separating systems to compute the fundamental group of the embedding space.  This is joint work with Rachael Boyd.
Sep 20Beibei Liu (MIT) – in person The critical exponent: old and new
Abstract: The critical exponent is an important numerical invariant of discrete groups acting on negatively curved Hadamard manifolds, Gromov hyperbolic spaces, and higher-rank symmetric spaces. In this talk, I will focus on discrete groups acting on hyperbolic spaces (i.e., Kleinian groups), which is a family of important examples of these three types of spaces. In particular, I will review the classical result relating the critical exponent to the Hausdorff dimension using the Patterson-Sullivan theory and introduce new results about Kleinian groups with small or large critical exponents.
Sep 29
Yulan Qing (Fudan) – in person Gromov boundary extended
Abstract: The Gromov boundary provides a useful compactification for all infinite-diameter Gromov hyperbolic spaces. It consists of all geodesic rays starting at a given base-point and it has been an essential tool in the study of the coarse geometry of hyperbolic groups. In this study We find the natural analogue of the Gromov boundary for a larger class of metric spaces. We start in the setting of metric spaces that resemble the geometry of relatively hyperbolic groups. We define a notion of a boundary that is compact, metrizable and invariant under quasi-isometries. Furthermore, it contains the sublinearly Morse boundary as a dense, topological subspace. When the space in question has a cocompact group action, this boundary coincides with the Bowditch boundary. This is a joint work (in progress) with Kasra Rafi and Giulio Tiozzo.
Oct 4no seminar
Oct 11Martin Bridgeman (BC) – in personTBA
Abstract: TBA.
Oct 18no seminar
Oct 25Yu-Chan Chang (Wesleyan) – in personTBA
Abstract: TBA.
Nov 1 Brendan Mallery (Tufts) – in personTBA
Abstract: TBA.
Nov 8 no seminar
Nov 15Daniel Gulbrandsen (UW Milwaukee) – in personTBA
Abstract: TBA.
Nov 22Alex Margolis (Vanderbilt) – in personTBA
Abstract: TBA.
Nov 29Assaf Bar-Natan (Brandeis) – in personTBA
Abstract: TBA.
Dec 6Jone Lopez de Gamiz Zearra (Vanderbilt) – in personTBA
Abstract: TBA.