Starting in Spring 2023 the seminar will go back to in-person talks. We will also attempt to run the seminar as hybrid using zoom. Zoom doors will open a few minutes before the seminar for chatter and self provided coffee, tea, beer, wine, cocktail, aperitif, digestif, cheese, and snacks depending on your time zone and predilection. If you would like to be put on the email list contact Ara Basmajian (abasmajian@gc.cuny.edu). The zoom link for the upcoming seminar will be included in the weekly mailing to the email list.
Tuesdays 2:45pm–3:45pm, room 5417.
Organizers
Ara Basmajian (CUNY, Graduate Center and Hunter College)
Email: abasmajian@gc.cuny.edu
Dragomir Saric (CUNY, Graduate Center and Queens College)
Email: dragomir.saric@qc.cuny.edu
Nick Vlamis (CUNY, Graduate Center and Queens College)
Email: nvlamis@gc.cuny.edu
September 16: Tarik Aougab (Haverford College)
Title: Sharp bounds for 1-systems
Abstract: On a closed orientable surface of genus g, a 1-system is a collection of pairwise non-homotopic simple closed curves that pairwise intersect at most once. Obtaining bounds on the maximum size of a 1-system has proved to be a surprisingly hard problem. Constructions with roughly g^2 curves have been known for the last few decades, but upper bounds are trickier: in 2012, Malestein-Rivin-Theran produced an upper bound that is exponential in g. Przytycki in 2014 improved this to a bound that is O(g^3), and in 2018 Josh Greene improved this to a bound that behaves like g^2*log(g).
Our main result is a quadratic-in-g upper bound, resolving the problem up to explicit multiplicative constants. We achieve this by choosing an appropriate hyperbolic metric and paying careful attention to how certain polygons formed by curves in the 1-system distribute their area over the surface. This represents joint work with Jonah Gaster.
September 23: No Seminar (CUNY Closed)
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September 30: Matthew Durham (Hunter College)
Title: Asymptotically CAT(0) metrics, Z-structures, and the Farrell-Jones Conjecture
Abstract: will discuss recent work with Minsky and Sisto, in which we prove that mapping class groups of finite-type surfaces---and more generally, colorable hierarchically hyperbolic groups (HHGs)---are asymptotically CAT(0). This is a simple but powerful non-positive curvature property introduced by Kar, roughly requiring that the CAT(0) inequality holds up to sublinear error in the size of the triangle.
We use the asymptotically CAT(0) property to construct visual compactifications for colorable HHGs that provide Z-structures in the sense of Bestvina and Dranishnikov. It was previously unknown that mapping class groups are asymptotically CAT(0) and admit Z-structures. As an application, we prove that many HHGs satisfy the Farrell-Jones Conjecture, providing a new proof for mapping class groups (Bartels-Bestvina) and establishing the conjecture for extra-large type Artin groups.
To construct asymptotically CAT(0) metrics, we show that every colorable HHG admits a manifold-like family of local approximations by CAT(0) cube complexes, where transition maps are cubical almost-isomorphisms.
October 14: No Seminar (CUNY on Monday Schedule)
October 15: Wednesday, 4:00pm. Sara Maloni Colloquium (math commons room)
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October 28:
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November 4:
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November 18: Charles Bordenave (IAS)
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November 25: No Seminar (Thanksgiving week)
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December 2:
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HISTORY OF THE HYPERBOLIC GEOMETRY SEMINAR : The hyperbolic geometry seminar has been running continuously since Fall 2008. In the early years it ran mostly as a student seminar with some research talks interspersed. The seminar topics span a wide range including hyperbolic and conformal geometry, geometric structures on manifolds, low dimensional topology, geometric group theory, and many others.
Past organizers have been Youngju Kim (2008-2010), Viveka Erlandsson (2010-2013), Chris Arettines (2013-2015), Blanca Marmolejo (2015-2017), and Daniel White (2017-2019).