Mdtop September 2022

mdtop@mathdept.okstate.edu

1 participants
4 discussions

This week in Topology seminar
by Hoffman, Neil 26 Sep '22

26 Sep '22

Hello everyone, This week we have Hannah Turner in town. She will be speaking at 3:30 tomorrow on Generalizing the (fractional) Dehn twist coefficient. The title and abstract are below. Also, next week Eric Sedgwick is in town. There is a slight conflict with the 3:30 time slot next week, so I wanted to check with everyone to see what conflicts would arise if the October 4 talk was moved to 2:30. Let me know if you can make that adjusted time on October 4th or if you have a conflict. Title: Generalizing the (fractional) Dehn twist coefficient. Speaker: Hannah Turner, Georgia Tech Date: Sep 27, 2022 Time: 3:30 PM Room: MSCS 445 Abstract: The fractional Dehn twist coefficient (FDTC) is a rational number associated to a mapping class on a (finite-type) surface with boundary. This 2-dimensional invariant has many applications to 3-manifold topology and contact geometry. One way to think of the FDTC is as a real-valued function on the mapping class group of a surface with many nice properties. In this talk, we will give sufficient conditions on a more general group to admit a function which behaves like the FDTC. In particular, we use this to generalize the FDTC to infinite-type surfaces (with boundary); in this setting, we show that the ”fractional” Dehn twist coefficient need not be rational. This is joint work with Peter Feller and Diana Hubbard. ______________________ Neil R. Hoffman Assistant Professor Department of Mathematics 523 Math Science Building Oklahoma State University Stillwater, OK 74078-1058 405-744-7791 http://math.okstate.edu/people/nhoffman

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No seminar today
by Hoffman, Neil 20 Sep '22

20 Sep '22

Hello everyone, There is no seminar today. We will have Hannah Turner (Georgia Tech) visiting next week. ______________________ Neil R. Hoffman Assistant Professor Department of Mathematics 523 Math Science Building Oklahoma State University Stillwater, OK 74078-1058 405-744-7791 http://math.okstate.edu/people/nhoffman

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Tomorrow in topology seminar
by Hoffman, Neil 12 Sep '22

12 Sep '22

Hello everyone, Tomorrow, we have Danny Calegari joining us. His title and abstract are below. The zoom link for the seminar is below. Also, I will be in MSCS 445 and plan to have the talk projected there for those interesting in watching the talk with other people. Neil Hoffman is inviting you to a scheduled Zoom meeting. Topic: Okstate Topology Seminar Time: This is a recurring meeting Meet anytime Join Zoom Meeting https://zoom.us/j/94529451960?pwd=ekkxYUsrRGt5bVdEQWJRN0JOZ04wZz09 Meeting ID: 945 2945 1960 Passcode: JSJDecomp Join by Skype for Business https://zoom.us/skype/94529451960 Homological stability of some big mapping class groups Speaker: Danny Calegari, University of Chicago Date: Sep 13, 2022 Time: 3:30 PM Room: Virtual meeting Abstract: Many surfaces of infinite type satisfy a kind of topological stability: the operation of boundary summing with certain surfaces of infinite type does not change their homeomorphism type. This phenomenon is often reflected in homological stability for mapping class groups, and gives techniques to help compute their homology. We illustrate this method with an example where it gives a complete answer: the homology of the mapping class group of the disk (resp. plane) minus a Cantor set is trivial (resp. is isomorphic to the homology of CP∞). This is joint work with Lvzhou Chen and Nathalie Wahl. This is a virtual talk. Contact Neil Hoffman for the zoom link ______________________ Neil R. Hoffman Assistant Professor Department of Mathematics 523 Math Science Building Oklahoma State University Stillwater, OK 74078-1058 405-744-7791 http://math.okstate.edu/people/nhoffman

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This week in Topology seminar
by Hoffman, Neil 05 Sep '22

05 Sep '22

Hello everyone, I hope you had a great weekend. Tomorrow (Tuesday) will mark the first topology seminar of the semester and the first in person seminar in a while. Having said that, there is the possibility of a virtual option, if you need that. Contact me and we can try to set that up. Our speaker is our own Jonathan Johnson we will be in MSCS 445 (on the 4th floor). Time: 3:30 central Date: Tuesday, September 6th. Title: Non-standard bi-orders on punctured torus bundles Abstract: Consider a once punctured surface bundle over the circle. Perron-Rolfsen shows that having an Alexander polynomial with real positive roots is a sufficient condition for the bundle to have bi-orderable fundamental group. This is done by showing the action of the monodromy induced on the fundamental group of the surface preserves a “standard” bi-ordering. In this talk, we discuss if there are other ways to bi-order the fundamental group of a punctured torus bundle. This work is joint with Henry Segerman. ______________________ Neil R. Hoffman Assistant Professor Department of Mathematics 523 Math Science Building Oklahoma State University Stillwater, OK 74078-1058 405-744-7791 http://math.okstate.edu/people/nhoffman

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Mdtop September 2022