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247 discussions

Today in topology seminar - Nick Miller
by Hoffman, Neil 06 Dec '22

06 Dec '22

Hello everyone, Today in topology seminar we have Nick Milling visiting from OU. This will be the last topology seminar for the semester and we are likely going to pick back up in February, because Tuesday will be claimed for Job talks, but please keep the 3:30-4:30 time open for next semester. Nick's title and abstract are below. Best, Neil Topology Seminar 3:30 PM MSCS 445 Unmarked simple length spectral rigidity for covers Nick Miller, University of Oklahoma Host: Neil Hoffman Abstract: A long studied problem in hyperbolic (or more generally, negatively curved) geometry is the extent to which a manifold M is determined by its collection of lengths of closed geodesics on M. For instance, Otal showed that any negatively curved metric on a surface is determined up to isometry by its marked length spectrum, that is, by the function which associates to each closed curve the length of the unique geodesic in its free homotopy class. By classic work of Fricke, the similar result is true if one restricts this function only to simple closed curves. By celebrated constructions of Vigneras and Sunada, we now know that the corresponding statement is false when one forgets the marking, that is, there exist non-isometric surfaces which have the same collections of lengths of closed geodesics. In this talk, we will explore the extent to which surfaces arising from Sunada's construction can have the same collection of lengths of simple closed curves. Along the way we will also discuss some new general results about how simple lifts of curves can determine equivalence of covers. This represents joint work with Tarik Aougab, Max Lahn, and Marissa Loving. ______________________ 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 topology seminar this week - Nick Miller next week
by Hoffman, Neil 28 Nov '22

28 Nov '22

Hello everyone, There is no topology seminar this week. We will pick up next week with Nick Miller (OU). ______________________ 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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Tuesday in Topology seminar, usual time 3:30 central
by Hoffman, Neil 07 Nov '22

07 Nov '22

Hello everyone, Tomorrow in topology seminar we are very happy to have Dan Mathews (Monash University). He will be speaking at 3:30 pm our time. His title and abstract are below along with a NEW zoom link: Title: Symplectic structures in hyperbolic 3-manifold triangulations Abstract: In the 1980s, Neumann and Zagier introduced a symplectic vector space associated to an ideal triangulation of a cusped 3-manifold, such as a knot complement. We give an interpretation for this symplectic structure in terms of the topology of the 3-manifold, via intersections of certain curves on a Heegaard surface. We also give an algorithm to construct curves forming a symplectic basis for this vector space. This approach gives a description of hyperbolic structures on a knot complement via Ptolemy equations, which can be used to calculate the A-polynomial. This talk involves joint work with Jessica Purcell, Joshua Howie and Yi Huang. Neil Hoffman is inviting you to a scheduled Zoom meeting. Topic: Oklahoma State Topology Seminar Time: Nov 8, 2022 03:20 PM Central Time (US and Canada) Join Zoom Meeting https://zoom.us/j/96439236106?pwd=b2MvZ3BHbUw1eVBDbGU1ODhOS0puQT09 Meeting ID: 964 3923 6106 Passcode: JSJDecomp Join by Skype for Business https://zoom.us/skype/96439236106 ______________________ 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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Seminar today at 3:30
by Hoffman, Neil 01 Nov '22

01 Nov '22

Hello everyone, Just a reminder of the seminar today at 3:30. For anyone wishing to view seminar from the normal room, MSCS 445. I will be down there with zoom open and the talk projected on the screen. If you prefer to watch seminar from somewhere else, once again here is the link: 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 ______________________ 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 (virtual) topology seminar
by Hoffman, Neil 31 Oct '22

31 Oct '22

Hello everyone, This week we have Roger Casals, from UC Davis speaking in topology seminar at 3:30 central (1:30 pacific). The talk will be virtual, and the link is here: 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 The title and abstract are below: Title: A microlocal invitation to Legendrian links Abstract: We present recent developments in symplectic geometry and explain how they motivated new results in the study of cluster algebras. First, we introduce a geometric problem: the study of Lagrangian surfaces in the standard symplectic 4-ball bounding Legendrian knots in the standard contact 3-sphere. Thanks to results from the microlocal theory of sheaves, which we will survey, we then show that this geometric problem gives rise to an interesting moduli space. In fact, we establish a bridge translating geometric operations, such as Lagrangian disk surgeries, into algebraic properties of this moduli space, such as the existence of cluster algebra structures. The talk is intended for a broad mathematical audience and all key ideas will be introduced and motivated. Best, Neil ______________________ 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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Eric Sedgwick Today - at 2:30 in MSCS 101
by Hoffman, Neil 04 Oct '22

04 Oct '22

Hi Everyone, Sorry for the late email on this. Things were a little out of whack with the room scheduling. So we have a different time and place for the seminar this week. Today we will hold the seminar at 2:30 in MSCS 101. Topology Seminar Title: Embeddability in R 3 is NP-hard Speaker: Eric Sedgwick, Depaul University Date: Oct 4, 2022 Time: 2:30 PM Room: MSCS 101 Abstract: We prove that the problem of deciding whether a 2–or 3–dimensional simplicial complex embeds into R 3 is NP-hard. This stands in contrast with the lower dimensional cases which can be solved in linear time, and a variety of computational problems in R 3 like unknot or 3–sphere recognition which are in NP∩co-NP (assuming the generalized Riemann hypothesis). Our reduction encodes a satisfiability instance into the embeddability problem of a 3–manifold with boundary tori, and relies extensively on techniques from lowdimensional topology, most importantly Dehn fillings on link complements. This is joint work with Arnaud de Mesmay (CNRS, GIPSA-Lab, France), Yo’av Rieck (University of Arkansas, USA) and Martin Tancer (Charles University, Czech Republic). Best, Neil ______________________ 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 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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