[Topology.beta] DDT&G seminar: upcoming talks (Fall 2025)

[Rot, T.O. (Thomas)]

Dear all,

We are very pleased to announce the upcoming talks in the fall session of the “Dutch Differential Topology & Geometry seminar”, our joint seminar with Utrecht and Leiden. You can find the announcement below. 

In Fabio's talk you will learn why there is a picture of a scared hamster in the common room.

Best,
Thomas

Dear all,

*
26-09-2025 at Amsterdam: Fabio Gironella<https://fabiogironella.com> <https://fabiogironella.com>>, On symplectic foliations in high dimensions
*
31-10-2025 at Leiden: Martijn Kool<https://webspace.science.uu.nl/~kool0009/>,<https://www.mathematik.hu-berlin.de/~kegemarc/> <https://webspace.science.uu.nl/~kool0009/>,<https://www.mathematik.hu-berlin.de/~kegemarc/>> Isotropic Hopf index for orthogonal bundles and Magnificent Four
*
12-12-2025 at Utrecht: Pedro Boavida de Brito<https://www.math.tecnico.ulisboa.pt/~pbrito/> <https://www.math.tecnico.ulisboa.pt/~pbrito/>>, TBA








For more information please visit the seminar’s webpage: https://www.few.vu.nl/~trt800/ddtg.html <https://www.few.vu.nl/~trt800/ddtg.html>



If you wish to be added to the seminar mailing list and receive reminders before each individual talk, please send an email to f.pasquotto at math.leidenuniv.nl <mailto:f.pasquotto at math.leidenuniv.nl><mailto:f.pasquotto at math.leidenuniv.nl <mailto:f.pasquotto at math.leidenuniv.nl>>






We really encourage master students to attend the seminar. If you have any students who might be interested in these topics, please let them know that the seminar exists and let them sign up for the mailing list.






Hope to see you at one of our seminars!




Best wishes,


Alvaro del Pino (UU)


Federica Pasquotto (UL)


Thomas Rot (VU)




Fabio: On symplectic foliations in high dimensions:


The end goal of the two-hour presentation is to describe the results of a joint work with Klaus Niederkrueger and Lauran Toussaint, where we give a new obstruction, generalizing a 3-dimensional one due to Novikov in a symplectic-topological direction, for a symplectic foliation to be of a special type, called strong. This is based on the use of pseudo-holomorphic curves theory, which is an essential (and very powerful) tool to prove rigidity phenomena in symplectic topology.
The aim of the first hour of the talk is twofold. First, I will describe the overall idea of (one possible way) of using pseudo-holomorphic techniques to study symplectic manifolds with contact-type boundary, also called symplectic fillings, which is a very common setup in symplectic topology. Then, I will motivate the question underlying our joint work, by explaining (at least one reason) why one should care about (strong) symplectic foliations in high dimensions: they are one of the best candidates of subclass of foliations in high-dimensions to play the role of rigid objects analogously to taut foliations in ambient dimension 3. While giving the context for the rest of the talk in this first hour, I will mention some related problems and questions which are currently also of interest in symplectic topology.
The second hour of the presentation will then be dedicated to explain how the previously mentioned pseudo-holomorphic techniques can be adapted to the symplectically foliated setup in order to give the above claimed new obstruction to strongness of symplectic foliations. Time permitting, I will also sketch an explicit construction of a symplectic foliation which is not strong due to this new criterion, but cannot be deduced to be non-strong with other more elementary criteria.


Martijn: Isotropic Hopf index for orthogonal bundles and Magnificent Four:


The Hopf index (or Brouwer degree) of a smooth section of a smooth vector bundle plays a fundamental role in topology. When the section and vector bundle are holomorphic, it serves as a model for invariants in enumerative geometry such as Donaldson-Thomas invariants of Calabi-Yau 3-folds.
In part 1 (introductory), I introduce a Hopf-type index of a holomorphic isotropic section of a holomorphic orthogonal vector bundle, and discuss its various characterizations. It serves as a model for Donaldson-Thomas invariants of Calabi-Yau 4-folds. Joint work with Oh-Rennemo-Thomas.
In part 2 (more advanced), I will illustrate its use in the simplest possible counting problem on Calabi-Yau 4-folds: points on C^4. In this case, the (equivariant) isotropic Hopf index can be used to prove a formula discovered in supersymmetric Yang-Mills theory on C^4 by Nekrasov-Piazzalunga. Joint work Rennemo.
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