Topology & Geometry

The Topology & Geometry seminar meets on Tuesdays at 13:00 at room 70 in the Ross Building.
2019 Jul 31

T&G: Mikhail Gromov (IHES and Courant), Scalar curvature

2:00pm to 3:00pm

Location:

Room B221, Rothberg Building, Jerusalem
2019 May 21

T&G: David Nadler (Berkeley), What kind of an invariant are microlocal sheaves?

11:00am to 12:30pm

Location:

Room 07, Levi Building, Jerusalem, Israel
I will give an introduction to sheaves and microlocal sheaves, as pioneered by Kashiwara-Schapira. The goal will be to explain recent work with Shende establishing that microlocal sheaves on a Weinstein manifold are a symplectic invariant.
2019 Mar 26

T&G: Vivek Shende (Berkeley), Quantum topology from symplectic geometry

1:00pm to 2:30pm

Location:

Room 110, Manchester Building, Jerusalem, Israel
The discovery of the Jones polynomial in the early 80's was the beginning of quantum topology'': the introduction of various invariants which, in one sense or another, arise from quantum mechanics and quantum field theory. There are many mathematical constructions of these invariants, but they all share the defect of being first defined in terms of a knot diagram, and only subsequently shown by calculation to be independent of the presentation. As a consequence, the geometric meaning has been somewhat opaque.
2019 Mar 12

T&G: John Pardon (Princeton), Structural results in wrapped Floer theory

1:00pm to 2:30pm

Location:

Room 110, Manchester Building, Jerusalem, Israel
I will discuss results relating different partially wrapped Fukaya categories. These include a K\"unneth formula, a `stop removal' result relating partially wrapped Fukaya categories relative to different stops, and a gluing formula for wrapped Fukaya categories. The techniques also lead to generation results for Weinstein manifolds and for Lefschetz fibrations. The methods are mainly geometric, and the key underlying Floer theoretic fact is an exact triangle in the Fukaya category associated to Lagrangian surgery along a short Reeb chord at infinity.
2019 Mar 19

T&G: Viatcheslav Kharlamov (Strasbourg), Segre indices, Welschinger weights, and an invariant signed count of real lines on real projective hypersurfaces

1:00pm to 2:30pm

Location:

Room 110, Manchester Building, Jerusalem, Israel
As it was observed a few years ago, there exists a certain signed count of real lines on real projective hypersurfaces of degree 2n+1 and dimension n that, contrary to the honest "cardinal" count, is independent of the choice of a hypersurface, and by this reason provides, as a consequence, a strong lower bound on the honest count. Originally, in this invariant signed count the input of a line was given by its local contribution to the Euler number of an appropriate auxiliary universal vector bundle.
2019 Jan 23

T&G: Sylvain Cappell (NYU), Atiyah-Bott classes and extending representations of fundamental groups of 3-manifolds from part of the boundary

1:00pm to 2:00pm

Location:

Room 70, Ross Building, Jerusalem, Israel
We consider the problem of extending a representation of the fundamental group of 3-manifolds from part of the boundary surfaces. Applications to links will be discussed. Combining this with some cohomology classes of Atiyah and Bott leads to new multivariable polynomial invariants of 3-manifolds with boundary. This is joint work with Edward Miller. No background in 3-dimensional topology will be assumed in this survey and research talk.
2019 Jan 15

T&G: Michael Khanevsky (Technion), Geometry of sets of Hamiltonian isotopic curves in a symplectic surface

2:00pm to 3:30pm

Location:

Room 209, Manchester Building, Jerusalem, Israel
Given two Hamiltonian isotopic curves in a surface, one would like to tell whether they are "close" or "far apart". A natural way to do that is to consider Hofer's metric which computes mechanical energy needed to deform one curve into the other. However due to lack of tools the large-scale Hofer geometry is only partially understood. On some surfaces (e.g. S^2) literally nothing is known.
2019 Jan 08

T&G: David Treumann (Boston College), The Fargues-Fontaine curve for symplectic geometers -- NOTE special time and location

4:00pm to 5:30pm

Location:

Room 70, Ross Building, Jerusalem, Israel
I will review homological mirror symmetry for the torus, which describes Lagrangian Floer theory on T^2 in terms of vector bundles on the Tate elliptic curve --- a version of Lekili and Perutz's works "over Z", where t is the Novikov parameter. Then I will describe a modified form of this story, joint with Lekili, where the Floer theory is altered by a locally constant sheaf of rings on T^2 (an "F-field").
2018 Dec 25

T&G: Or Hershkovits (Stanford), Mean Curvature Flow of Surfaces -- NOTE special time and location

1:00pm to 2:00pm

Location:

Room 70, Ross Building, Jerusalem, Israel
In the last 35 years, geometric flows have proven to be a powerful tool in geometry and topology. The Mean Curvature Flow is, in many ways, the most natural flow for surfaces in Euclidean space. In this talk, which will assume no prior knowledge, I will illustrate how mean curvature flow could be used to address geometric questions.
2018 Dec 04

T&G: Pierrick Bousseau (ETH - ITS), Quivers and curves

2:00pm to 3:30pm

Location:

Room 209, Manchester Building, Jerusalem
I will talk about old and new results relating curve counting on complex surfaces and quiver representations.
2018 Nov 27

T&G: Graham Denham (Western University), Cohomological vanishing and abelian duality

2:00pm to 3:30pm

Location:

Room 209, Manchester Building, Jerusalem
Cohomology jump loci are secondary cohomological invariants of discrete groups and topological spaces. I will describe some recent work on the cohomology jump loci of complements of unions of smooth complex hypersurfaces, and I will motivate the notion of abelian duality spaces that I introduced in joint work with Alex Suciu and Sergey Yuzvinsky. The study of such hypersurface arrangements involves a mix of combinatorics and complex geometry.
2018 Nov 20

T&G: Gangotryi Sorcar (Hebrew University), On the topology of the Teichmuller space of negatively curved Riemannian metrics

2:00pm to 3:30pm

Location:

Room 209, Manchester Building, Jerusalem
This talk is a survey on results concerning the Teichmuller space of negatively curved Riemannian metrics on M. It is defined as the quotient space of the space of all negatively curved Riemannian metrics on M modulo the space of all isotopies of M that are homotopic to the identity. This space was shown to have highly non-trivial homotopy when M is real hyperbolic by Tom Farrell and Pedro Ontaneda in 2009.
2018 Oct 08

T&G: Stephan Rosebrock (Karlsruhe), Asphericity, Relative Asphericity and Labelled Oriented Trees

12:30pm to 2:00pm

Location:

Room 70, Ross Building, Jerusalem, Israel
The Whitehead conjecture asks whether a subcomplex of an aspherical 2-complex is always aspherical. This question is open since 1941. Howie has shown that the existence of a finite counterexample implies (up to the Andrews-Curtis conjecture) the existence of a counterexample within the class of labelled oriented trees. Labelled oriented trees are algebraic generalisations of Wirtinger presentations of knot groups.
2018 Jun 19

T&G: Yaron Ostrover (Tel Aviv), Quantitative symplectic geometry in the classical phase space.

12:00pm to 1:30pm

Location:

Room 110, Manchester Buildling, Jerusalem, Israel
We shall discuss several topics regarding symplectic measurements in the classical phase space. In particular: Viterbo's volume-capacity conjecture and its relation with Mahler conjecture, the symplectic size of random convex bodies, the EHZ capacity of convex polytopes (following the work of Pazit Haim-Kislev), and (if time permits) also computational complexity aspects of estimating symplectic capacities.
2018 Jun 12

T&G: Sara Tukachinsky (IAS), An enhanced quantum product and its associativity relation

1:00pm to 2:30pm

Location:

Room 110, Manchester Buildling, Jerusalem, Israel
Open Gromov-Witten (OGW) invariants count pseudoholomorphic maps from a Riemann surface with boundary to a symplectic manifold, with constraints that make sure the moduli space of solutions is zero dimensional. In joint work with J. Solomon (2016-2017), we defined OGW invariants in genus zero under cohomological conditions. In this talk, also based on joint work with J. Solomon, I will describe a family of PDEs satisfied by the generating function of our invariants. We call this family the open WDVV equations.