Tag - Symplectic geometry

Mark McLean: Minimal Discrepancy of Isolated Singularities and Reeb Orbits

4th April, 2014

Let A be an affine variety inside a complex N-dimensional vector space which either has an isolated singularity at the origin or is smooth at the origin. The intersection of A with a very small sphere turns out to be a contact manifold called the link of A. Any contact manifold contactomorphic to the link of A is said to be Milnor fillable by A. If the first Chern class of our link is 0 then we can assign an invariant of our singularity called the minimal discrepancy, which is an important invariant in birational geometry. We relate the minimal discrepancy with indices of certain Reeb orbits on our link. As a result we show that the standard contact 5 dimensional sphere has a unique Milnor filling up to normalization.

Keon Choi: New combinatorial computations of embedded contact homology

7th March, 2014

Embedded contact homology is an invariant of a contact three-manifold, which is recently shown to be isomorphic to Heegaard Floer homology and Seiberg-Witten Floer homology. However, ECH chain complex depends on the contact form on the manifold and the almost complex structure on its symplectization. This fact can be used to extract symplectic geometric information (e.g. ECH capacities) but explicit computation of the chain complexes has been carried out only on a few cases. Extending the work of Hutchings-Sullivan, we combinatorially describe the ECH chain complexes of T3 with general T2-invariant contact forms and certain almost complex structures.

Steven Sivek: Contact invariants in sutured monopole and instanton homology

5th March, 2014

Kronheimer and Mrowka recently used monopole Floer homology to define an invariant of sutured manifolds, following work of Juhász in Heegaard Floer homology. In this talk, I will construct an invariant of a contact structure on a 3-manifold with boundary as an element of the associated sutured monopole homology group. I will discuss several interesting properties of this invariant, including gluing maps and an exact triangle associated to bypass attachment, and explain how this construction leads to an invariant in the sutured version of instanton Floer homology as well.

Sheel Ganatra: A criterion for generating Fukaya categories of fibrations

21st February, 2014

The Fukaya category of a fibration with singularities W : M→C, or Fukaya-Seidel category, enlarges the Fukaya category of M by including certain non-compact Lagrangians and asymmetric perturbations at infinity involving W; objects include Lefschetz thimbles if W is a Lefschetz fibration. I will recall this category and then explain a criterion, in the spirit of work of Abouzaid and Abouzaid-Fukaya-Oh-Ohta-Ono, for when a finite collection of Lagrangians split-generates such a fibration. The new ingredients needed include a Floer homology group associated to (M,W) and the Serre functor.

Mohammed Abouzaid: On Floer cohomology and non-archimedian geometry

14th February, 2014

Ideas of Kontsevich-Soibelman and Fukaya indicate that there is a natural rigid analytic space (the mirror) associated to a symplectic manifold equipped with a Lagrangian torus fibration. I will explain a construction which associates to a Lagrangian submanifold a sheaf on this space, and explain how this should be the mirror functor.

Jo Nelson: Cylindrical contact homology as a well-defined homology?

7th February, 2014

In this talk I will explain how the heuristic arguments sketched in literature since 1999 fail to define a homology theory. These issues will be made clear with concrete examples and we will explore what stronger conditions are necessary to develop a theory without the use of virtual chains or polyfolds in 3 dimensions. It turns out that this can be accomplished by placing strong conditions on the growth rates of the indices of Reeb orbits. In addition we sketch a new approach allowing us to compute cylindrical contact for a large class of examples which admit contact forms that are admissible under the stronger conditions required. This approach is applicable to prequantization spaces and the links of simple singularities.

Ralph Kaufmann: Feynman categories, universal operations and master equations

6th December, 2013

Feynman categories are a new universal categorical framework for generalizing operads, modular operads and twisted modular operads. The latter two appear prominently in Gromov-Witten theory and in string field theory respectively. Feynman categories can also handle new structures which come from different versions of moduli spaces with different markings or decorations, e.g., open/closed versions or those appearing in homological mirror symmetry. For any such Feynman category there is an associated Feynman category of universal operations. These give rise to Gerstenhaber's famous bracket, the pre-Lie structure of string topology, as well as to the Lie bracket underlying the three geometries of Kontsevich built from symplectic vector spaces. As time permits, we will also briefly discuss bar, co-bar and Feynman transforms and how these give rise to master equations, such as the Maurer-Cartan equation or the BV master equation.

Tim Perutz: Calabi-Yau mirror symmetry: from categories to curve-counts

15th November, 2013

I will report on joint work with Nick Sheridan concerning structural aspects of mirror symmetry for Calabi-Yau manifolds. We show (i) that Kontsevich's homological mirror symmetry (HMS) conjecture is a consequence of a fragment of the same conjecture which we expect to be much more amenable to proof; and, in ongoing work, (ii) that from HMS one can deduce (some of) the expected equalities between genus-zero Gromov-Witten invariants of a CY manifold and the Yukawa couplings of its mirror.

Michael Hutchings: How not to define cylindrical contact homology

18th October, 2013

We consider the problem of defining cylindrical contact homology, in the absence of contractible Reeb orbits, using "classical" methods. The main technical difficulty is failure of transversality of multiply covered cylinders. One can fix this difficulty by using S1-dependent almost complex structures, but at the expense of introducing another difficulty which we will explain. We outline how fixing the latter difficulty ultimately leads to a different theory, an analogue of positive symplectic homology. This talk is intended to be part of a series of expository talks on the foundations of contact homology, but prerequisites should be minimal.