Topology and Symplectic Geometry Seminar

Spring 2020

January 30 - Francesco Lin (Columbia University)

• Talk: Monopole Floer homology and the length spectrum of hyperbolic three-manifolds (click for my notes)
  • Abstract: By studying the Seiberg-Witten equations, Kronheimer and Mrowka defined a package of invariants of three-manifolds called monopole Floer homology. In this talk, we focus on the case of a hyperbolic three-manifold, and discuss interactions between this invariant and geometric quantities coming from Riemannian geometry such as volume and lengths of closed geodesics. This is joint work with Mike Lipnowski.

February 6 - Yuhan Sun (Stony Brook University)

• Talk: Lagrangian submanifolds near Lagrangian spheres (click for Yuhan's notes)
  • Abstract: In the cotangent bundle of a smooth sphere, there are lots of interesting Lagrangian submanifolds with non-zero Floer invariants. These local Lagrangian submanifolds naturally sit inside a neighborhood of a Lagrangian sphere. We study how Floer invariants change when the ambient space changes, from the cotangent bundle to an abstract symplectic manifold. The strategy is to use the local information to control the global information to some extent. Applications include the existence of continuum families of nondisplaceable Lagarangian tori near a chain of Lagrangian 2-spheres and a new estimate of the displacement energy of Lagrangian 3-spheres.

February 13 - Marco Castronovo (Rutgers University)

• Talk: Exotic Lagrangian tori in Grassmannians (click for my notes)
  • Abstract: The complex Grassmannians contain a nondisplaceable monotone Lagrangian torus, which is a fibre of an integrable system introduced by Guillemin-Sternberg in the ‘80s. Usually, it does not generate the whole Fukaya category. I will talk about “exotic” Lagrangian tori that generate some of the missing parts. Their existence is a rather natural consequence of general ideas in mirror symmetry, cluster algebras and the theory of Okounkov bodies. Time permitting, I will mention how these ideas fit in a broader picture of mirror symmetry for coadjoint orbits of Lie groups.

February 20 - Vardan Oganesyan (Stony Brook University)

• Talk: Lagrangian Delzant Theorem and its applications
  • Abstract: We associate a closed Lagrangian submanifold L of C^n to each Delzant polytope. We prove that L is monotone if and only if the polytope P is Fano. It turns out that two Delzant polytopes P1 and P2 provide Hamiltonian isotopic Lagrangians if and only if P1 = gP2, where g is an element of SL(n, Z). Similar theorems can be proved for Lagrangians of CP^n and (CP^n)^k. Using this construction we can construct a huge number of monotone Lagrangian submanifolds. Many of the constructed monotone Lagrangians have equal minimal Maslov numbers and are smoothly isotopic, but they are not Hamiltonian isotopic. Also, the method allows the construction of infinitely many non-monotone embedded Lagrangians, no two of which are related by Hamiltonian isotopies (but they are smoothly isotopic). All these Lagrangians have many other interesting properties. If time permits, we will discuss applications to monotone Lagrangian cobordisms.

February 27 - Laura Starkston (UC Davis)

• Talk: Weinstein Trisections
  • Abstract: Gay and Kirby proved that every smooth 4-manifold admits a trisection--a decomposition into three pieces, each of which is a 1-handlebody. A Weinstein trisection is a trisection which is nicely compatible with a symplectic structure on the 4-manifold. We will explain this structure and show that every symplectic 4-manifold admits a Weinstein trisection. This is joint work with Peter Lambert-Cole and Jeffrey Meier.

March 5 - Ian Zemke (Princeton University)

• Talk: Ribbon concordances and knot Floer homology.
  • Abstract: A ribbon concordance is a concordance which has only critical points of index 0 and 1. In this talk, we will prove that the concordance maps on knot Floer homology are injective, which places a strong restriction on the knot Floer homologies of the two ends. We will describe several topological applications concerning the Seifert genera. We will also describe some generalizations, which are joint with Andras Juhasz, Adam Levine, and Maggie Miller, as well as survey some further developments by other authors.

No more talks for the semester due to COVID-19.