Information up to (and including) January 2021 can be found on the original seminar webpage at https://dms.umontreal.ca/~cornea/Seminar.html
Note: The next session will be held in DST in North America and Israel.
Thus, starting times for the next session are — in Paris: 2:15pm; Tel Aviv: 4:15pm; Montréal/Princeton: 9:15am.
Next session – Mar. 24: Yaron Ostrover (TAU)
Title: Symplectic Barriers
Abstract:
In this talk we discuss the existence of a new type of rigidity of symplectic embeddings coming from obligatory intersections with symplectic planes. This is based on a joint work with P. HaimKislev and R. Hind.
About the seminar
 Regular research talks are of 60 minutes. There will be 30 min at the end of each talk reserved for discussion. The first 15 minutes (roughly) are, mainly, for questions addressed to the speaker. After that, questions and answers may involve different participants.
 Once in several sessions we intend to have a seminar consisting of three 20min talks (followed each by 10min of discussion time) given by young researchers/recent PhD's. Suggestions, nominations, and volunteers (including a title and short abstract) should be sent to Egor Shelukhin at egorshel@gmail.com (with cc to octav.cornea@gmail.com).
 It is intended that all talks be accessible to a global community in symplectic geometry/topology and beyond (thus, they should contain an introduction of interest to a broad audience).
 Please do not hesitate to ask questions.
 We post links to the slides of the talks as well as links to recordings of the talks.
 In addition to this webpage, announcements are posted on researchseminars.org and sent out via the virtual symplectic seminars group.
The Zoominar promotes an atmosphere of collegiality, equity and respect and is committed to creating a welcoming and inclusive environment for all participants, enabling them to fully focus on mathematics.
Current Zoominar organizers: Octav Cornea (Montréal), Helmut Hofer (IAS), Vincent Humilière (Paris), Agustin Moreno (IAS), Leonid Polterovich (Tel Aviv), Egor Shelukhin (Montréal), Shira Tanny (IAS), Sara Tukachinsky (Tel Aviv), Claude Viterbo (Paris).
Future talks

Mar. 31: Georgios Dimitroglou Rizell (Uppsala),
A relative CalabiYau structure for Legendrian contact homology,
(abstract)
The duality long exact sequence relates linearised Legendrian contact homology and cohomology and was originally constructed by Sabloff in the case of Legendrian knots. We show how the duality long exact sequence can be generalised to a relative CalabiYau structure, as defined by Brav and Dyckerhoff. We also discuss the generalised notion of the fundamental class and give applications. The structure is established through the acyclicity of a version of Rabinowitz Floer Homology for Legendrian submanifolds with coefficiens in the ChekanovEliashberg DGA. This is joint work in progress with Legout.
 Apr. 7: Cancelled on account of the Symplectix seminar http://symplectix.blogspot.com/
 Apr. 14: Pierrick Bousseau (UGA), TBA

Apr. 21: Three 20min research talks
 Brayan Ferreira (IMPA), TBA
 Roman Krutowski (UCLA), TBA
 Amanda Hirschi (Cambridge), TBA
 Apr. 28: Michael Bialy (TAU), TBA
 May 5: Michael Entov (Technion), TBA
 May 12: Cancelled on account of the Symplectix seminar http://symplectix.blogspot.com/
 May 19: Vinicius Ramos (IMPA), TBA
 May 26: Joé Brendel (TAU), TBA
 Jun. 2: Cancelled on account of the Symplectix seminar http://symplectix.blogspot.com/
 Jun. 9: TBD
 Jun. 16: TBD
 Jun. 26: TBD
 Jun. 30: TBD
Past talks
Winter 2023

Mar. 17: Yuhan Sun (Rutgers),
Heaviness and relative symplectic cohomology,
(video),
(slides),
(abstract)
For a compact subset \(K\) of a closed symplectic manifold, EntovPolterovich introduced the notion of (super)heaviness, which reveals surprising symplectic rigidity. When \(K\) is a Lagrangian submanifold, there is a wellestablished criterion for its heaviness, by using closedopen maps. We will discuss an equivalence between the heaviness and the nonvanishing of the relative symplectic cohomology, for a general compact set \(K\). Joint with C.Y.Mak and U.Varolgunes.
 Mar. 10: Cancelled on account of the Symplectix seminar http://symplectix.blogspot.com/

Mar. 3: Marco Mazzucchelli (ENSLyon),
Surfaces of section, Anosov Reeb flows, and the \(C^2\)stability conjecture for geodesic flows,
(video),
(slides),
(abstract)
In this talk, based on joint work with Gonzalo Contreras, I will briefly sketch the proof of the existence of global surfaces of section for the Reeb flows of closed 3manifolds satisfying a condition à la KupkaSmale: nondegeneracy of the closed Reeb orbits, and transversality of the stable and unstable manifolds of the hyperbolic closed Reeb orbits.
I will then present an application of this theorem to hyperbolic Reeb dynamics: a Reeb flow on a closed 3manifold is Anosov if and only if the closure of the subspace of closed Reeb orbits is hyperbolic and the KupkaSmale transversality condition holds. This result implies the validity of the \(C^2\) stability conjecture for Riemannian geodesic flows of closed surfaces: any such geodesic flow that is \(C^2\) structurally stable within the class of Riemannian geodesic flows must be Anosov. 
Feb. 24: Noah Porcelli (Imperial),
Floer theory and framed cobordisms between exact Lagrangian submanifolds,
(video),
(slides),
(abstract)
Lagrangian Floer theory is a useful tool for studying the structure of the homology of Lagrangian submanifolds. In some cases, it can be used to detect more we show it can detect the framed bordism class of certain Lagrangians and in particular recover a result of AbouzaidAlvarezGavelaCourteKragh about smooth structures on Lagrangians in cotangent bundles of spheres. The main technical tool we use is Large's recent construction of a stablehomotopical enrichment of Lagrangian Floer theory.
This is based on joint workinprogress with Ivan Smith. 
Feb. 17: Yusuke Kawamoto (ETH),
Hypersurface singularities and spectral invariants,
(video),
(slides),
(abstract)
We discuss the relation between hypersurface singularities (e.g. ADE, \(\widetilde{E}_{6}\), \(\widetilde{E}_{7}\), \(\widetilde{E}_{8}\), etc) and spectral invariants, which are symplectic invariants coming from Floer theory.

Feb. 10: Three 20min research talks

David White (NSCU),
Symplectic instanton homology of knots and links in 3manifolds,
(video),
(slides),
(abstract)
Powerful homology invariants of knots in 3manifolds have emerged from both the gaugetheoretic and the symplectic kinds of Floer theory: on the gaugetheoretic side is the instanton knot homology of KronheimerMrowka, and on the symplectic the (Heegaard) knot Floer homology developed independently by OzsváthSzabó and by Rasmussen. These theories are conjecturally equivalent, but a precise connection between the gaugetheoretic and symplectic sides here remains to be understood. We describe a construction designed to translate singular instanton knot homology more directly into the symplectic domain, a socalled symplectic instanton knot homology: We define a Lagrangian Floer homology invariant of knots and links which extends a 3manifold invariant developed by H. Horton. The construction proceeds by using specialized Heegaard diagrams to parametrize an intersection of traceless \(SU(2)\) character varieties. The latter is in fact an intersection of Lagrangians in a symplectic manifold, giving rise to a Lagrangian Floer homology. We discuss its relation to singular instanton knot homology, as well as the formal properties which this suggests and methods to prove these properties.

Kai Hugtenburg (Edinburgh),
Open GromovWitten invariants from the Fukaya category,
(video),
(slides),
(abstract)
Enumerative mirror symmetry is a correspondence between closed GromovWitten invariants of a space \(X\), and period integrals of a family \(Y\). One of the predictions of Homological Mirror Symmetry is that the closed GromovWitten invariants can be obtained from the Fukaya category. For CalabiYau varieties this has been demonstrated by GanatraPerutzSheridan. Recently, enumerative mirror symmetry has been extended, by including open GromovWitten invariants and extended period integrals. It is natural to expect that open GromovWitten invariants can be obtained from the Fukaya category. In this talk I will outline a construction which will demonstrate this for certain open GromovWitten invariants.

Patricia Dietzsch (ETH),
Lagrangian Hofer metric and barcodes,
(video),
(slides),
(abstract)
Filtered Lagrangian Floer homology gives rise to a barcode associated to a pair of Lagrangians.
It is wellknown that the lengths of the finite bars and the spectral distance are lower bounds of the Lagrangian Hofer metric. In this talk we are interested in a reverse inequality.
I will explain an upper bound of the Lagrangian Hofer distance between equators in the cylinder in terms of a weighted sum of the lengths of the finite bars and the spectral distance.

David White (NSCU),
Symplectic instanton homology of knots and links in 3manifolds,
(video),
(slides),
(abstract)
 Feb. 3: Cancelled on account of the Symplectix seminar http://symplectix.blogspot.com/

Jan. 27: Semon Rezchikov (Princeton/IAS),
Hyperbolicity of periodic points of Hamiltonian maps,
(abstract)
The basic invariant of a fixed point of a Hamiltonian diffeomorphism, besides its existence (which is implied by the proven Arnol'd Conjecture), is the number of eigenvalues of unit norm of the linearization of the map at the fixed point. When there are no such eigenvalues, the fixed point is said to be purely hyperbolic, and has characteristically different local dynamics from the contrasting partially elliptic case. In this talk, I will discuss how period doubling bifurcations can be used to make periodic points purely hyperbolic without appreciably changing Floertheoretic invariants. Via a limiting process one can approximate Hamiltonian diffeomorphisms by hameomorphisms which behave as if they have only hyperbolic periodic points. We will review the dynamical background for such constructions, and if time permits, discuss upper and lower bounds on the growth rate of periodic points of these hameomorphisms.

Jan. 20: Shaoyun Bai (SCGP),
Arnold conjecture over integers,
(video),
(slides),
(abstract)
We show that for any closed symlectic manifold, the number of 1periodic orbits of any nondegenerate Hamiltonian is bounded from below by a version of total Betti number over Z, which takes account of torsions of all characteristics. The proof relies on an abstract perturbation scheme (FOP perturbations) which allows us to produce integral pseudocycles from moduli space of Jholomorphic curves, and a geometric regularization scheme for moduli space of Hamiltonian Floer trajectories generalizing the recent work of AbouzaidMcLeanSmith. I will survey these ideas and indicate potential future developments. This is joint work with Guangbo Xu.

Jan. 13: Christian Lange (LMU München),
Orbifolds and systolic inequalities,
(video),
(slides),
(abstract)
In this talk, I will first discuss some instances in which orbifolds occur in geometry and dynamics, in particular, in the context of billiards and systolic inequalities. Then I will present topological conditions for an orbifold to be a manifold together with applications to foliations and to Besse geodesic and Reeb flows (joint work with Manuel Amann, Marc Kegel and Marco Radeschi). Here a flow is called Besse if all its orbits are periodic. Such flows are related to systolic inequalities. Namely, I will explain a characterization of contact forms on 3manifolds whose Reeb flow is Besse as local maximizers of certain ''higher" systolic ratios, and mention other related systoliclike inequalities (joint work with Alberto Abbondandolo, Marco Mazzucchelli and Tobias Soethe).
 Jan. 6: Cancelled on account of the Symplectix seminar http://symplectix.blogspot.com/
Fall 2022

Dec. 16: Marcelo Alves (UAntwerp),
Hofer's geometry and braid stability,
(video),
(slides),
(abstract)
The Hofer’s metric \(d_H\) is a remarkable biinvariant metric on the group of Hamiltonian diffeomorphisms of a symplectic manifold. In my talk, I will explain a result, obtained jointly with Matthias Meiwes, which says that the braid type of a set of periodic orbits of a Hamiltonian diffeomorphism on a closed surface is stable under perturbations that are sufficiently small with respect to Hofer’s metric. As a consequence of this we obtained that the topological entropy, seen as a function on the space of Hamiltonian diffeomorphisms of a closed surface, is lower semicontinuous with respect to the Hofer metric \(d_H\).
If time permits, I will explain related questions for Reeb flows on 3manifolds and Hamiltonian diffeomorphisms on higherdimensional symplectic manifolds, and recent progress on these problems obtained by myself, Meiwes, Abror Pirnapasov and Lucas Dahinden. 
Dec. 9: Robert Cardona (ICMAT),
Periodic orbits and Birkhoff sections of stable Hamiltonian structures,
(video),
(slides),
(abstract)
In this talk, we start by reviewing recent results on the dynamics of Reeb vector fields defined by contact forms on threedimensional manifolds, and then introduce Reeb fields defined by stable Hamiltonian structures. These are more general and arise, for instance, in stable regular energy level sets of Hamiltonian systems. We give a characterization of Reeb fields that are aperiodic or that have finitely many periodic orbits (under a certain nondegeneracy assumption). Finally, we give sufficient conditions for the existence of an adapted broken book decomposition or the existence of a Birkhoff section. This is joint work with A. Rechtman.
 Dec. 2: Cancelled on account of the Symplectix seminar http://symplectix.blogspot.com/

Nov. 25: Three 20min research talks

Yash Deshmukh (Columbia),
Moduli spaces of nodal curves from homotopical algebra,
(video),
(slides),
(abstract)
I will discuss how the DeligneMumford compactification of curves arises from the uncompactified moduli spaces of curves as a result of some algebraic operations related to (pr)operadic structures on the moduli spaces. I will describe how a variation of this naturally gives rise to another new partial compactification of moduli spaces curves. Time permitting, I will indicate how it is related to secondary operations on symplectic cohomology and discuss some ongoing work in this direction.

Lea Kenigsberg (Columbia),
Coproduct structures, a tale of two outputs,
(video),
(slides),
(abstract)
I will motivate the study of coproducts and describe a new coproduct structure on the symplectic cohomology of Liouville manifolds. Time permitting, I will indicate how to compute it in an example to show that it's not trivial. This is based on my thesis work, in progress.

Thomas Massoni (Princeton),
NonWeinstein Liouville domains and threedimensional Anosov flows,
(video),
(slides),
(abstract)
Weinstein domains and their symplectic invariants have been extensively studied over the last 30 years. Little is known about nonWeinstein Liouville domains, whose first instance is due to McDuff. I will describe two key examples of such domains in dimension four, and then explain how they fit into a general construction based on Anosov flows on threemanifolds. The symplectic invariants of these “Anosov Liouville domains” constitute new invariants of Anosov flows. The algebraic structure of their wrapped Fukaya categories is in stark contrast with the Weinstein case.
This is mostly based on joint work arXiv:2211.07453 with Kai Cieliebak, Oleg Lazarev and Agustin Moreno.

Yash Deshmukh (Columbia),
Moduli spaces of nodal curves from homotopical algebra,
(video),
(slides),
(abstract)

Nov. 18: Cancelled on account of
the Symplectix seminar
http://symplectix.blogspot.com/
and the conference Floer homotopical methods in low dimensional and symplectic topology, https://www.msri.org/workshops/1024 
Nov. 11: Roger Casals (UC Davis),
A microlocal invitation to Lagrangian fillings,
(video),
(slides),
(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 4ball bounding Legendrian knots in the standard contact 3sphere. 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 symplectic audience and all key ideas will be introduced and motivated.

Nov. 4: Ipsita Datta (IAS),
Lagrangian cobordisms, enriched knot diagrams, and algebraic invariants,
(video),
(abstract)
We introduce new invariants to the existence of Lagrangian cobordisms in \(\mathbb{R}^4\). These are obtained by studying holomorphic disks with corners on Lagrangian tangles, which are Lagrangian cobordisms with flat, immersed boundaries.
We develop appropriate sign conventions and results to characterize boundary points of 1dimensional moduli spaces with boundaries on Lagrangian tangles. We then use these to define (SFTlike) algebraic structures that recover the previously described obstructions.
This talk is based on my thesis work under the supervision of Y. Eliashberg and on work in progress joint with J. Sabloff. 
Oct. 28: Three 20min research talks

PierreAlexandre Mailhot (UdeM),
The spectral diameter of a Liouville domains and its applications,
(video),
(slides),
(abstract)
The spectral norm provides a lower bound to the Hofer norm. It is thus natural to ask whether the diameter of the spectral norm is finite or not. During this short talk, I will give a sketch of the proof that, in the case of Liouville domains, the spectral diameter is finite if and only if the symplectic cohomology of the underlying manifold vanishes. With that relationship in hand, we will explore applications to symplecticaly aspherical symplectic manifolds and Hofer geometry.

Nicole Magill (Cornell),
A correspondence between obstructions and constructions for staircases in Hirzebruch surfaces,
(video),
(slides),
(abstract)
The ellipsoidal embedding function of a symplectic four manifold M measures how much the symplectic form on M must be dilated in order for it to admit an embedded ellipsoid of some eccentricity. It generalizes the Gromov width and ball packing numbers. In most cases, finitely many obstructions besides the volume determine the function. If there are infinitely many obstructions determining the function, M is said to have an infinite staircase. This talk will give a classification of which Hirzebruch surfaces have infinite staircases. We will focus on explaining the correspondence between the obstructions coming from exceptional classes and the constructions from almost toric fibrations. We define a way to mutate triples of exceptional classes to produce new triples of exceptional classes, which corresponds to mutations in almost toric fibrations. This is based on various joint work with Dusa McDuff, Ana Rita Pires, and Morgan Weiler.

Ofir Karin (Tel Aviv),
Approximation of Generating Function Barcode for HamiltonianDiffeomorphisms,
(video),
(slides),
(abstract)
Persistence modules and barcodes are used in symplectic topology to define new invariants of Hamiltonian diffeomorphisms, however methods that explicitly calculate these barcodes are often unclear. In this talk I will define one such invariant called the GFbarcode of compactly supported Hamiltonian diffeomorphisms of \(\mathbb{R}^{2n}\) by applying Morse theory to generating functions quadratic at infinity associated to such Hamiltonian diffeomorphisms and provide an algorithm (i.e a finite sequence of explicit calculation steps) that approximates it along with a few computation examples. This is joint work with Pazit HaimKislev.

PierreAlexandre Mailhot (UdeM),
The spectral diameter of a Liouville domains and its applications,
(video),
(slides),
(abstract)

Oct. 21: Jean Gutt (Albi and Toulouse),
Symplectic convexity? (an ongoing story...),
(video),
(slides),
(abstract)
What is the symplectic analogue of being convex? We shall present different ideas to approach this question. Along the way, we shall present recent joint results with J.Dardennes and J.Zhang on monotone toric domains nonsymplectomorphic to convex domains and with M.Pereira and V.Ramos on cubenormalized capacities.

Oct. 14: Igor Uljarević (Belgrade),
Contact nonsqueezing via selective symplectic homology,
(video),
(slides),
(abstract)
I will introduce a new version of symplectic homology that resembles the relative symplectic homology and that is related to the symplectic homology of a Liouville sector. This version, called selective symplectic homology, is associated with a Liouville domain and an open subset of its boundary. The selective symplectic homology is obtained as the direct limit of the Floer homology groups for Hamiltonians whose slopes tend to infinity on the open subset but remain close to 0 and positive on the rest of the boundary. As an application, I will prove a contact nonsqueezing phenomenon on homotopy spheres that are fillable by Liouville domains with infinite dimensional symplectic homology: there exists a smoothly embedded closed ball in such a sphere that cannot be made arbitrarily small by a contact isotopy. These homotopy spheres include examples that are diffeomorphic to standard spheres and whose contact structures are homotopic to standard contact structures.
Spring 2022

Jun. 24: Julian Chaidez (IAS/Princeton),
The Ruelle invariant and convexity in higher dimensions,
(video),
(slides),
(abstract)
I will explain how to construct the Ruelle invariant of a symplectic cocycle over an arbitrary measure preserving flow. I will provide examples and computations in the case of Hamiltonian flows and Reeb flows (in particular, for toric domains). As an application of this invariant, I will construct toric examples of dynamically convex domains that are not symplectomorphic to convex ones in any dimension.
This talk is based on joint works arXiv:2012.12869 and arXiv:2205.00935 with Oliver Edtmair. 
Jun. 17: Yoel Groman (HUJI),
Locality and deformations in relative symplectic cohomology,
(video),
(slides),
(abstract)
Relative symplectic cohomology is a Floer theoretic invariant associated with compact subsets K of a closed or geometrically bounded symplectic manifold M. The motivation for studying it is that it is often possible to reduce the study of global Floer theory of M to the Floer theory of a handful of local models covering M which one hopes will be easier to compute (Varolgunes’ spectral sequence). As an example, it is expected that at least in the setting of the GrossSiebert program, the mirror can be pieced together from the relative symplectic cohomologies of neighborhoods of fibers of an SYZ fibration (singular or not). However, even when K is a well understood model, such as the Weinstein neighborhood of a Lagrangian torus, the construction of relative SH is rather unwieldy. In particular, it is not entirely obvious how to relate the symplectic cohomology of K relative to M with Floer theoretic invariants intrinsic to K. I will discuss a number of results, most of them in preparation, which aim to alleviate this difficulty in the setting Lagrangian torus fibrations with singularities. Partly joint with U. Varolgunes.

Jun. 3: Guangbo Xu (Texas A&M),
Integervalued GromovWitten type invariants,
(video),
(slides),
(abstract)
GromovWitten invariants for a general target are rationalvalued but not necessarily integervalued. This is due to the contribution of curves with nontrivial automorphism groups. In 1997 Fukaya and Ono proposed a new method in symplectic geometry which can count curves with a trivial automorphism group. While ordinary GromovWitten invariants only use the orientation on the moduli spaces, this integervalued counts are supposed to also use the (stable) complex structure on the moduli spaces. In this talk I will present the recent joint work with Shaoyun Bai in which we rigorously defined the integervalued GromovWitten type invariants in genus zero for a symplectic manifold. This talk is based on the preprint https://arxiv.org/abs/2201.02688.

May 27: Three 20min research talks

Daniel Rudolf (Bochum),
Viterbo‘s conjecture for Lagrangian products in \(\mathbb{R}^4\),
(video),
(slides),
(abstract)
We show that Viterbo‘s conjecture (for the EHZcapacity) for convex Lagrangian products in \(\mathbb{R}^4\) holds for all Lagrangian products (any trapezoid in \(\mathbb{R}^2\))x(any convex body in \(\mathbb{R}^2\)). Moreover, we classify all equality cases of Viterbo’s conjecture within this configuration and show which of them are symplectomorphic to a Euclidean ball. As byproduct, we conclude sharp systolic Minkowski billiard inequalities for geometries which have trapezoids as unit balls. Finally, we show that the flows associated to the above mentioned equality cases (which are polytopes) satisfy a weak Zoll property, namely, that every characteristic that is almost everywhere away from lowerdimensional faces is closed, runs over exactly 8 facets, and minimizes the action.

Miguel Pereira (Augsburg),
The Lagrangian capacity of toric domains,
(video),
(slides),
(abstract)
In this talk, I will state a conjecture giving a formula for the Lagrangian capacity of a convex or concave toric domain. First, I will explain a proof of the conjecture in the case where the toric domain is convex and 4dimensional, using the GuttHutchings capacities as well as the McDuffSiegel capacities. Second, I will explain a proof of the conjecture in full generality, but assuming the existence of a suitable virtual perturbation scheme which defines the curve counts of linearized contact homology. This second proof makes use of Siegel's higher symplectic capacities.

Maksim Stokić (Tel Aviv),
\(C^0\) contact geometry of isotropic submanifolds,
(video),
(slides),
(abstract)
Homeomorphism is called contact if it can be written as \(C^0\)limit of contactomorphisms. The contact version of EliashbergGromov rigidity theorem states that smooth contact homeomorphisms preserve contact structure. Submanifold \(L\) of a contact manifold \((Y,\xi)\) is called isotropic if \(\xi_{TL}=0\). Isotropic submanifolds of maximal dimension are called Legendrian, otherwise we call them subcritical isotropic.
In this talk, we will try to answer whether the isotropic property is preserved by contact homeomorphisms. It is expected that subcritical isotropic submanifolds are flexible, while we expect that Legendrians are rigid. We show that subcritical isotropic curves are flexible, and we give a new proof of the rigidity of Legendrians in dimension 3. Moreover, we provide a certain type of rigidity of Legendrians in higher dimensions.

Daniel Rudolf (Bochum),
Viterbo‘s conjecture for Lagrangian products in \(\mathbb{R}^4\),
(video),
(slides),
(abstract)

May 20: Claude Viterbo (Paris),
Gammasupport, gammacoisotropic subsets and applications,
(video),
(slides),
(abstract)
To an element in the completion of the set of Lagrangians for the spectral distance we associate a support. We show that such a support is \(\gamma\)coisotropic (a notion we shall define in the talk) and we shall give examples and counterexamples of \(\gamma\)coisotorpic sets that can be (or cannot be) \(\gamma\)supports. Finally we give some applications of these notions to singular support of sheaves (joint work with S. Guillermou) and dissipative dynamics, allowing us to extend the notion of Birkhoff attractor (joint with V. Humilière).

May 6: Kevin Ruck (Augsburg),
Tate homology and powered flybys,
(video),
(slides),
(abstract)
In this talk I want to show that in the planar circular restricted three body problem there are infinitely many symmetric consecutive collision orbits for all energies below the first critical energy value. By using the LeviCivita regularization we will be able to distinguish between two different orientations of these orbits and prove the above claim for both of them separately. In the first part of the talk I want to explain the motivation behind this result, especially its connection to powered flybys. Afterwards I will introduce the main technical tools, one needs to prove the above statement, like Lagrangian Rabinowitz Floer Homology and its \(G\)equivariant version. To be able to effectively calculate this \(G\)equivariant Lagrangian RFH, we will relate it to the Tate homology of the group \(G\). With this tool at hand we will then finally be able to prove that there are infinitely many consecutive collision orbits all facing in a specific direction.

Apr. 29: Joel Fine (ULB),
Knots, minimal surfaces and Jholomorphic curves,
(video),
(slides),
(abstract)
Let \(K\) be a knot or link in the 3sphere, thought of as the ideal boundary of hyperbolic 4space, \(H^4\). The main theme of my talk is that it should be possible to count minimal surfaces in \(H^4\) which fill \(K\) and obtain a link invariant. In other words, the count doesn’t change under isotopies of \(K\). When one counts minimal disks, this is a theorem. Unfortunately there is currently a gap in the proof for more complicated surfaces. I will explain “morally” why the result should be true and how I intend to fill the gap. In fact, this (currently conjectural) invariant is a kind of Gromov–Witten invariant, counting \(J\)holomorphic curves in a certain symplectic 6manifold diffeomorphic to \(S^2\times H^4\). The symplectic structure becomes singular at infinity, in directions transverse to the \(S^2\) fibres. These singularities mean that both the Fredholm and compactness theories have fundamentally new features, which I will describe. Finally, there is a whole class of infinitevolume symplectic 6manifolds which have singularities modelled on the above situation. I will explain how it should be possible to count \(J\)holomorphic curves in these manifolds too, and obtain invariants for links in other 3manifolds.

Apr. 22: Jack Smith (Cambridge),
From Floer to Hochschild via matrix factorisations,
(video),
(slides),
(abstract)
The Hochschild cohomology of the Floer algebra of a Lagrangian \(L\), and the associated closedopen string map, play an important role in the generation criterion for the Fukaya category and in deformation theory approaches to mirror symmetry. I will explain how, in the monotone setting, one can build a map from the Floer cohomology of \(L\) with certain local coefficients to (a version of) Hochschild cohomology. This map makes things much more geometric, by transferring the algebraic complexity to the world of matrix factorisations, and is an isomorphism when \(L\) is a torus.

Apr. 15: Kyler Siegel (USC),
Singular plane curves and stable nonsqueezing phenomena,
(video),
(slides),
(abstract)
The existence of rational plane curves of a given degree with prescribed singularities is a subtle and active area in algebraic geometry. This problem turns out to be closely related to difficult enumerative problems which arise in symplectic field theory, which in turn play a central role in the theory of high dimensional symplectic embeddings. In this talk I will discuss various perspectives on these enumerative problems and present a new closed formula for relevant curve counts as a sum over decorated trees.

Apr. 8: Yann Rollin (Nantes),
Lagrangians, symplectomorphisms and zeroes of moment maps,
(video),
(slides),
(abstract)
I will present two constructions of Kähler manifolds, endowed with Hamiltonian torus actions of infinite dimension. In the first example, zeroes of the moment map are related to isotropic maps from a surfaces in \(\mathbb{R}^{2n}\). In the second example, which is actually a hyperKähler moment map, the zeroes are related to symplectic maps of the torus \(T^4\). The corresponding modified moment map flows have short time existence. Polyhedral analogues of these constructions can be used to investigate piecewise linear symplectic geometry.
Winter 2022

Mar. 25: Three 20min research talks

Benoît Joly (Bochum),
Barcodes for Hamiltonian homeomorphisms of surfaces,
(video),
(slides),
(abstract)
In this talk, we will study the Floer Homology barcodes from a dynamical point of view. Our motivation comes from recent results in symplectic topology using barcodes to obtain dynamical results. We will give the ideas of new constructions of barcodes for Hamiltonian homeomorphisms of surfaces using Le Calvez's transverse foliation theory. The strategy consists in copying the construction of the Floer and Morse Homologies using dynamical tools like Le Calvez's foliations.

Marco Castronovo (Columbia),
Polyhedral Liouville domains,
(video),
(slides),
(abstract)
I will explain the construction of a new class of Liouville domains that live in a complex torus of arbitrary dimension, whose boundary dynamics encodes information about the singularities of a toric compactification. The primary motivation for this work is to find a symplectic interpretation of some curious Laurent polynomials that appear in mirror symmetry for Fano manifolds; it also potentially opens a path to bound symplectic capacities of polarized projective varieties from below.

Agniva Roy (Georgia Tech),
Constructions of high dimensional Legendrians and isotopies,
(video),
(slides),
(abstract)
I will talk about an ongoing project that explores the construction of high dimensional Legendrian spheres from supporting open books and contact structures. The input is a Lagrangian disk filling of a Legendrian knot in the binding. We try to understand the relationship between different constructions from the same input, and suggest parallels, in the \(S^{2n+1}\) case, to a construction defined by Ekholm for \(\mathbb{R}^{2n+1}\).

Benoît Joly (Bochum),
Barcodes for Hamiltonian homeomorphisms of surfaces,
(video),
(slides),
(abstract)

Mar. 18: Anton Izosimov (Arizona),
Dimers, networks, and integrable systems,
(video),
(slides),
(abstract)
I will review two combinatorial constructions of integrable systems: GoncharovKenyon construction based on counting perfect matchings in bipartite graphs, and GekhtmanShapiroTabachnikovVainshtein construction based on counting paths in networks. After that I will outline my proof of equivalence of those constructions. The talk is based on my recent preprint arXiv:2108.04975.

Mar. 4: MarieClaude Arnaud (Paris),
Invariant submanifolds for conformal dynamics,
(video),
(slides),
(abstract)
In a work with Jacques Fejoz, we consider the conformal dynamics on a symplectic manifold , i.e. for which the symplectic form is transformed colinearly to itself. In the nonsymplectic case, we study the problem of isotropy and uniqueness of invariant submanifolds. More precisely, in this talk, I will explain a relation between topological entropy and isotropy and some uniqueness results.

Feb. 25: Erman Çineli (Paris),
Topological entropy of Hamiltonian diffeomorphisms: a persistence homology and Floer theory perspective,
(video),
(slides),
(abstract)
In this talk I will introduce barcode entropy and discuss its connections to topological entropy. The barcode entropy is a Floertheoretic invariant of a compactly supported Hamiltonian diffeomorphism, measuring, roughly speaking, the exponential growth under iterations of the number of nottooshort bars in the barcode of the Floer complex. The topological entropy bounds from above the barcode entropy and, conversely, the barcode entropy is bounded from below by the topological entropy of any hyperbolic locally maximal invariant set. As a consequence, the two quantities are equal for Hamiltonian diffeomorphisms of closed surfaces. The talk is based on a joint work with Viktor Ginzburg and Başak Gürel.

Feb. 18: Umut Varolgunes (Boğaziçi),
Reynaud models from relative Floer theory,
(video),
(slides),
(abstract)
I will start by explaining the construction of a formal scheme starting with an integral affine manifold \(Q\) equipped with a decomposition into Delzant polytopes. This is a weaker and more elementary version of degenerations of abelian varieties originally constructed by Mumford. Then I will reinterpret this construction using the corresponding Lagrangian torus fibration \(X\to Q\) and relative Floer theory of its canonical Lagrangian section. Finally, I will discuss a conjectural generalization of the story to decompositions of CY symplectic manifolds into symplectic log CY's whose boundaries are "opened up".

Feb. 11: Ely Kerman (UIUC),
On symplectic capacities and their blind spots,
(video),
(slides),
(abstract)
In this talk I will discuss a joint project with Yuanpu Liang in which we establish several properties of the sequence of symplectic capacities defined by Gutt and Hutchings for starshaped domains using \(S^1\)equivariant symplectic homology. Among the results discussed will be the fact that, unlike the first of these capacities, the others all fail to satisfy the symplectic version of the Brunn Minkowski established by ArtsteinAvidan and Ostrover. We also show that the GuttHutchings capacities, together with the volume, do not constitute a complete set of symplectic invariants even for convex bodies with smooth boundary. The examples constructed to prove these results are not exotic. They are convex and concave toric domains. The main new tool used is a significant simplification of the formulae of Gutt and Hutchings for the capacities of such domains, that holds under an additional symmetry assumption. This allows us to compute the capacities in new examples and to identify and exploit blind spots that they sometimes share.

Jan. 28: Three 20min research talks

Dustin ConneryGrigg (UdeM),
Geometry and topology of Hamiltonian Floer complexes in lowdimension,
(video),
(slides),
(abstract)
In this talk, I will present two results relating the qualitative dynamics of nondegenerate Hamiltonian isotopies on surfaces to the structure of their Floer complexes.
The first will be a topological characterization of those Floer chains which represent the fundamental class in \(CF_*(H,J)\) and which moreover lie in the image of some chainlevel PSS map. This leads to a novel symplectically biinvariant norm on the group of Hamiltonian diffeomorphisms, which is both \(C^0\)continuous and computable in terms of the underlying dynamics. The second result explains how certain portions of the Hamiltonian Floer chain complex may be interpreted geometrically in terms of positively transverse singular foliations of the mapping torus, with singular leaves given by certain maximal collections of unlinked orbits of the suspended flow. This construction may be seen to provide a Floertheoretic construction of the `torsionlow’ foliations which appear in Le Calvez’s theory of transverse foliations for surface homeomorphisms, thereby establishing a bridge between the two theories. 
Pazit HaimKislev (Tel Aviv),
Symplectic capacities of pproducts,
(video),
(slides),
(abstract)
A generalization of the cartesian product and the free sum of two convex domains is the pproduct operation.
We investigate the behavior of symplectic capacities with respect to symplectic pproducts, and we give applications related to Viterbo's volumecapacity conjecture and to pdecompositions of the symplectic ball. 
Thibaut Mazuir (Paris),
Higher algebra of Ainfinity algebras in Morse theory,
(video),
(slides),
(abstract)
In this short talk, I will introduce the notion of nmorphisms between two Ainfinity algebras. These higher morphisms are such that 0morphisms correspond to standard Ainfinity morphisms and 1morphisms correspond to Ainfinity homotopies. Their combinatorics are then encoded by new families of polytopes, which I call the nmultiplihedra and which generalize the standard multiplihedra.
Elaborating on works by Abouzaid and Mescher, I will then explain how this higher algebra of Ainfinity algebras naturally arises in the context of Morse theory, using moduli spaces of perturbed Morse gradient trees.

Dustin ConneryGrigg (UdeM),
Geometry and topology of Hamiltonian Floer complexes in lowdimension,
(video),
(slides),
(abstract)

Jan. 21: Susan Tolman (UIUC),
Beyond semitoric,
(video),
(slides),
(abstract)
A compact four dimensional completely integrable system \(f:M \to R^2\) is semitoric if it has only nondegenerate singularities, without hyperbolic blocks, and one of the components of \(f\) generates a circle action. Semitoric systems have been extensively studied and have many nice properties: for example, the preimages \(f^{1}(x)\) are all connected. Unfortunately, although there are many interesting examples of semitoric systems, the class has some limitation. For example, there are blowups of \(S^2 \times S^2\) with Hamiltonian circle actions which cannot be extended to semitoric systems. We expand the class of semitoric systems by allowing certain degenerate singularities, which we call ephemeral singularities. We prove that the preimage \(f^{1}(x)\) is still connected for this larger class. We hope that this class will be large enough to include not only all compact four manifolds with Hamiltonian circle actions, but more generally all complexity one spaces. Based on joint work with D. Sepe.

Jan. 14: Michael Sullivan (UMass Amherst),
Quantitative Legendrian geometry,
(video),
(slides),
(abstract)
I will discuss some quantitative aspects for Legendrians in a (more or less) general contact manifold. These include lower bounds on the number of Reeb chords between a Legendrian and its contact Hamiltonian image, the nondegeneracy of the Chekanov/Hofer/Shelukhin Legendrian metric, and some 3dimensional nonsqueezing results. The main tool is the barcode of a relative Rabinowitz Floer theory. This is joint work with Georgios Dimitroglou Rizell.
Fall 2021

Dec. 17: Three 20min research talks

Wenyuan Li (Northwestern),
Estimating Reeb chords using microlocal sheaf theory,
(video),
(slides),
(abstract)
We show that, for closed Legendrians in 1jet bundles, when there is a sheaf with singular support on the Legendrian, then (1) its self Reeb chords are bounded from below by half the sum of Betti numbers, and (2) the Reeb chords between itself and its Hamiltonian push off is bounded from below by Betti numbers when the \(C^0\)norm of the Hamiltonian is small. I will show how to visualize Reeb chords/Lagrangian intersections in sheaf theory, and then explain the duality exact triangle and the persistence structure used in the proof. If time permits, I will state a conjecture on the relative CalabiYau structure that arises from the duality exact triangle.

Jakob Hedicke (Bochum),
Lorentzian distance functions on the group of contactomorphisms,
(video),
(slides),
(abstract)
The notion of positive (nonnegative) contact isotopy, defined by Eliashberg and Polterovich, leads to two relations on the group of contactomorphisms.
These relations resemble the causal relations of a Lorentzian manifold.
In this talk we will introduce a class of Lorentzian distance functions on the group of contactomorphisms, that are compatible with these relations.
The Lorentzian distance functions turn out to be continuous with respect to the Hofernorm of a contactomorphism defined by Shelukhin. 
Johan Asplund (Uppsala),
Simplicial descent for ChekanovEliashberg dgalgebras,
(video),
(slides),
(abstract)
In this talk we introduce a type of surgery decomposition of Weinstein manifolds we call simplicial decompositions. We will discuss the result that the ChekanovEliashberg dgalgebra of the attaching spheres of a Weinstein manifold satisfies a descent (cosheaf) property with respect to a simplicial decomposition. Simplicial decompositions generalize the notion of Weinstein connected sum and there is in fact a onetoone correspondence (up to Weinstein homotopy) between simplicial decompositions and socalled good sectorial covers. The motivation behind these results is the sectorial descent result for wrapped Fukaya categories by GanatraPardonShende.

Wenyuan Li (Northwestern),
Estimating Reeb chords using microlocal sheaf theory,
(video),
(slides),
(abstract)

Dec. 10: Urs Frauenfelder (Augsburg),
GIT quotients and symplectic data analysis,
(video),
(abstract)
This is joint work with Agustin Moreno and Dayung Koh. The restricted threebody problem is invariant under various antisymplectic involutions. These real structures give rise to the notion of symmetric periodic orbits which simultaneously have a closed string interpretation namely as a periodic orbit as well as an open string interpretation as Hamiltonian chords. This makes the bifurcation analysis of symmetric periodic orbits very intriguing since under bifurcations two local Floer homologies are invariant, the periodic one as well as the Lagrangian one. In this talk we explain how methods from symmetric space theory can help to extract efficiently datas from reduced monodromy matrices of periodic orbits helping to analyse the possible bifurcation patterns.

Nov. 26: Mohammed Abouzaid (Columbia),
Complex cobordism and Hamiltonian fibrations,
(video),
(slides),
(abstract)
I will discuss joint work with McLean and Smith, lifting the results of Seidel, Lalonde, McDuff, and Polterovich concerning the topology of Hamiltonian fibrations over the 2sphere from rational cohomology to complex cobordism. In addition to the use of Morava Ktheory (as in the recent work with Blumberg on the Arnold Conjecture), the essential new ingredient is the construction of global Kuranishi charts for genus 0 pseudoholomorphic curves; i.e. their realisation as quotients of zero loci of sections of equivariant vector bundles on manifolds.

Nov. 19: Fabio Gironella (HU Berlin),
Exact orbifold fillings of contact manifolds,
(video),
(slides),
(abstract)
The topic of the talk will be Floer theories on exact symplectic orbifolds with smooth contact boundary. More precisely, I will first describe the construction, which only uses classical transversality techniques, of a symplectic cohomology group on such symplectic orbifolds. Then, I will give some geometrical applications, such as restrictions on possible singularities of exact symplectic fillings of some particular contact manifolds, and the existence, in any odd dimension at least 5, of a pair of contact manifolds with no exact symplectic (smooth) cobordisms in either direction. This is joint work with Zhengyi Zhou.

Nov. 5: Three 20min research talks

Rohil Prasad (Princeton),
The smooth closing lemma for areapreserving surface diffeomorphisms,
(video),
(slides),
(abstract)
In this talk, I will discuss recent joint work with D. CristofaroGardiner and B. Zhang showing that a generic areapreserving diffeomorphism of a closed surface has a dense set of periodic points. This follows from a result called a “smooth closing lemma” for areapreserving surface diffeomorphisms; this answers in the affirmative Smale’s 10th problem in the setting of areapreserving surface diffeomorphisms. The proof uses quantitative analysis of spectral invariants from periodic Floer homology via various estimates in SeibergWitten theory.

Alex Pieloch (Columbia),
Sections and unirulings of families over the projective line,
(video),
(slides),
(abstract)
We will discuss the existence of rational (multi)sections and unirulings for projective families \(f: X \rightarrow P^1\) with at most two singular fibres. Specifically, we will discuss two ingredients for constructing the above rational curves. The first is local symplectic cohomology groups associated to compact subsets of convex symplectic domains. The second is a degeneration to the normal cone argument that allows one to produce closed curves in \(X\) from open curves (which are produced using local symplectic cohomology) in the complement of \(X\) by a singular fibre.

Jimmy Chow (CUHK),
Hofer geometry of coadjoint orbits and Peterson's theorem,
(video),
(slides),
(abstract)
We will discuss a complete computation of Savelyev's homomorphism associated to any coadjoint orbit of a compact Lie group \(G\), where the domain is restricted to the based loop homology of \(G\). This gives at the same time some applications to the Hamiltonian groups of these spaces and a geometric proof of an unpublished theorem of Peterson. This theorem tells us explicitly how the multiplicative structure constants of the based loop homology of \(G\) determine those of the quantum cohomology of its coadjoint orbits.

Rohil Prasad (Princeton),
The smooth closing lemma for areapreserving surface diffeomorphisms,
(video),
(slides),
(abstract)

Oct. 29: Yakov Eliashberg (Stanford),
Detecting nontrivial elements in the spaces of Legendrian knots via Algebraic Ktheory,
(video),
(slides),
(abstract)
This talk is based on a joint work with Thomas Kragh.
Using the generating function theory we split inject homotopy groups of pseudoisotopy and/or hcobordism spaces into various spaces of Legendrian manifolds, e.g. the space of Legendrian unknots in \({\mathbb R}^{2n+1}\) for a sufficiently large \(n\). For instance, there is a nontrivial element in \(\pi_2\) of the space of Legendrian unknots in \({\mathbb R}^{2n+1}\) for \(n\geq 12\). 
Oct. 22: Yaniv Ganor (Technion),
Big fiber theorems and idealvalued measures in symplectic topology,
(video),
(slides),
(abstract)
In various areas of mathematics there exist "big fiber theorems", these are theorems of the following type: "For any map in a certain class, there exists a 'big' fiber", where the class of maps and the notion of size changes from case to case.
We will discuss three examples of such theorems, coming from combinatorics, topology and symplectic topology from a unified viewpoint provided by Gromov's notion of idealvalued measures.
We adapt the latter notion to the realm of symplectic topology, using an enhancement of Varolgunes’ relative symplectic cohomology to include cohomology of pairs. This allows us to prove symplectic analogues for the first two theorems, yielding new symplectic rigidity results.
Necessary preliminaries will be explained.
The talk is based on a joint work with Adi Dickstein, Leonid Polterovich and Frol Zapolsky. 
Oct. 15: Umberto Hryniewicz (RWTH Aachen),
Results on abundance of global surfaces of section,
(video),
(slides),
(abstract)
One might ask if global surfaces of section (GSS) for Reeb flows in dimension 3 are abundant in two different senses. One might ask if GSS are abundant for a given Reeb flow, or if Reeb flows carrying some GSS are abundant in the set of all Reeb flows. In this talk, answers to these two questions in specific contexts will be presented. First, I would like to discuss a result, obtained in collaboration with Florio, stating that there are explicit sets of Reeb flows on \(S^3\) which are righthanded in the sense of Ghys; in particular, for such a flow all finite (nonempty) collections of periodic orbits spans a GSS. Then, I would like to discuss genericity results, obtained in collaboration with Colin, Dehornoy and Rechtman, for Reeb flows carrying a GSS; as a particular case of such results, we prove that a \(C^\infty\)generic Reeb flow on the tight 3sphere carries a GSS.

Oct. 8: Three 20min research talks

JeanPhilippe Chassé (UdeM),
Convergence and Riemannian bounds on Lagrangian submanifolds,
(video),
(slides),
(abstract)
Recent years have seen the appearance of a plethora of possible metrics on spaces of Lagrangian submanifolds. Indeed, on top of the betterknown Lagrangian Hofer metric and spectral norm, Biran, Cornea, and Shelukhin have constructed families of socalled weighted fragmentation metrics on these spaces. I will explain how — under the presence of bounds coming from Riemannian geometry — all these metrics behave well with respect to the settheoretic Hausdorff metric.

Leo Digiosia (Rice),
Cylindrical contact homology of links of simple singularities,
(video),
(slides),
(abstract)
In this talk we consider the links of simple singularities, which are contactomoprhic to \(S^3/G\) for finite subgroups \(G\) of \(SU(2,C)\). We explain how to compute the cylindrical contact homology of \(S^3/G\) by means of perturbing the canonical contact form by a Morse function that is invariant under the corresponding rotation subgroup. We prove that the ranks are given in terms of the number of conjugacy classes of \(G\), demonstrating a form of the McKay correspondence. We also explain how our computation realizes the Seifert fiber structure of these links.

Rima Chatterjee (Cologne),
Cabling of knots in overtwisted contact manifolds,
(video),
(slides),
(abstract)
Knots associated to overtwisted manifolds are less explored. There are two types of knots in an overtwisted manifold – loose and nonloose. Nonloose knots are knots with tight complements whereas loose knots have overtwisted complements. While we understand loose knots, nonloose knots remain a mystery. The classification and structure problems of these knots vary greatly compared to the knots in tight manifolds. Especially we are interested in how satellite operations on a knot in overtwisted manifold changes the geometric property of the knot. In this talk, I will discuss under what conditions cabling operation on a nonloose knot preserves nonlooseness. This is a joint work with Etnyre, Min and Mukherjee.

JeanPhilippe Chassé (UdeM),
Convergence and Riemannian bounds on Lagrangian submanifolds,
(video),
(slides),
(abstract)
Spring 2021

Jul. 16: Joint with Berlin Mathematical School https://www.mathberlin.de/academics/bmsfridays

Helmut Hofer (IAS),
The Floer Jungle: 35 years of Floer Theory,
(video),
(slidesppt),
(slidespdf),
(abstract)
An exceptionally gifted mathematician and an extremely complex person, Floer exhibited, as one friend put it, a "radical individuality." He viewed the world around him with a singularly critical way of thinking and a quintessential disregard for convention. Indeed, his revolutionary mathematical ideas, contradicting conventional wisdom, could only be inspired by such impetus, and can only be understood in this context.
Poincaré's research on the Three Body Problem laid the foundations for the fields of dynamical systems and symplectic geometry. From whence the ancestral trail follows Marston Morse and Morse theory, Vladimir Arnold and the Arnold conjectures, through to breakthroughs by Yasha Eliashberg. Likewise, Charles Conley and Eduard Zehnder on the Arnold conjectures, Mikhail Gromov's theory of pseudoholomorphic curves, providing a new and powerful tool to study symplectic geometry, and Edward Witten's fresh perspective on Morse theory. And finally, Andreas Floer, who counterintuitively combined all of this, hitting the "jackpot" with what is now called Floer theory.
https://mathberlin.de/images/poster/Hofer_202107.pdf

Helmut Hofer (IAS),
The Floer Jungle: 35 years of Floer Theory,
(video),
(slidesppt),
(slidespdf),
(abstract)

Jul. 9: Laurent Côté (IAS/Harvard),
Action filtrations associated to smooth categorical compactifications,
(video),
(slides),
(abstract)
There is notion of a smooth categorical compactification of dg/Ainfinity categories: for example, a smooth compactification of algebraic varieties induces a smooth categorical compactification of the associated bounded dg categories of coherent sheaves. In symplectic topology, wrapped Fukaya categories of Weinstein manifolds admit smooth compactifications by partially wrapped Fukaya categories. The goal of this talk is to explain how to associate an "action filtration" to a smooth categorical compactifications, which is invariant (up to appropriate equivalence) under zigzags of smooth compactifications. I will then discuss applications to symplectic topology and categorical dynamics. This talk reports on joint work with Y. Baris Kartal.

Jul. 2: Joint with Institut Henri Poincaré https://indico.math.cnrs.fr/event/5767/

Felix Schlenk (UniNE),
Symplectically knotted cubes,
(video),
(slides),
(abstract)
While by a result of McDuff the space of symplectic embeddings of a closed 4ball into an open 4ball is connected, the situation for embeddings of cubes \(C^4 = D^2 \times D^2\) is very different. For instance, for the open ball \(B^4\) of capacity 1, there exists an explicit decreasing sequence \(c_1, c_2, \dots \to 1/3\) such that for \(c \lt c_k\) there are at least \(k\) symplectic embeddings of the closed cube \(C^4(c)\) of capacity \(c\) into \(B^4\) that are not isotopic. Furthermore, there are infinitely many nonisotopic symplectic embeddings of \(C^4(1/3)\) into \(B^4\).
A similar result holds for several other targets, like the open 4cube, the complex projective plane, the product of two equal 2spheres, or a monotone product of such manifolds and any closed monotone toric symplectic manifold.
The proof uses exotic Lagrangian tori.
This is joint work with Joé Brendel and Grisha Mikhalkin.

Felix Schlenk (UniNE),
Symplectically knotted cubes,
(video),
(slides),
(abstract)

Jun. 25: Three 20min research talks

Mohan Swaminathan (Princeton),
Superrigidity and bifurcations of embedded curves in CalabiYau 3folds,
(video),
(slides),
(abstract)
I will describe my recent work, joint with Shaoyun Bai, which studies a class of bifurcations of moduli spaces of embedded pseudoholomorphic curves in symplectic CalabiYau 3folds and their associated obstruction bundles. As an application, we are able to give a direct definition of the GopakumarVafa invariant in a special case.

Ben Wormleighton (WashU),
Lattice formulas for rational SFT capacities of toric domains,
(video),
(slides),
(abstract)
Siegel has recently defined ‘higher’ symplectic capacities using rational SFT that obstruct symplectic embeddings and behave well with respect to stabilisation. I will report on joint work with Julian Chaidez that relates these capacities to algebrogeometric invariants, which leads to computable, combinatorial formulas for many convex toric domains.

Jonathan Zung (Princeton),
Reeb flows transverse to foliations,
(video),
(slides),
(abstract)
Eliashberg and Thurston showed that \(C^2\) taut foliations on 3manifolds can be approximated by tight contact structures. I will explain a new approach to this theorem which allows one to control the resulting Reeb flow and hence produce many hypertight contact structures. Along the way, I will explain how harmonic transverse measures may be used to understand the holonomy of foliations.

Mohan Swaminathan (Princeton),
Superrigidity and bifurcations of embedded curves in CalabiYau 3folds,
(video),
(slides),
(abstract)

Jun. 18: Agustin Moreno (Uppsala),
On the spatial restricted threebody problem,
(video),
(slides),
(abstract)
In his search for closed orbits in the planar restricted threebody problem, Poincaré’s approach roughly reduces to:
(1) Finding a global surface of section;
(2) Proving a fixedpoint theorem for the resulting return map.
This is the setting for the celebrated PoincaréBirkhoff theorem. In this talk, I will discuss a generalization of this program to the spatial problem.
For the first step, we obtain the existence of global hypersurfaces of section for which the return maps are Hamiltonian, valid for energies below the first critical value and all mass ratios. For the second, we prove a higherdimensional version of the PoincaréBirkhoff theorem, which gives infinitely many orbits of arbitrary large period, provided a suitable twist condition is satisfied. Time permitting, we also discuss a construction that associates a Reeb dynamics on a moduli space of holomorphic curves (a copy of the threesphere), to the given dynamics, and its properties.
This is based on joint work with Otto van Koert. 
Jun. 11: Francisco Presas (ICMAT),
The homotopy type of the space of tight contact structures and the overtwisted mirage,
(video),
(slides),
(abstract)
We compute the homotopy type of any connected component of the space of tight contact structures on a 3fold. In fact, we actually prove a partial hprinciple for the inclusion of the contactomorphism group into the diffeomorphism group. The basic building block is the homotopy equivalence induced by the inclusion of the contactomorphism group of the sphere relative to a point and the diffeomorphism group relative to a point result recently proven by Elisahberg and Mishachev.
Then, we wonder how these sets of techniques work for overtwisted manifolds? i.e. we just try to prove the same theorem than in the tight case, assuming that the triangulation is very small, we easily obtain that all the cells are tight and then, everything looks like working, so however, there must be something wrong because we find several contradictions: the overtwisted mirage. Once the mistake is understood, we proceed to compute the homotopy type of the space of contact structures/contactomorphisms by using just MishachevEliiashberg result, i.e. we reprove the 3dimensional overtiwsted hprinciple as a corollary. We will compute the space of embeddings of overtwisted disks in some particular manifolds. Finally we end by explaining the conjecture tight \(\Longleftrightarrow\) overtwisted.
This is j/w with Dahyana Farias, Eduardo Fernández and Xabi Martínez 
Jun. 4: Simion Filip (Chicago),
Degenerations of Kahler forms on K3 surfaces, and some dynamics,
(video),
(slides),
(abstract)
K3 surfaces have a rich geometry and admit interesting holomorphic automorphisms. As examples of CalabiYau manifolds, they admit Ricciflat Kähler metrics, and a lot of attention has been devoted to how these metrics degenerate as the Kähler class approaches natural boundaries. I will discuss how to use the full automorphism group to analyze the degenerations and obtain certain canonical objects (closed positive currents) on the boundary. While most of the previous work was devoted to degenerating the metric along an elliptic fibration (motivated by the SYZ picture of mirror symmetry) I will discuss how to analyze all the other points. Time permitting, I will also describe the construction of canonical heights on K3 surfaces (in the sense of number theory), generalizing constructions due to Silverman and Tate.
Joint work with Valentino Tosatti. 
May 28: Three 20min research talks

Oğuz Şavk (Boğaziçi University),
Classical and new plumbings bounding contractible manifolds and homology balls,
(video),
(slides),
(abstract)
A central problem in lowdimensional topology asks which homology 3spheres bound contractible 4manifolds and homology 4balls. In this talk, we address this problem for plumbed 3manifolds and we present the classical and new results together. Along the way, we touch symplectic geometry by using the classical results of Eliashberg and Gompf. Our approach is based on Mazur’s famous argument which provides a unification of all results.

Irene Seifert (Heidelberg),
Periodic delay orbits and the polyfold IFT,
(video),
(slides),
(abstract)
Differential delay equations arise very naturally, but they are much more complicated than ordinary differential equations. Polyfold theory, originally developed for the study of moduli spaces of pseudoholomorphic curves, can help to understand solutions of certain delay equations. In my talk, I will show an existence result about periodic delay orbits with small delay. If time permits, we can discuss possible further applications of polyfold theory to the differential delay equations. This is joint work with Peter Albers.

Hang Yuan (Stony Brook),
Disk counting via family Floer theory,
(video),
(slides),
(abstract)
Given a family of Lagrangian tori with full quantum corrections, the nonarchimedean SYZ mirror construction uses the family Floer theory to construct a nonarchimedean analytic space with a global superpotential. In this talk, we will first briefly review the construction. Then, we will apply it to the Gross’s fibrations. As an application, we can compute all the nontrivial open GW invariants for a Chekanovtype torus in \(CP^n\) or \(CP^r \times CP^{nr}\). When \(n=2\), \(r=1\), we retrieve the previous results of Auroux an ChekanovSchlenk without finding the disks explicitly. It is also compatible with the PascaleffTonkonog’s work on Lagrangian mutations.

Oğuz Şavk (Boğaziçi University),
Classical and new plumbings bounding contractible manifolds and homology balls,
(video),
(slides),
(abstract)
 May 21: Cancelled on account of Advances in Symplectic Topology, https://indico.math.cnrs.fr/event/5787/

May 14: Daniel ÁlvarezGavela (MIT),
Caustics of Lagrangian homotopy spheres with stably trivial Gauss map,
(video),
(slides),
(abstract)
The hprinciple for the simplification of caustics (i.e. Lagrangian tangencies) reduces a geometric problem to a homotopical problem. In this talk I will explain the solution to this homotopical problem in the case of spheres. More precisely, I will show that the stably trivial elements of the \(n\)th homotopy group of the Lagrangian Grassmannian \(U_n/O_n\), which lies in the metastable range, admit representatives with only fold type tangencies. By the hprinciple, it follows that if \(D\) is a Lagrangian distribution defined along a Lagrangian homotopy sphere \(L\), then there exists a Hamiltonian isotopy which simplifies the tangencies between \(L\) and \(D\) to consist only of folds if and only if \(D\) is stably trivial. I will give two applications of this result, one to the arborealization program and another to the study of nearby Lagrangian homotopy spheres. Joint work with David Darrow (in the form of an undergraduate research project).

May 7: Laura Starkston (UC Davis),
Unexpected fillings, singularities, and plane curve arrangements,
(video),
(slides),
(abstract)
I will discuss joint work with Olga Plamenevskaya studying symplectic fillings of links of certain complex surface singularities, and comparing symplectic fillings with complex smoothings. We develop characterizations of the symplectic fillings using planar Lefschetz fibrations and singular braided surfaces. This provides an analogue of de Jong and van Straten's work which characterizes the complex smoothings in terms of decorated complex plane curves. We find differences between symplectic fillings and complex smoothings that had not previously been found in rational complex surface singularities.
 Apr. 30: Cancelled on account of the conference From Hamiltonian Systems to Symplectic Topology and Beyond, https://indico.math.cnrs.fr/event/5786/
 Apr. 23: Cancelled on account of the Spring School on Symplectic and Contact Topology, https://conferences.cirmmath.fr/2329.html

Apr. 16: Three 20min research talks

Maxim Jeffs (Harvard),
Mirror symmetry and Fukaya categories of singular varieties,
(video),
(slides),
(abstract)
In this talk I will explain Auroux' definition of the Fukaya category of a singular hypersurface and two results about this definition, illustrated with some examples. The first result is that Auroux' category is equivalent to the FukayaSeidel category of a LandauGinzburg model on a smooth variety; the second result is a homological mirror symmetry equivalence at certain large complex structure limits. I will also discuss ongoing work on generalizations.

Côme Dattin (Nantes),
Wrapped sutured Legendrian homology and the conormal of braids,
(video),
(slides),
(abstract)
In this talk we will discuss invariants of sutured Legendrians. A sutured contact manifold can be seen as either generalizing the contactisation of a Liouville domain, or as a presentation of a contact manifold with convex boundary. Using the first point of view, we define the wrapped sutured homology of Legendrians with boundary, employing ideas coming from Floer theory. To illustrate the second aspect, we apply the unit conormal construction to braids with two strands, which yields a sutured Legendrian. We will show that, if the conormals of two 2braids are Legendrian isotopic, then the braids are equivalent.

Bingyu Zhang (Institut Fourier, Université Grenoble Alpes),
Capacities from the ChiuTamarkin complex,
(video),
(slides),
(abstract)
In this talk, we will discuss the ChiuTamarkin complex. It is a symplectic/contact invariant that comes from the microlocal sheaf theory. I will explain how to define some capacities using the ChiuTamarkin complex in both symplectic and contact situations. The main result is the structure theorem of the ChiuTamarkin complex of convex toric domains. Consequently, we can compute the capacities of convex toric domains.

Maxim Jeffs (Harvard),
Mirror symmetry and Fukaya categories of singular varieties,
(video),
(slides),
(abstract)

Apr. 9: Sara Tukachinsky (IAS),
Relative quantum cohomology and other stories,
(video),
(slides),
(abstract)
We define a quantum product on the cohomology of a symplectic manifold relative to a Lagrangian submanifold, with coefficients in a Novikov ring. The associativity of this product is equivalent to an open version of the WDVV equations for an appropriate disk superpotential. Both structures — the quantum product and the WDVV equations — are consequences of a more general structure we call the tensor potential, which will be the main focus of this talk. This is joint work with Jake Solomon.

Apr. 2: Sheel Ganatra (USC),
Categorical nonproperness in wrapped Floer theory,
(video),
(slides),
(abstract)
In all known explicit computations on Weinstein manifolds, the selfwrapped Floer homology of noncompact exact Lagrangian is always either infinitedimensional or zero. We will explain why a global variant of this observed phenomenon holds in broad generality: the wrapped Fukaya category of any positivedimensional Weinstein (or nondegenerate Liouville) manifold is always either nonproper or zero, as is any quotient thereof. Moreover any noncompact connected exact Lagrangian is always either a "nonproper object" or zero in such a wrapped Fukaya category, as is any idempotent summand thereof. We will also examine where the argument could break if one drops exactness, which is consistent with known computations of nonexact wrapped Fukaya categories which are smooth, proper, and nonvanishing (e.g., work of RitterSmith).
Winter 2021

Mar. 26: Three 20min research talks

Jesse Huang (UIUC),
Variation of FLTZ skeleta,
(video),
(slides),
(abstract)
In this short talk, I will discuss an interpolation of FLTZ skeleta mirror to derived equivalent toric varieties. This is joint work with Peng Zhou.

Shaoyun Bai (Princeton),
SU(n)–Casson invariants and symplectic geometry,
(video),
(slides),
(abstract)
In 1985, Casson introduced an invariant of integer homology 3spheres by counting SU(2)representations of the fundamental groups. The generalization of Casson invariant by considering Lie groups SU(n) has been long expected, but the original construction of Casson encounters some difficulties. I will present a solution to this problem, highlighting the equivariant symplectic geometry and AtiyahFloer type result entering the construction.

Thomas Melistas (UGA),
The LargeScale Geometry of Overtwisted Contact Forms,
(video),
(slides),
(abstract)
Inspired by the symplectic BanachMazur distance, proposed by Ostrover and Polterovich in the setting of nondegenerate starshaped domains of Liouville manifolds, we define a distance on the space of contact forms supporting a given contact structure on a closed contact manifold and we use it to biLipschitz embed part of the 2dimensional Euclidean space into the space of overtwisted contact forms supporting a given contact structure on a smooth closed manifold.

Jesse Huang (UIUC),
Variation of FLTZ skeleta,
(video),
(slides),
(abstract)

Mar. 19: Egor Shelukhin (UdeM),
Lagrangian configurations and Hamiltonian maps,
(video),
(slides),
(abstract)
We study configurations of disjoint Lagrangian submanifolds in certain lowdimensional symplectic manifolds from the perspective of the geometry of Hamiltonian maps. We detect infinitedimensional flats in the Hamiltonian group of the twosphere equipped with Hofer's metric, showing in particular that this group is not quasiisometric to a line. This answers a wellknown question of KapovichPolterovich from 2006. We show that these flats in \(Ham(S^2)\) stabilize to certain product fourmanifolds, prove constraints on Lagrangian packing, find new instances of Lagrangian Poincare recurrence, and present a new hierarchy of normal subgroups of areapreserving homeomorphisms of the twosphere. The technology involves Lagrangian spectral invariants with Hamiltonian term in symmetric product orbifolds. This is joint work with Leonid Polterovich.

Mar. 12: Oleg Lazarev (Harvard),
Inverting primes in Weinstein geometry,
(video),
(slides),
(abstract)
A classical construction in topology associates to a space \(X\) and prime \(p\), a new "localized" space \(X_p\) whose homotopy and homology groups are obtained from those of \(X\) by inverting \(p\). In this talk, I will discuss a symplectic analog of this construction, extending work of AbouzaidSeidel and CieliebakEliashberg on flexible Weinstein structures. Concretely, I will produce primelocalized Weinstein subdomains of highdimensional Weinstein domains and also show that any Weinstein subdomain of a cotangent bundle agrees Fukayacategorically with one of these special subdomains. The key will be to classify which objects of the Fukaya category of \(T^*M\) – twisted complexes of Lagrangians – are quasiisomorphic to actual Lagrangians. This talk is based on joint work with Z. Sylvan.

Mar. 5: Sobhan Seyfaddini (Paris),
Periodic Floer homology and the largescale geometry of Hofer's metric on the sphere,
(video),
(slides),
(abstract)
The group of Hamiltonian diffeomorphisms of a symplectic manifold admits a remarkable biinvariant metric, called Hofer’s metric. My talk will be about a recent joint work with Dan CristofaroGardiner and Vincent Humilière resolving the following two openquestions related to the largescale geometry of this metric. The first, due to Kapovich and Polterovich, asks whether the twosphere, equipped with Hofer’s metric, is quasiisometric to the real line; we show that it is not. The second, due to Fathi, asks whether the group of area and orientation preserving homeomorphisms of the twosphere is a simple group; we show that it is not. Key to our proofs is a new sequence of spectral invariants defined via Hutchings’ Periodic Floer Homology.
 For two somewhat related talks by Rémi Leclercq and Vincent Humilière on Mar. 6, see the link: https://dms.umontreal.ca/~cornea/MicroC0.

Feb. 26: Generating Functions Day

9:15am EST: Sylvain Courte (Université Grenoble Alpes),
Twisted generating functions and the nearby Lagrangian conjecture,
(video),
(slides),
(abstract)
I will explain the notion of twisted generating function and show that a closed exact Lagrangian submanifold L in the cotangent bundle of M admits such a thing. The type of function arising in our construction is related to Waldhausen's tube space from his manifold approach to algebraic Ktheory of spaces. Using the rational equivalence of this space with BO, as proved by Bökstedt, we conclude that the stable Lagrangian Gauss map of L vanishes on all homotopy groups. In particular when M is a homotopy sphere, we obtain the triviality of the stable Lagrangian Gauss map and a genuine generating function for L. This is a joint work with M. Abouzaid, S. Guillermou and T. Kragh.

12pm EST, at the
WHVSS:
Simon Allais (ENS Lyon),
Periodic points of Hamiltonian diffeomorphisms and generating functions,
(abstract)
Ginzburg and Gürel recently showed that a hamiltonian diffeomorphism of \(CP^d\) a hyperbolic periodic point have infinitely many periodic points whereas fixed points of a pseudorotation are isolated as an invariant set. In 2019, Shelukhin proved a homology version of the HoferZehnder conjecture in a large class of symplectic manifolds \(M\) that includes \(CP^d\): a Hamiltonian diffeomorphism with more homologically visible fixed points than the dimension of the homology of \(M\) has infinitely many periodic points. These results rely on the quantum structure of the Floer homology.
In this talk, I will explain how the study of sublevel sets of generating functions can replace the use of \(J\)holomorphic curves and Floer theory in the study of periodic points of \(CP^d\), based on ideas of Givental and Théret in the 90s. 
3pm EST, at the
WHVSS:
Yael Karshon (Toronto University),
Nonlinear Maslov index on lens spaces,
(abstract)
Let L be a lens space with its standard contact structure. We use generating functions to construct a "nonlinear Maslov index", which associates an integer to any contact isotopy of L that starts at the identity, and whose properties allow us to prove rigidity properties of L as a contact manifold.
This is joint work with Gustavo Granja, Milena Pabiniak, and Sheila (Margherita) Sandon, and it follows earlier work of Givental and Theret that applied to real and complex projective spaces.

9:15am EST: Sylvain Courte (Université Grenoble Alpes),
Twisted generating functions and the nearby Lagrangian conjecture,
(video),
(slides),
(abstract)

Feb. 19: Daniel Pomerleano (UMass Boston),
Intrinsic mirror symmetry and categorical crepant resolutions,
(video),
(slides),
(abstract)
Gross and Siebert have recently proposed an "intrinsic" programme for studying mirror symmetry. In this talk, we will discuss a symplectic interpretation of some of their ideas in the setting of affine log CalabiYau varieties. Namely, we describe work in progress which shows that, under suitable assumptions, the wrapped Fukaya category of such a variety \(X\) gives an intrinsic "categorical crepant resolution" of \(Spec(SH^0(X))\). No background in mirror symmetry will be assumed for the talk.

Feb. 12: Cheuk Yu Mak (Edinburgh),
Nondisplaceable Lagrangian links in fourmanifolds,
(video),
(slides),
(abstract)
One of the earliest fundamental applications of Lagrangian Floer theory is detecting the nondisplaceablity of a Lagrangian submanifold. Many progress and generalisations have been made since then but little is known when the Lagrangian submanifold is disconnected. In this talk, we describe a new idea to address this problem. Subsequently, we explain how to use FukayaOhOhtaOno and ChoPoddar theory to show that for every \(S^2 \times S^2\) with a nonmonotone product symplectic form, there is a continuum of disconnected, nondisplaceable Lagrangian submanifolds such that each connected component is displaceable. This is a joint work with Ivan Smith.

Feb. 5: Yusuf Barış Kartal (Princeton),
Algebraic torus actions on Fukaya categories,
(video),
(slides),
(abstract)
The purpose of this talk is to explore how Lagrangian Floer homology groups change under (nonHamiltonian) symplectic isotopies on a (negatively) monotone symplectic manifold \((M,\omega)\) satisfying a strong nondegeneracy condition. More precisely, given two Lagrangian branes \(L,L',\) consider family of Floer homology groups \(HF(\phi_v(L),L')\), where \(v\in H^1(M,\mathbb R)\) and \(\phi_v\) is the time1 map of a symplectic isotopy with flux \(v\). We show how to fit this collection into an algebraic sheaf over the algebraic torus \(H^1(M,\mathbb G_m)\). The main tool is the construction of an "algebraic action" of \(H^1(M,\mathbb G_m)\) on the Fukaya category. As an application, we deduce the change in Floer homology groups satisfy various tameness properties, for instance, the dimension is constant outside an algebraic subset of \(H^1(M,\mathbb G_m)\). Similarly, given closed \(1\)form \(\alpha\), which generates a symplectic isotopy denoted by \(\phi_\alpha^t\), the Floer homology groups \(HF(\phi_\alpha^t(L),L')\) have rank that is constant in \(t\), with finitely many possible exceptions.
Earlier
 March 27, 2020 – January 29, 2021: https://dms.umontreal.ca/~cornea/Seminar.html