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Hamiltonian systems, symplectic flows, classical integrable systems

26 votes

Has anything precise been written about the Fukaya category and Lagrangian skeletons?

I noticed this question has been bumped up to the front page, and the most recent answer is about 8 years old: the subject has moved on since then, and more has been written. Here is my understanding …
Jonny Evans's user avatar
  • 7,005
21 votes

Why are Gromov-Witten invariants of K3 surfaces trivial?

Here are two answers to your first question: Yes your argument works. To see that there are no curves for a generic K3 observe that their homology classes must be Poincare dual to an integral (1,1)- …
Jonny Evans's user avatar
  • 7,005
14 votes
Accepted

Why Donaldson's Four-Six Conjecture?

I think that YangMills is probably right that Donaldson never wrote the conjecture down. But there are some interesting circles of ideas surrounding the conjecture which deserve mention which, again h …
Jonny Evans's user avatar
  • 7,005
12 votes

Why believe Kontsevich cosheaf conjecture?

On the suggestion of DamienC, I'm converting my comments into an answer. I didn't do this before because I don't really know the answer to the deeper question of why the microlocal sheaf category is t …
Jonny Evans's user avatar
  • 7,005
11 votes
Accepted

Is P^2 important in Kontsevich's recursion formula?

The Kontsevich recursion formula is not special to $\mathbf{CP}^2$. It is a particular application of the more general associativity formula for quantum cohomology, which is something true for symplec …
Jonny Evans's user avatar
  • 7,005
11 votes

Physical intuition behind prequantization spaces

If you think instead of the prequantum line bundle (i.e. the complex line bundle associated to your prequantum circle bundle using the standard representation of the circle on $\mathbb{C}$) then the s …
Jonny Evans's user avatar
  • 7,005
10 votes
Accepted

Reference Request: "Neck Stretching Procedure" (In Symplectic Field Theory)

Neck-stretching is a deformation of an almost complex structure in a neighbourhood of a hypersurface. In the Eliashberg-Givental-Hofer paper, neck-stretching is called "splitting along a contact subma …
Jonny Evans's user avatar
  • 7,005
9 votes

How not to use J-holomorphic curves

One classic thing to do is to take a sequence of holomorphic curves with a tangency condition and assume that the tangency condition still holds in the limit: if the limit is a multiple cover with a b …
Jonny Evans's user avatar
  • 7,005
9 votes
Accepted

Lagrangian intersection Floer homology: understanding some assumptions

When you try and prove that $d^2=0$ ($d$ being the Floer differential) you need to look at the boundary of the moduli space of index 2 J-holomorphic strips with one boundary on $L_0$, one on $L_1$. Ce …
Jonny Evans's user avatar
  • 7,005
8 votes
Accepted

Applications of Floer homology

Floer homology has, in one form or another, become ubiquitous in symplectic geometry and to give a complete list of its applications would be a mammoth task. Here are a few. 1) One early incarnation …
Jonny Evans's user avatar
  • 7,005
8 votes
Accepted

Cotangent bundles of surfaces as varieties

This is not possible. There is something called the growth rate of symplectic cohomology which is subexponential for affine varieties and exponential for cotangent bundles of higher genus surfaces (am …
Jonny Evans's user avatar
  • 7,005
7 votes

Simple examples of Gromov-Witten invariants not being enumerative

I'm not sure if this is quite what you're looking for, but I always found it a useful example to keep in mind. Take the genus 1 invariant for degree 1 maps into $P^1$. There are no degree 1 holomorphi …
Jonny Evans's user avatar
  • 7,005
7 votes
Accepted

Pseudo-holomorphic disk which is constant along boundary

Extend $u$ to get a $C^1$ pseudoholpmorphic map defined on $\mathbb{C}$ by setting $u$ constant outside the unit disc. It's $C^1$ because you know the derivative of $u$ along the unit circle vanishes …
Jonny Evans's user avatar
  • 7,005
7 votes
Accepted

Lagrangian torus fibrations and Arnol'd-Liouville theorem

By the time I finished writing this answer someone has explained the whole idea in a comment, but I thought I'd post it anyway as there is some more detail here. I assume the version of Arnold-Liouvil …
Jonny Evans's user avatar
  • 7,005
6 votes

Introduction to Floer Theory?

I wholeheartedly agree with both of Chris Gerig's suggestions. The small McDuff-Salamon book on holomorphic curves ("J-holomorphic curves and quantum cohomology", available on McDuff's webpage) has a …

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