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Hamiltonian systems, symplectic flows, classical integrable systems

3 votes
0 answers
233 views

What is rigidity of Hirzebruch, and Witten genera?

I would like to find some good references (or any insight) that would help me to understand a few articles mentioning rigidity of Hirzeburch genus. One of the consequences of this phenomenon is that w …
aglearner's user avatar
  • 14.3k
15 votes
5 answers
2k views

Reading list for Equivariant Cohomology

I was applying equivaraint cohomology, in particular in the symplectic setting, for some time, but I feel like I am missing some nice books/course notes/articles. Could you advise me some literature, …
aglearner's user avatar
  • 14.3k
7 votes
0 answers
132 views

Representations of $\mathbb Z^2$ in ${\rm Symp}(S^2)$

Suppose $f_1$ and $f_2$ are two commuting symplectomorphisms of the sphere $\mathbb S^2$, of orders different from $2$. Is it possible to deform the pair $(f_1,f_2)$ to the pair of identity maps via a …
aglearner's user avatar
  • 14.3k
10 votes
2 answers
521 views

Two smooth tangent almost complex curves in a $4$-manifold

I would like to know if following is correct. Statement. Suppose we have a smooth (i.e., $C^\infty$) almost complex structure on $\mathbb R^4$ and $C_1, C_2$ are two $J$-holomorphic curves passing t …
aglearner's user avatar
  • 14.3k
4 votes
1 answer
184 views

2-faces of reflexive Delzant polytopes

Question 1. Can a reflexive Delzant polytope of some dimension contain a $2$-face with more than $11$ edges? Motivation. I would like more generally to get an answer to the following question: Questio …
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  • 14.3k
7 votes
2 answers
351 views

Two embedded symplectic spheres with zero square in a symplectic $4$-manifold

I am aware that the following result is a classical one (by now). But I am not able to understand who proved it. What should be a proper reference to this statement? Theorem. Let $M^4$ be a compact s …
aglearner's user avatar
  • 14.3k
6 votes
0 answers
269 views

Varying a $J$-holomorphic sphere in a symplectic $4$-manifolds

I am certain that the following result holds, but was not able to find a reference. Do you know one? Or maybe you can give a short proof? Statement. Let $(M^4,\omega)$ be a compact symlectic manifold …
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  • 14.3k
2 votes
0 answers
204 views

Are rational varieties symplectically rationally connected?

Was it proven already that smooth rational complex projecitve varieties are symplectically rationally connected? I.e. some GW invariant with two point insertions is non zero. What about smooth toric v …
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  • 14.3k
3 votes
1 answer
192 views

Constructing a Hamiltonian $S^1$-action on a neighborhood of a symplectic divisor

Let $M^{2n}$ be a symplectic manifold and let $M^{2n-2}$ be a symplectic submanifold. How to construct a non-trivial Hamiltonian $S^1$-action on $M^{2n-2}$ on a small neighborhood of $M^{2n-2}$, that …
aglearner's user avatar
  • 14.3k
5 votes
1 answer
252 views

Almost complex structures on a 4-ball that are not tamed

Recall that an almost complex structure $J$ on a manifold $M^{2n}$ is called tamed if there exists a symplectic form $\omega$ on $M^{2n}$ such that $\omega(v,Jv)>0$ for any non-zero tangent vector $v$ …
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  • 14.3k
10 votes
1 answer
618 views

Almost complex structures on $\mathbb CP^2$ that are not tamed

Recall that an almost complex structure $J$ on a manifold $M^{2n}$ is called tamed if there exists a symplectic form $\omega$ on $M^{2n}$ such that $\omega(v,Jv)>0$ for any non-zero tangent vector $v$ …
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  • 14.3k
9 votes
1 answer
644 views

Reeb flows on $S^3$ versus volume preserving flows

Is there an example of a smooth vector field $v$ on $S^3$ such that $v$ preserves a volume form and $v$ is not a Reeb vector field? Recall that $v$ is a Reeb vector field if there exists a contact $ …
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  • 14.3k
3 votes
1 answer
179 views

Level sets of Hamiltonians of S^1 actions

Suppose that $(M,\omega)$ is a (connected compact) symplectic manifold with a Hamiltonian $S^1$-action given by Hamiltonian $H$. I would like to find a reference for the fact that every level set of …
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  • 14.3k
56 votes
9 answers
7k views

Examples in mirror symmetry that can be understood.

It seems to me, that a typical science often has simple and important examples whose formulation can be understood (or at least there are some outcomes that can be understood). So if we consider mirr …
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  • 14.3k